pluto puzzles astronomers again

It’s bad enough that some scientists are still debating whether Pluto is a planet at all, but now there’s another Plutonian mystery. Completely unexpectedly, Pluto’s thin nitrogen atmosphere has been found to be expanding, researchers report in the July 10 Nature. Why is the finding surprising? Currently, Pluto is moving rapidly away from the sun, so astronomers expected that as the planet’s temperature dropped, its atmosphere would contract. Instead, MIT’s James Elliot and his colleagues have found that the atmosphere is getting larger, and in another study published in the same issue, Bruno Sicardy of the Observatoire de Paris and his colleagues estimate that Pluto’s atmospheric pressure has doubled over the past 14 years. A commentary by William Hubbard of the Lunar and Planetary Laboratory of the University of Arizona suggests that the unexpected expansion of the atmosphere could be due to a time-lag: it may take many years for a change in solar heat to affect Pluto’s surface layers.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 7/15/2003.