They may be dwarf planets, but they’re not dead planets.
NASA’s James Webb Space Telescope has provided scientists with evidence of geothermal activity deep within two far-out dwarf planets, Eris and Makemake.
“We see some interesting signs of hot times in cool places,” Christopher Glein, an expert in planetary geochemistry at the Southwest Research Institute, said this week in a news release. Glein is the lead author of a study analyzing the JWST findings that was recently published by the journal Icarus.
The evidence of geothermal activity comes in the form of methane detected on the surfaces of the icy worlds. Glein and his colleagues analyzed the composition of the methane in detail, focusing on the ratio of two types of hydrogen contained in the methane molecules.
A heavy isotope of hydrogen known as deuterium, or D for short, is thought to have been formed in the Big Bang. By measuring the ratio of deuterium to garden-variety hydrogen (D/H), scientists can trace the origin and the timeline for the formation of compounds that contain hydrogen — such as methane (CH4).
Glein had thought the D/H ratio would point to a primordial origin for the methane on the dwarf planets’ frozen surfaces. “Instead, the James Webb Space Telescope gave us a surprise!” he said.
The readings from JWST’s near-infrared spectrograph showed that the D/H ratio was too low for primordial methane. That led the researchers to conclude that the methane was of more recent origin.
“The D/H ratio is like a window,” Glein explained. “We can use it in a sense to peer into the subsurface. Our data suggest elevated temperatures in the rocky cores of these worlds so that methane can be cooked up. Molecular nitrogen could be produced as well, and we see it on Eris. Hot cores could also point to potential sources of liquid water beneath their icy surfaces.”
Lowell Observatory astronomer Will Grundy, a co-author on Glein’s paper and the lead author of a companion study, said the methane could have been delivered to the planetary surfaces by cryovolcanic processes, “perhaps in geologically recent times.”
“We found a carbon isotope ratio (13C/12C) that suggests relatively recent resurfacing,” he said.
The findings are consistent with what scientists saw on Pluto’s surface when NASA’s New Horizons probe flew past in 2015. In Pluto’s case, researchers suspect that cryovolcanic processes brought up ammonia-laden water ice or slush from a subsurface ocean in recent times.
The discovery of Eris, Makemake and other mini-worlds in the early 2000s led some folks to think that Pluto and its newfound cousins in the solar system’s far-flung Kuiper Belt weren’t worthy of planetary status. One of the most prolific discoverers of dwarf planets, Caltech astronomer Mike Brown, even proclaimed that “Pluto is dead.”
But the more we find out about the little guys of the solar system, the livelier they seem. “After the New Horizons flyby of the Pluto system, and with this discovery, the Kuiper Belt is turning out to be much more alive in terms of hosting dynamic worlds than we would have imagined,” Glein said. “It’s not too early to start thinking about sending a spacecraft to fly by another one of these bodies to place the JWST data into a geologic context. I believe that we will be stunned by the wonders that await!”
In addition to Glein and Grundy, the authors of “Moderate D/H Ratios in Methane Ice on Eris and Makemake as Evidence of Hydrothermal or Metamorphic Processes in Their Interiors: Geochemical Analysis” include Jonathan Lunine, Ian Wong, Silvia Protopapa, Noemi Pinilla-Alonso, John Stansberry, Bryan Holler, Jason Cook and Ana Carolina de Souza Feliciano.
The authors of “Measurement of D/H and 13C/12C ratios in Methane Ice on Eris and Makemake: Evidence for Internal Activity” include Grundy, Wong, Glein, Protopapa, Holler, Cook, Stansberry, Lunine, A.H. Parker, H.B. Hammel, S.N. Milam, R. Brunetto, Pinilla-Alonso, A.C. de Sousa Feliciano, J.P. Emery and J. Licandro.
