Messenger: Mercury's New Moon

Some 96 million miles away, the Messenger spacecraft had fired its braking rocket and thrusters for nearly 15 minutes, a long burn begun at 8:45 p.m. EDT that slowed the hurtling craft by 1,929 miles per hour (0.86 km per second). A few anxious minutes later, an interplanetary communiqué arrived at the mission's control center at Johns Hopkins University's Applied Physics Laboratory. The burn had gone flawlessly, placing the spacecraft safely in a looping 12-hour polar orbit.

It's taken more than 6½ years for Messenger to reach its new home away from home. Along the way was one flyby of Earth, two of Venus, and three of Mercury itself — all part of an intricate, carefully designed interplanetary billiard shot designed to deliver the biggest payload possible on a Delta II 7925 launch vehicle. As planetary scientist Mike Brown commented via Twitter, "Clearly, physics works really really well."

NASA's science team packed eight instruments onto Messenger (a contraction for Mercury Surface, Space Environment, Geochemistry and Ranging).

But don't expect a glut of images to start flowing into the computers at mission control right away. For the moment, however, the ball is in the engineers' court to ensure that onboard systems are working properly. Most instruments won't be turned on until March 23rd, the cameras five days later.

The planned year-long study of all things Mercurian will begin in earnest on April 4th, along with gravity studies derived from the craft's motion and radio transmissions. According to project scientist Sean Solomon (Carnegie Institution of Washington), the first full-up release of results won't occur until May 10th.

In the meantime, check the mission website for progress reports and to see images of Mercury obtained during the trio of earlier flybys. You'll also get a kick touring the planet at close range by downloading this Mercury KML file for use with Google Earth.

Finally, don't miss the chance to spot the innermost planet making its best evening appearance of the year.

The scars of impacts on Mars

Elongated crater on Mars

 
4 March 2011
ESA’s Mars Express has returned new images of an elongated impact crater in the southern hemisphere of Mars. Located just south of the Huygens basin, it could have been carved out by a train of projectiles striking the planet at a shallow angle.
 
 

	Elongated crater, south of Huygens crater

The large Huygens basin (not visible in the main image but seen in the wider contextual image) is about 450 km in diameter and lies in the heavily cratered southern highlands. In this area there are many impact scars but none perhaps are more intriguing than the ‘elongated craters’.

One of these craters is seen in this new image, which covers an area of 133 x 53 km at 21°S / 55°E. The scene was captured on 4 August 2010 and the smallest objects distinguishable by the camera are about 15 m across.
 
 

Features in the elongated crater

This unnamed elongated crater sits just to the south of the much larger Huygens basin. It is about 78 km in length, opens from just under 10 km wide at one end to 25 km at the other, and reaches a depth of 2 km.
 
 

	Elevation of the elongated crater

Impact craters are generally round because the projectiles that create them push into the ground before the shockwave of the impact can explode outwards. So why is this one elongated?

The clue comes from the surrounding blanket of material, thrown out in the initial impact. This ‘ejecta blanket’ is shaped like a butterfly’s wings, with two distinct lobes. This hints that two projectiles, possibly halves of a once-intact body, slammed into the surface here.
 
 

Elongated crater in high resolution

 
In the crater itself, there are three deeper areas that could be evidence for more than two projectiles. In addition, a second elongated crater lies to the north-northwest. It can be seen in the wider contextual image and is in line with the one seen here, reinforcing the notion that these structures were the result of a train of projectiles.
 
 

Perspective view of elongated crater

 
In the early 1980s, scientists proposed that elongated impact craters were formed by incoming chains of orbital debris following trajectories that decayed with time. As the debris spiralled downwards, it eventually struck the planet at shallow angles, gouging out the elongated craters.
 
 

Perspective view of elongated crater

 
This particular ejecta blanket contains many smaller craters, indicating that the original formed a relatively long time ago and then itself become a target.

In addition, there are several small channels on the blanket, suggesting that the strike took place into a surface rich in volatiles, perhaps even water, that were melted by the heat of impact and flowed away.
 
 

Perspective view of elongated crater

Below the eastern crater rim are two well-formed and relatively deep craters. They have punched through the ejecta blanket and so must have appeared after the formation of the large crater. Despite their sizes of 4 km and 5 km, these smaller craters show no indication of the presence of water.
 
 

	Perspective view of elongated crater

To the north there is another crater that must be older because the butterfly-ejecta blanket has partially flowed into it. Several landslides have modified the steep crater rim. This can be most clearly seen on the two smaller craters on the rim, which are only partially preserved, parts of them having fallen away.
 
 

Elongated crater in 3D

The formation of these elongated features is not over: the martian moon Phobos will plough into the planet in a few tens of millions of years, breaking up in the process, and likely creating new chains across the surface.

