With an atmospheric pressure one hundred thousand times less than that on Earth, Pluto becomes an even more intriguing object than usual when it moves closer to the Sun in its 248-year orbit. This period, occurring now, causes the temperature of the surface to increase, and that causes what had been frozen nitrogen (with trace amounts of methane and, probably, carbon dioxide) to sublimate into gas. Studying these matters with ESO's Very Large Telescope, astronomers have now found unexpectedly large amounts of methane in that atmosphere. Image: Artist's impression of how the surface of Pluto might look, according to one of the two models that a team of astronomers has developed to account for the observed properties of Pluto's atmosphere. The image shows patches of pure methane on the surface. At the distance of Pluto, the Sun appears about 1000 times fainter than on Earth. Credit: ESO/L Calçada. A second discovery: The atmosphere of the distant ice world is some forty degrees Celsius...

With the Kepler launch scheduled for no earlier than Friday, I'm keeping one eye on the mission site while I develop today's material. Kepler launches aboard a Delta II, but engineers are now having to check common hardware between that rocket and the Taurus XL launch vehicle that failed to get NASA's Orbiting Carbon Observatory into orbit last week. Thus the March 5 launch date slips to March 6, which itself is still tentative. Meanwhile, an unusually interesting story in Nature also has my attention, dealing not with exoplanets but with the early Solar System and what may have been a period of planet migration that caused heavy asteroidal bombardment of the inner planets. This one comes out of the University of Arizona, where scientists have been looking at the distribution of asteroids with diameters greater than fifty kilometers. UA's David Minton and Renu Malhotra ran simulations beginning with a uniform asteroid belt to see how the present-day gaps in the belt may have arisen...