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TESS, the first earth-sized planet discovered

The nearest system provides the world's first planet-sized planet and a warm Neptune-sized world discovered by NASA's Transiting Exoplanets Survey Satellite.

This is in accordance with a new paper by an astronomer team including Carnegie's Johanna Teske, Paul Butler, Steve Shectman, Jeff Crane and Sharon Wang.

Their work was published in the Astrophysical Journal Letters.

"It is very interesting that TESS, which started about a year ago, has already become a game changer in the planet hunting business," said Teske, the second author of the newspaper. "The ship explores the sky and collaborates with the TESS follow-up community to use terrestrial-based telescopes and instruments to display additional observations on potentially interesting objects."

One such tool, the Planet Finder Spectrograph on the Magellan II telescope at the Campemas Observatory in Carnegal, Chile, was a decisive factor in this endeavor. It helped to identify the planetary characteristics of the TESS signal and measure the mass of the newly discovered sub-Neptune.

Using the method pioneered by Butler and co-workers, Shectman and Crane's PFS is now working using a technique called radial velocity, which is currently the only way astronomers can measure the mass of an individual planet . Without a known mass, it is very difficult to determine the density or general chemical composition of a planet.

This method exploits the fact that not only does the gravitational force of the stars affect the orbiting of the planet, but also the gravity of the planet also affects the star. PFS allows astronomers to detect these small fluctuations that the planet's gravity derives from the orbit of the star.

"PFS is one of the only instruments in the Southern Hemisphere that can perform this type of measurement," added Teske. Therefore, characterizing the planets discovered by the TESS mission will be a very important part. "

In its orbit, which takes about 36 days to complete, the sub-Neptune HD 21749b has the longest period of TESS discovery so far. Due to the technology used by TESS, the HD 21749b is unusual in this regard, as most of the planets discovered by the mission are expected to have an orbital period of less than 10 days. In fact, this also made the detection of planets an additional challenge in TESS data.

Diana Dragomir, senior author of MIT's Kavli Astrophysics and Space Research, said, "There was a legitimate detective work and the right people were in place." But we were lucky, we caught the signal, I did."

Its main component is about 80 percent of the sun's mass and is found about 53 light years from Earth. The HD 21749b has a radius of about 23 times the Earth's mass and about 2.7 times the Earth's radius. Its density indicates that the planet has considerable atmospheric, but not rock. So astronomers can help you understand the composition and evolution of the cooler sub-Neptune planetary atmosphere.

Interestingly, it is not alone that the sub-Neptune planet lasts longer in this system. It has a brother planet HD 21749c, which takes about 8 days to enter the host star into orbit and is similar in size to Earth.

"It would be difficult to measure the exact mass and composition of a small planet, but it is important to compare HD 21749c with Earth," said the king. "Carnegie's PFS team continues to collect data on this object with this goal in mind."

Thanks to TESS, astronomers have been able to measure the mass, atmospheric composition and other properties of many small alien planets for the first time. Although small alien planets are common in our galaxy, we can still learn a lot about their diversity and how to compare them with our solar system planets.

"For very close and very bright stars, we expected to find 2 to 10 planets of Earth size," Dragomir said. The first goal of TESS is the milestone of TESS, which has opened the way to discover a smaller planet around a small star, and the planet can potentially be habitable. "

Support for this research was provided by the Hubble Fellowship grant at NASA, the Torres post-doctoral researcher at the MITs Kavli Institute, the Sagan Fellowship program at NASA's Exoplanet Science Laboratory, the postdoctoral fellow Harvard Future Faculty Leaders, and Branco Weiss Fellowship-Society in Science.

Carnegie Institution for Science ( is a nonprofit civil society organization headquartered in Washington, DC, with six research departments across the United States. Since its founding in 1902, the Carnegie Institution has been a pioneer in basic science research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, earth ecology, and earth and planetary science.

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