Sky-High Lunar Eclipse Late Monday Night

Everyone in North and Central America -- weather permitting -- will have ringside seats for a total eclipse of the Moon high in the sky late Monday night, December 20th, and/or early Tuesday morning the 21st.

Earth's shadow will totally engulf the Moon, turning it spooky orange-red, from 2:41 to 3:53 a.m. Eastern Standard Time, or 11:41 p.m. to 12:53 a.m. Pacific Standard Time (see full timetable below). The eclipse will be partial for a little more than an hour before and after.

Unlike a solar eclipse, a lunar eclipse is visible to everyone on the entire Moon-facing side of Earth at once. "We're all looking at this together," says Sky & Telescope
editor in chief Robert Naeye.

Skywatchers in Europe, West Africa, and South America get to see only part of the eclipse before it's interrupted by moonset and sunrise on the morning of the 21st. In East Asia, Australia, and New Zealand, the eclipse is already in progress at sunset and moonrise on 21st local date.

Program for the Show

A total lunar eclipse has five stages. It begins when the Moon first enters the *penumbra,* or pale outer fringe, of Earth's shadow. But that event can't be seen; the shading in the outer part of the penumbra is extremely slight. Only when the Moon's leading edge is about halfway across the penumbra does the first slight dimming become detectable to the eye.

The second stage, *partial eclipse,* starts when the Moon's edge reaches the *umbra,* or Earth's inner shadow. "It's eerie watching this weird, red-brown shadow creeping across the bright Moon," says Sky & Telescope senior editor Alan MacRobert. "Look carefully, and you'll notice that Earth's shadow has a curved edge. This was the first visible proof to the ancients -- at least the ones who knew what they were seeing, like the Greeks -- that the Earth is round."

As more of the Moon slides into the umbra, look around the sky. A second, deeper night is falling -- "night within night," says MacRobert. If you're far from city lights, hundreds of additional stars start appearing in what just a little earlier was a bright, moonlight-washed sky. An hour or so into partial eclipse, only a final bright sliver of the Moon remains outside the umbra -- and the rest of it shows an eerie reddish glow.

The third stage, *total eclipse,* begins when the last bit of the Moon slips into the umbra. For this eclipse, totality lasts a generous 72 minutes, with the Moon looking, says MacRobert, "like a luminous rotten orange."

Then, as the Moon continues moving eastward along its orbit, events unwind in reverse order. Totality ends when the Moon's leading edge reemerges into sunlight, returning once again to a partial eclipse (stage four). Then, after all of the Moon escapes the umbra, the dusky penumbral shading (stage five) gradually fades away, leaving the full Moon shining as brightly as if nothing had happened.



Red in the Darkness

The umbra is the part of Earth's shadow where the Sun is blocked from the Moon completely. So why does the Moon here glow deep orange or red, rather than being totally blacked out?

"That red light you see on the Moon during a lunar eclipse comes from all the sunrises and sunsets around the Earth at the time," says Naeye. Our atmosphere scatters and refracts (bends) the sunlight that grazes the rim of our globe, sending it into Earth's shadow. "If you were an astronaut on the Moon," he says, "you'd see the Sun covered up by a dark Earth that was ringed all around with a thin, bright band of sunset- and sunrise-colored light."

On rare occasions the eclipsed Moon does go black. Other times it appears as bright and coppery orange as a fresh penny. And sometimes it turns brown like chocolate, or as dark red-black as dried blood. Two factors affect an eclipse's color and brightness. The first is simply how deeply the Moon goes into the umbra. The center of the umbra is much darker than its edges. This time the Moon will pass fairly deep through the umbra, and at mid-eclipse the Moon's southern edge almost reaches the umbra's center. The other factor is the state of Earth's atmosphere along the sunrise-sunset line. If the air is very clear, the eclipse is bright. But if a major volcanic eruption has polluted the stratosphere with thin haze, the eclipse will be dark red, ashen gray-brown, or red-black.

In addition, a little blue light refracted by Earth's clear, ozone-rich upper atmosphere can also add to the mix, especially near the umbra's edge, creating a subtle combination of changing colors. Such variable shading can give the eclipsed Moon a very three-dimensional appearance.

Next Eclipses

This is the first total eclipse of the Moon in almost three years (since the night of Feb. 20-21, 2008).

The next eclipse of the Moon is a deep total one on June 15, 2011, but North America misses out; our side of the world will be facing the wrong way.

Skywatchers on the West Coast can catch part of the following lunar eclipse, on the morning of December 10, 2011, until it's interrupted by moonset and sunrise.

The next total lunar eclipse for the whole continent doesn't come until April 14-15, 2014 -- an unusually long wait. So hope for good weather this time!

It's Geminid Time!

It's Geminid Time!

Mention "meteors," and casual skywatchers usually think of the annual Perseid shower on display every August.

But the Geminid meteor shower of mid-December ties or even surpasses the Perseids as the year's richest and most reliable meteor display. Geminid meteors come from 3200 Phaethon, an asteroid discovered in 1983.

This year the Geminids are predicted to peak on the morning of December 14th around 11h UT, more or less. That's excellent timing for North America, especially out West. The Moon that night is only a day past first quarter and sets around midnight or 1 a.m. local time, depending on where you live. Even before then, on the evening of the 13th, the moonlight isn't bright enough to dampen the shower's visibility too much — and the Geminids, with their radiant near Castor and Pollux, pick up steam as early as 8 or 9 p.m. But the radiant is highest around 2 a.m., so the morning hours are the usually the most productive.

Bundle up as warmly as you possibly can, and lie back in a dark spot with an open sky. You may see as many as two meteors a minute on average if you have a very dark sky and are watching after midnight.


Sky map of Geminid radiant
The radiant (apparent source point) of the Geminid meteor shower is near Castor, the fainter of the Twin Stars in the constellation Gemini. You'll see this view if you face east at about 9 p.m. (The number of meteors is exaggerated.)
Sky & Telescope illustration

If your sky is not too light-polluted, you might try making a careful meteor count and reporting it to the International Meteor Organization. Such counts by amateurs supply much of what we know about meteor showers' behavior. For your count to be useful, you'll need to follow the procedures described on our page or at the IMO's website.

Don't forget that the shower lasts more than one night. Counts are especially needed on nights away from the maximum, because fewer people are watching. In any case, enjoy the show!

A Steamy Super-Earth

A Steamy Super-Earth

In the latest breakthrough for exoplanet science, a team using one of the European Southern Observatory’s 8.2-meter Very Large Telescope reflectors has obtained a crude spectrum for the atmosphere of a super-Earth orbiting a dim red dwarf star 40 light-years away. The planet’s upper atmosphere is apparently dominated by steam or cloudy haze.

The star, 14.7-magnitude GJ (Gliese-Jahreiss) 1214 in Ophiuchus, is 300 times dimmer than the Sun with a spectral type of M4.5. Its planet was discovered in 2009 when the MEarth Project detected the planet's silhouette periodically dimming the star. The planet has 6.5 Earth masses, as determined later by the star’s gravitational wobbles, and it circles the little star very closely in just 38 hours. The transits reveal the planet’s diameter to be 2.6 times Earth’s — making its average density very low, only about a third of Earth’s density.

The astronomers detected a telltale absorption spectrum caused by a tiny fraction of the star’s light filtering through the planet’s atmosphere during each transit. The spectrum was featureless, indicating that the upper atmosphere either consists mostly of water vapor or is dominated by high-altitude clouds or haze.

“This is the first super-Earth to have its atmosphere analyzed. We’ve reached a real milestone on the road toward characterizing these worlds,” said team leader Jacob Bean (Harvard–Smithsonian Center for Astrophysics) in a press release.

Before this observation, astronomers had suggested three possible atmospheres for GJ1214b. The planet could be shrouded by water — which, given its high temperature so close to the star (200ºC; 400ºF), would be in the form of steam. Or it could be a rocky world with an atmosphere of mostly hydrogen obscured by high clouds or hazes. Or it might be a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere, the upper part of which would be clear.

The measurements clearly show no sign of hydrogen and thus rule out the third option. So the atmosphere is either rich in steam or blanketed by clouds or hazes. The planet’s low density, meanwhile, indicates that it's a waterworld.

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean. “Followup observations in longer-wavelength infrared light are needed to determine which of these atmospheres exists on GJ 1214b.

Troubles Surface for Webb Telescope

Troubles Surface for Webb Telescope
In the blur of astro-news from last week — the deaths of two prominent astronomers, fabulous Comet Hartley 2 results, asteroid dust inside Hayabusa, and a planet from another galaxy — we couldn't quite get to an important story involving Hubble's eventual replacement: the James Webb Space Telescope.

