TESS finds its first planet the size of the Earth

A neighboring system hosts the first Earth-sized planet discovered by NASA's Transiting Exoplanets Survey Satellite, as well as a warm world the size of Sub-Neptune, according to a new paper written by a team of experts. astronomers and including Johanna Teske, Paul Butler, Steve of Carnegie. Shectman, Jeff Crane and Sharon Wang.

Their work is published in the Letters from the Astrophysical Journal.

"It's so exciting that TESS, which was launched about a year ago, is already changing the game in the global hunting industry," said Teske, the newspaper's second author. "The probe is monitoring the sky and we are collaborating with the TESS community to identify potentially interesting targets for additional observations using telescopes and ground instruments."

One of these tools, the Planet Finder spectrograph on the Magellan II telescope at the Carnegie Observatory in Las Campanas, Chile, was a crucial part of this effort. This confirmed the global nature of the TESS signal and measured the mass of newly discovered sub-Neptune.

The PFS – built by Shectman and Crane with the help of a method developed by Butler and his collaborators – uses a technique called the radial velocity method, which is currently the only way for astronomers to measure the masses of individual planets. Without known masses, it is very difficult to determine the density of a planet or its overall chemical composition.

This method takes advantage of the fact that not only does the gravity of a star influence the planet orbiting it, but that the gravity of the planet also affects the star in turn. The PFS allows astronomers to detect these tiny oscillations induced by the gravity of the planet on the orbit of the star.

"The PFS is one of the only instruments in the southern hemisphere that can do this type of measurement," said Teske. "So, this will be a very important part of the subsequent characterization of the planets found by the TESS mission."

With an orbit that lasts about 36 days, the sub-Neptune, HD 21749b, has the longest period of all TESS discoveries published to date. Due to the technique used by TESS, it is expected that most of the planets discovered by the mission will have orbital periods of less than 10 days. HD 21749b is therefore unusual in this regard. In fact, the detection of the planet in TESS data was also an additional challenge.

"There was a lot of detective work involved and the right people were there at the right time," said lead author Diana Dragomir of the Kavli Institute for Space Research and Astrophysics at MIT. "But we were lucky and we picked up the signals and they were really clear."

Its host star represents about 80% of the mass of our Sun and is about 53 light-years away from Earth. The HD 21749b has about 23 times the Earth's mass and a radius of about 2.7 times that of the Earth. Its density indicates that the planet has a substantial atmosphere but is not rocky. It could therefore help astronomers understand the composition and evolution of Neptune's warmer planet atmospheres.

Excitingly, the sub-Neptune's longer-lived planet of this system is not the only one. The HD 21749c, its twin planet, takes about eight days to revolve around the host star and is much smaller, similar in size to the Earth.

"Measuring the exact mass and composition of such a small planet will be a challenge, but it's important to compare the HD 21749c to the Earth," Wang said. "The Carnegie PFS team continues to collect data on this object with this goal in mind."

Thanks to TESS, astronomers will be able to measure the masses, atmospheric compositions and other properties of many smaller exoplanets for the first time. Although small exoplanets are common in our galaxy, much remains to be learned about their diversity and their comparison with the planets of our own solar system.

"For very close and very bright stars, we expected to find about twenty planets the size of the Earth," said Dragomir. "And here we are – it would be our first, and it's an important step for TESS." This paves the way for finding smaller planets around even smaller stars, and these planets can potentially be livable. "