NASA's TESS Planet Hunting Satellite Discovers Third New Exoplanet

Katie Ramirez
January 9, 2019

HD 21749b completes one orbit of its host star, which is almost as bright as our sun, every 36 Earth days. The planet orbits a binary star system consisting of two stars that are smaller than our own Sun.

The scientists announced the results at the annual American Astronomical Society meeting in Seattle.

This year, Kevin Hardegree-Ullman, postdoctoral scholar in astronomy at the California Institute of Technology, announced that the Spitzer space telescope followed up on that discovery and discovered a sixth planet, K2-138 g, smaller than Neptune, that orbits the star every 42 days.

"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.

A freaky planet at least 23 times the mass of Earth, unveiled on 7 January, is among the confirmed planets-some of which have been reported before.

"It's the coolest planet we know of around a star this bright". But the gas that makes it up it is probably more dense than that of Uranus or Neptune.

"It's the coolest small planet that we know of around a star this bright", Dragomir said. "The planet likely has a density of water, or a thick atmosphere".

The new exoplanet, named HD 21749b, was discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), which launched in April. If it is confirmed as a planet, it could be the first Earth-sized planet discovered by TESS.

She and her colleagues compared the pattern to the first full transit they had originally discovered, and found a near ideal match - an indication that the planet passed again in front of its star, in a 36-day orbit. "In contrast, the new planet, called Pi Mensae c, has a circular orbit close to the star, and these orbital differences will prove key to understanding how this unusual system formed". This is relatively cool considering its proximity to its star. The surface of the new planet is hotter than 100 degrees Celsius.

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They also used data from the Planet Finder Spectrograph, an instrument installed on the Magellan Telescope in Chile, to further validate their findings and constrain the planet's mass and orbit.

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.

During the first month of data collection, TESS captured images of six supernovae, said Michael Fausnaugh, another researcher at the MIT Kavli Institute. "But we re-extracted the data and zoomed in to look more carefully, and found what looked like the end of a transit". Every three months, Kepler would stare at a differentpatch of sky.

TESS is in the process of scanning the entire southern sky, after which it will turn and canvass the northern sky.

Like NASA's recently departed Kepler space telescope, TESS watches for the faint dip in light that occurs when an unseen planet passes in front of a star's disk. Bright stars allow for easier followup study through ground- and space-based telescopes. Of these, officials anticipate, 300 will be Earth-size exoplanets or double-Earth-size Super Earths.

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

K2-288Bb lies within its star's habitable zone, meaning it is possible for it to hold liquid water.

These exoplanets will be studied so that NASA can determine the best targets for future missions, like the James Webb Space Telescope.

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