LHS 1140b scaled next to Earth, with the “eyeball planet” scenario shown (Image Credit: B. Gougeon/Université de Montréal).
The planet making headlines recently is named LHS 1140b. It orbits a small and cool red dwarf star, completing a full lap in under 25 days compared to Earth’s 365 days. This is because it sits very close to the star, at just 10% the distance Earth is from the Sun. However, since the star is so dim, this puts LHS 1140b comfortably within the star’s habitable zone, the area where water is at its liquid form. The planet receives just under 50% the amount of sunlight Earth gets, but its potentially thick atmosphere may warm it up significantly.
How Big Is It?
In terms of size, this world is larger and more massive than Earth. Current estimates place it around 70% larger, or 1.7x the size of our own planet. Its mass is even more dramatic, at around 5-6 times the mass of Earth. LHS 1140b’s density is surprisingly low, which indicates that its composition is made up of more than just rock. Some astronomers are even estimating that 10-20% of the planet’s mass may be from water.
A true-size comparison between LHS 1140b and Earth (Image Credit: Credit: NASA, Vleider).
Atmospheric Composition
The James Webb Space Telescope has taken measurements of LHS 1140b to see what its atmosphere is made of. Currently, the data seems to suggest a hydrogen-rich atmosphere, which could indicate that this planet has an envelope similar to Neptune’s. Underneath this thick coat is where the water would be, covering potentially its entire globe.
A graph showing the transmission lines of LHS 1140b’s atmosphere, taken by the JWST (Graph Credit: ransmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS by Keith Cowing).
Is There a Solid Surface?
While the planet may contain large amounts of water, it’s very plausible there is still a solid surface. This is due to LHS 1140b being tidally locked, meaning one side of the planet always faces the star while the other side has a permanent night. Because of this, the temperature would vary and could cause an “eyeball planet” effect.
LHS 1140b is one of the best candidates for a water world, and for finding life beyond Earth. As Webb continues to make observations, we will learn more about this planet’s alien environment.