Nasa spacecraft spots gaseous planet 23 times the size of Earth

These three planets were all discovered in the first three months of TESS observations.

Known to scientists as HD 21749b, it is a mere 53 light-years from Earth in the southern constellation of Reticulum. 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.

"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", Dr Dragomir said.

The planet is in the K2-288 system, which contains a pair of dim, cool M-type stars that are 5.1 billion miles apart, about six times the distance between Saturn and the sun. Despite being only three times as large as the Earth, the planet is said to be 23 times as massive.

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

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".

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. Bright stars allow for easier followup study through ground- and space-based telescopes.

NASA's Transiting Exoplanet Survey Satellite (TESS) recorded more than 100 short-lived changes - a lot of them likely stellar outbursts of various types - in its first observing sector. Its discovery was announced by scientists at the annual American Astronomical Society meeting in Seattle. His team is now writing a proposal to NASA asking that TESS's mission be extended past its initial two years.

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.

"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.

Its four wide-field cameras will view the sky in 26 segments, each of which it will observe one by one. "NASA's Kepler space telescope caught six of these events as they brightened during its first four years of operations".

A different group of astronomers had studied the HD 21749 system a decade ago using HARPS, which finds planets by noticing the tiny wobbles that their gravitational tugs induce in their host stars.

While impressive, it does not appear the planet has the attributes required to support life as a habitable world.

TESS is considered to be a "bridge to the future", finding exoplanet candidates to study in more detail.

The team began follow-up observations using NASA's Spitzer Space Telescope, the Keck II telescope at the W. M. Keck Observatory and NASA's Infrared Telescope Facility (the latter two in Hawaii), and also examined data from ESA's (the European Space Agency's) Gaia mission.

Vanessa Coleman