More Surprises From Pluto
by Jason Major on April 24, 2011
Ah, Pluto. Seems every time we think we‚Äôve 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 system‚Äôs most distant planet. Then a controversial decision in 2006 by the International Astronomical Union, spurred by suggestions from astronomer (and self-confessed ‚Äúplanet-killer‚ÄĚ) Mike Brown*, relegated Pluto to a new class of worlds called ‚Äúdwarf planets‚ÄĚ. 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 ‚ÄúMy Very Eager Mother Just Served Us Nine Pies‚ÄĚ 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 ‚Äúlast‚ÄĚ planet, and didn‚Äôt 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.
But‚Ä¶that‚Äôs getting ahead of ourselves. First things first.
Recent discoveries by a UK team of astronomers points to the presence of carbon monoxide in Pluto‚Äôs 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 planet‚Äôs ‚Äď er, dwarf planet‚Äôs ‚Äď 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 Pluto‚Äôs largest moon, Charon.
It‚Äôs 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 ‚Äúheating‚ÄĚ is used scientifically here‚Ä¶remember, at around -240¬ļC (-400¬ļF) Pluto would seem anything but balmy to us!) by the Sun‚Äôs 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 Pluto‚Äôs surface ‚Äď possibly caused by the thawing of frozen areas that shift and reveal lighter surface material below.
‚ÄúSeeing 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 Earth‚Äôs atmosphere.‚ÄĚ
‚Äď 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 Pluto‚Äôs 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