Icy rocks in the outer solar system might have unexpected subsurface oceans. Eris and Makemake are both dwarf planets in the Kuiper belt – the ring of frozen objects that encircles our solar system beyond Neptune’s orbit – and new observations from the James Webb Space Telescope (JWST) hint that these small worlds could have unexpected activity beneath their surfaces.
Kuiper belt objects, or KBOs, are generally thought of as similar to large, inactive comets, preserving pristine ices that formed in the early solar system. But at the Southwest Research Institute in Texas and his colleagues have found evidence that conception might not be quite right.
“The JWST data on the surface compositions of Eris and Makemake show that they’re not just these frozen ice balls that we might imagine them to be because they’re so far from the sun,” says Glein. “They’re much more active than we imagined.”
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The evidence comes in the form of measurements of the amounts of two different types of hydrogen: Deuterium, sometimes called heavy hydrogen because of its extra neutron, and regular hydrogen. This ratio can be used as a sort of clock to track the evolution of a planetary body’s surface.
The ratios on Eris and Makemake indicate that their surfaces have been reset – although it’s unclear exactly when – replenished through some sort of underground process that produces temperatures in excess of 150°C. “It’s an interesting hint that something unexpected and geologically recent has happened,” says Glein.
There are two plausible ways to reproduce the hydrogen ratios that we see: There could be hydrothermal processes on the floor of liquid water oceans buried beneath Eris and Makemake’s icy exteriors; alternatively, liquid water may be absent, but there could be heat-generating mechanisms in the dwarf planets’ cores. These environments are more ubiquitous on much larger icy bodies such as the moons Europa and Titan. Evidence that they are present on smaller worlds is surprising – Eris is slightly more massive than Pluto, and Makemake is a bit less massive.
So far, we don’t have enough data to discriminate between the two scenarios or to completely unravel how this will affect our understanding of KBOs more generally. “It’s a really intriguing hint, but we don’t have the geological context – we have this chemical information about the surface, but we can’t actually see the surface,” says Glein. “We’re getting a piece of the puzzle, but the rest of the puzzle is all jumbled up.”
We’ll have to study the small icy bodies of the solar system in more detail to figure out if they really are geologically active – and why.
References: arXiv, ˛ą˛Ô»ĺĚý
