Space Pictures This Week: Red Auroras, Mars Avalanche

Guest Star
Image courtesy SAO/CXC/UCLA/Caltech/ESA/NASA
A new picture combining data from four NASA telescopes is helping to solve the mystery of the "guest star"—a supernova spotted 2,000 years ago by Chinese astronomers.
Formally known as RCW 86, the supernova remnant we see today is two to three times bigger than expected, based on current understanding of how such stellar remains expand.
Now, infrared data from NASA's Spitzer Space Telescope suggest that the explosion happened in a cavity in the surrounding cloud of gas and dust. With no material to slow it down, the supernova's debris spread quickly, leading to the remnant's unusually large size.
Published October 28, 2011
Tasmanian Aurora
Photograph courtesy NASA
Multicolored lights dance over the Tasman Sea in a picture of the aurora australis, or southern lights, taken in September from the International Space Station.
Auroras are created when charged solar particles collide with molecules in Earth's atmosphere, infusing the molecules with extra energy that then gets emitted as light. Colors are based on which types of molecules are affected and how high they are in Earth's atmosphere.
(Also see "Aurora Pictures: Rare Northern Lights Seen in U.S. South.")
Published October 28, 2011
Toothy Pac Man
Image courtesy UCLA/Caltech/NASA
The Pac Man Nebula has sprouted teeth, as seen in a new picture from NASA's Wide-field Infrared Survey Explorer, or WISE.
In visible light, the cloud of gas and dust has a smooth triangular "mouth" reminiscent of the classic arcade game character. But the new infrared view shows the nebula's lower jaw lined with pillars of dense material that look like jagged teeth—regions where new stars may be forming.
Published October 28, 2011
Approaching Earth
Photograph courtesy Rolando Ligustri
Comet C/2009 P1, seen from Italy's Cast Observatory on October 15, is approaching Earth.
Comets are balls of rock and ice that grow tails as they approach the sun in the course of their highly elliptical orbits. As comets heat up, gas and dust are expelled and trail behind them. The sun illuminates this trail, causing it to glow, and thereby making it visible in the night sky, given the right conditions.
(See "New Comet Found; May Be Visible From Earth in 2013.")
Published October 28, 2011
Aurora Layers
Photograph courtesy Branislav Beliancin
Curtains of red and green auroras seem to drop from the skies in a picture taken October 25 from Spjelkavik, Norway.
A cloud of charged particles from the sun slammed into Earth Monday, setting off an intense geomagnetic storm that spawned a burst of northern lights seen farther south than normal.
In the U.K., for instance, reports of auroras came in from as far as Ayrshire (map), just south of Glasgow, according to the BBC.
Published October 28, 2011
Martian Avalanche
Image courtesy U. Arizona/NASA
A cloud of dust 600 feet (200 meters) wide is evidence of an avalanche on Mars, as seen in a recently released picture from NASA's Mars Reconnaissance Orbiter.
The satellite's high-resolution camera snapped its first avalanche in action in 2008. Since then the MRO has been searching for them along the steep cliffs of layered deposits around Mars's north pole.
Studying pictures of such events can help scientists figure out if the landslides are being triggered by seasonal climate changes, strong winds, or as yet unknown phenomena on the red planet.
Published October 28, 2011
Moon Quartet
Image courtesy Cassini/ESA/NASA
If you look closely, you can spot four moons in this one picture of the Saturn system recently taken by NASA's Cassini orbiter.
At center, the bright moon Dione stands out against the darker grey of Saturn's largest moon, Titan. The smaller moon Pandora sits to the right, near the edge of part of Saturn's many rings. To the left, the moon Pan appears as a speck within a dark gap in between the rings.
Published October 28, 2011
Satellite's Final Fall
Image courtesy Franhofer FHR/DLR
On October 23 the German research satellite ROSAT (picured on October 20) reentered the atmosphere over the Bay of Bengal, though it's unknown whether any parts of the satellite reached Earth's surface.
"With the reentry of ROSAT, one of the most successful German scientific space missions has been brought to its ultimate conclusion," the German Aerospace Center's Johann-Dietrich Wörner said in a statement.
(See "Another Dead Satellite to Fall to Earth This Weekend.")
Published October 28, 2011
Ice Classes
Image courtesy Jesse Allen and Robert Simmon, EO-1/NASA
In Antarctica, not all ice is created equal: This recently released picture from NASA's Earth Observing-1 satellite shows several different types of ice in a single frame.
So-called fast ice—named because it holds fast to the shore—fills the right side of the image. This ice is very thick and so appears bright white. Near the edges of the fast ice are icebergs, thick hunks of ice saturated with meltwater, which gives them a bluish tinge.
To the left of the frame is pack ice, which is much thinner and so shows more of the underlying seawater, giving the ice a blue-gray hue. In between the pack ice are swirls of newly formed sea ice called frazil and thin sheets known as nilas.
Published October 28, 2011