See Venus in Broad Daylight!

Look southeast before sunrise to spot the waning
Moon and Venus. These scenes are drawn for the middle of North America.
European observers: move each Moon symbol a quarter of the way toward
the one for the previous date. For clarity, the Moon is shown three
times actual size.

If it's clear at dawn on Monday and Tuesday, February 28th and March 1st, you can see one of nature's loveliest sights — Venus near the thin crescent Moon.

Thoughtful readers looking at the chart at right might have two questions. First, if the Moon is above Venus on Monday and below it on Tuesday, it must be very near it some time in between. When will this close approach happen, and where will it be visible?

Second, just how long into dawn will you be able to see this scene? The Moon is often visible during broad daylight. Is that true of Venus, too?

Let's answer the second question first. Yes, Venus is indeed visible to the unaided eye during broad daylight, assuming that the air is reasonably free of haze. In fact, it's startlingly easy to see — but equally hard to find. It's just a tiny pinprick of light amid the vast sea of blue sky. Even after you succeed in finding Venus, it's very easy to lose sight of it if you glance away for a moment.

For this reason, by far your easiest chance to observe Venus during the day is when it happens to be near the Moon — a much easier object to find. And that will happen twice for observers in the Americas: on Monday and again on Tuesday.

There's one way to be absolutely sure of observing Venus after the Sun has risen, but it requires a lot of time and patience. Go out a half hour before sunrise, when Venus is blindingly obvious, and track its position until the Sun rises, and even after. The way to do this is to periodically look down from Venus to the horizon, and see what landmark lies directly below it. Then it's relatively easy to relocate Venus by scanning upward from that landmark.


Venus and the Moon in broad daylight In these daylight scenes, the Moon is shown its actual apparent size relative to the distance between it and Venus. Venus is shown bright here for clarity, but appears much fainter against the bright daytime sky. Binoculars are not necessary to see either the Moon or Venus, but they're extremely helpful.

If you don't want to hang around outside for 45 minutes on a chilly late-winter morning, your second-best bet is to look when the Moon and Venus are due south and at their highest, which happens around 9 a.m. these mornings. Bring binoculars, because even the Moon is none too easy to spot during the day when it's a thin crescent.

Once you've located the Moon, use your binoculars to scan carefully to the left on Monday morning, using the February 28th diagram to tell you how far to scan. Most 7× to 10× binoculars actually have a field of view a bit bigger than what's shown, but the outer edge of the field is often a little hard to see.


Venus and the Moon in broad daylight In these daylight scenes, the Moon is shown its actual apparent size relative to the distance between it and Venus.

The closest approach between Venus and the Moon takes place when the Moon is below the horizon for the Americas. But it's a fine sight from eastern and central Asia, as shown in the March 1st diagram. By the time the Moon rises in the Americas on Tuesday morning, it's already well to the left of Venus. This is a second opportunity to spot Venus during daylight hours, but it's a bit tougher than on Monday because the Moon's phase has shrunk from roughly 15% to 10%, making it significantly harder to spot in the blue day sky.

As Solar Flares Grip The Nation

A series of solar flares have been gripping the nation's interest as the sun enters a period of increased activity. Solar Stormwatchers are just some of the enthusiasts who have been keeping an eye on the large explosions in the sun's atmosphere as they release intense bursts of radiation.

The Solar Stormwatch project  allows members of the public to use images from the NASA STEREO  to spot the explosions from the sun and the resulting clouds of particles as they make their way towards the earth. These particles, at their most disruptive, can cause communications to fail and lead to cuts to power supplies.

Professor Richard Harrison, Solar physicist and Principal Investigator for STEREO said; "We've just witnessed the brightest flares seen for four years. This was a series of so-called X-class flares - the highest category on the solar flare 'Richter scale'. The flares were near the centre of the Sun which means associated eruptions and clouds of solar particles can travel in our direction."

Dr Chris Davis, STEREO Project Scientist and leading scientist in Solar Stormwatch talks further about these latest developments.

The impact on on Earth depends on how the clouds of particles disrupt our magnetic field. The clouds themselves are magnetised and the direction of their magnetic fields and the speed they travel determines the type of impact. If their magnetic fields turn southward (opposite to the direction of the Earth's magnetic field) and their speed over the Earth exceeds 700 km per second, then we might expect some disruption - this is also the time to look out for aurora!

You can find out more by looking at the NOAA Space Weather Prediction Center website.

Here you can see the space environment in front of the Earth in real time - as measured using NASA's ACE (link opens in a new window) spacecraft. The areas to watch are the charts on the left and right hand side of page. The chart on the left shows significant activity when the dials reach the yellow or red areas; the Auroral map on the right of the page shows increased activity when areas of the map become more red.

