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.

LCROSS: is Moon's water due to comet impacts?

This image shows the plume that was raised when the LCROSS booster rocket struck the Moon in a region that is permanently shadowed from the Sun. The mission's goal is to search for the water-ice that might be frozen in these shadowed regions, since such ice would be a valued resource for any astronauts that might return to the Moon.

There are two likely sources for this water-ice. One is the solar wind, which can implant hydrogen into the lunar soil, which would then combine with the oxygen in soil to make water. Another source is comet impacts, which can deposit water as well as other volatiles that can then freeze out in these permanently shadowed regions. Since the spectra collected by LCROSS also reveals other volatiles, such as methane, ethanol, ammonia and carbon dioxide, all of which are known to exist in comets, cometary impacts are now a favoured theory for depositing water on the Moon.

Circumstellar debris disk orbiting HD 32297

This is the circumstellar debris disk that orbits the star HD 32997, imaged with the Palomar 5m telescope by Dimitri Mawet and colleagues. The star lies at the cross, but its light has been blocked by a phase mask coronograph, which is a device that shifts the phase some of that starlight so that the star's light waves interfere with itself destructively, effectively making the very bright star dissapear from this image. This is very useful, since it also reveals the light from the much fainter circumstellar material.

The colored blobs indicate that there is a ring or perhaps a disk of dust in orbit about this star, with that disk/ring seen nearly edge on. The dust grains are visible because they are reflecting starlight, and the colors indicate the intensity of that reflected light. Of particular interest to me is the asymmetry seen in this disk, with one side being brighter than the other by ~50%.

These dusty disks usually have rather short lifetimes, since dust grains destroy each other when the collide with each other. Consequently, other unseen `planetesimals' are implicated here, since collisions by these asteroidal or cometary bodies are needed to continually resupply the disk with the dust seen here. And since comets or asteroids are evidently forming in this system, it seems plausible that larger planets might have formed here, too. Additional details are also available in the paper by Mawet et al.

Ingredients for prebiotic life found in comet

The Stardust spacecraft encountered comet Wild 2 on January 2, 2004, and collected samples of the comet's coma and tail. Those samples parachuted to Earth on January 15, 2006, and have been studied in labs ever since. From these samples, Jamie Elsila at NASA/Goddard reports the first ever detection of glycine in a comet. Glycine is a common amino acid, which when combined with others can build proteins, which are important building blocks in the chemistry of life. The detection of glycine in comet Wild 2 strengthens the argument that comet impacts on the early Earth provided the prebiotic chemistry that ultimately allowed life to begin on Earth. However, critics of this cometary-delivery theory would argue that comet impacts are far too fiery and energetic to deposit complex organic molecules on Earth whole and unscathed. Regardless, this interesting finding highlights the value of sample-return missions, which can provide valuable insight into composition of ancient and primitive bodies, like as comets and asteroids, that are the primordial building blocks of the planets. See this press release for more details.

Split Comet Schwassmann-Wachmann 3

Comet Schwassmann-Wachmann 3 broke up into several fragments in 1995. Its orbit period is 5.4 years, so came closest to the Sun again in 2001 and 2006. Bill Reach and colleagues used the Spitzer Space Telescope to observe this comet in infrared wavelengths in May 2006. The faint band connecting the fragments is a trail of debris that traces their orbit about the Sun. These astronomers detected 55 fragments along this comet's orbit, several of which are seen above. The color image of two brighter components show their dusty tails in red with a hint of green to show that CO2 gas is emitted from the sunward-facing parts of the comet nuclei. These fragments comae and tails are generated as the icy cometary nuclei warm and sublimate (evaporate) in the sunlight, whose weak pressure also sweeps the dust away in the anti-sunward direction. A preprint by Reach et al on these Spitzer observations is also available.