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Researchers discover Earth-like exoplanet that completes orbit in 8.5 hours

MIT researchers have discovered one of the shortest orbital periods ever detected. The Earth-sized exoplanet, named Kepler 78B, whips around its host star in a mere 8.5 hours. The discovery was reported in The Astrophysical Journal.

Most importantly, scientists were able to detect light emitted by the planet — a first for an exoplanet as small as Kepler 78b. Once analyzed with larger telescopes, this light could provide detailed information about the planet’s surface composition and reflective properties.

Because of its proximity to its star, scientists have estimated the planet’s surface temperatures to be more than 5,000 degrees Fahrenheit, which has likely created a massive, roiling ocean of lava. This proximity also lends hope to scientists expecting to measure the planet’s gravitational influence on the star, which could be used to measure the planet’s mass and make Kepler 78b the first Earth-sized planet outside our solar system whose mass is known.

Previously, the same team of researchers observed KOI 1843.03, an exoplanet with an orbital period of just 4.5 hours. The researchers determined that for the planet to maintain such a tight orbit it would have to be incredibly dense, otherwise, immense tidal forces would rip the planet apart.

To discover Kepler 78b, the research team used the Kepler Telescope to look at more than 150,000 stars. Data from Kepler are being analyzed in hopes of identifying habitable, Earth-sized planets.

The researchers’ goal was to look for Earth-sized planets with very short orbital periods. To do this, the team analyzed light data from thousands of stars, looking for telltale dips that would indicate a planet periodically passing in front of a star.

To speed up this time-intensive ordeal, the group developed an automated approach by applying a basic mathematical method to the large dataset, essentially whittling the field to light curves that are periodic.

There are other periodic stellar phenomena outside of orbiting planets that could affect light emission, such as a star eclipses. To pick out the signals associated with planets, the researchers used the periodic dataset to identify frequent smaller dips in the data partway between planetary transits.

By measuring the amount of overall dimming each time the planet passed behind its star, the group was able to detect the light given off. From this measurement, the team posits that the planet is roughly 40 times closer to its star than Mercury is to our sun, making it uninhabitable due to the extreme proximity to its host star.