NASA Probe Discovers Third New Planet Outside Solar System

James Marshall
January 8, 2019

NASA's latest planet-hunting mission, TESS, will be providing more light curves that are full of potential planets waiting to be found.

Although NASA's Kepler space telescope ran out of fuel and ended its mission in 2018, citizen scientists have used its data to discover an exoplanet 226 light-years away in the Taurus constellation.

HD 21749b completes one orbit of its host star, which is almost as bright as our sun, every 36 Earth days. It has also discovered a super-Earth and a rocky world, making three exoplanet discoveries in the first three months since it began surveying the sky in July.

The surface of the new planet is likely around 300 degrees Fahrenheit and is relatively cool, given its proximity to its star, which is nearly as bright as the sun, said the team from the Massachusetts Institute of Technology in Boston.

"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 think of TESS as an exoplanet-hunter, but in addition TESS is very effective at finding many other types of objects", said Dr. George Ricker, principal investigator with the TESS mission.

Its size, three times that of Earth, makes it a sub-Neptune - but it's also 23 times as massive as Earth.

According to NASA, the planet is half the size of Neptune and could be gas-rich, though it's possible that it's rocky instead. "The planet likely has a density of water, or a thick atmosphere", Dragomir said.

The researchers also detected hints of another, smaller planet in the system, a planet that would have an orbital period of 7.8 days.

Scientists have used data from NASA's Kepler space telescope to discover a new planet that is twice as large as Earth. Because TESS is programmed to look at a portion of the sky for only 27 days, any planets with a longer orbit are hard to identify.

To complicate matters, the star itself is relatively active, and Dragomir wasn't sure if the single transit she spotted was a result of a passing planet or a blip in stellar activity.

Its size is unusual for an exoplanet (the term for a planet that orbits a star outside our solar system).

A different group of astronomers had studied the HD 21749 system a decade ago using HARPS, which finds planets by noticing the tiny wobbles that their gravitational tugs induce in their host stars.

It turned out that they did not analyze all of the data. From this, they estimated that, if they indeed had seen a transit in the TESS data from sector 1, then another transit should appear 36 days later, in data from sector 3.

"Because there was an interruption in data around that time, we initially didn't see a second transit, and were pretty disappointed", Dragomir recalls. K2-288Bb orbits this smaller and dimmer star every 31.3 days.

"There was quite some detective work involved, and the right people were there at the right time", Dragomir says. "But we were lucky and we caught the signals, and they were really clear". With the launch of the James Webb Telescope, planet-hunters and scientists will be able to glean more information about TESS' discoveries and look closer for planets just like ours.

"Reorienting Kepler relative to the Sun caused miniscule changes in the shape of the telescope and the temperature of the electronics, which inevitably affected Kepler's sensitive measurements in the first days of each campaign", said study co-author Geert Barentsen, an astrophysicist at NASA's Ames Research Center, in a statement.

So the reprocessed, "cleaned-up" light curves were uploaded through the Exoplanet Explorers project on online platform Zooniverse, and the public was invited to "go forth and find us planets", Feinstein said.

Other reports by Click Lancashire

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