Exomoon Discovery Questioned by New Data Analysis

Monday - December 25 2023, 20:32 UTC - 11 months ago

The two exomoons discovered around Kepler-1625b and Kepler-1708b have been called into question. A new data analysis has been conducted by scientists from the Max Planck Institute for Solar System Research and the Sonnenberg Observatory of Germany with the help of the Pandora search algorithm. This new analysis suggests that the planet-only interpretations of the observations is more conclusive, thus, raising doubt about the discoveries.

Discovery of giant exomoons around the planets Kepler-1625b and Kepler-1708b called into question.

Just as it can be assumed that the stars in our Milky Way are orbited by planets, moons around these exoplanets should not be uncommon. This makes it all the more difficult to detect them. So far, only two of the more than 5300 known exoplanets have been found to have moons. A new data analysis now demonstrates that scientific statements are rarely black or white, that behind every result there is a greater or lesser degree of uncertainty and that the path to a statement often resembles a thriller.

In observations of the planets Kepler-1625b and Kepler-1708b from the Kepler and Hubble space telescopes, researchers had discovered traces of such moons for the first time. A new study now raises doubts about these previous claims. As scientists from the Max Planck Institute for Solar System Research and the Sonnenberg Observatory, both in Germany, report in the journal Nature Astronomy, “planet-only” interpretations of the observations are more conclusive.

For their analysis, the researchers used their newly developed computer algorithm Pandora, which facilitates and accelerates the search for exomoons. They also investigated what kind of exomoons can be found in principle in modern space-based astronomical observations. Their answer is quite shocking.

In our Solar System, the fact that a planet is orbited by one or more moons is rather the rule than the exception: apart from Mercury and Venus, all other planets have such companions; in the case of the gas giant Saturn researchers have found 140 natural satellites until today. Scientists therefore consider it likely that planets in distant star systems also harbor moons. So far, however, there has only been evidence of such exomoons in two cases: Kepler-1625b and Kepler-1708b. This low yield is not surprising. After all, distant satellites are naturally much smaller than their home worlds — and therefore much harder to find. And it is extremely time-consuming to comb through the observational data of thousands of exoplanets for evidence of moons.

To make the search easier and faster, the authors of the new study rely on a search algorithm called Pandora that they developed and optimized themselves for the search for exomoons. They published their method last year and the algorithm is available to all researchers as open source code. When applied to the observational data from Kepler-1625b and Kepler-1708b, the results were astonishing.

“We would have liked to confirm the discovery of exomoons around Kepler-1625b and Kepler-1708b,” says first author of the new study, MPS scientist Dr. René Heller. “But unfortunately, our analyses show otherwise,” he adds.

The Jupiter-like planet Kepler-1625b made headlines five years ago. Researchers at Columbia University in New York reported strong evidence of a giant moon in its orbit that would dwarf all the moons in the Solar System. The scientists had analyzed data from NASA’s Kepler space telescope, which observed more than 100,000 stars during its first mission fr2012-2018 seeking for planets beyond Earth.