NASA's latest probe named Transiting Exoplanet Survey Satellite (TESS) launched in April last year. This probe is launched by NASA for planet hunting purpose. As it was intended, today ( 7 January 2019) TESS has discovered a new planet outside our solar system. The new planet named HD21749b is the third planet that discovered in the first three months of TESS observations.

The planet, named HD 21749b, orbits a bright, nearby dwarf star which lies about 53 light-years away from Earth in the faint constellation Reticulum and appears to have the longest orbital period of the three planets so far identified by TESS.
HD 21749 B travels around its star in a relatively leisurely 36 days in comparison to the two other planets - Pi Mensay B, with a "super-Earth"  with 6.3-day orbit and LHS 3844 B, a rocky planet  Moves around its star only in 11 hours.

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HD21749b is a "sub-Neptune" which is about three times bigger than the Earth, which means that it is gaseous rather than rocky. But HD 21749b is composed of intensive material compared to the gaseous world we use because it is 23 times more massive than the Earth.

There is a possibility that the temperature of the surface of the new planet may be around 300 degrees Fahrenheit - relatively quiet, given its proximity to its star, as the brightness of the star is almost as bright as the sun.
“It’s the coolest small planet that we know of around a star this bright. We know a lot about atmospheres of hot planets, but because it’s very hard to find small planets that orbit farther from their stars, and are therefore cooler, we haven’t been able to learn much about these smaller, cooler planets. But here we were lucky, and caught this one, and can now study it in more detail.” discovery team leader Diana Dragomir, a postdoctoral researcher at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research, said in a statement.

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“Because there was an interruption in data around that time, we initially didn’t see a second transit and were pretty disappointed. But we re-extracted the data and zoomed in to look more carefully, and found what looked like the end of the transit.” Dragomir said.
The team initially observed an intriguing signal from the HD21749 system in the TESS "Sector 1" data. It was not clear that this signal was due to the variation in the activity of a planet or host star, hence Dragomir and her colleagues have installed another device, High Accuracy Radial Velocity Planet Search (HARPS), which is a spectrograph installed on the telescope at the La Silla Observatory of the European Southern Observatory in Chile and analyzed observations.

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Using the HARPS, a different group of astronomers had studied the HD 21749 system a decade ago, which notice the small stars and detects the planets that inspire their gravitational stars in their host stars. Those researchers also detected an indication, but they could not decisively feature it for a planet, said Dragomir.
In HARPS data, She and her colleagues compared the patterns in the form of complete transit, which they originally searched, found in a perfect match - an indication that HD 21749 signal repeats every 36 days in front to its star. They determined that they should be able to find the signal again in the "Sector 3" data of TESS - which they were successful in doing.

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Dragomir and her team also used data collected from Planet Finder Spectrograph, which is a tool installed on the Magellan II telescope in Chile, which is to pursue their findings and inhibit the HD 21749b's mass and orbital parameters.

Researchers today announced the discovery of the American Astronomical Society's 233rd meeting in Seattle. They have also presented their research paper to Astrophysical Journal Letters.
"We've confirmed three planets so far, and there are so many more that are just waiting for telescope and people time to be confirmed," Dragomir says. "So it's going really well, and TESS is already helping us to learn about the diversity of these small planets."

TESS is just starting. The mission has already given green signal to hundreds of planet candidates, and its confirmed search will run in thousands when all is said and done, NASA officials have said. And some of these world astronomers will be closer to the Earth to study planets using powerful instruments, such as NASA's $ 8.9 billion James Web Space Telescope, which is about to be launched in 2021.

Once TESS has completed two years of supervision of the entire sky, the science team has expressed commitment to provide information on 50 small planets in less than four times the size of Earth to the astronomy community for further follow-up, either with ground-based telescopes or the future James Webb Space Telescope.