Published On: Fri, Oct 13th, 2017

Odd, potato-shaped dwarf planet has ring, may not be a planet

Enlarge (credit: IAA-CSIC/UHU)

Thanks largely to the improvements in our instrumentation, we’ve started to get a picture of what the far reaches of our Solar System look like. Beyond the orbit of the outermost planet, there is a large collection of icy dwarf planets called trans-Neptunian objects, or TNOs. Pluto may have been the founding member of the TNOs, but there are now more than 1,200 known bodies in the list; only 270 of those have even been observed well enough to have their orbits characterized. It’s a safe bet that there will be some surprises among them.

In a paper being released today, researchers are reporting on one such surprise, courtesy of the dwarf planet Haumea: it’s got a ring. The observations that spotted the ring also suggest that Haumea is larger than we thought it was, which means that gravity hasn’t yet pulled it into a stable, rounded shape. Awkwardly, this means that Haumea may not fit the definition of dwarf planet set down by astronomers.

Meet the dwarf

Haumea, named after a Hawaiian goddess, has a closest approach to the Sun of 35 Astronomical Units (AU, the typical distance between the Earth and Sun). For context, Neptune is typically about 30 AU. Due to its highly elliptical orbit, Haumea is over 50 AU at its farthest distance from the Sun. At those distances, not a lot of sunlight reaches it, so most observations of the dwarf planet involve just a few smeary pixels. But we have observed it enough to know that it’s consistently associated with two smaller smears of pixels, its moons Hi’iaka and Namaka. The moons’ orbits told us something about Haumea’s mass.

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Ars Technica UK


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