NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered a third exoplanet outside our solar system. TESS has been hunting for three months now.

The new planet, named HD 21749b, orbits a bright, nearby dwarf star about 53 light-years away, in the constellation Reticulum. It has the longest orbital period at 36 days.

The surface of the exoplanet is likely about 1,650°C (3,000°F). This is relatively cool considering its proximity to its star.

Diana Dragomir, a Hubble fellow at MIT’s Kavli Institute for Astrophysics and Space Research who led the discovery team, said: “It’s the coolest planet we know of around a star this bright. It’s very hard to find small planets that orbit farther from their stars, and are therefore cooler. But here we were lucky, and can now study this one in more detail.”

The planet is about three times the size of Earth, which puts it in the category of a “sub-Neptune”. Surprisingly, it is also a whopping 23 times as massive as the Earth.

But it is unlikely that the planet is rocky and therefore habitable.

HD 21749b is likely a gas planet, a gas type denser than the atmospheres of either Neptune or Uranus.

“We think this planet wouldn’t be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy,” Dragomir says. “The planet likely has a density of water or a thick atmosphere.”

However, the ‘Super-Earth’ is among a trio of planets and six supernovae detected by Tess mission.

But the researchers have also detected evidence of another planet. If scientists confirm it, the world could be the first Earth-sized discovery by Tess.

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.”

Transiting Exoplanet Survey Satellite (TESS)

NASA launched TESS into orbit around Earth in April. The space telescope is the successor to NASA’s planet-hunting spacecraft, Kepler, which found thousands of distant exoplanets from a distance of nearly 100 million miles from Earth. Kepler ran out of fuel in October, just after TESS’s mission started to get into full swing. But both of the spacecraft search the sky the same way, the transit method; they look for tiny dips in a distant star’s light, whenever a planet crosses in front and momentarily blocks part of the star.

Once TESS has completed its two-year monitoring of the entire sky, the science team has committed to delivering information on 50 small planets less than four times the size of Earth to the astronomy community for further follow-up, either with ground-based telescopes or the future James Webb Space Telescope.

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Thumbnail image: NASA’s TESS mission has already discovered three new exoplanets around nearby stars. Credit: NASA’s Goddard Space Flight Center, edited by MIT News.