TESS Discovers Its Third Small Planet Outside Our Solar System

TESS Discovers Its Third Small Planet Outside Our Solar System

The Kepler space telescope ran out of fuel late October, as expected, ending its nine and a half year mission of hunting for planets outside our solar system.

Less than a year after NASA's TESS spacecraft was launched, the scientists behind the mission have unveiled their third confirmed planet, a weird alien world that's between Earth and Neptune in size.

The most recent discovery, an exoplanet named HD 21749b, has the longest orbital period at 36 days. The exoplanet likely has an average surface temperature around 300 degrees Fahrenheit (150 degrees Celsius), discovery team members said.

"It's the coolest small planet that we know of around a star this bright", said Diana Dragomir, a postdoc in Massachusetts Institute of Technology (MIT) in the United States, who led the discovery. "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".

Estimated to be about 1.9 times Earth's size, K2-288Bb is half the size of Neptune. Surprisingly, it is also a whopping 23 times as massive as the Earth.

Further details about the planet are less clear, with experts unsure whether it is rocky or gas-rich.

"We think this planet wouldn't be as gaseous as Neptune or Uranus, which are mostly hydrogen and really puffy".

"I'm very interested to know whether [it] has an Earth-like density to match its Earth-like radius - this will contribute to our understanding whether Earth-sized planets have diverse compositions or are all roughly similar to Earth", said Johanna Teske, a co-author of the report.

On the bright side, there is evidence of a second, still unconfirmed planet in the same system, this one with a much shorter 7.8-day orbit. Data gathered during the course of its scientific mission, however, paved way to the discovery of a new exoplanet.

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TESS will look for exoplanets using the transit method, observing slight dips in the brightness of stars as planets pass in front of them. For what it's worth, several TESS finds have been the subject of pre-print research papers.

Even though the Kepler spacecraft ceased operations months ago, after almost a decade in service, its legacy continues: Today, researchers announced that they have found a planet roughly twice as big as Earth, located within what could be its parent star's habitable zone.

Each of the planets, which orbit a dwarf star just 39 million light years, likely holds water at its surface.

Kepler found a planet that orbits two stars, known as a binary star system, in 2011.

"There was quite some detective work involved, and the right people were there at the right time", Dragomir said. It was unclear whether this signal was caused by a planet or variations in the host star's activity, so Dragomir and her colleagues analyzed observations taken by another instrument, the High Accuracy Radial velocity Planet Searcher (HARPS), a spectrograph installed on a telescope at the European Southern Observatory's La Silla Observatory in Chile.

The discoveries of a new planet and several supernovae are exciting enough and what's to come should give us even more information about the phenomena already discovered.

Follow-up observations were made with multiple telescopes to confirm the exoplanet.

TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by Goddard.

These exoplanets will be studied so that NASA can determine the best targets for future missions, like the James Webb Space Telescope.

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