“Scientists have now confirmed the detection of over 5,000 exoplanets, but there are fewer planets than expected with a diameter between 1.5 and 2 times that of Earth,” said Dr. Jessie Christiansen, who is a research scientist at Caltech/IPAC, along with being the science lead for the NASA Exoplanet Archive and lead author of the study. “Exoplanet scientists have enough data now to say that this gap is not a fluke. There’s something going on that impedes planets from reaching and/or staying at this size.”

For the study, the team analyzed photoevaporation data obtained from NASA’s K2 mission for two star clusters called Praesepe and Hyades, which are both estimated to be between 600 and 800 million years old. The longstanding hypothesis among astronomers is that planets and stars are broadly the same age. Therefore, the team hypothesized that any sub-Neptunes within these star clusters would be old enough to undergo photoevaporation but still young enough to not undergo core-powered mass loss.

In the end, the team observed close to 100 percent of stars observed in Praesepe and Hyades possessed at least one sub-Neptune exoplanet or a sub-Neptune candidate and were confident they still have their atmospheres. This contrasts stars older than 800 million years observed by K2, as these stars are typically comprised of only 25 percent sub-Neptunes. Since these stars are older, this indicates that core-powered mass loss is responsible for these planets stripping their atmospheres away. Therefore, the team concluded that Praesepe and Hyades have not experienced photoevaporation and that core-powered mass loss being the likely cause of atmospheric stripping of these planets.

While the study consists of five years of data, the team aspires to conduct follow-up observations to confirm these findings and hopefully conclude the reasons behind the gap in planetary sizes discussed earlier.

What new discoveries will astronomers make about exoplanets and gaps in their sizes in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!