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NASA's planet finder discovers weird new world and 6 exploding stars

TESS takes a closer look at our cosmic backyard and finds an unusual, cool exoplanet.


NASA's planet-hunting telescope is making landmark discoveries at an astonishing pace and has now confirmed discovery of a third new planet and a handful of exploding stars in our "cosmic backyard". 

The new exoplanet, named HD 21749b, was discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), which launched in April. The recently discovered world is categorized as a "sub-Neptune", about three times larger than Earth but approximately 23 times as massive. 

Of the planets yet discovered, HD 21749b has the longest orbital period around its star, taking 36 days to perform a transit. At a cool 300 degrees Fahrenheit (~149 degrees Celsius), it's also "relatively cool" for a planet orbiting so close to its star. It has a greater density than the Neptune of our solar system, but it is not expected to be rocky. 

The discovery, discussed at the 233rd meeting of the American Astronomical Society (AAS) and in pre-print at arXiv, is just one of several now coming thick and fast for TESS. During the meeting, Chelsea Huang, an MIT researcher working on the TESS datasets, stated that TESS has confirmed the existence of eight new exoplanets, and that "there are probably 20 or 30" other potential discoveries "almost ready to be published". 

TESS looks for new planets by examining the light from about 200,000 stars and detecting any noticeable changes in brightness. If the light "dips", momentarily decreasing in brightness, it suggests that a planet may be orbiting the star.

This has already led to the discovery of two other planets, Pi Mensae c and LHS 3844b, back in September. Those planets tear around their stars much more quickly than HD 21749b, completing orbits at 6.3 days and a meagre 11 hours. Because TESS is programmed to look at a portion of the sky for only 27 days, any planets with a longer orbit are difficult to identify.

However, TESS is not just a planet-hunter.

"We think of TESS as an exoplanet-hunter, but in addition TESS is very effective at finding many other types of objects," said Dr. George Ricker, principal investigator with the TESS mission.

TESS has a suite of instruments that can seek out a number of other cosmic phenomena, including asteroids, comets and exploding stars or "supernovae". Observing just one sector of the sky once it began science operations, researchers announced at AAS that TESS has already identified six supernovae -- a remarkable finding. To put it in context, Michael Fausnaugh, a pipeline scientist on TESS, discussed this in comparison to NASA's now defunct Kepler telescope.

"The only other mission that could really do this was the Kepler spacecraft and Kepler found five supernovae in four years of observation," he said during the AAS conference.

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. Dr. Ricker briefly touched on a potential extended mission for the planet-hunting telescope that would begin in 2020 and carry on until 2022, in which it would look at additional sectors of the sky that were missed during its first years of operation.

The discoveries of a new planet and several supernovae are exciting enough and what's to come should give us even more information about the phenomena already discovered. With the launch of the James Webb Telescope, planet-hunters and scientists will be able to glean more information about TESS' discoveries and look closer for planets just like ours.

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