The JWST effort has been under way in earnest since 2002, when NASA managers selected TRW as the project's prime contractor and renamed the spacecraft (formerly the Next Generation Space Telescope) to honor James E. Webb, the agency's second administrator. The plan was, and is, to place a giant space observatory far from Earth (to minimize interference) and give it a primary mirror 21 feet (6.5 m) across — more than seven times Hubble's light grasp — to probe the visible and (especially) infrared universe as never before.

Back then, rosy announcements predicted a total cost of around $1 billion and a launch sometime this year.

If only! Along the way, reality set in. By 2005 the construction cost-to-launch estimate had ballooned to $2.4 billion, and the debut had slipped to 2014. That's where things stood until this year, when an Independent Comprehensive Review Panel took a hard look at the numbers. The bottom line is that JWST's total cost to launch and operate is likely about $6½ billion, $1½ billion more than NASA budgeted. Moreover, the earliest possible launch date is September 2015.

Given that construction is so far along, you've got to wonder why NASA misjudged things so badly. You would think that the agency had learned its lesson building the Hubble Space Telescope, which was supposed to take just four years to assemble when construction began in 1979 but ended up taking 11 years to reach space. The loss of the Space Shuttle Challenger in 1986 didn't help, but the HST project had numerous problems of its own making.

So what went wrong with JWST?

According to the review panel's final report, NASA officials made two "fundamental mistakes" when the project underwent a major Confirmation Review in July 2008. First, the panel found, "the Project Budget presented for Confirmation was not based upon a current, bottom-up estimate of projected costs." Second, project managers failed to factor in — and provide funds for — development problems that were likely to occur.



Hubble and Webb mirrors compared
Measuring more than 21 feet (6.5 m) across, the primary mirror for the James Webb Space Telescope will have a diameter some 2½ times that of the Hubble Space Telescope.

Even to meet a 2015 launch date, NASA will need to pump an additional $250 million into the project's budget in fiscal 2011 and 2012 — funds that the agency isn't likely to get from Congress. If forced to find that money internally, the agency will likely have to cancel or defer other space-science programs already under way.

Perhaps more urgently, the panel recommended that NASA administrator Charles Bolden yank project management from its Goddard Space Flight Center and instead run the effort from a dedicated office at the agency's Washington headquarters. Bolden, in response, supported the panel's findings and is appointing a new JWST program director.

The news isn't all bad. The review panel found the technical state of the project to be sound and its scientific goals intact. Money spent to date hasn't been wasted, it noted in an Afterword, and "no technical constraints to successful completion have been identified." Once in orbit, the Webb telescope is expected to have the ability to look back 13½ billion years, to when the universe was just 2% of its current age and the first galaxies were forming.

Silica on a Mars Volcano Tells of Wet and Cozy Past

PASADENA, Calif. -- Light-colored mounds of a mineral deposited on a volcanic cone more than three billion years ago may preserve evidence of one of the most recent habitable microenvironments on Mars.

Observations by NASA's Mars Reconnaissance Orbiter enabled researchers to identify the mineral as hydrated silica and to see its volcanic context. The mounds' composition and their location on the flanks of a volcanic cone provide the best evidence yet found on Mars for an intact deposit from a hydrothermal environment -- a steam fumarole, or hot spring. Such environments may have provided habitats for some of Earth's earliest life forms.

"The heat and water required to create this deposit probably made this a habitable zone," said J.R. Skok of Brown University, Providence, R.I., lead author of a paper about these findings published online today by Nature Geoscience. "If life did exist there, this would be a promising type of deposit to entomb evidence of it -- a microbial mortuary."

No studies have yet determined whether Mars has ever supported life. The new results add to accumulating evidence that, at some times and in some places, Mars has had favorable environments for microbial life. This specific place would have been habitable when most of Mars was already dry and cold. Concentrations of hydrated silica have been identified on Mars previously, including a nearly pure patch found by NASA's Mars Exploration Rover Spirit in 2007. However, none of those earlier findings were in such an intact setting as this one, and the setting adds evidence about the origin.

Skok said, "You have spectacular context for this deposit. It's right on the flank of a volcano. The setting remains essentially the same as it was when the silica was deposited."

The small cone rises about 100 meters (100 yards) from the floor of a shallow bowl named Nili Patera. The patera, which is the floor of a volcanic caldera, spans about 50 kilometers (30 miles) in the Syrtis Major volcanic region of equatorial Mars. Before the cone formed, free-flowing lava blanketed nearby plains. The collapse of an underground magma chamber from which lava had emanated created the bowl. Subsequent lava flows, still with a runny texture, coated the floor of Nili Patera. The cone grew from even later flows, apparently after evolution of the underground magma had thickened its texture so that the erupted lava would mound up.

"We can read a series of chapters in this history book and know that the cone grew from the last gasp of a giant volcanic system," said John Mustard, Skok's thesis advisor at Brown and a co-author of the paper. "The cooling and solidification of most of the magma concentrated its silica and water content."

Observations by cameras on the Mars Reconnaissance Orbiter revealed patches of bright deposits near the summit of the cone, fanning down its flank, and on flatter ground in the vicinity. The Brown researchers partnered with Scott Murchie of Johns Hopkins University Applied Physics Laboratory, Laurel, Md., to analyze the bright exposures with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the orbiter.

Silica can be dissolved, transported and concentrated by hot water or steam. Hydrated silica identified by the spectrometer in uphill locations -- confirmed by stereo imaging -- indicates that hot springs or fumaroles fed by underground heating created these deposits. Silica deposits around hydrothermal vents in Iceland are among the best parallels on Earth.

Murchie said, "The habitable zone would have been within and alongside the conduits carrying the heated water." The volcanic activity that built the cone in Nili Patera appears to have happened more recently than the 3.7-billion-year or greater age of Mars' potentially habitable early wet environments recorded in clay minerals identified from orbit

Mr. Hartley's Amazing Comet

Today the Deep Impact spacecraft zipped past Comet 103P/Hartley 2 at a distance of about 435 miles (700 km) at 6:59:47 a.m. PDT (13:59:47 Universal Time). After confirming that the spacecraft had survived its 27,000-mile-per-hour brush with this icy interloper, the scientists and engineers who'd gathered at the Jet Propulsion Laboratory in California held their collective breath for about 20 minutes while waiting for the first images to be radioed to the ground.

Any apprehension quickly turned to joy, as the views revealed the craft's pinpoint targeting and crisp images of an elongated, irregularly shaped body spewing gas and dust from a plethora of jets.

Spacecraft have now photographed five comets at close range, and with a length of just 1¼ miles (2 km), Hartley 2 is the smallest. However, as investigator Jessica Sunshine (University of Maryland) noted today during a press briefing, "It's the most interesting and, for its size, the most active."

Radar images acquired by Arecibo Observatory last week had prepared the mission scientists to expect an elongated body. But no one was anticipating such an unusual visage: the comet's two ends, both roughly textured, are the sources of perhaps dozens of individual jets, while the midsection looks completely smooth, as if covered deeply by a blanket of fine dust. "We have a lot of work to do to try to understand what's going on here," Sunshine admitted.

Project scientist Michael A'Hearn (University of Maryland) noted that images of the comet taken continuously since October 1st had shown periodic surges of carbon dioxide (CO2) emanating from the nucleus. Judging from the close-ups, he says it's now clear that "one area on the comet is incredibly rich in dry ice, and that's what drags out the grains and produces all the phenomena that we see."

Unlike spacecraft that veritably drip with instrumentation, Deep Impact carries a minimalist payload: medium- and high-resolution cameras, along with an infrared spectrometer.

Today's views were not the most detailed frames — those will be radioed back to Earth in the coming days. According to project manager Tim Larson, the spacecraft will continue to photograph the comet's nucleus for three more weeks as it recedes into the distance.

The rendezvous was the second cometary encounter for this spacecraft, which previously looked on as a large copper bullet slammed into Comet 9P/Tempel on January 4, 2005. After that eventful encounter, NASA managers recommissioned the still-viable craft as the EPOXI mission, a combination of its two extended mission components: Extrasolar Planet Observations and Characterization (EPOCh), and the second cometary flyby, called the Deep Impact Extended Investigation (DIXI).

On hand for today's festivities at JPL were Malcolm Hartley and his wife. Hartley discovered this object in March 1986 on glass plates taken with the Siding Spring Observatory's UK Schmidt telescope in New South Wales, Australia. Its high eccentric path carries the comet from a perihelion near Earth's orbit out to beyond Jupiter and back every 6½ years. In fact, right now this periodic visitor is quite close to Earth and putting on a decent showing in the predawn sky.

Finally, here's something for you space-trivia buffs: There's actually been a sixth close flyby of a comet — in fact, it was a fly-through. Do you know which spacecraft it was? Offer your guess in the comments section below; I'll congratulate the first person to post the correct answer in a future story about the Comet Hartley 2 results!

