Kepler-69c

Lore & Background

Kepler-69c was discovered by NASA's Kepler spacecraft using the transit method, in which the dimming effect caused by a planet crossing in front of its star is measured. The discovery was announced in April 2013 as part of the Kepler spacecraft data release. The planet orbits its host star every 242 days at a distance of 0.64 times that of Earth, similar to Venus's orbital period and distance in the Solar System. The host star, Kepler-69, is a G-type star with a mass of 0.81 solar masses and a radius of 0.93 solar radii, a surface temperature of 5638 K, and an estimated age of around 9.8 billion years, meaning it is probably nearing the end of its lifetime. The star has an apparent magnitude of 13.7, too dim to be seen with the naked eye.

Kepler-69c is a super-Earth with an estimated mass of at least 2.14 times that of Earth and a radius of around 2.2 times that of Earth. Its estimated equilibrium temperature is 325 K, but its likely surface temperature is far hotter at 548 K. These characteristics make it an analog to Venus, but more massive, leading to its classification as a 'super-Venus'. The planet resides in the inner edge of the habitable zone or even outside of it, and is thus highly likely to resemble Venus with temperatures and conditions far too hot to sustain any life, making it uninhabitable.

Reader's Guide

Kepler-69c was initially announced in the media as being located within its star's habitable zone, a region where liquid water could exist on the surface, and was described as one of the most Earth-like planets in terms of size and temperature yet found, a 'prime candidate to host alien life'. However, due to uncertainties in the stellar parameters, the error bars on the incident flux are quite large, at 1.91 times the level of Earth. Using nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility it may lie in the innermost region of the habitable zone and be a desert planet. Even with the lowest error bar measurement, a stellar flux of 1.35 S🜨 would still be high enough to boil away any oceans. A more recent analysis has shown the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable. The discovery, along with the planetary system of Kepler-62, prompted a congressional hearing by two U.S. House of Representatives subcommittees on 9 May 2013 discussing 'Exoplanet Discoveries: Have We Found Other Earths?', and a related special issue of the journal Science described the discovery.

Did You Know?

• Kepler-69c is located about 2,430 light-years from Earth.
• Its orbital period of roughly 242.46 days is similar to Venus's orbital period in the Solar System.
• The planet has an estimated surface temperature of 548 K, far hotter than Earth.
• Kepler-69c is classified as a 'super-Venus' due to its Venus-like conditions but greater mass.