Researchers at MIT have discovered an Earth-sized exoplanet named
Kepler 78b that whips around its host star in a mere 8.5 hours — one of the shortest orbital periods ever
The planet is extremely close to its star — its orbital radius is only about three times the radius of
the star — and the scientists have estimated that its surface temperatures may be as high as 3,000 degrees
Kelvin, or more than 5,000 degrees Fahrenheit.
In such a scorching environment, the top layer of the planet is likely completely melted, creating a massive,
roiling ocean of lava.
They were also able to detect light emitted by the planet — the first
time that researchers have been able to do so for an exoplanet as small as Kepler 78b.
Click on image to enlarge
Photo credits: Cristina Sanchis Ojeda
This light, once analyzed with larger telescopes, may give scientists detailed information about the planet’s
surface composition and reflective properties.
Kepler 78b is so close to its star that scientists hope to measure its gravitational influence on the star.
Such information may be used to measure the planet’s mass, which could make Kepler 78b the first Earth-sized
planet outside our own solar system whose mass is known.
In a separate paper, published in Astrophysical
Journal Letters, the same group of scientists described a previously discovered exoplanet - KOI 1843.03 - with an even
shorter orbital period: just 4 1/4 hours.
“Just the fact that it’s able to survive there implies that it’s very dense,” says Josh Winn, an associate professor
of physics at MIT, and co-author on both papers.
“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.”
The goal for Winn and his colleagues was to look for Earth-sized planets with very short orbital periods.
To find them, the team analyzed light data from thousands of stars, looking for telltale dips indicating that
a planet may periodically pass in front of a star.
From their measurements of Kepler 78b, the team determined that the planet is about 40 times closer to its star than
Mercury is to our sun. The star around which Kepler 78b orbits is likely relatively young, as it rotates more than twice
as fast as the sun — a sign that the star has not had as much time to slow down.
While it is about the size of Earth, Kepler 78b is most certainly not habitable, due to its extreme proximity to its host star.
“You’d have to really stretch your imagination to imagine living on a lava world,” Winn says. “We certainly wouldn’t
But this doesn’t entirely rule out the possibility of other habitable, short-period planets. Winn’s group is now looking
for exoplanets that orbit brown dwarfs — cold, almost-dead stars that somehow failed to ignite.
“If you’re around one of those brown dwarfs, then you can get as close in as just a few days,” Winn says. “It would
still be habitable, at the right temperature.”
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objects during a visual spectroscopic study of stars in the constellation Cygnus at the Observatoire de Paris, France.
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