Geology of Pluto

The topic of this month's Accretionary Wedge is geology in space.

There is a lot of sexy stuff to talk about, but I thought, what about a space body that has been through some tough times recently. Pluto used to be a planet, the select club of only 8 other members in our solar system. But in 2006 it was downgraded to just a dwarf planet. It deserves some attention.

The hardest thing about studying the geology of Pluto is the distance. Pluto is at a minimum 4.28 billion km from earth. A little to far for a rock hammer. At that distance, even satellites have problems.



First, what is Pluto made of? Using spectroscopy, Pluto's surface has been determined to be mostly frozen N₂ with a small amounts of CH₄ and CO. Based on its density, Pluto is thought to have a solid rock core. The radioactive decay from this core could be enough to melt the bottom of Pluto's frozen surface, resulting in a layer of liquid between the core and surface.

Pluto's surface, however, is not flat and featureless, as Hubble images have reveled. Pluto has locations of varying albedo that are probably a result of not only surface frost, but also impact craters.



Despite Pluto's great distance from the sun, its atmosphere's composition is still controlled by the sun. Just like with ice caps on Earth, although the sun may not have enough energy to melt the frozen material, it can sublimate some of it. Because of this sublimation, Pluto's atmosphere has a similar composition to its surface. Pluto, like Saturn's moon, Titan, Neptune's moon, Triton, and the Earth, has a N₂ dominated atmosphere. However, this atmosphere is sparse, at only 3 microbars of pressure versus the Earth's average of 10130 microbars. Because of Pluto's thin atmosphere and great distance from the sun, the average surface temperature is only 40 Kelvin.

Pluto has not been forgotten. In 2006, the New Horizons mission was launched to study Pluto and the Kuiper belt. Pluto won't be reached 2015, but the satellite should great expand our knowledge of Pluto, the distant 9th planet dwarf plant of our solar system.

References
NASA's New Horizons Mission. What We Know About Pluto, Charon and the
Kuiper Belt. http://pluto.jhuapl.edu/science/whatWeKnow.html

Owen, T. C., Roush, T. L., Cruikshank, D. P., Elliot J. L., Young, L. A., De Bergh, C., Schmitt, B., Geballe, T. R., Brown, R. H., Bartholomew, M. J. 1993. Surface Ices and the Atmospheric Composition of Pluto. Science 261(5122): 745 - 748.

Stern, A., Buie, M. 1996. Hubble Reveals Surface of Pluto for First Time. Hubble Newscenter. http://hubblesite.org/newscenter/archive/releases/1996/09/

Williams, D. R. 2006. Pluto Fact Sheet. NASA Planetary Fact Sheets. http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html