More Surprises From Pluto
by Jason Major on April 24, 2011
Ah, Pluto. Seems every time we think weâ€™ve got it figured out, it has a new surprise to throw at us.
First spotted in 1930 by a young Clyde Tombaugh, for 76 years it enjoyed a comfortable position as the solar systemâ€™s most distant planet. Then a controversial decision in 2006 by the International Astronomical Union, spurred by suggestions from astronomer (and self-confessed â€śplanet-killerâ€ť) Mike Brown*, relegated Pluto to a new class of worlds called â€śdwarf planetsâ€ť. Not quite planets and not quite asteroids, dwarf planets cannot entirely clear their orbital path with their own gravitational force and thus miss out on full planetary status. Besides immediately making a lot of science textbooks obsolete and rendering the handy mnemonic â€śMy Very Eager Mother Just Served Us Nine Piesâ€ť irrelevant (or at least confusing), the decision angered many people around the world, both in and out of the scientific community. Pluto is a planet, they said, it always has been and always will be! Save Pluto! the schoolkids wrote in crayon to planetarium directors. The world all of a sudden realized how much people liked having Pluto as the â€ślastâ€ť planet, and didnâ€™t want to see it demoted by decision, especially a highly contested one.
Yet as it turns out, Pluto really may not be a planet after all.
It may be a comet.
Butâ€¦thatâ€™s getting ahead of ourselves. First things first.
Recent discoveries by a UK team of astronomers points to the presence of carbon monoxide in Plutoâ€™s atmosphere. Yes, Pluto has an atmosphere; astronomers have known about it since 1988. At first assumed to be about 100km thick, it was later estimated to extend out about 1500km and be composed of methane gas and nitrogen. This gas would expand from the planetâ€™s â€“ er, dwarf planetâ€™s â€“ surface as it came closer to the Sun during the course of its eccentric 248-year orbit and then freeze back onto the surface as it moved further away. The new findings from the University of St Andrews team, made by observations with the James Clerk Maxwell telescope in Hawaii, identify an even thicker atmosphere containing carbon monoxide that extends over 3000 km, reaching nearly halfway to Plutoâ€™s largest moon, Charon.
Itâ€™s possible that this carbon monoxide atmosphere may have expanded outwards from Pluto, especially in the years since 1989 when it made the closest approach to the Sun in its orbit. Surface heating (and the term â€śheatingâ€ť is used scientifically hereâ€¦remember, at around -240ÂşC (-400ÂşF) Pluto would seem anything but balmy to us!) by the Sunâ€™s radiation would have warmed the surface and expelled these gases outwards. This also coincides with observations made by the Hubble Space Telescope over the course of four years, which revealed varying patterns of dark and light areas on Plutoâ€™s surface â€“ possibly caused by the thawing of frozen areas that shift and reveal lighter surface material below.
â€śSeeing such an example of extra-terrestrial climate-change is fascinating. This cold simple atmosphere that is strongly driven by the heat from the Sun could give us important clues to how some of the basic physics works, and act as a contrasting test-bed to help us better understand the Earthâ€™s atmosphere.â€ť
â€“ Dr. Jane Greaves, Team Leader
In fact, carbon monoxide may be the key to why Pluto even still has an atmosphere. Unlike methane, which is a greenhouse gas, carbon monoxide acts as a coolant; it may be keeping Plutoâ€™s fragile atmosphere from heating up too much and escaping into space entirely! Over the decades and centuries that it takes for Pluto to complete a single year, the balance between these two gases must be extremely precise.Share