Five Things About NASA's EPOXI Mission

Here are five quick facts about the EPOXI mission, scheduled to fly by comet Hartley 2 on Nov. 4, 2010.

1. High Fives - This is the fifth time humans will see a comet close-up, and the Deep Impact spacecraft flew by Earth for its fifth time on Sunday, June 27, 2010.

2. Eco-friendly Spacecraft: Recycle, Reuse, Record - The EPOXI mission is recycling the Deep Impact spacecraft, whose probe intentionally collided with comet Tempel 1 on July 4, 2005, revealing, for the first time, the inner material of a comet. The spacecraft is now approaching a second comet rendezvous, a close encounter with Hartley 2 on Nov. 4. The spacecraft is reusing the same trio of instruments used during Deep Impact: two telescopes with digital imagers to record the encounter, and an infrared spectrometer.

3. Small, Mighty and Square-Dancing in Space - Although comet Hartley 2 is smaller than Tempel 1, the previous comet visited by Deep Impact, it is much more active. In fact, amateur skywatchers may be able to see Hartley 2 in a dark sky with binoculars or a small telescope. Engineers specifically designed the mighty Deep Impact spacecraft to point a camera at Tempel 1 while its antenna was directed at Earth. This flyby of comet Hartley 2 does not provide the same luxury. It cannot both photograph the comet and talk with mission controllers on Earth. Engineers have instead programmed Deep Impact to dance the do-si-do. The spacecraft will spend the week leading up to closest approach swinging back and forth between imaging the comet and beaming images back to Earth.

4. Storytelling Comets - Comets are an important aspect of studying how the solar system formed and Earth evolved. Comets are leftover building blocks of solar system formation, and are believed to have seeded an early Earth with water and organic compounds. The more we know about these celestial bodies, the more we can learn about Earth and the solar system.

5. What's in a Name? - EPOXI is a hybrid acronym binding two science investigations: the Extrasolar Planet Observation and Characterization (EPOCh) and Deep Impact eXtended Investigation (DIXI). The spacecraft keeps its original name of Deep Impact, while the mission is called EPOXI.

Our "New, Improved" Solar System

Compared with the systems of planets being found around other stars, our solar system is an orderly place, with each planet tracking around the Sun in a stable, roughly circular orbit. For centuries, the planets' long-term stability has been taken as evidence that they formed where they are now, sucking up gas, dust, and larger building blocks from the protoplanetary disk around them until reaching their final sizes.

But dig a little deeper, and you find serious problems with that simplistic view. For example, Uranus and Neptune should have ended up much smaller and less massive, because billions of miles from the infant Sun the protoplanetary pickings were slim and the assembly process too slow. Conversely, Mars formed in the fat of the disk and should have ended up at least 10 times more massive than it is today. And no one really understands the asteroid belt's existence — particularly why it's crudely divided into rocky bodies (called S types) nearer the Sun and dark, carbon-dominated hunks (C types) farther out.

Dynamicists solved the Uranus-Neptune dilemma several years ago by positing that the four giant planets were initially a much closer-knit family, coming together in a cozy zone 5 to 12 astronomical units from the Sun.

The Big Four coexisted peacefully at first, but after a couple of million years things got ugly. Jupiter's gravity jostled Saturn into an unstable, wide-swinging orbit, triggering a chain reaction of close encounters that ultimately threw Neptune and Uranus out to the distant depths of interplanetary space they now occupy.

Theorists now have computer models that get the outer solar system to come out right, more or less, but they're still vexed by the inner planets. The thorny problems of a too-small Mars and a compositionally stratified asteroid belt remain.

Worse, discoveries of other solar systems were revealing radically different inner-planet architectures: "hot Jupiters" whirling so close to their suns that a year for them is just days long, and massive planets in orbits so wildly out of round that any lesser worlds they encountered would have been tossed out. Given all the disorder so common among the exoplanets, it's remarkable that the Sun ended up with any small, close-in worlds at all.

But there's been a breakthrough in modeling our solar system's formation, details of which emerged at last week's meeting of the American Astronomical Society's Division for Planetary Sciences. It turns out that getting four right-size terrestrial planets and the right kind of asteroid belt is a snap — but it requires dramatic new thinking about the path Jupiter (and Saturn) took getting to their current locations.

Solving for Mars

The stage for this revolution was actually set last year, when Brad Hansen (University of California, Los Angeles) tried assembling the inner solar system an entirely new way. He took a cue from the one other place known to have close-in, Earth-size planets: the system surrounding the millisecond pulsar B1257+12. Discovered in 1991, these pulsar planets are often overlooked because their host "star" is so extreme.

Prior computer simulations assumed that the inner planets accreted from a dense, massive belt of mile-wide planetesimals extending almost out to Jupiter. But invariably the outcome was a too-massive Mars and jumbled mess in the asteroid belt. However, Hansen realized that PSR B1257+12's planets must have assembled from a limited disk of hot material closely surrounding the pulsar.

When he tried that approach with our solar system, starting with a disk confined to just 0.7 to 1.0 astronomical unit from the Sun, voilà! — his computer runs routinely coughed up sets of planets with bigger ones (think "Earth" and "Venus") in the middle and smaller ones ("Mercury" and "Mars") near the inner and outer edges.

So why should Earth and its immediate neighbors have formed from such a limited disk? Hansen had no clue when he published his results last year. "In my paper I freely admit the choice was ad hoc," he allows. But it worked — far better, in fact, than any of the previous trials.

Meanwhile, the outer-planet crowd had wondered how Jupiter managed to avoid becoming a close-in captive of the Sun, as so many other beefy exoplanets had. On paper, tidal interactions between the King of Planets and the Sun's protoplanetary disk should have drawn Jupiter inward to its doom, or nearly so.

As early as 1999, however, theorists Frederic Masset and Mark Snellgrove (then at Queen Mary College) showed that Jupiter would have indeed migrated inward — but only until it linked up with Saturn in a 3:2 resonance, that is, with the two spaced such that Jupiter completed three orbits for every two of Saturn's. At that point the pair would have reversed direction and headed outward. (The mechanics of this coupled migration are a little involved; if interested, you can get the details here.)

Hansen's shot-in-the-dark simulations, combined with the realization that the gas giants could have migrated both inward and outward, gave solar-system modelers a "Eureka!" moment. What would have happened, they wondered, if young Jupiter had ventured much closer to the Sun than where it finally ended up?

The amazing answers came to light at last week's meeting. Kevin Walsh, who'd worked this problem with Alessandro Morbidelli while post-docing at Côte d'Azur Observatory in France, ran computer simulations that put Jupiter initially 3½ a.u. from the Sun and allowed it to creep inward to 1½ a.u. (about where Mars orbits now). The results were remarkable in their breadth and significance.

First, Jupiter's gravity would have forced the small stuff in its path inward too, creating a perturbation-driven snowplow that piled all the rocky planetesimals into a mini-disk with an outer edge 1 a.u. from the Sun. According to presenter David O'Brien (Planetary Science Institute), a member of Walsh's team, Jupiter took only 100,000 years to drive inward to 1½ a.u.and another 500,000 years to reach its current orbit, 5.2 a.u. from the Sun.

Second, the new computer runs confirmed what Hansen had already shown: a mini-disk of rocky material extending only to 1 a.u. provided just what's needed to assemble four terrestrial planets — and a Mars that's not too big.

At the meeting, David Minton and Hal Levison (Southwest Research Institute) described their own simulations using a truncated mini-disk, and they come to much the same conclusions. One key variation is that, in the Minton-Levison runs, Mars forms well within the disk and migrates to its outer edge and beyond.

This could be a good thing, because a moving Mars would provide the gravitational perturbations needed to kick iron-rich planetesimals out of the disk and into the inner asteroid belt, where they're commonly found today. "The original locations of Mars in the [disks] I calculated were quite variable," Hansen comments. "The outward migration was driven by scattering, so things shake up quite a bit."

Third, Jupiter probably would likely have come in even closer, perhaps sliding all the way into the Sun, had not Saturn (already in tow via the 3:2 resonance) grown massive enough to hit the tidal brakes and reverse both planets' movement. In this sense, the formation and survival of the terrestrial planets hinged not on Jupiter's existence but on Saturn's.

Fourth, Jupiter's inward trek would have completely swept clear the asteroidal region from 2 to 4 a.u. Most of the objects there were lost completely, but roughly 15% ended up scattered into a disk beyond Saturn. After reversing course and moving outward, the two planets scattered some of those previously displaced objects again, this time inward, returning them to what's now the inner asteroid belt.

