Distant, Possibly Habitable Planet Spotted by Citizen Scientists

NASA  Goddard

NASA's Kepler Mission K2 team announced the discovery of another new world today, two months after the Kepler spacecraft ran out of fuel on October 30th, and ended its mission after nine years, during which it discovered 2,600 confirmed planets around other stars - the bulk of those now known - along with thousands of additional candidates astronomers are working to confirm.

The latest discovery - an exoplanet called HD 21749b, has the longest orbital period at 36 days. The first two candidates - known as Pi Mensae c and LHS 3844b - were reported in September, and they've now taken their place as the first two confirmed planets on TESS' list. As hot as that is, it's cool considering the proximity to the host star, which is said to be nearly as bright as the sun. "But here we were lucky, and caught this one, and can now study it in more detail". As NASA's JPL notes in a blog post, planets between 1.5 and 2 times the size of Earth are seemingly rare based on the exoplanet data we've gathered thus far. But HD 21749b is made of denser stuff than the gaseous worlds we're used to, because it's 23 times more massive than Earth. "So it's going really well, and TESS is already helping us to learn about the diversity of these small planets".

Johanna Teske, a Hubble fellow and co-author of the report, said: "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".

On the bright side, there is evidence of a second, still unconfirmed planet in the same system, this one with a much shorter 7.8-day orbit.

TESS - that is, the Transiting Exoplanet Survey Satellite - is in the midst of surveying almost the entire sky for exoplanets orbiting stars up to 300 light-years away from Earth. If the light "dips", momentarily decreasing in brightness, it suggests that a planet may be orbiting the star.

Huang said several more planets have had their status confirmed, but she didn't provide specifics. Every six days, the new planet orbits the star Pi Mensae, located about 60 light-years away and visible to the unaided eye in the southern constellation Mensa.

The scientists announced the results at the annual American Astronomical Society meeting in Seattle. Over the course of two years, the four wide-field cameras on board will stare at different sectors of the sky for days at a time.

Its size is unusual for an exoplanet (the term for a planet that orbits a star outside our solar system).

"Some of the most interesting science occurs in the early days of a supernova, which has been very hard to observe before TESS", said Michael Fausnaugh, a TESS researcher at the MIT Kavli Institute.

The new world, named K2-288Bb, was found using data from NASA's now defunct Kepler space telescope. "TESS found as many in its first month". "We're only halfway through TESS's first year of operations, and the data floodgates are just beginning to open", he said.

While impressive, it does not appear the planet has the attributes required to support life as a habitable world. Using ground-based telescopes, astronomers are now conducting follow-up observations on more than 280 TESS exoplanet candidates.

An illustration of NASA's Kepler space telescope.

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