New Horizons has revealed a world that still hides many mysteries
THE FIRST SCIENCE results from the New Horizons probe have been released, three months after the initial flyby. Even from these early findings it appears that the dwarf planet is a highly complex world.
At first glance the tranche of images sent back seem to show mountains and ridges made of nitrogen, carbon monoxide and methane ices, but these are far too weak to support the weight of such large features. Instead it appears that there is a crust of water ice acting as bedrock with a veneer of the more volatile ices on top. Undulations in this bedrock, as large as 150km across, may indicate that it is undergoing some kind of tectonic activity.
The majority of the surface is a reddy-brown colour, thought to be organic residues called tholins. Tholins are created when nitrogen and methane, both of which are plentiful on Pluto, react with ultraviolet light and charged particles, and only a small amount are needed to create the colours seen on the dwarf planet.
One of the most unexpected regions was the Sputnik Planum, a smooth region devoid of craters and divided into polygonal and ovoid shapes. The cause of these strange shapes is unknown, but they may originate from surface cracking, which could be caused by either contraction or from the underlying rock pushing upwards. To add to the mystery, the region’s surface looks to be no more than a few hundred million years old, suggesting some geological activity is replenishing the surface, possibly from surface erosion, crater relaxation or some other method of recycling the crust. However most of these rely on an internal heat source and Pluto is too small to have maintained a molten core on its own, nor does it have the frictional pull of gravity to heat it as the Galilean moon Io does.
“Pluto’s diverse surface geology and longterm activity also raise fundamental questions about how it has remained active many billions of years after its formation,” says the paper, whose lead author Alan Stern is New Horizon’s principal investigator. “This suggests that other small planets of the Kuiper Belt, such as Eris, Makemake and Haumea, could express similarly complex histories that rival those of terrestrial planets.” http://pluto.jhuapl.edu