Fifth, as Saturn and Jupiter continued outward to their final orbits, they encountered another group of asteroids. Unlike the rocky bodies that had boomeranged out and back, these were carbon- and water-rich objects that had formed 6 to 9 a.u. from the Sun. Tossed inward by perturbations from the dynamic duo, they formed most of what's now the outer asteroid belt.

A New Paradigm?

To recap: in one sweeping narrative, these theorists propose solutions for both a minimalist Mars and a stratified asteroid belt with a rock-rich inner region and a carbonaceous, water-harboring outer belt. As a bonus, the new mindset leads naturally to a set of four inner planets (correct sizes, correct orbits) that assembled on the right time scale (within about 30 million years of the Sun's formation). It even provides a source of water for Earth (C-type asteroids) and a near-Earth environment conducive to the presumed giant impact that formed the Moon.

This radical scenario represents "a paradigm shift in our understanding of the evolution of the inner solar system," says Walsh. That's an understatement! It all seems hauntingly Velikovskian to me, except that these folks have clearly done their homework.

Will "Jupiter's Grand Tack" (as Morbidelli dubs it) hold up to further scrutiny? Walsh and his team have submitted a fuller treatment to Nature for publication, but other dynamicists are already weighing in based on the presentations heard last week. "Many aspects of their model look good to me," observes SwRI officemate William Bottke, "but lots of first-order things have to be tested before they can declare victory on all fronts."

For example, it's now widely accepted that most of Earth's water was imported from the outer asteroid belt. Yet Bottke thinks the scenario envisioned by Walsh, Morbidelli, O'Brien, and others would require a vast reservoir of water-rich (C-type) bodies, totaling hundreds of times the mass of the current asteroid belt. "We need to vet these models with more physics and more cosmochemistry," he says. Also, the depth of Jupiter and Saturn's inward penetration would have depended critically on how fast Saturn grew to nearly full size and when. The broader the range of initial conditions that "work," the more confidence there'll be that this scenario is the right one.

Morbidelli remains confident that they're onto something profound. "We consider ourselves celestial geologists," he quips. "We're now able to 'read' the current solar-system arrangement well enough to figure out what the early planets did."

NASA Spacecraft Hurtles Toward Active Comet Hartley 2

 NASA's Deep Impact/EPOXI spacecraft is hurtling toward Comet Hartley 2 for a breathtaking 435-mile flyby on Nov. 4th. Mission scientists say all systems are go for a close encounter with one of the smallest yet most active comets they've seen.

"There are billions of comets in the solar system, but this will be only the fifth time a spacecraft has flown close enough to one to snap pictures of its nucleus," says Lori Feaga of the EPOXI science team. "This one should put on quite a show!"

Cometary orbits tend to be highly elongated; they travel far from the sun and then swing much closer. At encounter time, Hartley 2 will be nearing the sun and warming up after its cold, deep space sojourn. The ices in its nucleus will be vaporizing furiously – spitting dust and spouting gaseous jets.

"Hartley 2's nucleus is small, less than a mile in diameter," says Feaga. "But its surface offgasses at a higher rate than nuclei we've seen before. We expect more jets and outbursts from this one."

EPOXI will swoop down into the comet's bright coma – the sparkling aura of debris, illuminated by the sun – shrouding the nucleus. The spacecraft's cameras, taking high-resolution (7 meters per pixel at closest approach) pictures all the while, will reveal this new world in all its fizzy glory.

"We hope to see features of the comet's scarred face: craters, fractures, vents," says Sebastien Besse of the science team. "We may even be able to tell which features are spewing jets!"

The spacecraft's instruments are already trained on their speeding target.

"We're still pretty far out, so we don't yet see a nucleus," explains Besse. "But our daily observations with the spectrometer and cameras are already helping us identify the species and amounts of gases in the coma and learn how they evolve over time as we approach."

Artist's concept of the spacecraft's previous encounter with Comet Tempel 1.

The aim of the mission is to gather details about what the nucleus is made of and compare it to other comets. Because comets spend much of their time far from the sun, the cold preserves their composition – and that composition tells a great story.

"Comets are left-overs from the 'construction' of our solar system," explains Besse. "When the planets formed out of the 'stuff' in the solar nebula spinning around the sun, comets weren't drawn in."

Researchers study these pristine specimens of the primal solar system to learn something about how it formed, and how it birthed a life-bearing planet like Earth.

"These flybys help us figure out what happened 4 1/2 billion years ago," says Feaga. "So far we've only seen four nucleii. We need to study more comets to learn how they differ and how they are the same. This visit will help, especially since Hartley 2 is in many ways unlike the others we've seen."

EPOXI will provide not only a birds-eye view of a new world but the best extended view of a comet in history.

"This spacecraft is built for close encounters. Its instruments and our planned observations are optimized for this kind of mission. When, as Deep Impact, it flew by Tempel 1, it turned its instruments away from the nucleus to protect them from debris blasted up by the impactor. This time we won't turn away."

The EPOXI team will be waiting at NASA's Jet Propulsion Laboratory.

"We'll start diving into the data as soon as we receive it," says Feaga. "We'll work round the clock, on our toes the whole time, waiting for the next thing to come down."

Sounds like it could be intense.

"It's already intense," says Besse. "We're getting more and more data, but at encounter we'll be flooded!"

And that will be only the beginning.

Ah, Comet Hartley… THERE you are!

Ah, Comet Hartley… THERE you are!

…or at least, there you were, last night. Yes, after several tries I finally tracked down Comet Hartley last night – exactly where it was supposed and predicted to be, i.e. close to the Double Cluster in Perseus – but boy, it was faint, So faint, waaay fainter than naked eye brightness. It didn’t look at all impressive, just a small, blurry, fuzzy, smeary ball of… mistiness… but it was elongated, not like a star at all, so I was delighted to find it!

Going to head out again soon for another look, as the sky is quit clear here in Kendal tonight. And I know exactly where to look…

Click on Photo for Large View

Chang'E 2. In Orbit and Returning Data

Chang'E 2. In Orbit and Returning Data

Chang'E 2 launched successfully on October 1 at 10:59:57 UTC. It launched on a direct transfer trajectory to the Moon, and successfully entered orbit on October 6 at 03:40. That orbit insertion maneuver put Chang'E 2 into an 12-hour orbit with a perilune of 100 kilometers and an apolune of 8,000 kilometers. Another maneuver on October 8 at 02:45 put Chang'E 2 into its 3.5-hour nominal science orbit 100 kilometers above the lunar surface. By October 5, Chang'E 2 was returning science data to Earth.

New Views of Saturn's Aurora, Captured by Cassini

PASADENA, Calif. -- A new movie and images showing Saturn's shimmering aurora over a two-day period are helping scientists understand what drives some of the solar system's most impressive light shows.

The new, false-color images and video are available online at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

The movie and images are part of a new study that, for the first time, extracts auroral information from the entire catalogue of Saturn images taken by the visual and infrared mapping spectrometer instrument (VIMS) aboard NASA's Cassini spacecraft. These images and preliminary results are being presented by Tom Stallard, lead scientist on a joint VIMS and Cassini magnetometer collaboration, at the European Planetary Science Congress in Rome on Friday, Sept. 24.

In the movie, the aurora phenomenon clearly varies significantly over the course of a Saturnian day, which lasts around 10 hours 47 minutes. On the noon and midnight sides (left and right sides of the images, respectively), the aurora can be seen to brighten significantly for periods of several hours, suggesting the brightening is connected with the angle of the sun. Other features can be seen to rotate with the planet, reappearing at the same time and the same place on the second day, suggesting that these are directly controlled by the orientation of Saturn's magnetic field.

"Saturn's auroras are very complex and we are only just beginning to understand all the factors involved," Stallard said. "This study will provide a broader view of the wide variety of different auroral features that can be seen, and will allow us to better understand what controls these changes in appearance."
Auroras on Saturn occur in a process similar to Earth's northern and southern lights. Particles from the solar wind are channeled by Saturn's magnetic field toward the planet's poles, where they interact with electrically charged gas (plasma) in the upper atmosphere and emit light. At Saturn, however, auroral features can also be caused by electromagnetic waves generated when the planet's moons move through the plasma that fills Saturn's magnetosphere.

Previous data from Cassini have contributed to a number of detailed snapshots of the aurora. But understanding the overall nature of the auroral region requires a huge number of observations, which can be difficult because Cassini observation time close to Saturn is in high demand, Stallard said.

However, VIMS observations of numerous other scientific targets also include auroral information. Sometimes the aurora can be clearly seen, but sometimes Stallard and colleagues add multiple images together to produce a signal. This wide set of observations allows Cassini scientists to understand the aurora in general, rather than the beautiful specific cases that dedicated auroral observations allow, Stallard said.

Stallard and his colleagues have investigated about 1,000 images from the 7,000 that VIMS has taken to date of Saturn's auroral region.

