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Could Eris and Makemake be Ocean Worlds?

Building on the November post about the trans-Neptunian objects (TNOs) and the remarkable observations made by the James Webb Space Telescope (JWST), we delve here into JWST's recent observations of two TNO additional dwarf planets: Eris and Makemake. What these new observations suggest is no less than remarkable.

Just as a reminder, TNOs are celestial bodies that orbit the Sun at a greater distance than Neptune. Some of these TNOs, like Eris and Makemake, are large enough to be classified as dwarf planets. These objects are of particular interest because they are remnants from the formation of our solar system, and their surfaces contain a mixture of water, methane, and nitrogen ices. When New Horizons visited the most famous of all TNOs—Pluto—in 2015, everyone was stunned as the surface images showed signs of past geological activity, hinting at ongoing activity and even suggesting the presence of a subsurface ocean. With Pluto leading the way, it seems that it might be theoretically possible for TNOs of a certain size to undergo differentiation, the separation of the constituents of a planetary body creating distinct layers within its interior, potentially allowing them to host a subsurface ocean in the past, and perhaps even at present. This is why the JWST observation programs of TNOs are crucial.

As such, the JWST, with its advanced Near InfraRed Spectrograph (NIRSpec) instrument, has been pivotal in expanding our understanding of these distant objects. Recently, it provided us with fascinating data on Sedna, Gonggong, and Quaoar, which revealed that their surfaces are covered with complex organic molecules, the products of methane (CH4) irradiation.

Recent observations by JWST of Eris and Makemake reveal that their surfaces are not only showing signs of complexity similar to the aforementioned three TNOs, but may actually harbor subsurface oceans at present!

The observations focused on methane, and in particular its D/H ratio, the deuterium (heavy hydrogen, D) to hydrogen (H) ratio found in methane. Deuterium is thought to have originated from the Big Bang, while hydrogen is the most prevalent nucleus in the universe. The D/H ratio observed on a celestial body provides insights into the origin, geological evolution, and formation processes of hydrogen-containing compounds. It is like a window of what occurs within the dwarf planet.

The D/H ratio measured by JWST on both Eris and Makemake points to geochemical origins for methane produced within their deep interior. The latest models suggest that methane must have originated from the high temperatures found in the rocky cores of these dwarf planets. It is thus possible that Eris and Makemake still host cryovolcanic processes within their rocky cores, therefore delivering the methane to their surfaces. Both dwarf planets will probably exhibit evidence of recent resurfacing such as seen on Pluto, although no mission is planned to visit these distant worlds in the near future. The crucial point here is that the discovery of newly formed methane, along with the suggested resurfacing events and geochemical activity, indicates that there might likely be enough energy within the interiors of these dwarf planets to melt a substantial portion of the icy mantle, potentially leading to the formation of a subsurface ocean.

Eris and Makemake could thus be viewed as potential members of the small group of Ocean Worlds within our Solar System, joining the likes of Europa, Enceladus, Ganymede, Callisto, and Titan. These new insights not only enrich our understanding of these specific dwarf planets but also shed light on the broader population of TNOs and the likelihood that many of them might support a subsurface body of liquid water. This underscores once more the incredible diversity and complexity of these distant worlds, which, despite their cold and remote nature, exhibit geochemical evolutions.

With the JWST expected to operate for many years to come, we can look forward to regular observations of these fascinating objects.

As I always say, we live in remarkable times!



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