Exomoons detected by the Kepler satellite are mirages, says study – 01/07/2024 – Messenger Sideral

The search for exomoons – natural satellites around planets outside the Solar System – remains an inglorious task. The only two most firmly established candidates now appear to have gone through the roof, according to a new study by a pair of German astronomers. As a result, astronomers seem to be going back to square one in this regard.

It’s not at all surprising that exomoons are so difficult to detect. If exoplanets are no longer a breeze to detect and require the observation of indirect effects (such as the reduction in brightness of the parent star when the star passes in front of it, or the gravitational wobble caused by it as it rotates around it), exomoons would be even more difficult.

The only method that to date has brought minimal hope for detection is that of transits, explored by missions such as the famous Kepler space telescope. The idea is that, along with the reduction in brightness caused by the planet as it passes in front of the star, it might be possible to detect the presence of moons due to different patterns with each transit, depending on its position in relation to the planet.

In fact, it was from Kepler data that the few possible detections came. In 2018, David Kipping’s group, from Columbia University, in New York, announced a possible exomoon around the planet Kepler-1625 b. It was a gas giant the size of Jupiter. And amazingly, it was the size of Neptune, with a diameter about four times that of Earth.

In contrast, the largest moon in the Solar System, the Jovian Ganymede, is about 40% the diameter of Earth. And no model of moon formation could explain how this Neptune-sized mammoth could have emerged as a moon, even around a giant like Jupiter.

If that wasn’t enough, Kipping’s team returned to work in 2022, indicating that a similar pair of stars could exist around the star Kepler-1708. Could nature, contrary to expectations, theories and models, really be an expert at producing giant exomoons?

The answer is “probably not”, according to René Heller, from the Max Planck Institute, and Michael Hippke, from the Sonneberg Observatory in Germany. Writing in Nature Astronomy, the duo presents a new analysis of the data that led to the two identifications by Kippling’s group and demonstrates that they appear to be the result of a fitting artifact when equating observations with transit models. In other words, a mirage. “We conclude that Kepler-1625 b and Kepler-1708 b are probably not orbited by a large exomoon,” they state.

In fact, if there were stars like those described by Kipping’s group, their signal would be much stronger in the Kepler data than it actually appeared in what is shaping up as a false positive.

Could this be the end of the story? Certainly not. This is just a demonstration that our observation technologies have not yet reached the point where they can reliably detect exomoons – even more so with the expectation that they tend to be smaller than most planets. Future telescopes will be able to do better, and it remains a firm bet among astronomers that the moons are not a phenomenon exclusive to the Solar System. But, according to the scientific method, you always have to see it to believe it.

This column is published on Mondays in print, in Folha Corrida.

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