There is also more on Lancaster University's Aurora watch website.

The Coolest Star. Literally.

The Coolest Star. Literally.

"It seems like once people grow up, they have no idea what's cool." -Bill Watterson

Well, at least we can all agree on what's not cool. The Sun.

With a surface temperature of around 6,000 Kelvins, the Sun is one of the hottest objects that we're all familiar with.

But when it comes to stars, the Sun is merely a "G-type" star.
It turns out that there are many types of stars that are -- typically
-- more massive, bluer, and hotter than our Sun.

In fact, O-stars, the hottest type, can have surface temperatures over 40,000 Kelvin, hot enough that they would be classified as "Ultraviolet stars," if only our eyes could see light that energetic.

But going down in temperature, we find that smaller, less
massive stars burn at lower temperatures. Once you get down to below
about 40% of the mass of the Sun, you go down to being a red-colored
M-star, with a temperature of only around 3,000 Kelvins.

M-stars still burn hydrogen into helium, like our Sun does, but
don't have enough mass to burn anything past that, and will die with
the weakest of whimpers, simply contracting and fading away.

But even M-stars need to have at least 7 to 8% of the Sun's
mass in order to be able to make helium in their cores. What happens if
you're less massive than that? Well, we do observe stars even cooler than M-stars, but we've had to look very hard to find them.

Dropping dramatically in temperature and brightness, we come to the newest class of stars: brown dwarfs. (That's dwarfs, not dwarves.)
These stars, of spectral type L, T, and (theoretically, thus far) Y,
are too small to burn hydrogen into helium. The brighter brown dwarfs can form deuterium, the lightest stable isotope of hydrogen, but the dimmest ones can't even do that.

Still, there's a fine line somewhere in between a large planet like Jupiter and a Y-type brown dwarf. And we are starting to figure out just what's in that grey area.

The lowest temperature brown dwarfs that we've discovered out there are right around 500 to 550 Kelvin, like this guy, which makes them much colder than Venus, and barely warmer, on average, than the planet Mercury.

That's right. We've discovered stars that are cooler than some of our planets.

The WISE spacecraft,
which took the picture above as its final image, may break this record
and discover the first Y-type brown dwarf when its data is completely
analyzed. How would this happen?

All stars made out of atoms that have run out of fuel: Y-type
brown dwarfs, stellar corpses (like white dwarfs), etc., contract under
their own gravity, and that's the source of their energy. Although it
will take at least hundreds of trillions of years (which is many times
the age of the Universe), eventually these stars will shrink to a
minimum, most stable configuration. At that point, there will be no
energy left to release, and these stars will become black dwarfs, huge clumps of matter with a temperature approaching absolute zero!

NASA Releasing First Views Of The Entire Sun On Super Sun-Day

NASA Releasing First Views Of The Entire Sun On Super Sun-Day


WASHINGTON -- NASA will score big on super SUN-day at 11 a.m. EST, Sunday, Feb. 6, with the release online of the first complete view of the sun's entire surface and atmosphere.

Seeing the whole sun front and back simultaneously will enable significant advances in space weather forecasting for Earth, and improve planning for future robotic or crewed spacecraft missions throughout the solar system.

These views are the result of observations by NASA's two Solar TErrestrial Relations Observatory (STEREO) spacecraft. The duo are on diametrically opposite sides of the sun, 180 degrees apart. One is ahead of Earth in its orbit, the other trailing behind.

Launched in October 2006, STEREO traces the flow of energy and matter from the sun to Earth. It also provides unique and revolutionary views of the sun-Earth system. The mission observed the sun in 3-D for the first time in 2007. In 2009, the twin spacecraft revealed the 3-D structure of coronal mass ejections which are violent eruptions of matter from the sun that can disrupt communications, navigation, satellites and power grids on Earth.

STEREO is the third mission in NASA's Solar Terrestrial Probes program within the agency's Science Mission Directorate in Washington. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the mission, instruments and science center.

The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., designed and built the spacecraft and is responsible for mission operations.

The STEREO imaging and particle detecting instruments were designed and built by scientific institutions in the U.S., UK, France, Germany, Belgium, Netherlands and Switzerland.

Asteroids Ahoy! Jupiter Scar Likely from Rocky Body

A hurtling asteroid about the size of the Titanic caused the scar that appeared in Jupiter's atmosphere on July 19, 2009, according to two papers published recently in the journal Icarus.

Data from three infrared telescopes enabled scientists to observe the warm atmospheric temperatures and unique chemical conditions associated with the impact debris. By piecing together signatures of the gases and dark debris produced by the impact shockwaves, an international team of scientists was able to deduce that the object was more likely a rocky asteroid than an icy comet. Among the teams were those led by Glenn Orton, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Leigh Fletcher, researcher at Oxford University, U.K., who started the work while he was a postdoctoral fellow at JPL.

