Trusty Comet Garradd - Observing Highlights

Comet Garradd and M71
Comet Garradd passed M71 in Sagitta on the evening of August 26th.

Comet Elenin has been getting a lot of press in recent months — and now it seems almost certain to be a total bust. Meanwhile, people in the know have been following a comet that has never been hyped much, but seems almost certain to be a fine, though not spectacular performer for many months to come.

We're talking about Comet C/2009 P1 Garradd. At the end of August it was already a fine sight through telescopes of all sizes, shining high in the evening sky at 7th magnitude. It has a bright head, a sharp starlike nucleus, and a tail that's stubby but well defined. And it's forecast to shine near its 6th-magnitude best all the way from October to mid-March. Not since Hale-Bopp has any comet remained so bright for so long.

Comet Garradd passes through the Coathanger asterism on the evening of Friday, September 2nd, then crosses the northwest corner of Sagitta, and soon enters Hercules, where it will remain until February. That means it’s high in the west after nightfall in October, lower but still in good view in November, and near the west-northwest horizon at the end of twilight around Christmas. But by then it’s already up higher in the east before the first light of dawn; the best viewing tips from evening to morning on December 16th.



Path of Comet Garradd Oct 2011 - Jan 2012
Comet Garradd crosses Vulpecula and Sagitta in early September, then remains in Hercules for the next six months.

As the comet climbs high in the early-morning sky of January and February, it will pass the Keystone of Hercules, skim ½° by the globular cluster M92 on the morning of February 3rd (mark your calendar), then sail northward past the head of Draco. It should stay bright all the way into spring as it returns to the evening sky.

Why is it changing so slowly? Comet Garradd is unusually large and distant as 6th-magnitude comets go. It never comes closer to the Sun than Mars’s average distance; at perihelion on December 23rd it’s 1.55 astronomical units from the Sun. Nor does the comet ever come near Earth; it’s about 2 a.u. from us all through October and November, and when closest next March 5th it will still be 1.27 a.u. away. Too bad! Garradd might have qualified for “Great Comet” status if had been on a trajectory to pass close to the Sun and if Earth weren’t on the wrong side of its orbit at the time.

Astronomer Gordon J. Garradd discovered the comet at 17th magnitude on August 13, 2009, at Australia’s Siding Spring Observatory while hunting for — ironically — near-Earth objects.

Supernova in M101

Supernova in M101. The new Type Ia supernova is still brightening in M101, the Pinwheel Galaxy off the Big Dipper's handle. Supernova 2011fe was discovered on August 24th at magnitude 17.2, reached 13.8 on the 25th, 12.5 on the 27th, and 11.6 on the 29th. By then it was easier to see than the galaxy itself in amateur telescopes through suburban light pollution. On the evening of August 31st it was up to about magnitude 10.8.

A normal Type Ia supernova at M101's distance, 23 million light-years, should reach magnitude 10.0 at its peak, assuming none of its light is lost to interstellar absorption in M101 itself. It's well within visual reach in a 4-inch scope. You'll be using the supernova to find the galaxy, not the other way around!

Moonlight will increasingly return to the evening sky starting around September 3rd or 4th.

Opportunity Reaches Its New Home

The west rim of Endeavour Crater, seen from outside
A portion of the west rim of Endeavour crater sweeps southward in this color view
from NASA's Mars Exploration Rover Opportunity. Click for full-size image.
It shouldn't be long until Opportunity is peering over the rim inside.

Yet another adventure is about to begin for NASA’s Mars Exploration Rover B, more famously known as Opportunity. The golf-cart-size, solar-powered vehicle reached the outer hills of its new destination, Endeavour crater, on August 9th after a 3-year, 13-mile (21-km) trek across the flat Martian terrain from the previous big crater it explored, Victoria.

The site from which Opportunity radioed Earth has been named “"Spirit Point,” in memory of its smaller twin, Spirit, that collected data on Mars from January 2004 to March 2011.

Launched in 2003, both Spirit and Opportunity were expected to complete a 90-Martian-day mission; instead, Opportunity has endured 30 times longer and traversed a total of 20.81 miles. Since touching down south of the Martian equator on January 25, 2004, the rover has explored five craters: Eagle, Endurance, Erebus, Victoria, and Santa Maria.

Endeavour, its new destination, is huge: 14 miles (22 km) wide — 25 times as large as Victoria, whose geology the rover studied for two years. A spectrometer aboard NASA’s Mars Reconnaissance Orbiter has detected clay minerals inside Endeavour, which likely formed during a warmer and wetter period on the Red Planet.

"We're soon going to get the opportunity to sample a rock type the rovers haven't seen yet," says science-team member Matthew Golombek (Jet Propulsion Laboratory, Pasadena, California).

Mission scientists will next choose the safest way to have Opportunity descend into the crater. There’s no word on how long they expect this epic exploration to last.

However, we do know that Opportunity's larger successor, Curiosity, will soon be launched on its way to Gale crater on another side of Mars.