The new, false-color images show Saturn's aurora glowing in green around the planet's south pole. The auroral information in the two images was extracted from VIMS data taken on May 24, 2007, and Nov. 1, 2008. The video covers about 20 Earth hours of VIMS observations, from Sept. 22 and 23, 2007.

Phobos: A Chip Off of Mars

NASA's Mars Reconnaissance Orbiter captured this view of the Martian moon Phobos on March 23, 2008, from a distance of about 4,200 miles. It's actually a false-color view, combining data from the camera's blue-green, red, and near-infrared channels.The smallest resolved features are about 65 feet across

Asaph Hall's discovery of Mars's two small moons in 1878 is one of the greatest success stories of observational astronomy. For nearly a century thereafter, however, Phobos and Deimos were little more than dynamical curiosities that traveled oh-so-close to their parent planet.

With the Space Age came the opportunity to see these objects at closer range, and a succession of spacecraft (beginning with Mariner 9 in 1971) has revealed Deimos and especially Phobos with ever-greater detail. Some particularly dramatic views have come from the HiRISE camera aboard Mars Reconnaissance Orbiter.

Yet, despite decades of careful scrutiny from space and from ground-based telescopes, astronomers still debate where these little worlds came from. They're very dark, implying a carbon-rich composition akin to bodies at the outer margins of the asteroid belt. Both also have a low density, suggesting they're riddled with internal cavities. All this evidence points to the notion that Mars somehow captured a couple of wandering objects that happened to stray too close by. (One big "gotcha": both moons have extremely circular orbits very close to Mars's equatorial plane — not exactly the outcome you'd get from two random encounters.)

Now a team of observers has stirred up the pot of possibilities. Yesterday, at the European Planetary Science Congress in Rome, hometown researcher Marco Giuranna (IFSI/INAF) argued that far-infrared spectra of Phobos acquired with the Mars Express orbiter don't match the composition of any known chondritic asteroid or meteorite type. (Chondrites are rocky bodies that have remained unaltered since the solar system's formation.)

As seen by a spectrometer aboard the Mars Express orbiter, the thermal-infrared spectrum of Phobos is a close match to certain phyllosilicates (clay minerals). Also, the position of the peak labeled CF suggests a composition rich in ultramafic (iron- and magnesium-rich) minerals.

What he and others have found instead is a distinct composition rich in dark ultramafic minerals (having lots of iron and magnesium) and clay minerals, called phyllosilicates. The clay signature appears strongest near the large crater Stickney, hinting that deposits were dredged up from deeper down.

Moreover, Martin Pätzold (Köln University) also announced at the ESPC that Phobos has a density of just 1.86 ±0.02 g/cm3. To be so low, the moon's interior must be incredibly porous, with voids taking up 25% to 35% of the total volume. The new density value is based on careful tracking of Mars Express during close flybys of Phobos, including a brush-by just 42 miles (67 km) away last March 3rd.

That mix of clay and ultramafic minerals might be rare among the asteroids, but it's likely a lot more common on the Martian surface down below. The upshot, Giuranna suggests, is that Phobos wasn't captured but more likely formed in place from debris blasted off the surface of Mars during a large, long-ago collision. Most of the debris would have escaped to interplanetary space, but enough of it (11 trillion tons, more or less) hung around to recollect into the two Martian moons.

It's a dramatic hypothesis, to be sure, but is it the correct one? First, as Giuranna's team points out, the new compositional clues don't rule out that Phobos (and Deimos) were captured. Observers have found plenty of asteroids with clay minerals on their surfaces, and ultramafic meteorites (achondrites) aren't exactly rare. Second, the moons' spongy interiors could have resulted if a single body broke apart during its capture by Mars and then then reassembled into a pair of not-quite-solid satellites. Finally, someone needs to run a computer simulation to see if this smash-and-dash scenario makes dynamical sense (according to impact modeler Robin Canup, no one's done it yet).

In any case, we might not have to wait too long to learn the Martian moons' pedigree. A Russian mission called Phobos-Grunt is being readied for launch late next year. The effort has encountered technical problems — it was supposed to head off toward Mars a year ago — but if it succeeds, scientists will have 100 to 200 grams of Phobos to analyze when the sample-return capsule lands in July 2014.

Jupiter Shines Extra Bright

If you look up on any clear September night, a big bright “star” will greet you. It’s low in the east after twilight, and higher in the southeast as the evening grows late. This is the planet Jupiter, and it's far brighter than any true star in the night sky.

Jupiter is always bright, but if you think it looks a little brighter than usual this month, you’re right. Jupiter is making its closest pass by Earth for the year. And this year’s pass is a little closer than any other between 1963 and 2022.

Jupiter is nearest to Earth on the night of Monday, September 20th: 368 million miles away. But it remains nearly this close and bright (magnitude -2.9) throughout the second half of September.

At the closest point of its previous swing-by, in August 2009, Jupiter was about 2% farther from both Earth and Sun than this time. That made it 8% dimmer. At its next pass, in October 2011, it will be 0.4% more distant than now.



Jupiter on Sepetember 2, 2010
Jupiter on September 2nd, shown with south up, as it appears in a reflecting telescope. The Great Red Spot is prominent at upper left, and the South Equatorial Belt is almost invisible.

Also, according to legendary planetary observer Richard Schmude, Jupiter is an additional 4% or so brighter than usual because one of its brown cloud belts has gone missing. For nearly a year the giant planet's South Equatorial Belt, usually plain to see in a small telescope, has been hidden under a layer of bright white ammonia clouds.

Because Jupiter is so close to Earth, this is a great opportunity to view it through a telescope. Jupiter is most interesting when the Gred Red Spot is visible and/or when one of the moons is casting a shadow on Jupiter's disk.

Encounters with Comet Hartley 2

An icy visitor is positioning itself for easier viewing in the coming weeks. Periodic Comet 103P/Hartley 2 won't have the pizzazz of Comet Hale-Bopp or the unexpected spectacle of Comet Holmes. But it will be high in the evening sky when at its best, glowing at perhaps 5th magnitude. It should be dimly visible to the unaided eye from very dark locations, and visible in binoculars and telescopes from almost anywhere in the Northern Hemisphere. (Most of you in the Southern Hemisphere will be able to observe it from mid-October onward.)

Hartley 2's brightness, and its unusually fast slide across the constellations, both result from how closely it will approach Earth: by just 0.12 astronomical unit (11 million miles; 18 million km) on October 20th. This will be its closest approach since its 1986 discovery and one of the closest approaches of any comet in the last few centuries.

The comet has reached 9th magnitude and is brightening by 0.1 magnitude per day. So right now, before the Moon washes the sky with light, is an especially good time to look for this faint visitor.

By September 1st Hartley 2 had climbed north into a corner of Lacerta, where it spent a few days before crossing into northern Andromeda. On the night of September 8-9, at new Moon, the comet was less than 1° from 3.6-magnitude Omicron (ο) Andromedae.

The waxing Moon will brighten the evening sky from about September 15th to 26th. On the 22nd Hartley 2 should be 7th or 8th magnitude and within a few degrees of Lambda (λ) Andromedae.

October 1st finds the comet passing 1.5° south of 2.2-magnitude Alpha (α) Cassiopeiae, high in the northeast during moonless evenings. Perhaps 6th magnitude by then, it should remain at least this bright for the next nine weeks. But it's important to note that, with the comet now just 0.18 a.u. from Earth and closing, its light is no longer concentrated into a small dot but instead is more spread out. So even if you can sight a 6th-magnitude star with the unaided eye, Hartley 2 will be tougher. It's closest to Earth on October 20th at a distance of just 0.121 a.u.

On the night of October 7th in the Americas, when the comet should be 5th or 6th magnitude, it creeps less than 1° south of the Double Cluster in Perseus, magnitudes 4.3 and 4.4. This will make for a wonderful wide-field sight and a great astrophoto opportunity — particularly since it's again new Moon!

From here on Hartley 2 turns southeast, passing near the head of Perseus. On October 20th the fuzzy visitor passes just south of brilliant Capella. By the end of October the comet should still be around 5th magnitude — but now in Gemini. So it doesn't gain a high altitude until later in the night. Perihelion, 1.06 a.u. from the Sun, comes on the 28th — but that morning the nearly last-quarter Moon is just a few degrees away.

Moonless viewing times return around November 1st. But now, with the comet moving away from both the Sun and Earth, it fades by about a magnitude every two weeks. Besides — by then our attention should surely be turning to the exploits of (and pictures from) NASA's EPOXI spacecraft, which swoops by it on November 4th at a distance of just 600 miles (1,000 km).

A Comet's Tale

How could a short-period comet, visible to the unaided eye, go undiscovered until just 24 years ago? Read on.