"Both the fact that the impact itself happened at all and the implication that it may well have been an asteroid rather than a comet shows us that the outer solar system is a complex, violent and dynamic place, and that many surprises may be out there waiting for us," said Orton. "There is still a lot to sort out in the outer solar system."

The new conclusion is also consistent with evidence from results from NASA's Hubble Space Telescope indicating the impact debris in 2009 was heavier or denser than debris from comet Shoemaker-Levy 9, the last known object to hurl itself into Jupiter's atmosphere in 1994.

Before this collision, scientists had thought that the only objects that hit Jupiter were icy comets whose unstable orbits took them close enough to Jupiter to be sucked in by the giant planet's gravitational attraction. Those comets are known as Jupiter-family comets. Scientists thought Jupiter had already cleared most other objects, such as asteroids, from its sphere of influence. Besides Shoemaker-Levy, scientists know of only two other impacts in the summer of 2010, which lit up Jupiter's atmosphere.

The July 19, 2009 object likely hit Jupiter between 9 a.m. and 11 a.m. UTC. Amateur astronomer Anthony Wesley from Australia was the first to notice the scar on Jupiter, which appeared as a dark spot in visible wavelengths. The scar appeared at mid-southern latitudes. Wesley tipped off Orton and colleagues, who immediately used existing observing time at NASA's Infrared Telescope Facility in Mauna Kea, Hawaii, the following night and proposed observing time on a host of other ground-based observatories, including the Gemini North Observatory in Hawaii, the Gemini South Telescope in Chile, and the European Southern Observatory's Very Large Telescope in Chile. Data were acquired at regular intervals during the week following the 2009 collision.

The data showed that the impact had warmed Jupiter's lower stratosphere by as much as 3 to 4 Kelvin at about 42 kilometers above its cloudtops. Although 3 to 4 Kelvin does not sound like a lot, it is a significant deposition of energy because it is spread over such an enormous area.

Plunging through Jupiter's atmosphere, the object created a channel of super-heated atmospheric gases and debris. An explosion deep below the clouds – probably releasing at least around 200 trillion trillion ergs of energy, or more than 5 gigatons of TNT -- then launched debris material back along the channel, above the cloud tops, to splash back down into the atmosphere, creating the aerosol particulates and warm temperatures observed in the infrared. The blowback dredged up ammonia gas and other gases from a lower part of the atmosphere known as the troposphere into a higher part of the atmosphere known as the stratosphere.

"Comparisons between the 2009 images and the Shoemaker-Levy 9 results are beginning to show intriguing differences between the kinds of objects that hit Jupiter," Fletcher said. "The dark debris, the heated atmosphere and upwelling of ammonia were similar for this impact and Shoemaker-Levy, but the debris plume in this case didn't reach such high altitudes, didn't heat the high stratosphere, and contained signatures for hydrocarbons, silicates and silicas that weren't seen before. The presence of hydrocarbons, and the absence of carbon monoxide, provide strong evidence for a water-depleted impactor in 2009."

The detection of silica in this mixture of Jovian atmospheric gases, processed bits from the impactor and byproducts of high-energy chemical reactions was significant because abundant silica could only be produced in the impact itself, by a strong rocky body capable of penetrating very deeply into the Jovian atmosphere before exploding, but not by a much weaker comet nucleus. Assuming that the impactor had a rock-like density of around 2.5 grams per cubic centimeter (160 pounds per cubic foot), scientists calculated a likely diameter of 200 to 500 meters (700 to 1,600 feet).

Scientists computed the set of possible orbits that would bring an object into Jupiter in the right range of times and at the right locations. Then they searched the catalog of known asteroids and comets to find the kinds of objects in these orbits. An object named 2005 TS100 – which is probably an asteroid but could be an extinct comet – was one of the closest matches. Although this object was not the actual impactor, it has a very chaotic orbit and made several very close approaches to Jupiter in computer models, demonstrating that an asteroid could have hurtled into Jupiter.

"We weren't expecting to find that an asteroid was the likely culprit in this impact, but we've now learned Jupiter is getting hit by a diversity of objects," said Paul Chodas, a scientist at NASA's Near-Earth Object Program Office at JPL. " Asteroid impacts on Jupiter were thought to be quite rare compared to impacts from the so-called 'Jupiter-family comets,' but now it seems there may be a significant population of asteroids in this category."

Scientists are still working to figure out what that frequency at Jupiter is, but asteroids of this size hit Earth about once every 100,000 years. The next steps in this investigation will be to use detailed simulations of the impact to refine the size and properties of the impactor, and to continue to use imaging at infrared, as well as visible wavelengths, to search for debris from future impacts of this size or smaller.