Dusty planetesimal ring orbiting star HR 4796 A

This image of a circumstellar dust ring was recently acquired by C. Thalmann and colleagues at the 8 meter Subaru telescope that the Japanese operate on the summit of mount Mauna Kea in Hawaii. Although the dust ring is nearly circular, the line-of-sight to the ring is oblique which makes the ring appear elongated. To reveal the faint ring, the astronomers must subtract a model image of the very bright central star, but imperfections in the star-subtraction results in the radial residuals seen in the image. Nonetheless the dust ring is still quite prominent despite those residuals, and its radius is about 80 AU. This dust is thought to be the result of collisions occurring among unseen planetesimals also orbiting within the ring. These planetesimals probably resemble the comets that inhabit our Kuiper Belt, which is the Sun's outermost debris belt that is of radius 45 AU. Another interesting feature of this image is that the dust ring's center is offset slightly from the star. Although the origin of this offset is uncertain, an unseen extra-solar planet is implicated, because its gravitational influence can displace the ring's center. But if there is an exoplanet here, it is too faint to be seen or is obscured by the residual starlight. For more information about this circumstellar dust ring, see this press release.

Giant exoplanet confirmed orbiting in debris disk

Beta Pictoris b is a giant extrasolar planet, having a mass of about 10 Jupiter masses. It was first detected by direct imaging in 2003, but not seen again in followup images acquired in 2008, so the suspicion then was that this faint dot was just a background star, and not a planet that is actually bound to the star. However that expolanet was later recovered again in images acquired in late 2009 by Anne-Marie Lagrange; those images show that the dot seen above is indeed bound to Beta Pictoris, and orbits at a distance of about 10 AU from the star. So it seems that beta Pic b wasn't seen in 2008 because it was passing in front of or behind the very much brighter star.

Beta Pictoris is also known for its huge circumstellar debris disk; that disk is seen edge-on by astronomers at Earth, and the above graphic---which by the way is not a real telescopic image, but is probably the merger of two separate images---shows that the planet's orbit is coplanar with the debris disk. This in fact is to be expected, because such debris disks are composed of dust grains that are produced by collisions among unseen planetesimals, which are also the seeds from which planets form from. See this press release from the European Southern Observatory for more details.

Hubble image of dust trail in asteroid belt

David Jewitt (UCLA) acquired this new Hubble image of the mysterious dust trail that appeared recently in the asteroid belt. This trail is also discussed in this January 20 post. Current thinking says that this debris from a recent collision among two asteroids. Check the Hubble page for more details.

Recent collision in the asteroid belt?

This dust trail was imaged by the LINEAR (Lincoln Near Earth Asteroid Research) survey on January 6. The trail is named P/2010 A2, and the arrows point to a faint 200 meter object that is the likely source of this dust. Ordinarily, dusty streaks such as this are comet tails, which form when as the comet's icy surface sublimates (melts). That process also liberates small dust grains from the comet's surface. Pressure due to sunlight then sweeps that dust cloud out into a long tail. Comets are known to inhabit the asteroid belt, but only in the outer part. But this dust trail lies in the inner asteroid belt, where comets are not known to reside. So the current thinking is that this trail, which might only be weeks old, could instead be debris from a recent collision between two asteroids. So this picture could be the first view of the aftermath of a never-before-seen astronomical event---the collision between two asteroids. See this New Scientist article for more details.