A Redder, Darker Dwarf Planet
The combined power of two major telescopes has enabled astronomers to re-assess the size and albedo of the dwarf planet 2007 OR10, which moves around the Sun in an elliptical orbit beyond Neptune. This extended scattered disk object, currently located beyond the traditional Kuiper Belt, lies about twice the distance of Pluto away. It turns out to have a remarkably slow rotation, is darker than previously thought, and is significantly larger with a diameter of 955 miles. Its size upgrade makes it the largest un-named body in the solar system; a situation which is unlikely to remain so for much longer:
“According to the new measurements, the diameter of 2007 OR10 is some 155 miles (250 kilometers) larger than previously thought. The larger size also implies higher gravity and a very dark surface — the latter because the same amount of light is being reflected by a larger body. This dark nature is different from most dwarf planets, which are much brighter. Previous ground-based observations found 2007 OR10 has a characteristic red color, and other researchers have suggested this might be due to methane ices on its surface.
“”Our revised larger size for 2007 OR10 makes it increasingly likely the planet is covered in volatile ices of methane, carbon monoxide and nitrogen, which would be easily lost to space by a smaller object,” said András Pál at Konkoly Observatory in Budapest, Hungary, who led the research. “It’s thrilling to tease out details like this about a distant, new world — especially since it has such an exceptionally dark and reddish surface for its size.”
“As for when 2007 OR10 will finally get a name, that honor belongs to the object’s discoverers. Astronomers Meg Schwamb, Mike Brown and David Rabinowitz spotted it in 2007 as part of a survey to search for distant solar system bodies using the Samuel Oschin Telescope at Palomar Observatory near San Diego, California.
“”The names of Pluto-sized bodies each tell a story about the characteristics of their respective objects. In the past, we haven’t known enough about 2007 OR10 to give it a name that would do it justice,” said Schwamb. “I think we’re coming to a point where we can give 2007 OR10 its rightful name.”” (1)
Just as well they didn’t stick with Dr Mike Brown’s initial suggestion of ‘Snow White’! He seems less than keen to come up with a new name, and next year, ten years on from its initial discovery, the floor will be opened to anyone wishing to make a proposal.
2007 OR10 turned out to be one of the reddest objects in the Kuiper Belt, most likely due to methane frosts on the surface when bombarded by dim sunlight (2). This is somewhat contentious, as we shall see. The red colour may well be attributable to the presence of organic substrates on the surface of the dwarf planet, but one wonders why some Kuiper Belt Objects are strongly coloured in this way, while others show no evidence of methane frosts at all.
Panspermia theorists N.C. Wickramasinghe and F. Hoyle advocated the idea that the redness of some of these objects indicate that they carry complex organic, even biological, materials. They argued that chemical and biochemical processes are going on below the surface of these worlds, whereupon biological pigments are being lifted to the surface. Regarding the evident variety of colourations, they note that subjecting hydrocarbon mixtures to radiation under laboratory conditions tends to create neutral, even grey mixtures – not red – and that the action of sunlight alone on, say, methane, may not be sufficient to explain the redness seen on some KBOs:
“The fact that the distribution of colour amongst these objects does not correlate with heliocentric distance indicates that the intensity of solar radiation does not play an important role in the colouring process.” (3)
Again, one might wonder why such biological processes are taking place on some of these outer solar system objects, but not others. The cold, classical Kuiper Belt Objects are uniformly red, for instance. But many KBOs are white, with relatively high albedos. Why?
Previous work to try to understand the evident distinction between sub-sets of the Kuiper Belt Objects has looked at the way sunlight might affect the organic components contained within different layers of ice. Perhaps the surfaces of these worlds might be ‘sand-blasted’ by plasma ions in the solar wind (or, indeed larger meteorite material colliding with these objects), exposing lower, redder layers (4). Again, the organic materials within may turn out to be quite complex – including amino acids, the building blocks of life. These arguments rely upon a dynamic equilibrium between the removal of the upper layer of ice, and the generation of complex organic materials thus exposed below. This is, of course, an untested hypothesis.
Another possibility is that this diversity reflects a straightforward difference in composition between these objects, implying different conditions during their initial formation:
“We have two basic ideas about the origin of the color diversity. Firstly, it is possible that the KBOs possess intrinsically different compositions, and that the different colors are tracers of the compositional variation. Is this likely? In the main asteroid belt, asteroids indeed possess different compositions that seem to be related to their sites and temperatures of formation. The KBOs, as far as we know, all formed more or less where we now see them, in the space beyond Neptune. Their formation temperatures would all have been about 40 or 50 K, so it is hard to see how pronounced compositional differences might arise. But they might, and this is a possible interpretation of the data.” (5)
Herein lies a most interesting possibility. Could the Kuiper Belt, as well as the extended zone of scattered objects beyond, be composed of a mixture of cosmic bodies of two quite separate origins? This seems a far more straightforward solution, but one which brings with it a new set of challenges for planetary scientists trying to understand the complex anomalies of the outer solar system. Which of the objects are Kuiper belt ‘natives’, the red or the white? And where did the ‘others’ come from, exactly?
14th May 2016
1) Preston Dyches “2007 OR10: Largest Unnamed World in the Solar System” 11th May 2016, http://www.nasa.gov/feature/ames/kepler/2007-or10-largest-unnamed-world-in-the-solar-system with thanks to Lee
2) “(225088) 2007 OR10” https://en.wikipedia.org/wiki/(225088)_2007_OR10
3) N.C. Wickramasinghe and F. Hoyle “The Astonishing Redness of Kuiper-Belt Objects” Astrophysics and Space Science, 1999, v 268, p 369-372, http://www.panspermia.org/kuiper.htm
4) Space.com Staff “Icy Red Objects at Solar System’s Edge May Point to Life’s Building Blocks” 29th October 2010 http://www.space.com/9418-icy-red-objects-solar-system-edge-point-life-building-blocks.html
5) Dave Jewitt “Surfaces of Kuiper Belt Objects” http://www2.ess.ucla.edu/~jewitt/kb/kb-colors.html