2011 Perseid Meteor Showers

The Perseid meteor shower is an annual meteor shower that is extremely regular in its timing and can potentially be visible for weeks in the late summer sky, depending on weather and location.

The Perseid meteor shower is named after the constellation Perseus, which is located in roughly the same point of the night sky where the Perseid meteor shower appears to originate from. This is a useful naming convention, but not very accurate!

The source of the Perseid meteor shower is actually debris from the comet Swift-Tuttle. Every year, the earth passes through the debris cloud left by the comet when the earth's atmosphere is bombarded by what is popularly known as "falling stars."

When and where to look for Perseids in 2011

In 2011, visibility (the weather also notwithstanding) will be somewhat limited by a full moon on August 13 which will likely wipe out fainter meteors from view.

Because of the way the earth hits this debris cloud, the Perseid meteor shower is much more visible in the Northern hemisphere.

People in Canada, for instance, can see the meteor shower by mid-July, but generally there isn't much activity at such an early date. Throughout Europe, the US and the rest of North America, meteor shower activity usually peaks sometime around August 12th, when it is not unusual to see at least 60 meteors per hour streaking across the Northeast sky.

The meteors are certainly bright, but they are actually only tiny objects, usually no more than a grain of sand. However, as they travel at speeds of up to 71 kilometers per second, these small particles put on quite a brilliant show.

The Perseid meteor showers were observed as far back as two thousand years ago, and in ancient Europe, the Perseid meteor shower was known as the "Tears of St. Lawrence."

How to view Perseids

Today, the best place to observe the Perseid meteor shower (or any meteor shower for that matter), is somewhere dark, away from light pollution, and with the moon out of the field of vision. The less light visible, the more brilliant the meteor shower will be.

Telescope or camera?

While mostly viewable to the naked eye, the annual Perseid meteor show may be partially obstructed by the moon, clouds or night mist, so amateur astronomers may want to carry along a pair of binoculars or a camera with a telescopic lens. Even on clear nights, some kind of viewing aid comes in handy for catching sight of even the faintest of falling stars, aptly named "telescopic" meteors. Experts usually just advise to forget the telescope, and simply look up toward the northeast sky.

For photographing the annual event, a digital camera mounted on a tripod helps to steady the images that swiftly move across the sky. A quick trigger finger also helps. Even random clicks during the height of Perseid "prime-time" will guarantee that you'll catch something! Be sure to have the camera focused on infinity and, if your camera permits, leave the shutter open for several minutes for the most spectacular photographic effects.

New Video Showing Water Maybe Flowing on Mars

Scientists believe they have found water on Mars after finding that lines on the planet's surface are more visible in warm seasons.

Scientists announced on Thursday that they saw dark, finger-like features appearing and extending down some Martian slopes during late spring through summer, which fade in the winter and return during next spring.

These recurring features were located on several steep slopes in Mars' southern hemisphere, according to NASA, and are believed to be briny water.

"The best explanation for these observations so far is the flow of briny water," said Alfred McEwen of the University of Arizona, Tucson, in a statement. McEwen is the principal investigator for the orbiter's High Resolution Imaging Science Experiment, or HiRISE, and the lead author of a report about the recurring flows published in Thursday's edition of the journal Science.

Water flows that appear in spring and summer on a slope inside Mars' Newton crater are shown in this combination of orbital imagery with 3-D modeling in this NASA handout photo released to Reuters August 4, 2011. This image has been reprojected to show a view of a slope as it would be seen from a helicopter inside the crater, with a synthetic Mars-like sky. The source observation was made May 30, 2011, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Color has been enhanced.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of Horowitz crater, at 32 degrees south latitude, 141 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from late summer of one Mars year to mid-summer of two years later. The images taken from oblique angles have been adjusted so that all steps in the sequence show the scene as if viewed from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of a steep crater slope in the Terra Cimmeria region of Mars, at 38.8 degrees south latitude, 159.5 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from the end of summer of one Mars year to mid-summer of two years later. The images taken from oblique angles have been adjusted so that all steps in the sequence show the scene as if viewed from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of Newton crater, at 41.6 degrees south latitude, 202.3 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from early spring of one Mars year to mid-summer of the following year. The images have been adjusted to correct those taken from oblique angles to show how the scene would look from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood. The series is timed to dwell two seconds on the first and last frames and one second on intermediate frames, though network or computer performance may cause this to vary.

Earth's Traveling Companion

Earth's Trojan asteroid
Not much to look at, the asteroid 2010 TK7 nonetheless represents Earth's first Trojan asteoid. NASA's WISE spacecraft captured the view at top in October 2010 at the infrared wavelength of 4 microns. Then, in April 2011, a follow-up image was recorded by the Canada-France-Hawaii Telescope in Hawaii. M. Connors & P. Wiegert (top); C. Veillet (bottom)

There's something deeply intriguing about the interplanetary objects known as Trojan asteroids.

The great French dynamicist Joseph-Louis Lagrange predicted in 1772 that small bodies might be sharing Jupiter's orbit, in gravitationally stable sweet spots (now called Lagrange points) located ahead of and behind the planet by 60°. But it wasn't until 1906 that the first of these, 588 Achilles, was spotted. Today more than 4,800 Jupiter Trojans are known, with roughly two-thirds in the preceding "Greek camp" (L4) and a third in the trailing "Trojan camp" (L5).

