Orcus Patera, a mysterious crater on Mars

This image of Orcus Patera was acquired by ESA's Mars Express orbiter; see press release. Orcus is an elliptical depression near Mars's equator, near the well-known volcanoes of Elysium Mons and Olympus Mons. Its origin is unknown, possibly a volvanic feature, or perhaps a circular impact crater that was later deformed by tectonic forces.

Closeup of Helene

Cassini acquired this interesting image of the satellite Helene on March 3. Helene is a small 30km-wide satellite of Saturn. Its orbit is also very curious, since it resides at the L4 Lagrange point of the much larger 1000km-wide satellite Dione. The L4 Lagrange point leads Dione's motion by 60 degrees in longitude. Such satellites are known as coorbitals, since they co-orbit with another larger body, and only a few such coorbital satellites are known. This coorbital motion is analgous to the Trojan asteroids, which lead/trail Jupiter by 60 degrees. Note also Helene's smooth surface. Although the outlines of large craters are clearly evident, their filled-in appearance suggests that this satellite is also being bombarded and coated by dust that might also be present in this part of the Saturnian system. Keep an eye on the CICLOPS website for information about this small but interesting satellite.

3D model of Mojave Crater, Mars

This image is a rendering of a 3D model of the Mojave Crater on Mars. The image was crafted from stereo images acquired by the Mars Reconnaissance Orbiter, and spans about 4km. This is just a small portion of the crater's edge, since the crater itself is 60km across. This image also has its vertial relief enhanced 3x over that in the horizontal direction. Note that this part of the crater appears filled in, like a pond. This ponding is thought to occur when melt generated by an impact is captured behind mountainous walls. The dearth of additional smaller craters tells us this feature is relatively young for Mars, only 10 million years old. Note also the flows into and out of this region. They suggest that the impact event might have melted underground ice that also flooded this region.

Closeup of the Deathstar moon

Cassini's closest ever approach to Saturn's satellite Mimas occurred Saturday Feb. 13. Other pictures of the Deathstar moon are also available at the CICLOPS website.

LCROSS: is Moon's water due to comet impacts?

This image shows the plume that was raised when the LCROSS booster rocket struck the Moon in a region that is permanently shadowed from the Sun. The mission's goal is to search for the water-ice that might be frozen in these shadowed regions, since such ice would be a valued resource for any astronauts that might return to the Moon.

There are two likely sources for this water-ice. One is the solar wind, which can implant hydrogen into the lunar soil, which would then combine with the oxygen in soil to make water. Another source is comet impacts, which can deposit water as well as other volatiles that can then freeze out in these permanently shadowed regions. Since the spectra collected by LCROSS also reveals other volatiles, such as methane, ethanol, ammonia and carbon dioxide, all of which are known to exist in comets, cometary impacts are now a favoured theory for depositing water on the Moon.

Recent impacts on Mars exposes subsurface ice

The Mars Reconnaissance Orbiter (MRO) took these images of a 6m crater on Mars in October 2008 (left) and again in January 2009; see this press release for more details. This crater is absent from images acquired in 2007, so it must be due to a relatively recent impact. Note also the bright material in the crater that fades over time. This is to be expected if this were subsurface ice that was suddenly exposed to the surface. Water ice is not stable at the surface of Mars, and will sublimate (vaporize) over time. The MRO spacecraft has discovered several new craters where fresh ice appears to fade over time. This particular crater has a latitude of 43 degrees, which indicates that subsurface ice on Mars extends all the way from from the poles to Mars' mid-latitudes.