TESS: NASA Announces Its Exoplanet-Hunting Satellite's First Two Candidates

After only five months, TESS has delivered.

NASA’s Transiting Exoplanet Survey Satellite, better known as TESS, has one mission: To find exoplanets around the brightest stars near the Earth. In just five months, it’s clear TESS is up to the task. On Tuesday, NASA announced TESS had just identified two potential planets around distant stars and released the first set of images captured by TESS. In the same week, collaborators at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research submitted two papers outlining the evidence for the two planets.

In papers uploaded to the preprint server arXiv, the MIT researchers described a “super-Earth” that orbits its star once every 6.27 days and a “hot Earth” with an even shorter orbital period of just 11 hours. The first planet has a radius between four and five times that of Earth — hence its designation as a “super-Earth,” or a planet that is more than two but fewer than ten times the size of Earth. The hot Earth is a little closer in size to our planet, with a radius about 1.32 times that of Earth.

A closer look at the papers reveals what we know about the two new planets.

The Super-Earth

On Sunday, a team led by Xu Chelsea Huang, Ph.D., a postdoctoral fellow at MIT’s Kavli Institute, submitted its findings on8the planet that orbits the star Pi Mensae (HD 39091) to arXiv. About 59.6 light years from Earth, this star is visible to the naked eye, and astronomers have previously discovered another planet orbiting it — a gas giant with a 5.7-year orbit. The newly discovered one orbits the star in just about that many days.

The researchers found the planet by measuring how the light emitted by its star dimmed periodically. This dimming indicated that something was intermittently coming between us and the star — in this case, a planet. This finding is evidence that TESS’s concept is working, as the satellite’s sole purpose is to map the sky and investigate transiting planets.

This graph shows how the light emitted by the star Pi Mensae (HD 39091) dipped when the planet passes between it and us.

Huang et al

It’s too early to tell what the conditions on this planet are like, but its size suggests that it could have a gas atmosphere like Neptune or Uranus.

“We also think this planet might be evaporating right now, given the intense irradiation it gets from its host star,” Huang told

Since Pi Mensae (HD 39091) is an exceptionally bright star, scientists are confident that they will be able to further study its super-Earth using atmospheric spectroscopy, giving insights into its composition and habitability.

The Hot Earth

On Wednesday, hot on the tail of TESS’s first images, a team led by Roland Vanderspek, Ph.D., the TESS deputy principal investigator at MIT’s Kavli Institute, submitted its findings on a hot Earth that orbits the M dwarf star LHS 3844, which is just under 49 light years away. And no, this hot Earth is not a sexy version of our planet.

So-called because of its extremely short orbital period and similar size to our planet, a hot Earth usually orbits very close to its home star. Often, its orbital distance is only a few times the radius of the star itself. This makes it a very hot Earth, indeed.

The planet’s extremely short 11-hour orbital period indicates that it almost certainly is tide-locked, meaning that one side of the planet always faces the star and one side always faces away. Therefore, this planet probably has one side that is molten lava and one side that is completely frozen. Imagine the Moon, but more extreme.

But despite the fact that this planet is almost certainly not a candidate for finding life, its proximity to LHS 3844 will allow scientists to study it closely as it transits twice a day.

These two discoveries come extremely early on in TESS’s two-year mission, indicating that many more exoplanet candidates will be identified soon. With over 200,000 stars on TESS’s mission schedule, odds are many of them will reveal transiting planets. At that point, astronomers will have their hands full studying all of them.

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