Astronomy Wiki

Kepler 442b is an Earth sized exoplanet orbiting within the habitable zone of the K-type main sequence star, Kepler 442, around 1206 light years from Earth in the Lyra constellation.


In 2009, NASA's Kepler spacecraft was observing stars on its photometer, the instrument used to detect transit events (where a planet periodically dims the light of its star by passing in front of it). In this last test, Kepler observed 50000 stars, including Kepler-442; the preliminary light curves of Kepler 442b were sent to the Kepler science team for analysis. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-442b occurred roughly every 113 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic transits. Finally, on January 6th, 2015, Kepler 442b was confirmed by NASA’s Kepler spacecraft.

Planetary Characteristics[]

The planet itself is likely rocky and considered to be a Super Earth, a planet that has a greater mass and radius than Earth but less than the Ice Giants. Kepler 442b has a mass around double that of the Earth and a radius 30% greater than the Earth. The equilibrium temperature, that is the temperature of the planet if there wasn’t an atmosphere, is 233 K (-40°C; -40°F). Kepler 442b orbits its star from 38,000,000 miles (61,200,000 kilometers) from its star and takes approximately 112 Earth days to complete a full revolution. Determining the atmospheric composition of the planet cannot be conducted due to it being too far from the Earth.

Stellar characteristic[]

The planet orbits a K-type star named Kepler-442. The star has a mass of 0.61 M and a radius of 0.60 R. It has a temperature of 4402 K and is around 2.9 billion years old, with some uncertainty. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The luminosity (L) of Kepler 442 is 12% that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.76.

Potential Habitability[]

Since the planet is in the habitable zone of its star, it could harbor liquid water on its surface, potentially allowing life to emerge. Furthermore, due to its mass and radius, it could have a rocky surface, plate tectonics, a magnetosphere, and an atmosphere.

Other factors that contributes to Kepler 442b’s possible habitability is its star. K type sequence stars, the type of star Kepler 442 is, are smaller than our sun and live 2 to 3 times as long. Additionally, K type stars emit less UV rays then our sun, but still provide enough non UV radiation to provide life-bearing temperatures.