Malcolm Hartley first spotted it on March 16, 1986, at magnitude 17 or 18 during a sky survey by the 1.2-meter U.K. Schmidt telescope at Siding Spring, Australia. A series of position measurements soon revealed it to be a short-period comet orbiting the Sun about every 6 years. It was the second short-period comet discovered solely by Hartley, hence the "2" in its name. The appellation 103P indicates that it was the 103rd comet with a known orbital period.

A backtrack of Hartley 2's path revealed that it fell into its current orbit only recently. Three close encounters with Jupiter (0.33 a.u. in 1982, 0.09 a.u. in 1971, and 0.23 a.u. in 1947) had shifted the comet's track closer to the Sun. Prior to those encounters, Hartley 2 never came closer than 2 a.u. from the Sun, leaving it beyond visual detection.

Hartley 2's next return came in 1991, when it brightened that September to 8th magnitude. It did so again at its following return in December 1997. The 2004 apparition was a poor one, with the comet far from Earth.

Now it's arriving front and center for its best showing yet. So enjoy it while you can!

Hubble Revisits Supernova 1987A

Supernova 1987A's ring, about a light-year across,
was probably shed by the star about 20,000 years before it exploded.
The dozens of bright spots around the ring mark where a shock wave
unleashed by the stellar blast is slamming into the ring's material.

It's been more than two decades since we Earthlings got word that a star in the Large Magellanic Cloud had blown itself to smithereens.

Supernova 1987A peaked at 3rd magnitude, making it a snap to spot by eye. But, with its declination of -69°, the blast was invisible to virtually everyone north of the equator. I'm jealous of my southern astro-friends because I never got to see it. (In fact, I wonder how the popular perception of and appreciation for astronomy might be different had this event been in view from northern skies — a topic for another day!)

Fortunately, the Hubble Space Telescope started observing SN 1987A within months of its launch in 1990. Those first views revealed a ring of matter thrown out by the star about 20,000 years before its demise. The supernova's expanding shock wave eventually crashed into that ring, creating a necklace of bright knots first spotted in 1995 HST images. Observers have kept tabs on this ring ever since — primarily with an instrument called the Space Telescope Imaging Spectrograph, or STIS, which astronauts installed on Hubble in 1997.

Unfortunately, an electronic failure in 2004 rendered STIS inoperable, and astronomers had to make do without its services until last year, when spacewalking astronauts replaced a faulty circuit board and brought STIS back to life.

In the September 2nd edition of Science Express, a star-studded international team of astronomers describe observations of the supernova made with STIS earlier this year, the first in six years. The ejected ring is still there, now studded with about 30 hotspots. Over time, as the supernova's shock wave continues to barrel outward, these should merge into a single bright band.

More interesting is the insight being gleaned from a second shock wave, this one triggered by the ring itself and propagating back toward what's left of the progenitor star and through the supernova's expanding debris. The team reports that spectra of this inner shock reveal lots of hydrogen, as you'd expect, but they also see some other emissions that are probably from nitrogen and perhaps from carbon.

Essentially, the now-gone star has laid bare whatever was inside when it exploded, and over time careful observations by HST and other telescopes will, in Humpty Dumpty fashion, attempt to put the progenitor star back together again.

"I think a great thing here is the resurrection of STIS," notes coauthor Robert Kirshner (Harvard-Smithsonian Center for Astrophysics). "Astronauts zipping out 114 screws while wearing boxing gloves were not just doing it for the challenge! This paper shows that the instrument is back working, and that we're finding out new things about an object that is about the same age as HST."

One Star, Seven Planets

Many worlds around HD 10180
An artist's impression of the many worlds orbiting the Sunlike star HD 10180.

Nestled in the Chilean Andes at altitude of 7,900 feet (2,400 m), the European Southern Observatory's 3.6-m reflector at La Silla is neither the highest nor the largest telescope in the region. Far from it. However, coupled with the incredible HARPS spectrograph, this telescope is cranking out discoveries of extrasolar planets faster than any other observatory on Earth.

Today, at a gathering of planet-hunting astronomers in France, Christophe Lovis (Geneva Observatory) announced that his team has identified a solar system packed with planets — five for sure, and probably seven — using the La Silla facility. It's the most populous exoplanet system known.

The central star is HD 10180, a type G dwarf situated 137 light-years away in the southern constellation Hydrus. It's one of 400 nearby Sunlike stars that astronomers have been monitoring from La Silla for years. HARPS can't see these worlds directly; instead it detects minuscule Doppler shifts in the stars' light, caused by back-and-forth wobbles in their motion that, over time, reveal the presence of planets circling around them. In the case of HD 10180, the telescope amassed 190 nights of observations over six years.

You could make a case that spotting alien planets has gotten a little ho-hum — after all, the total count (including those orbiting the Sun) now tops 500, and 15 systems involve at least three planets.

But HD 10180 definitely raises the bar. Its five sure-things, dubbed C, D, E, F, and G, have Neptune-class masses 13 to 25 times that of Earth. But all five are quite close to the star, in orbits that range from 0.06 to 1.4 astronomical units (5½ to 130 million miles out). So much mass packed so close together is bound to incite gravitational tussles among them, and future observations will follow the long-term evolution of the system.




Solar systems compared
A comparison of our solar system with that of HD 10180 and other stars encircled by at least three planets. Black lines indicate the range of distance due to eccentric orbits.

But wait — there's more! Lovis and his team are fairly certain there's a sixth planet, H, with at least 65 Earth masses (making it Saturn-ish) and orbiting 3.4 a.u. from the star. There's also strong evidence for a seventh sibling, B, zipping just 0.02 a.u (2 million miles) from the star. Although not yet confirmed, this innermost planet might be very close to Earth in mass. It causes a wobble in HD 10180 only about 2 miles (3 km) per hour — "slower than walking speed," notes team member Damien Ségransan — and is thus very hard to measure.

For all the details, read the team's article in the current issue of Astronomy & Astrophysics. At upper right is Figure 13, a concise comparison of solar systems with three or more planets (one is missing, however: the four-member set circling pulsar PSR 1257+12).

Now that we know of a system as crowded with planets as our own, isn't it about time we starting finding some that resemble Earth? That bar-raising exoplanet discovery may not be long in coming — NASA's Kepler spacecraft is looking for them right now.

The Incredible Shrinking Moon

At one point during the Apollo 17 mission, moonwalking astronauts Gene Cernan and Harrison "Jack" Schmitt tried to drive their lunar rover up the face of a 200-foot-high rise known as the Lincoln-Lee Scarp. It didn't seem that imposing a task, but the rover's wheels slipped so much that the astronauts were forced to climb it at an angle, much as a sailboat tacks into a stiff wind.


Thrust fault diagram
Thrust faults occur when the lunar crust is compressed laterally, breaking the rocky materials below and forming a long scarp on the surface.

Lincoln-Lee is the kind of feature created when one slab of rock overrides another due to horizontal compression (what geologists term a thrust fault). On Earth, good (if enormous) examples of thrust faults occur where crustal plates collide — think how the towering Andes rim the west coast of South America, and you get the idea.

What Cernan and Schmitt couldn't have known back in 1972 is that Lincoln-Lee is not an isolated feature but one of likely hundreds of small thrust faults all over the Moon. That revelation came to light only recently, thanks to the incredibly detailed images of the lunar surface being beamed to Earth by two Narrow Angle Cameras aboard NASA's Lunar Reconnaissance Orbiter. (These same cameras have taken snapshots of the historic Apollo 11 landing site and others.)


Map of lunar scarps
The distribution of lobate scarps known as of mid-2010. Black dots indicate previously known features, while white dots mark those found in images by the Lunar Reconnaissance Orbiter. Click here for a larger version.

It wasn't until LRO arrived on the scene that geologists realized the subtle fractures are pervasive. After poring over images from LRO, a team led by Thomas Watters (Smithsonian Institution) has identified 14 new scarps in addition to the three dozen already known. As the map here shows, half of the new finds are poleward of 60° in latitude. (Most of the previously recognized scarps had been spotted by cameras mounted into the orbiting command modules of Apollos 15, 16, and 17 — but these craft never strayed far from the lunar equator.)

In the August 20th issue of Science, the researchers reach a startling and unexpected conclusion: "We have now found that these lobate scarps occur everywhere on the Moon," Watters explains, "which means the Moon has been contracting or shrinking globally."


Scarp in Gregory crater
A thrust fault crossing the floor of Gregory crater on the lunar farside.

All told, the lunar diameter hasn't changed much, probably only about 700 feet (200 m). But the scarps look so fresh that they must have formed in the recent past, geologically speaking. "These scarps can't be any older than 800 million to 1 billion years," Watters noted during a press briefing yesterday, and they could be much younger. "We're finding the Moon is a truly dynamic planet," adds Michael Wargo, chief lunar scientist at NASA headquarters. "Who'd have thought that tectonic processes would still be occurring today?"