Within the past two decades, astronomers have found four Trojan asteroids sharing the orbit of Mars and seven accompanying Neptune. They've looked for companions to Earth as well, but the geometry is all wrong: Earth's Trojans would spend most of their time in the daylight sky.

But the odds tipped back in observers' favor with the 2009 launch of NASA's Wide-field Infrared Survey Explorer (WISE), which recorded big swaths of sky 90° away from the Sun. Late last year, Canadian astronomers Martin Connors (Athabasca University) and Paul Wiegert (University of Western Ontario) picked through the spacecraft's scans and identified one object, designated 2010 TK7, that seemed to have an Earthlike orbit. Follow-up was needed, but that wasn't possible until this past April, when it was swept up by two observers in Hawaii.

Their suspicions confirmed, Connors, Wiegert, and Christian Veillet (Canada-France-Hawaii Telescope) report the discovery in July 28th's Nature.

This little body is tied to Earth's preceding Lagrange point. But if you're imagining it circling the Sun in lock step with our planet, think again. The orbit of 2010 TK7 is distinctly eccentric (0.19) and inclined (21°). In fact, it's never actually at L4. Instead, it vacillates widely — almost wildly — in a 400-year-long epicyclic pattern that at times brings it relatively near Earth (though still many times the Moon's distance) and at others places it on the far side of the Sun from us, near the L3 point.



Orbit of asteroid 2010 TK₇
The small asteroid designated 2010 TK7 is locked in an orbital resonance with Earth. This plot shows the range of separation between the asteroid and our planet over a 400-year period. The red line is its average orbit, which is pinned to the L4 Lagrange point that precedes Earth by 60°.

Earth's little buddy is so wide ranging that it might even occasionally spend some time resonating around the distant L3 point. In fact, gravitational influences from Jupiter make the orbit chaotic, and there's no way to know with certainty where 2010 TK7 was or will be when its orbit is tracked for more than 10,000 years.

Unfortunately, even though Earth probably has other Trojans in its entourage, WISE won't be able to see them. The spacecraft ran out of its cryogenic coolant last October, and on February 17th principal investigator Ned Wright sent a command to turn off WISE's transmitter for good. Word is that the spacecraft will remain in hibernation, awaiting a possible wake-up call in the future.

Massive Meteorite Found in China

Xinjiang metoerite
Chinese researchers measure a huge iron meteorite found in a remote mountainous region in July 2011. The oblong metallic object has an estimated mass of 25 tons or more.

As the meteorite specialist for the Beijing Planetarium, Baolin Zhang gets all kinds of unusual reports — like the dramatic (but ultimately specious) tale of a peasant woman who recently found a blue-ice "meteorite" in her yard.


Map of China's Xinjiang region
Although the exact location of the newly found meteorite has not been announced, its general location is the mountainous border region of China's Xinjiang Uyghur province.

But credible reports of a massive, oddly shaped and colored stone in the remote Altai Mountains of Xinjiang Uygur province (in northwest China) got his attention. So earlier this month he assembled a small team to check it out firsthand. The trek was cold and arduous, involving a rented jeep, borrowed horses, and even a camel to cross rugged terrain and rivers still swollen with snowmelt.

On the afternoon of July 16th, after reaching a mountainous crest 9,500 feet (2,900 m) up Zhang and his team finally spotted their objective: a large dark-brown stone jutting from the ground. It took only moments for him to realize what they'd found. "This is a huge iron meteorite," he exulted as cameras recorded the scene.

Based on the size of the oblong portion above ground, 7.5 feet (2.3 m) long and about half as wide, Zhang thinks its mass is roughly 25 tons — and it could perhaps top 30 tons. Such an enormous find would rank as one of the largest meteorites known, perhaps even surpassing China's current record-holder, the 28-ton Armanty iron, found in the same region in 1898.

Apparently the big stone's existence has been well known among locals for decades. A few scrawls of graffiti have been cut into the exterior, which also bears "saw marks" that expose the interior. As Zhang reports, "The surface was shiny silver, and I can clearly see exposed not only the iron-nickel composition but also the unique grid lines," called a Widmanstätten pattern, that are common among iron meteorites.

Interestingly, the meteorite is wedged beneath an even larger granite slab, and apparently both were dragged to their current locations long ago by glaciers. It's not yet clear when or how the massive Xinjiang stone will be excavated — though this would seem too magnificent a prize to simply leave in place. The Armanty iron is on display outside the Xinjiang Geology and Mineral Museum in Urumqi, the region's capital city.


Graffiti in Xinjiang meteorite
A dozen names, some dating to 1980, are carved into the Xinjiang meteorite.

Conceivably, the Xinjiang and Armanty meteorites are part of the same fall; tests should soon establish whether they are siblings or just happen to be enormous unrelated hunks of meteoritic metal that fell to Earth from interplanetary space.