TESS, the planet hunting space telescope, is on track to discover a sky full of exoplanets

Back in April, TESS — the Transiting Exoplanet Survey Satellite — was launched into orbit to hunt for planets around nearby stars.  TESS is the successor mission to the tremendously successful Kepler mission which ended earlier this year.

The TESS team has already announced the discovery of two new exoplanets, and is expected to find at least 10,000 more in its two-year mission.

According to Patricia Boyd, Project Scientist for TESS, and the Chief of the exoplanets and stellar astrophysics lab at NASA's Goddard Space Flight Center, that haul of exoplanets should include "ten planets that are pretty similar to Earth."

Eyes wide open

The Kepler telescope stared at a small patch of sky and focussed on stars that were hundreds of light-years from Earth. TESS looks at most of the sky — it will cover about 85% of it — and is looking at stars that are in general nearer, including ones that we can see with our naked eye.

TESS doesn't look at planets in any detail — it focuses on detecting them. But the fact that it's identifying planets around nearby stars will make it easier to do follow-up observations with ground-based telescopes that will be able to provide further information on the planets and give astronomers information about their mass and tmospheric composition.

The TESS satellite's unusual 13.7-day orbit uses the moon's gravity to stabilize it, so it needs little fuel. During the part of the orbit colored blue, TESS will observe the sky. During the part marked in orange, it will transmit data back to Earth. The gray ring marks the moon's orbit. (NASA's Goddard Space Flight Center)

One important goal, according to Boyd, is to find other planets like ours that might be suitable for life.

Those planets will be between the size of Earth and Neptune, and TESS will take measurements to help scientists figure out their density.

"Once we've got the density, then we'll be able to tell whether that planet is mostly gaseous or mostly rocky like Earth," said Boyd.  

TESS will detect these exoplanets by looking for transits, which occur when a planet passes in front of its star and the observed light of the star dims slightly as a result.

"Extreme planets and extremely interesting planets"

TESS has already announced the discovery of two exoplanets. One was found around a star called Pi Mensa.

"It already had a planet around it, a very large planet in a long orbit that had been discovered from the ground," said Boyd. "What TESS found was it had another planet on a short orbit and it was a small planet."

This animation shows how a dip in the observed brightness of a star may indicate the presence of a planet passing in front of it, an occurrence known as a transit. (NASA's Goddard Space Flight Center)

The second planet it discovered is called LHS 3844 b. It also orbits a small star called LHS 3844, and has an extremely fast orbit of just 11 hours.

Mercury, the closest planet to our sun, in comparison, still takes months to complete its orbit.

"It's going to be a hellish environment for sure," said Boyd, "but now we know that TESS is going to find small planets, it's going to find them around bright stars, and it's going to find some really extreme planets and extremely interesting planets."