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.

EPOXI spacecraft flys by comet Hartley 2

NASA's EPOXI spacecraft flew by comet Hartley 2 this morning. This comet is about 2 kilometers long, with a narrow neck only 0.4 km thick. Note the material jetting off the sunlit end, which is due to the sublimation of surface ice there. Keep an eye on the EPOXI mission page for more images as they get released.

Movies of Saturn's B ring

The outer edge of Saturn's B ring is controlled by an orbital resonance with the satellite Mimas, whose gravitational perturbations there give the ring-edge a scalloped appearance. That ring-edge has been monitored by the Cassini spacecraft that also orbits there, and several movies showing ring's complex movements are now posted at the CICLOPS website. The above image shows a closeup of the B ring's outer edge seen during equinox, when the sunlight was streaming nearly parallel to the ring place. Note the shadows cast by the bright material at the ring's outer edge. It is thought that these shadows are due to one or more small moonlets also hidden somewhere at the ring-edge. If so, then the moonlet's gravitational pull might be responsible for displacing the ring particles perpendicular to the ring plane, causing particles to pile-up into kilometer-tall mountains that cast those very prominent shadows.

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.