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TESS finds Earth's first planet –



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The nearby system hosts the first Earth-sized planet discovered by NASA's Transatlantic Satellite Satellite, as well as a small sub-Neptune world, according to a new article by a team of astronomers that includes the Carnegie Tasca, Paul Butler, Steve Shatman, Jeff Crane and Sharon Wang.

Their work is published in Astrophysical journals.

"It's so exciting that TESS, which was launched about a year ago, is already a game changer in the business of hunting the planet," said Teska, who is the second author on paper. "The probe explores the sky and we are collaborating with the TESS surveillance community to mark interesting targets for further observations using ground telescopes and instruments."

One such instrument, the Planet Finder Spectrograph on the Magellan II telescope at the Las Campagni Observatory in Carnegie, was a crucial component of this effort. He helped confirm the planetary nature of the TESS signal, and to measure the mass of newly discovered sub-Neptune sub-cells.

The PFS, built by Shechtman and the announcer in the method begun by Butler and his collaborators, operates using a technique called the radial velocity method, which is now the only way for astronomers to measure the masses of individual planets. Without known mass, it is very challenging to determine the density of the planet or its general chemical composition.

This method takes advantage of the fact that not only does the gravitational force of a star affect the Earth encompassing it, but the gravity of the planet also affects the star in turn. The PFS allows astronomers to recognize these tiny vibrations that the star's gravity causes to the star orbit.

"PFS is one of the only devices in the southern hemisphere that can do these kinds of measurements," added Teska. "Therefore, this will be a very important part of the further characterization of the planets found by the TESS mission."

With this route taking about 36 days to complete, Sub Neptune, HD 21749b, has the longest period of all TESS manifestations published so far. Because of the technique that TESS employs, it is predicted that most planets in the mission will have orbital periods of less than 10 days, so the HD 21749b is unusual in this regard. In fact, it also made the discovery of Earth in TESS data an additional challenge.

"There were a few detective jobs, and the right people were there at the right time," said lead author Diana Dragomir of the MIT Institute for Astrophysics and Space. "But we were lucky, and we caught the signals, and they were really clear."

Its host star contains about 80% of our solar mass and is 53 light years away from Earth. HD 21749b has about 23 times the Earth's mass radius of about 2.7 times of the Earth. Its density indicates that the planet has a significant atmosphere, but it is not rocky, so it can help astronomers understand the composition and evolution of the sub-Neptune cool atmospheric stars.

Exciting, long period of time Neptune star in this system is not alone. It has a brother planet, the HD 21749c, which takes about eight days to orbit the host star and is much smaller – similar in size to Earth.

"Measuring the mass and precise composition of such a small planet will be challenging, but it is important to compare HD 21749c to Earth," Wang said. "Carnegie's 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 components, and other characteristics of smaller outer planets for the first time. Although small planets are common in our galaxy, there is still much to learn about their diversity and how they compare the planets in our solar system.

"Very close and very bright stars, we were expecting to find several dozen Earth-sized planets," Dragomir said. "And here we are – it will be our first, and this is a milestone for TESS, which sets the path for finding smaller planets around even smaller stars, and these planets may be habitable."

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