Pluto takes 248 years to orbit the Sun. Since it was discovered in 1930 it hasn't even gone through a third of that orbit, barely more than one of its four seasons. You'd expect seasonal change on Pluto to follow the same stately pace. So it's really quite surprising to find out that Pluto's appearance has changed in the very short time that we've been studying it. I've
written before on this blog about how the colors of its surface have been observed to shift over the last couple of decades. Now another team of astronomers, led by Jane Greaves, is reporting that the atmosphere has changed quite a lot over the same time scale. You can read their paper, "
Discovery of carbon monoxide in the upper atmosphere of Pluto," on arXiv.
Pluto's atmosphere is very thin, made of gaseous forms of the ices that cover its surface -- nitrogen, methane, carbon monoxide, and carbon dioxide, among others. The discovery of carbon monoxide in Pluto's atmosphere is actually new, part of Greaves' work; but that's not the most interesting part of their story. The most interesting part is that their detection of carbon monoxide was at a signal strength that was much higher than the sensitivity of a search for the same gas a decade previously -- that is, there was an earlier non-detection that put a more stringent limit on the amount of carbon monoxide in Pluto's atmosphere than the amount that Greaves et al. actually measured. That, in turn, means that Pluto's atmosphere (or, at least, the carbon monoxide in Pluto's atmosphere) has gotten substatially denser in the last decade.
