Kepler-737b

Lore & Background

Kepler-737b orbits an early M-star (Kepler-737, also known as KOI-947) with a mass of 0.51 solar masses and a radius of 0.48 solar radii. The star has a temperature of 3813 K, a metallicity of -0.24, and an age of 3.89 billion years. The planet was confirmed on May 10, 2016, and its mass is estimated at 4.5 Earth masses based on a mass-radius relationship, giving it a density of 3.3 times that of water. This density suggests it could be a mini-Neptune or, more favorably for habitability, a water world similar to GJ 1214b.

The planet receives a stellar flux 2.297 times that of Earth, greater than that of Venus, and has an equilibrium temperature of 298 K. Its orbit of 28.5992 days places it within the inner part of the habitable zone according to some optimistic models, though conservative models place it outside. If it has an Earth-like greenhouse effect, its surface temperature could reach about 60 °C; with twice the greenhouse effect, it could reach 90 °C. The planet is likely tidally locked due to its short orbit, with one side permanently facing the star and the other in constant darkness.

Reader's Guide

Kepler-737b's significance lies in its potential as a water world and its position near the habitable zone boundary. Its density, though estimated, allows for the possibility of a thick water layer, making it a candidate for studying ocean planets. The planet's high stellar flux, exceeding that of Venus, makes it unlikely to be habitable under most models, but it remains in the habitable zone according to the Open Exoplanet Catalogue's extremely optimistic model, which also places Venus in the habitable zone. If Kepler-737b has an atmosphere, heat circulation could make a portion of the terminator line habitable, though the most likely scenario is a surface too hot for life. The planet's unknown magnetic field could expose it to radiation, potentially requiring adaptations like those seen in tardigrades, which can repair DNA damage. The chance of intelligent life is reduced if it is a water world with no dry land. Its legacy includes serving as a comparison for other super-Earths like Kepler-186f, Ross 128 b, and the TRAPPIST-1 planets, as well as for water worlds like GJ 1214b and Kepler-22b.

Did You Know?

• Its equilibrium temperature is 298 K (25 °C), the same as Earth's average.
• It may be a water world similar to GJ 1214b.