Sunday, July 11, 2010

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.

Friday, July 9, 2010

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.

Wednesday, July 7, 2010

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.