A Distant Earth
10 November 2013

This picture is an artist’s impression, showing an Earth-like planet, orbiting outside the solar system.
Credit: NASA/Ames/JPL-Caltech

A team of astronomers has discovered the first Earth-sized planet beyond the solar system that has a rocky composition like that of Earth. The planet, known as Kepler-78b, orbits very close to its parent star, every 8.5 hours, making it a very hot object and not hospitable for life. Planets orbiting outside the solar system are known as exoplanets or extrasolar planets. Since 1992, astronomers have discovered more than 1,000 exoplanets.

Kepler-78b was discovered using data from NASA’s Kepler spacecraft, a sophisticated telescope, which, from an orbit around the Sun, searches for exoplanets, by continuously monitoring more than 150,000 stars, located within a small area on the sky. Sensitive Kepler can discover an exoplanet when it passes in front of its star, and causes a very slight decrease of the star’s brightness.

Two independent research teams then used telescopes, to confirm Kepler-78b, and deduce its characteristics. To determine Kepler-78b's mass, the teams studied its motion around its star. On the other hand, Kepler’s observations allow astronomers to determine the size of a planet by measuring the amount of starlight blocked when it crosses in front of its star.

Interestingly, a few of the known exoplanets are comparable to Earth in size or mass. Kepler-78b is the first to have both its mass and radius measured. Therefore, astronomers can calculate a density and determine the planet’s composition.
Kepler-78b has a mass of 1.7 times the terrestrial mass, and a radius only 1.2 that of Earth. Its density is similar to Earth's. This suggests that Kepler-78b consists primarily of rock and iron. Kepler-78b’s star is a Sun-like star, located about 400 light-years away from Earth.



Aymen Mohamed Ibrahem
Senior Astronomy Specialist

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