Newly-discovered exoplanet twice the size of Earth could have water

Newly-discovered exoplanet twice the size of Earth could have water

Although NASA's Kepler space telescope ran out of fuel and ended its mission in 2018, citizen scientists have used its data to discover an exoplanet 226 light-years away in the Taurus constellation.

HD 21749b has the longest orbit of the three planets that TESS has discovered so far making a trip around its host star once every 36 days.

The other two planets it has discovered are Pi Mensae c, a super-Earth that zips around its star in 6.3 days, and LHS 3844b, a rocky planet that flies around its planet in a whopping 11-hour orbit.

Three new planets and six supernovae outside our solar system have been observed by Nasa's planet-hunting Tess mission in its first three months.

"It's a very exciting discovery due to how it was found, its temperate orbit and because planets of this size seem to be relatively uncommon", said Adina Feinstein, a University of Chicago graduate student in astrophysics and lead author of a paper describing the new planet that was accepted for publication by The Astronomical Journal.

"It's the coolest small planet that we know of around a star this bright", said Diana Dragomir, a postdoc in Massachusetts Institute of Technology (MIT) in the USA, who led the discovery.

It is three times bigger than Earth, which classes it as a Sub-Neptune exoplanet, but it is surprisingly 23 times its mass.

Astronomers have discovered a planet twice the size of Earth, and it's within a zone that could allow liquid water to exist on its surface.

"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy", Dragomir says.

"I'm very interested to know whether [it] has an Earth-like density to match its Earth-like radius - this will contribute to our understanding whether Earth-sized planets have diverse compositions or are all roughly similar to Earth", said Johanna Teske, a co-author of the report.

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Researchers have also detected evidence of a second planet, with a shorter, 7.8-day orbitin the same planetary system, though it is yet to be confirmed.

A timely reminder of that fact comes in the form of an all-new exoplanet discovery made by citizen scientists who dedicated their time to combing through Kepler's logs.

Tess monitors sections of the sky and waits for momentary dips in the light of about 200,000 nearby stars - a sign that a planet has passed in front of that star.

TESS will continue to sweep the southern hemisphere until mid-2019, at which point it will turn its cameras to the Northern Hemisphere and start another observation phase.

To complicate matters, the star itself is relatively active, and Dragomir wasn't sure if the single transit she spotted was a result of a passing planet or a blip in stellar activity. It lies within its host star's habitable zone, which means the planet may have liquid water on its surface.

As far as what the planet may be like, the jury is still out. They determined that they should be able to find the signal again, in TESS's "sector 3" data - which they succeeded in doing. "TESS found as many in its first month".

"There was quite some detective work involved, and the right people were there at the right time", Dragomir said.

The pair were working as interns with Joshua Schlieder, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, at the time.

Astronomers are now conducting follow-up observations on more than 280 exoplanet candidates. "So it's going really well, and TESS is already helping us to learn about the diversity of these small planets". More than a dozen universities, research institutes, and observatories worldwide are participants in the mission.

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