TESS discovers its first planet the size of the Earth

NASA's Transiting Exoplanet Survey Satellite (TESS) discovered its first Earth-size exoplanet. The planet, named HD 21749c, is the smallest world outside our solar system that TESS has yet identified.

In an article published today in the journal Letters from the Astrophysical Journal, a team of astronomers led by MIT announced that the new planet was gravitating around the star HD 21749 – a very close star, only 52 light-years away from Earth. The star also hosts a second planet, the HD 21749b, a warm "sub-Neptune" with a 36-day longer orbit, which the team previously reported and which is detailed in more detail in this document.

The new Earth-sized planet is probably a rocky but uninhabitable world, as it surrounds its star in just 7.8 days – a relatively narrow orbit that would generate surface temperatures on the planet of up to 800 degrees Fahrenheit.

The discovery of this earth-sized world is exciting, however, as it demonstrates TESS's ability to select small planets around nearby stars. The TESS team expects the probe to reveal in the near future even colder planets, with conditions more conducive to housing life.

"For very close and very bright stars, we expected to find up to twenty Earth-sized planets," said Diana Dragomir, lead author and TESS member, postdoctoral fellow at the Kavli Institute. of MIT for astrophysics and space research. "And we are there. This would be our first project and it is an important step for TESS. This paves the way for finding small planets around even smaller stars, and these planets can potentially be livable. "

TESS has been looking for planets beyond our solar system since its launch on April 18, 2018. The satellite is NASA's astrophysics exploration mission led and operated by MIT. It is designed to observe almost the entire sky, overlapping for a month. long spots, or "sectors," orbiting the Earth. While touring our planet, TESS focuses its four cameras on the outside to monitor the brightest stars and closest to the sky, looking for periodic drops in stellar light that could indicate the presence of the stars. 39, an exoplanet during its passage in front of the star host.

During its two-year mission, TESS aims to identify for the astronomical community at least 50 small rocky planets, as well as estimates of their masses. To date, the mission has discovered 10 planets smaller than Neptune, four of their estimated masses, including π Men b, a planet twice the size of the Earth, orbiting its star for six days. LHS 3844b, a warm and rocky world slightly larger than the Earth and surrounds its star in 11 brilliant hours; and YOU 125b and c – two "sub-Neptunes" that revolve around the same star, both in about a week. The four planets were identified from the data obtained during the first two observation areas of TESS. A good clue, the team says in its article: "many more are to be found."

Dragomir chose this new Earth-sized planet from the first four TESS observation areas. When these data became available, in the form of light curves or light intensities, she introduced them into software code to search for interesting periodic signals. The code identified for the first time a possible transit that the team later confirmed as being the warm sub-Neptune announced earlier this year.

As is usually the case with small planets, where there is one, there will probably be more, and Dragomir and his colleagues decided to cross-check the same observations to see if they could spot other small hidden worlds. in the data.

"We know that these planets often come into families," says Dragomir. "So we searched for all the data again and that little signal came out."

The team identified a slight dip in the light from the HD 21749, which occurred every 7.8 days. In the end, the researchers identified 11 recesses or periodic transits of this type and determined that the star's light was momentarily blocked by a planet the size of the Earth.

Although this is the first Earth-sized planet discovered by TESS, other Earth-sized exoplanets have been discovered in the past, mainly by NASA's Kepler Space Telescope, a retrospective telescope that has since been retrieved. has watched more than 530,000 stars. In the end, the Kepler mission detected 2,662 planets, most of which were the size of the Earth, and some of them were considered to be in the habitable zone of their star, where the balance of conditions could be conducive to life.

However, Kepler observed distant stars of many leagues compared to those monitored by TESS. Therefore, Dragomir says that tracking one of the planets far from the planet, Kepler's size, would be much more difficult than studying planets orbiting TESS, much closer and brighter stars.

"As TESS watches much closer and brighter stars, we can measure the mass of this planet in the very near future, while for planets the size of Kepler, it was out of the question," says Dragomir. "This new discovery from TESS could therefore lead to the first mass measurement of a planet the size of the Earth. And we are excited about what this mass could be. Will it be the mass of the Earth? Or heavier? We do not really know. "