A Year On Exoplanet Kepler 78b Lasts As Long As A Good Night's Sleep

Researchers at Massachusetts Institute of Technology have discovered an exoplanet that completes a full orbit of its host star in just 8.5 hours. For most humans, that’s a day at the office or a good night’s sleep but for Kepler 78b that’s the equivalent of a year.

The newly discovered exoplanet is about the same size as Earth and is incredibly close to its parent star, the researchers said in the Astrophysical Journal. In a separate paper, published in Astrophysical Journal Letters, a group of researchers, some of whom were involved in this discovery, observed a similar exoplanet that had an even shorter orbital period: 4 1/4 hours. Scientists believe the previously discovered KOI 1843.03 is a dense planet made almost entirely of iron, which helps it survive being so close to its parent star.

While KOI 1843.03 is incredibly dense, Kepler 78b’s surface is incredibly hot, and researchers estimate its temperatures can reach up to 3,000 degrees Kelvin (4,940 degrees Fahrenheit). Indeed, the planet's surface temperatures are so hot that scientists have likened it to a large ocean of lava.

Josh Winn, an associate professor of physics at MIT, said the possibility of any life on Kepler 78b is unlikely. “You’d have to really stretch your imagination to imagine living on a lava world,” Winn said in a statement

Kepler 78b is about 40 times closer to its parent star than Mercury is to the sun. The researchers estimate the orbital radius of Kepler 78b to be three times that of the star’s own radius.

The researchers discovered Kepler 78b by examining data collected by NASA’s Kepler telescope. The team was looking for Earth-sized exoplanets, planets outside of our solar system, that have shorter orbital periods. These planets could, in theory, fall within the “Goldilocks zone,” the habitable zone of an exoplanet where liquid water could be found on the planet’s surface. These planets may contain water, as the temperature is neither too hot nor too cold.

To discover new exoplanets, researchers used an indirect method of observations by measuring a dip in brightness as the planet travels in front of its parent star. The MIT researchers applied this method and created a model to look for likely planet candidates and discovered a star with regular dips in light. The team was later able to observe the light given off by the planet, a combination of radiation and surface reflection, by measuring the dip in brightness as it traveled behind the star.

Roberto Sanchis-Ojeda, a graduate student on the project, said, “I was just looking by eye, and all of a sudden I see this extra drop of light right when it was expected, and it was really beautiful.”

Kepler 78b is definitely not in the habitable zone but the researchers are excited about its discovery and its potential for future research. The exoplanet’s star is way too young, rotating twice as fast as the sun, for any life to be found on the planet, but researchers believe exoplanets orbiting very closely to brown dwarfs, colder stars that failed to ignite, could sustain liquid water.

The next step for researchers will be examining the light given off by Kepler 78b with other telescopes to determine what the planet's composition and the true density of KOI 1843.03. Winn said researchers are curious if other planets orbiting as closely to their stars contain a similar composition.

“Whether nature actually makes planets that are dense enough to survive even closer in, that’s an open question, and would be even more amazing,” he said. 

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