The scarps escaped notice until now because they're only a mile or two long and just tens of feet high — completely invisible to backyard telescopes and even to previous lunar-orbiting craft. Most likely, they result from the gradual contraction of the lunar interior as it cools, a process that apparently didn't end when the last maria filled with lava some 3 billion years ago.

Thrust faults appear on the surfaces of Mars and especially Mercury, but they're huge by comparison. Some of the Mercurian scars are hundreds of miles long and more than a mile high, implying that the planet shrank by at least a couple of miles as its molten interior cooled and contracted.

Yet at one time the Moon must have been really, really hot as well. After all, it likely accreted by picking up the white-hot pieces after something enormous collided early on with Earth. So shouldn't there likewise be giant thrust faults jutting skyward across lunar landscape? Some researchers think the Moon did undergo substantial contraction, but the surface scars from that have been erased over time. Watters thinks otherwise. "Our results are really more consistent with a cooler initial starting temperature," he explains, "one that didn't allow the entire Moon to melt."


Astronaut collecting lunar soil
Astronaut Harrison "Jack" Schmitt uses a special rake to collect lunar soil during the Apollo 17 mission in December 1972.

As I listened to yesterday's press briefing, I wondered what Cernan and Schmitt were thinking as they struggled up the slope of Lincoln-Lee Scarp all those years ago. So I asked one of them.

"We were well aware of the Lee-Lincoln scarp and that it is a potential thrust fault or wrinkle ridge," Schmitt recalls. "We drove up it to Station 2 at the base of the South Massif, and along and down it going to Station 4 [Shorty crater]. It was entirely covered by a light mantle or avalanche deposit. The avalanche probably flowed off the South Massif about 100 million years ago, as it appears to have been triggered by [nearby impacts from] Tycho ejecta. Lee-Lincoln would be at least older than the avalanche and I suspect much older than that."

Watters and other lunar geologists should eventually be able to say more about how and when all these lobate scarps formed. As of now, LRO has mapped only about 10% of the lunar surface at high resolution. But give it another three years (assuming the funding holds out), and there'll be enough coverage to inspect the entire lunar glove down to a resolution of just a few feet.

A Solar Tsunami

Solar flare on August 1, 2010
A false-color composite shows the
solar flare (bright area at lower left) and large magnetic disturbance
that rippled across the Sun's disk on August 1, 2010. Recorded by
NASA's Solar Dynamics Observatory at extreme-ultraviolet wavelengths,
the hues correspond to coronal gases at temperatures of 1 to 2 million
kelvins. Click here for a larger view.

After oversleeping for more than a year, our star is finally stirring from hibernation. Experts don't expect solar activity to peak until until mid-2013 (and a weak one at that), but the signs of awakening are clearly evident.

A few days ago the Sun let loose with a massive belch. On August 1st at 8:55 Universal Time, orbiting satellites witnessed a sizable flare erupting from the large sunspot region designated 1092. The strength of this outburst was pegged at C3, modest as flares go, but it still triggered an impressive coronal mass ejection, or CME, that shot out from the solar disk at more than 600 miles (1,000 km) per second. Watch the amazing video from NASA's STEREO spacecraft here.

When the flare erupted, NASA's recently-launched Solar Dynamics Observatory also looked on as the magnetic disturbance caused an enormous filament of superheated gas to pulse across the Sun's disk.

All this tumult occurred on the Earth-facing side of the Sun, and skywatchers at far northern and southern locations briefly enjoyed colorful auroral displays on the night of August 3-4.

The Sun has since quieted down, but the big spot in region 1092 has been joined by a second, smaller group (1093) that rotated into view yesterday. Go have a look — but, as always, never try to look at the Sun by eye or using optical aid without using a safe solar filter.

Meanwhile, when the Sun's activity finally does peak, solar physicists will have more spacecraft at their disposal than ever before — despite the news that NASA managers pulled the plug on the Transition Region and Coronal Explorer (TRACE) on June 21st after 12 years of operation.

The workhorse Solar and Heliospheric Observatory (SOHO), a collaboration between NASA and the Rueopean Space Agency, just keeps on chugging (it's nearly 15 years old). Even with the loss of TRACE, NASA still has SDO, STEREO, and ACE (Advanced Composition Explorer) in its arsenal of orbiting sentinels. (By the way, teh STEREO team has a great iPhone app showing the Sun in 3D.)

In addition, the Japan Aerospace Exploration Agency continues to receive great high-resolution images from its Hinode spacecraft.

An Evening Dance of Planets

Saturn and Mars are five magnitudes fainter than Venus and thus only about 1% as bright. They're side by side in the sky, separately by three or four fingers held together at arm’s length. They'll spend the coming week sliding to the right with respect to Venus, creating a planetary triangle that changes shape from day to day. The crescent Moon joins the twilight planet scene on Thursday, August 12th (when it’s below Venus), and on Friday, the 13th (when it’s left of Venus).

An Evening Dance of Planets

Step outside as evening twilight fades, and from now through the middle of August you’ll find three planets shining low in the west — one much brighter than the other two. Venus will leap out at you, but you may need to wait for the sky to darken a bit more before fainter Saturn and Mars glimmer into view.

Three evening planets, Aug. 2010
In the western sky at dusk, bright Venus lights the way to fainter Mars and Saturn. The crescent Moon joins them on August 12th and 13th. Can you spot Mercury far to their lower right? Binoculars help.

Although the three planets look close together, they’re not. Venus is currently 6 light-minutes (73 million miles) from us, Mars is 17 light-minutes (190 million miles) distant, and Saturn is far in the background 85 light-minutes (950 million miles) away.

Venus's proximity is one of three reasons why it's so much brighter than the other two planets. It’s also much closer to the Sun, so it’s illuminated more intensely, and it’s covered with white, brilliantly reflective clouds. Mars and Saturn look similarly bright for reasons that cancel out: Saturn is 35 times larger than Mars, but it’s much farther both from us and from the Sun.

Don’t miss this chance to do some easy astronomy from your backyard, balcony, or rooftop

Dark Nights for the Perseids

The last time the annual Perseid meteor shower happened during a run of good moonless nights was in 2007. It turns out that every three years, the same phase of the Moon returns to roughly the same date each month (2.2 days earlier, on average). So in 2010 we're on for moonless Perseids again!

The shower lasts for many days, but according to the International Meteor Organization this year's peak should occur during a half-day-long window centered on 1:00 Universal Time on August 13th, which is ideal timing for skywatchers in Eurasia. For North Americans, the best viewing will probably be late Thursday night and early Friday morning, August 12-13, or possibly the night before.

In any case, prime viewing for the Perseids is from about 11 p.m. or midnight (local time) until the first light of dawn. This is when the shower's radiant (its perspective point of origin) is well up in your sky. The higher the radiant, the more meteors you'll see.

Many longtime skywatchers remember the fine displays the Perseids put on in the early 1990s, around when the shower's parent comet, 109P/Swift-Tuttle, last passed through the inner solar system. Those days are gone; the comet won't be back until 2126. But even now some, thin, dense filaments of meteoroids that the comet shed in recent centuries continue to liven up the shower's behavior. Strands left behind by the comet in 441 and 1479 might be in play this year, though only a little enhancement is expected from them.

At a very dark, rural site, you can probably expect to see 100 or more meteors per hour when the radiant (in northern Perseus) is highest in your sky before the first light of dawn. Any light pollution will cut down on the numbers, as will the radiant's lower altitude earlier in the night. But the brightest few meteors shine right through light pollution, and the few that happen when the radiant is low are especially long, skimming the upper atmosphere and flying far across the sky.

To get the most enjoyment while watching for Perseids, find a dark spot with an open sky view, bundle up thoroughly in blankets or a sleeping bag (for mosquito shielding as well as warmth, and don't forget the repellent), and lie back in a reclining chair. Gaze into the stars, and be patient. The best direction to watch is wherever your sky is darkest, usually straight up, perhaps with a little inclination toward the radiant. That's all there is to it!



If you're a little more ambitious, you can make a careful meteor count and report it to the International Meteor Organization. Such counts are analyzed to yield the shower's zenithal hourly rate, which is the number of meteors that a single observer would see per hour under ideal conditions: with the radiant directly overhead (at the zenith) and the sky dark enough to reveal 6.5-magnitude stars.

Not all the meteors you'll see are Perseids. In addition to occasional random, sporadic meteors, the weaker Delta Aquarid shower is also active during Perseid season. The Delta Aquarids are slower, often yellower, and track away from a radiant point in eastern Aquarius. Weaker still are the Kappa Cygnids, identifiable by their flight direction away from Cygnus in an altogether different part of the sky.

