sun and planets
July 31, 2017

Have researchers finally found the first-ever exomoon?

While astronomers have located more than 1,000 verified exoplanets and several thousand other potential candidates, they have yet to find a confirmed exomoon, but now, a new study posted to the arXiv prepublication server could provide evidence of the first such discovery.

According to Engadget and BBC News, Dr. David Kipping, an assistant professor of astronomy at Columbia University, and his colleagues used data from the Kepler Space Telescope to detect signs of what appears to be a Neptune-sized moon located about 4,000 light years from Earth.

Said exomoon was found orbiting a planet about the same size and approximately 10 times more massive than Jupiter in the Kepler-1625 system, and the authors detected its existence when they noticed a decrease in brightness before and/or after the planet passed in front of its host star.

The Kepler Space Telescope, BBC News explained, hunts for planets by looking for changes in brightness that occur when a planet passes in front of its star. In this study, Dr. Kipping’s group looked for dips in starlight that happened before and/or after the planet passed in front of its sun. Such a signal was detected during three of the planet’s transits, the researchers reported.

Ideally, the researchers told the UK news outlet that they would have liked to have detected more signals, as that would have increased the level of confidence that they had indeed located the first ever verified exomoon. “We would merely describe it at this point as something consistent with a moon,” Dr. Kipping said. “But, who knows, it could be something else.”

Follow-up observations needed to confirm the discovery

The researchers plan to further investigate the potential moon with the Hubble Space Telescope in October, and while the object is – in Engadget’s words – “one of the strongest candidates for an exomoon to date,” those follow-up observations will confirm or dismiss the discovery.

Dr. Kipping and his co-authors have assigned a confidence level of four sigma to their signal, which according to BBC News describes how unlikely that it is that an experimental result is due to pure luck. In this case, it’s like flipping a coin and getting 15 straight heads, they explained.

However, the researcher said that this was not the ideal way to evaluate the potential detection. He said that he and his colleagues were “excited about it... statistically, formally, it's a very high probability. But do we really trust the statistics? That's something unquantifiable. Until we get the measurements from Hubble, it may as well be 50-50 in my mind.”

So while there is a fairly good chance that this is indeed an exomoon, the researchers are unable to completely rule out that the object is something else completely – at least, not until manage to take a second look at it with Hubble later on this year. Hubble, Phys.org explained, is capable of collecting better data than Kepler, and if the discovery is confirmed, it would make this not only the first ever confirmed exomoon, but also the largest moon ever observed, they noted.

“I'd say it's the best [candidate] we've had. Almost every time we hit a candidate, and it passes our tests, we invent more tests until it finally dies – until it fails one of the tests,” Dr. Kipping told BBC News. “In this case, we've applied everything we've ever done and it's passed all of those tests.”

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Image credit: NASA/Tim Pyle