Rare-Sized Exoplanet Discovered By Citizen Scientists In Old Kepler Data

The newfound exoplanet has an uncommon size and was originally missed by astronomers.

Artist’s illustration of the newfound Kepler exoplanet, located in a double-star system 226 light-years away.
Francis Reddy / NASA's Goddard Space Flight Center

The newfound exoplanet has an uncommon size and was originally missed by astronomers.

Citizen scientists have come across a previously unknown exoplanet floating a mere 226 light-years from Earth in the Taurus constellation (“The Bull”). Dubbed K2-288Bb, the newfound exoplanet was discovered in old data from NASA’s Kepler Space Telescope, the space agency announced on Monday.

According to a statement from NASA, the newly discovered alien world could either be a gas giant like Neptune or a rocky planet like Earth. Either way, K2-288Bb orbits within its star’s habitable zone, which means that it sits at a distance that could allow liquid water to pool on its surface.

Unveiled on Monday at the 233rd meeting of the American Astronomical Society in Seattle, Washington, K2-288Bb is located in a binary star system made up of two dim, cool M-type stars. Known as K2-288A and K2-288B, the stars sit about 5.1 billion miles away from each other. That’s roughly six times the distance between Saturn and the sun, noted NASA.

“The brighter star is about half as massive and large as the sun, while its companion is about one-third the Sun’s mass and size. The new planet, K2-288Bb, orbits the smaller, dimmer star every 31.3 days.”

‘Rare’ Size

The interesting thing about K2-288Bb is its size. The newfound Kepler exoplanet is half the size of Neptune — or about 1.9 times bigger than Earth. This is a rarity among exoplanets, explained NASA, which makes K2-288Bb a rather exotic find.

As CNN points out, the size of K2-288Bb places this exoplanet in the so-called “Fulton gap” — a marker that divides all the known Kepler planets into super-Earths and sub-Neptunes based on their size.

Discovered in 2017, the Fulton gap is also known as the “radius valley” and states that planets rarely have a size between 1.5 and two times that of Earth. As the Inquisitr previously reported, the Fulton gap argues that most of the Kepler exoplanets are either super-Earths, with a radius smaller than 1.5 times that of our planet, or sub-Neptunes, with two to three times the radius of Earth.

This makes K2-288Bb perfect for studying planetary evolution, given that so few exoplanets of this size range have been found.

‘Hidden’ In The Kepler Data

Another intriguing thing about K2-288Bb is the way it was discovered. The exoplanet was spotted by citizen scientists after initially being missed by astronomers due to data collection procedures during Kepler’s early K2 campaigns.

The newfound exoplanet emerged from data gathered by the space telescope during the 4th Campaign of its K2 mission — a time when the first few days of observations were simply scrubbed by the software in order to eliminate possible errors produced by the repositioning of the spacecraft.

“Re-orienting Kepler relative to the sun caused minuscule 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 Geert Barentsen, an astrophysicist at NASA’s Ames Research Center in Silicon Valley, California, and the director of the guest observer office for the Kepler and K2 missions.

The first signs of K2-288Bb were picked up in 2017 by Adina Feinstein, a University of Chicago graduate student and lead author of a study on the discovery, which was recently published in the Astronomical Journal.

At the time, Feinstein, University of North Carolina’s undergraduate student Makennah Bristow, and NASA astrophysicist Joshua Schlieder detected two of the exoplanet’s transits in front of its parent star, K2-288B. However, a third transit was necessary in order to establish K2-288Bb as a planetary candidate.

As it turned out, this third detection was hidden within the scrubbed observations — and was eventually spotted by citizen scientists after all the data from Kepler’s fourth campaign was uploaded on Exoplanet Explorers, an online initiative for amateur astronomers hosted on Zooniverse.

“We eventually re-ran all data from the early campaigns through the modified software and then re-ran the planet search to get a list of candidates, but these candidates were never fully visually inspected,” explained Schlieder.

“Inspecting, or vetting, transits with the human eye is crucial because noise and other astrophysical events can mimic transits.”

After pouring over the Kepler data, citizen scientists vetted the third transit of K2-288Bb, pointing to the discovery of a possible Kepler exoplanet.

“It’s a very exciting discovery due to how it was found, its temperate orbit and because planets of this size seem to be relatively uncommon,” said Feinstein.

“That’s how we missed it — and it took the keen eyes of citizen scientists to make this extremely valuable find and point us to it.”

The Kepler Space Telescope, humanity’s most prolific exoplanet hunter, ended its long and fruitful career about three months ago. After nine years in space and more than 2,600 exoplanet discoveries, the venerable telescope ran out of fuel and went offline during the 19th Campaign of its K2 mission, the Inquisitr reported at the time. Although its watch has ended, Kepler’s legacy carries on as scientists are left with a treasure trove of data to explore.