Two dwarf planets in our solar system, Eris and Make make, may have enough geothermal activity to sustain oceans of liquid water inside. This is revealed by a model describing new observations from the James Webb Space Telescope. Located deep in the Kuiper Belt, Eris is an icy world that has threatened Pluto's place in the solar system.
Eris is only 44 kilometers smaller than Pluto, but the concentration of rock in its center makes it 25 percent heavier, making it the prototype for dwarf planets. Pluto was inevitably forced to follow suit.
Make make was discovered two months after Eris and, with a diameter of 1,430 kilometers, is about 1,000 kilometers smaller than Eris and Pluto. Due to their extreme distance from the Sun - Eris is 14.4 billion kilometers away and Make make is 7.7 billion kilometers away - little is known about these distant dwarf planets.
But recent observations by the James Webb Space Telescope have shed new light on these worlds and discovered a surprising origin for the frozen methane ice on their surfaces. "We found evidence that thermal processes are producing methane inside Eris and Makemake," said Christopher Grein of the Southwest Research Institute in San Antonio, Texas.
Methane is a so-called hydrocarbon, consisting of a mixture of hydrogen and carbon atoms. These atoms exist in different varieties, or isotopes, that contain the same number of protons but different numbers of neutrons.
If the methane on the surfaces of these dwarf planets originates from the original planet-forming disk that existed around the young Sun 4.5 billion years ago, they would have a specific isotopic ratio between two isotopes of hydrogen: ordinary hydrogen, with one proton and zero neutrons, and deuterium, with one proton and one neutron.
But the hydrogen isotope ratios measured by Webb are different from the ratios expected if the methane was primordial, as is found in most comets.
"The deuterium-to-hydrogen ratio points to a geochemical origin of the methane produced in the deep interior," Grein said. "Our data suggest that the temperatures of the rocky cores of these worlds were rising, allowing the methane to be cooked.
Nitrogen molecules could have also been produced, and we see that in Eris. In other words, hydrothermal reactions or metamorphic activity, that is, heat and pressure acting on the rocks, must have produced methane deep inside Eris and Make make." If that's the case, the methane must have reached the surface through outgassing or possibly volcanic activity.
--Bhautik Thummar
