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.

HD 10180, a five-exoplanet system

Astronomers used the HARPS radial-velocity instrument (at the European Southern Observatory) to detect five exoplanets orbiting the star HD 10180. Two additional planets are also suspected, but their existence is uncertain due to their weak signal. These five make this exo-planetary system one of the most abundant discovered to date. The five planets are Neptune-class, and they all reside at distances interior to Mar's orbit about the Sun. The above graphic is an artist's rendition of this system. A press release is also available.

Rosetta spacecraft flies by asteroid Lutetia

The Rosetta spacecraft aquired several images of asteroid Lutetia. Rosetta is headed towards comet Churyumov-Gerasimenko, and will go into orbit about that comet in 2014. But this spacecraft also made a close pass at asteroid Lutetia while en route. Additional images are also posted at the European Space Agency's website. Lutetia might be a C type asteroid, ie a carbonaceous chondrite, which is a fairly common rocky asteroid that is also rich in organic molecules. Or else it is an M type asteroid, which is rich in metallic nickel-iron. M-types must have once resided deep inside the core of a much larger asteroid that likely fragmented early in the Solar System's history. These observations by Rosetta should resolve this asteroid's composition, and may provide clues about its origin.

Daphnis maintains the Keeler Gap

The small Saturnian satellite Daphnis is responsble for maintaining the narrow Keeler gap, which lies near the outer edge of Saturn's main A ring. Daphnis' gravitational pull on the nearer ring particles also sculpts the gap's edges, resulting in wakes that are downstream of the satellite. This Cassini image is available at the CICLOPS website.

Mass transfer in circumstellar disks

The left graphic is a near-infrared image of the heirachical star system SR24. The lower object is the star SR24S, and the nebulosity surrounding it is a protoplanetary disk that is composed mostly of hydrogen gas plus some dust. The stellar contribution to this image has been subtracted, which is why the disk appear dark in its center. The upper object SR24N is actually an unresolved binary star; that binary also has its own circumbinary disk such that the SR24N stellar pair + disk orbits the SR24S star + disk. The right graphic is a computer simulation of this system, which reveals that these two disks can transfer mass between each other through a `bridge' that passes through this system's L1 Lagrange point, which is one of three sites in this system where gravity + Coriolis forces balance to zero. Observations such as this will hopefully reveal whether binary stars might one day form planets, or if their disks are too disturbed to produce planets. This image was acquire by Satoshi Mayami at the Subaru Telescope. A preprint on this work is also available.