Distance from Earth: 41 light-years
Mass: 0.69 Earths
Radius: 0.92 times Earth
Year: 6.1 days
A member of one of the most famous stellar systems, TRAPPIST-1 e is one of seven exoplanets around Trappist-1. Several of the worlds may be eyeball planets. But while all the planets could also have water, only three lie firmly within the star’s habitable zone.
A hot, bright, early stellar phase may have caused all the evolving planets to look like Venus: any early oceans long since evaporated, leaving behind a thick, uninhabitable atmosphere. But according to a 2018 study published in the Astrophysical Journal, Trappist-1 e is the most likely to have managed to retain water, perhaps even hosting an Earth-like ocean.
All seven of the Trappist-1 planets have similar densities, making the system very different from our own. Such similar densities suggest the planets also all have similar compositions. The James Webb Space Telescope will be able to probe further into the atmospheres of these exoplanets, searching for elements that could hint at the presence of life.
Open oceans aren’t the only possible surface conditions for Proxima b. A paper published in Nature Astronomy in 2019 suggests that oceans beneath the substellar point might freeze over because of sea-ice dynamics. Modeling conditions on Proxima b, the researchers found that as sea ice drifts into warmer waters, the ice cools the ocean as it melts. Gradually, more and more of the ocean freezes, even on the dayside. At that point, only an atmosphere with abundant greenhouse gases could prevent global freezeover.
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 regions to warm regions, heated waters can also serve as a transporter of heat from warm regions to cold regions and melt the ice, warming the climate instead. “Depending on the details,” Wolf says, “the climate could very literally be anything from the cold, icy states shown by [the 2019 study] to Venus-like, hot, CO2-dominated worlds, or they could even look like [Saturn’s moon] Titan with [methane] and hazes.” Not to mention that if continents are included in the mix, he adds, “all bets are off because the presence and location of continents significantly changes the patterns of ocean transports.”