Artists rendition of Kepler-78b.
Other names Unknown
Orbital Characteristics
Adjective none
Aphelion Unknown
Semimajor axis 0.01 AU
Orbital Period 0.355007 days (8.5 hours)
Average orbital speed Unknown
Satellites Unknown
Physical Characteristics
Surface area Unknown
Volume Unknown
Mass 1.69-1.85 Earth mass
Axial tilt Unknown
Surface temperature (min) Unknown
Surface temperature (avg) Unknown
Surface temperature (mean) 2330 K (2056 °C, 3734 °F) (estimated)
Surface temperature (max) Unknown
Other information
Population 0
Surface Pressure Unknown
Composition Unknown
Habitable No

Kepler-78b is an extrasolar planet which orbits its host star, Kepler-78, every 0.355007 days (8.5 hours).


Size, mass, compositionEdit

Kepler-78b is about 20% larger than Earth, and is 69% more massive. Two independent teams were involved in pioneering work to estimate the mass of the planet. The estimates were made possible, as Kepler-78b's gravity causes a "wobble" in the orbit of the host star. Although this method is usually used to characterize gas giants, ordinarily it is hard to estimate the mass of Earth-sized exoplanets because their gravity is too weak to produce a visible influence on their stars. So, in this case, the planets orbit is so close to the star that its gravitational influence actually has a detectable effect.

A team led by Francesco Pepe also estimated that Kepler-78b had a mass 1.86 times that of Earth, and a radius of about 1.16 times more then that of Earth. Another team used data from the Keck 1 Telescope at the W.M. Keck Observatory in Hawaii to estimate the mass is about 1.69 times that of Earth, and a radius of about 1.2 times that of Earth. Both estimates put the planet's density at about 5.5 grams per cubic centimeter, equivalent to that of the Earth and possibly indicative of a rock-iron composition like Earths.

Kepler-78b is very similar to other hot extrasolar planets with high-density, such as Kepler-10b, Kepler-36b, and CoRoT-7b.


Kepler-78b orbits around its star in an 8.5-hour orbit. The planet reflects around 20% to 60% of the starlight that it receives. As it orbits extremely closely to its star, approximately 40% closer then Mercury to the Sun, the estimated surface temperature is 2330 K (2056 °C, 3734 °F) to 3100 K (2830 °C, 5120 °F). The temperature is high enough to have stripped the planet of any atmosphere, thoug liquid water and solid portions on the planet would be stable. According to Francesco Pepe, one of the astronomers involved in the discovery of this planet, said "the planet may be Earth-sized, but it can be imagined like a lava planet rather than an Earth-like planet."

The acceleration of gravity on the planet surface is estimated to be ~11 m/s2, which is slightly larger than Earth's.

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