The planet has a 31.3 day long orbit around star K2-288B, the smaller half of a binary pair. Image Credit: NASA's Goddard Space Flight Center/Francis Reddy


An exoplanet has been discovered by a group of citizen scientists that lies within a size ‘gap’, where there are few known exoplanets.

K2-288Bb is around twice the radius of Earth and was found using data from the Kepler space telescope.

Its discovery was announced at the 233rd meeting of the American Astronomical Society on 7 January 2019.

“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,” says Adina Feinstein from University of Chicago, who was working as an intern with Joshua Schlieder, an astrophysicist at NASA’s Goddard Space Flight Centre.

The search was handed over to citizen scientists after Schlieder’s group of interns noticed the data they were analysing was missing the first few days of observations after the telescope reoriented itself.

These were initially removed to prevent errors caused as the telescope settled into its new position.

However, it's now possible to compensate for these errors and so the team reanalysed the observation run with this missing data, gaining a new list of candidate exoplanets that then required visual inspection.

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

The re-processed data was posted to the Exoplanet Explorers website, where members of the public help to search through the data and discover new planets.

In May 2017, the Exoplanet Explorers uncovered what appeared to be an Earth sized planet, and discussion on the forums brought it to the attention of the scientists.

After conducting follow up observations, the planet was revealed to be 1.9 times the size of Earth, around half the radius of Neptune.

The size of the planet puts it into a region discovered by previous planetary surveys known as the Fulton gap – the region between 1.5 and 2 Earth radii where there is a curious lack of worlds.


It’s thought this gap is due to starlight eroding planetary atmospheres – smaller planets have their atmospheres eroded away but larger planets are less effected, causing the size gap to widen.


Elizabeth Pearson
Ezzy PearsonScience journalist

Ezzy Pearson is the Features Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.