Don't forget that the Perseid shower lasts for more than one night! Rates are about a quarter to half the peak for one or two nights before and after. A few forerunners of the shower may show up as early as July 20th, and stragglers have been recorded as late as August 24th.

NASA Spacecraft Camera Yields Most Accurate Mars Map

PASADENA, Calif. -- A camera aboard NASA's Mars Odyssey spacecraft has helped develop the most accurate global Martian map ever. Researchers and the public can access the map via several websites and explore and survey the entire surface of the Red Planet.

The map was constructed using nearly 21,000 images from the Thermal Emission Imaging System, or THEMIS, a multi-band infrared camera on Odyssey. Researchers at Arizona State University's Mars Space Flight Facility in Tempe, in collaboration with NASA's Jet Propulsion Laboratory in Pasadena, Calif., have been compiling the map since THEMIS observations began eight years ago.

The pictures have been smoothed, matched, blended and cartographically controlled to make a giant mosaic. Users can pan around images and zoom into them. At full zoom, the smallest surface details are 100 meters (330 feet) wide. While portions of Mars have been mapped at higher resolution, this map provides the most accurate view so far of the entire planet.

The new map is available at: http://www.mars.asu.edu/maps/?layer=thm_dayir_100m_v11 .

Advanced users with large bandwidth, powerful computers and software capable of handling images in the gigabyte range can download the full-resolution map in sections at: http://www.mars.asu.edu/data/thm_dir_100m .

"We've tied the images to the cartographic control grid provided by the U.S. Geological Survey, which also modeled the THEMIS camera's optics," said Philip Christensen, principal investigator for THEMIS and director of the Mars Space Flight Facility. "This approach lets us remove all instrument distortion, so features on the ground are correctly located to within a few pixels and provide the best global map of Mars to date."

Working with THEMIS images from the new map, the public can contribute to Mars exploration by aligning the images to within a pixel's accuracy at NASA's "Be a Martian" website, which was developed in cooperation with Microsoft Corp. Users can visit the site at: http://beamartian.jpl.nasa.gov/maproom#/MapMars .

"The Mars Odyssey THEMIS team has assembled a spectacular product that will be the base map for Mars researchers for many years to come," said Jeffrey Plaut, Odyssey project scientist at JPL. "The map lays the framework for global studies of properties such as the mineral composition and physical nature of the surface materials."

Other sites build upon the base map. At Mars Image Explorer, which includes images from every Mars orbital mission since the mid-1970s, users can search for images using a map of Mars at: http://themis.asu.edu/maps .

"The broad purpose underlying all these sites is to make Mars exploration easy and engaging for everyone," Christensen said. "We are trying to create a user-friendly interface between the public and NASA's Planetary Data System, which does a terrific job of collecting, validating and archiving data."

Mars Odyssey was launched in April 2001 and reached the Red Planet in October 2001. Science operations began in February 2002. The mission is managed by JPL for NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems in Denver is the prime contractor for the project and built the spacecraft. NASA's Planetary Data System, sponsored by the Science Mission Directorate, archives and distributes scientific data from the agency's planetary missions, astronomical observations, and laboratory measurements.

Solar Activity Is Ramping Up

The Sun is finally awakening from its unusually long minimum. While it isn't rife with spots and flares, it seems that lately at least one sunspot, active region, or interesting prominence is now gracing our star on a weekly basis.

Today, AR 1087 is crackling with minor flares, and those of you with any kind of solar filter will be treated to a respectable show whenever it's clear. (For a real treat, check out this video recorded by the Solar Dynamics Observatory.)

I've recently dusted off my trusty Coronado PST (which hardly saw any action over the past two years) and have been rewarded with some excellent prominences and swirling filaments. Every clear day has been worth taking a solar break over the past two weeks alone; last week, AR 1084 paraded across the solar surface, presenting a nearly perfect spiral of plasma traveling along its unusually stable magnetic field.

Prominences and filaments (prominences that cross the solar disk) have been bigger lately too; over the July 4th weekend, I was able to wow my friends and relatives with views of a large prominence as it slowly detached from the solar disk and blew away into space.


The picturesque sunspot AR 1084 recorded in white light using a Baader Herschel Wedge on July 5th.

If AR 1087 doesn't fizzle out this week, I'm hoping it produces a strong eruption in Earth's direction, which may result in auroras visible from my backyard in Manchester, New Hampshire. If you'd like to keep an eye on the Sun, frequently check Spaceweather.com, or for an up-to-the-minute, full-disk image of the Sun in hydrogen light, check out this link to see if it's worth pulling out your solar equipment. You can also follow me on Facebook; I usually post my latest images there whenever I catch something interesting. Please be safe, and only view the Sun through an appropriate solar filter.

South Pacific Eclipse

On Sunday, July 11th, the new Moon will pass directly in front of the sun, producing a total eclipse over the South Pacific. The path of totality stretches across more than a thousand miles of ocean, making landfall in the Cook Islands, Easter Island, a number of French Polynesian atolls, and the southern tip of South America

"It's going to be a beautiful sight," says Lika Guhathakurta of NASA's Heliophysics Division in Washington DC. She herself has witnessed more than eight solar eclipses in a variety of environments from busy cities to lonely deserts to remote mountain peaks. "The South Pacific eclipse could top them all."


South Pacific Eclipse (Mir shadow)
As seen from space station Mir, the Moon's shadow sweeps across Earth during an eclipse in 1999.

She imagines how the event will unfold: First, the Moon's cool shadow will sweep across the landscape, bringing a breeze of its own to compete with the sea's. Attentive observers might notice shadow bands (a well-known but mysterious corrugation of the Moon's outermost shadow) rippling across the beach as the temperature and direction of the wind shift. The ensuing darkness will have an alien quality, not as black as genuine night, but dark enough to convince seabirds to fly to their island roosts. As their cries subside, the sounds of night creatures come to the fore, a noontime symphony of crickets and frogs.

Next comes the moment that obsesses eclipse chasers: The corona pops into view. When the Moon is dead-center in front of the sun, mesmerizing tendrils of gas spread across the sky. It is the sun's outer atmosphere on full display to the human eye.

"You can only see this while you are standing inside the shadow of the Moon," says Guhathakurta. "It is a rare and special experience."

Because the sun's atmosphere is constantly shape-shifting, every total eclipse is unique. Predicting what any given one will look like can be tricky.


South Pacific Eclipse (corona)
The sun's corona shows itself during the total solar eclipse of March 29, 2006.

Nevertheless, Guhathakurta is making a prediction. It's based on a new development in solar physics. For the first time, NASA has two spacecraft stationed on opposite sides of the sun. "STEREO-A and STEREO-B are giving us a realtime 3D view of the solar corona, something we've never had before," she explains. "This helps forecast the appearance of the corona during an eclipse."

Inspecting images from STEREO and also from the Solar and Heliospheric Observatory (SOHO), she predicts observers could see four ghostly-white streamers, two on either side of the sun. They will stretch out two to three degrees, forming a gossamer "X" in the sky with a black hole at the crossing point.

"I'm prepared to be wrong," she confesses. "This is the first time anyone has tried to make such a forecast using STEREO data. It will be interesting to see if it works."

STAR TRAK

The western sky will be crowded after sunset in July. Forming a long slanting line from highest to lowest above the horizon will be the planets Saturn, Mars and Venus, with the bright star Regulus included as well.

Brilliant white Venus will dominate the scene, shining low in the west-southwest an hour after sunset. The gleaming planet will be 40 times brighter than the most conspicuous stars in the evening sky. Venus will become even more dazzling as the month passes, far outshining the stars of the constellation Leo the Lion as it moves among them. On July 9, Venus will be just a degree north of Leo's brightest star, Regulus. By month's end, Venus will be closing in on Mars and Saturn to its upper left (south).

Mars, a hundred times fainter than Venus, will be easy to identify by its red-orange color, contrasting with the pale yellow of Saturn farther to the left. The two will be well separated at the start of the month, but the gap between them will close rapidly, and they will be only a couple of degrees apart at month's end. Mars will not show much detail in a telescope, but Saturn's rings and larger moons will put on a good show starting about an hour after sunset.

Around the middle of the month, Mercury will emerge from the afterglow of sunset low in the west-northwest, adding a fourth planet to the celestial chorus line. Mercury will be very close to Regulus on the evening of July 27. Binoculars may be needed to see this conjunction.

Jupiter will rise around the time Saturn sets, a little after midnight at the start of the month and about 10:30 p.m. EDT by month's end. Appearing well above the eastern horizon as a beautiful "morning star" in the brightening sky, Jupiter will get higher and brighter as the month passes. Its four largest moons will be on the same side of the planet on July 5, 8 and 18.