The strange case of eyeball planets

Distance from Earth: 41 light years

Mass: 0.69 Land

Ray: 0.92 times the Earth

Year: 6.1 days

A member of one of the most famous star systems, TRAPPIST-1 e is one of seven exoplanets around Trappist-1. Several of the worlds may be eyeball planets. But while all of the planets could also have water, only three lie firmly within the star’s habitable zone.

A hot and bright early stellar phase may have made all evolving planets look like Venus: all early oceans have long since evaporated, leaving behind a thick, uninhabitable atmosphere. But according to a 2018 study published in the Astrophysical Journal, Trappist-1e is the most likely to have managed to retain water, possibly even harboring an Earth-like ocean.

The seven Trappist-1 planets have similar densities, which makes the system very different from ours. Such similar densities suggest that the planets also all have similar compositions. The James Webb Space Telescope will be able to probe the atmospheres of these exoplanets further, looking for elements that could suggest the presence of life.


Open oceans are not the only possible surface conditions for Proxima b. An article published in natural astronomy in 2019 suggests that the oceans below the substellar point could freeze over due to sea ice dynamics. the ice cools the ocean as it melts. Gradually, more and more of the ocean is freezing, even on the daytime side. At this point, only an atmosphere rich in greenhouse gases could prevent the global freeze.

But, according to Eric Wolf, a research associate at the Laboratory for Atmospheric and Space Physics in Boulder, Colorado, other models have shown the opposite scenario. Just as ice can drift from cold to warm regions, heated waters can also serve as a carrier of heat from warm to cold regions and melt the ice, warming the climate instead. “Depending on the details,” says Wolf, “the climate could very literally be anything from cold and icy states shown by [the 2019 study] to hot, CO2-dominated, Venus-like worlds, or they might even look like [Saturn’s moon] Titan with [methane] and mists. Not to mention that if continents are included in the mix, he adds, “all bets are off because the presence and location of continents dramatically alter ocean transport patterns.”

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