Rare elongated crater on Mars

ESA's Mars Express imaged this elongated crater on Mars. Note that most craters are circular, even when the impactor strikes the planet at a shallow angle. However a train of interplanetary debris can leave an elongated scar, which might account for the crater seen here. But accounting for the origin of that hypothetical debris train can be problematic---perhaps this is debris from a comet or asteroid that was tidally disrupted by Mars? Or perhaps this debris is from a tidally disrupted satellite that had spiraled inwards and onto the planet due to the martian tide. Although this might seem farfetched, this in fact will be the ultimate fact of the Martian satellite Phobos, which will eventually impact Mars in tens of million years, due to its slow orbital decay that is driven by the martian tidal forces. See the Mars Express website for more details.

Monster solar flare imaged by Solar Dynamics Observatory

This massive solar flare erupted from the Sun's surface on February 24, and was imaged by NASA's Solar Dynamics Observatory. Check the SDO website for more info, plus a very dramatic movie of this explosion in space.

Stardust sees impact site on comet Tempel 1

The stardust spacecraft flew by comet Tempel 1 last night, and acquired the close-up image of the surface that is seen on the left. Recall that this comet was first visited by the Deep Impact spacecraft in 2005, which shot that comet with a one-ton projectile; the high-res image on the left shows the impact site prior to the collision. One of Deep Impact's science goals was to observe the resulting crater, but the impact generated so much dust, the crater was never seen by Deep Impact. Fortunately, the Stardust spacecraft could maneuvered so that it would encounter comet Tempel 1 six years later. Stardust acquired the fuzzy low-res image on the right, which does indeed show the impact site, with a shallow 100m crater just inside the smaller circle. Note also that the impact obliterated the dark region that is seen at 10 o'clock along the yellow circle (left), in the pre-impact image. The Deep Impact crater has been observed at last!

ISS transits the Sun during solar eclipse

Thierry Legault captured this amazing picture of the International Space Station as it transits the Sun during a partial solar eclipse by the Moon on January 4.

HR 8799 hosts jumbo planetary system

Christian Marois (Herzberg Institute of Astrophysics) and colleagues discovered a fourth giant planet orbiting HR 8799. The new planet, 'e' in the above image, lies inwards of planets b,c,d. This is typical when using imaging to hunt for extra-solar planets, since it is the closer-in planets that are harder to find, due to obscuration by the bright central star. A simulated star was actually removed from this image; the fuzzy blob seen in the center is due to imperfections in this star-subtraction process. These planets lie about 15 to 70 AU away from the central star, and have masses of ~5 to 10 Jupiter masses. So this is a jumbo planetary system, since the orbits and masses are several times larger than that the Solar System's. See the abstract of their paper in Nature for more details.

A densely packed planetary system at HD 10180

C. Lovis and colleagues at the European Southern Observatory in Chile used the 3.6m telescope there to discover 5 or more planets orbiting the star HD 10180. The five certain planets are all Neptune-class, having masses of 12-25 times that of Earth. Also, all orbit rather close to the star, at distances of 0.06-1.4 AU. There is also tentative evidence for an Earth-mass planet orbiting at r=0.02 AU, and a possible 3-Neptune-mass planet orbiting at r=3.4 AU. Ellipses in the above figure show the planets current orbits, while the colored regions indicate their range of motions over time that are due to their mutual gravities. As the figure shows, this system is quite dense with planets, which is actually rather typical for multi-planets extra-solar planetary systems. See the preprint for more details.

EPOXI spots snowballs coming off Hartley 2

The camera aboard EPOXI also spotted icy chunks jetting off the surface during that spacecraft's close approach to comet Hartley 2. The bigger chunks are golfball to basketball sized, according to this piece in New Scientist.