Volcanoes don’t always involve magma and lava. In fact, plenty of moons and dwarf planets in our Solar System have ice volcanoes – those that erupt plumes of warmer water, ammonia, hydrogen, and nitrogen compounds, surrounded by a mountain of ice.
Now, it seems that scientists have discovered that there may be far more cryovolcanoes in our galactic neighborhood than we previously thought.
Presenting their work at a gathering of the American Astronomical Society earlier this month, a pair of researchers from the Lowell Observatory and the SETI Institute drew everyone’s attention to Eris and Makemake. These two dwarf planets are found far beyond the orbit of Neptune and are the second and third-largest objects in the Kuiper Belt, respectively.
These chilly worlds are composed of various ices and rocky materials, so you’d expect them to bounce back a fair bit of sunlight even at distances of up to 98 times the Earth-Sun orbital axis. Observations of their surfaces, however, have revealed that they’re incredibly reflective – too reflective, in fact.
Both are coated in shiny methane ice, which evaporates to leave behind a red-tinted, less reflective compound named tholin. Calculations show that this frigid dust makes up about 10 percent of the ice covering Eris, and Makemake is coated in even more, but weirdly, that doesn’t match up to the observations.
Instead of being somewhat dull, they’re like distant mirrors, and the team thinks that additional nitrogen ice is to blame. It’s incredibly reflective, but also – thanks to its weird mechanical properties – it’s stretching as it’s being heated from below, ensuring it covers up more of the tholin-marked surfaces.
This excess vitreous ice must be emerging from volcanic activity; no other geological process could explain it. Unfortunately, this poses a bit of an astronomical problem for researchers.
Cryovolcanoes, or cryogeysers, are powered much like conventional volcanoes. Whatever the solid or molten component may be (rock and magma, ice and water), the object needs a heat source, which can come from primordial heat leftover from its violent formation, the decay of radioactive elements, or tidal heating caused by the gravitational pull of nearby, fairly massive moons or planets on their innards.
Generally speaking, large objects keep heat trapped for longer, and are more likely to have geologically active surfaces. Both Eris and Makemake are incredibly small compared to most planetary objects, though, and aren’t orbited by anything that would trigger tidal heating.
This all suggests that the internal heat source that would drive anything at the surface, from plate tectonics to cryovolcanism, has been all-but-extinguished. Clearly, this isn’t the case, and no-one at present can confidently explain why.
[H/T: New Scientist]