Researchers are debating back and forth over whether we have detected an exomoon. After years of Kepler being shut down, people are discussing whether it detected exomoons.
Discovery of Exomoons
In 2017, the astrophysicist was excited to announce the possibility of an exomoon around the exoplanet Jupiter Kepler-1625b. This was the first hint to anyone about the existence of an exomoon, followed by another candidate five years later around the planet Kepler-1708b.
Discussion about Exomoon Candidates
There are over five thousand exoplanets discovered so far, and we do not know for certain if they have moons orbiting them, which is what makes these announcements interesting. Exomoons provide more habitable zones where we can search for extraterrestrial life, and studying moons can be a valuable window into understanding the formation of the host planet.
Research and Results
But there is much debate over these exomoon candidates, with several groups examining data obtained from the Kepler and Hubble space telescopes.
The latest research paper on this topic, published by astronomers in Germany, indicated that the exomoon candidates around Kepler-1625b and Kepler-1708b are unlikely. Previous work also raised doubts about the exomoon candidate around Kepler-1625b.
However, this is not a clear-cut issue. David Kipping, the leader of the team that made both original discoveries and an assistant professor of astronomy at Columbia University, disagrees with the new analysis. He and his team are in the process of preparing a manuscript responding to the latest findings.
How to Detect Exomoons
The most common method for discovering exoplanets is the transit method. This technique measures the brightness of a star and looks for a slight dimming in brightness that corresponds to a planet passing in front of the star.
Photometry of stars can be expanded to search for exomoons, a pioneering approach developed by Kipping. In addition to the main dip caused by the planet, if there is a moon orbiting the planet, you should be able to see an additional, smaller dip caused by a moon blocking some of the star’s light.
Since moons are smaller, they generate a smaller signal, making them harder to see. But what complicates this case further is that the host stars Kepler-1625 and Kepler-1708 are not very bright. This makes the light drop more subtle – in fact, these systems must have large moons to be within the minimum threshold detectable by the Kepler space telescope.
Models and Data
Until scientists get more data from James Webb or from future missions like the European Space Agency’s Plato launch, everything depends on what they can do with the existing numbers.
“The aspects here relate to how the data itself is handled, what physics you incorporate when you model that data, and what possible false positive signals might be there that could produce the type of signal you are looking for,” said Eamon Kearns, a lecturer in astronomy at the University of Manchester who did not participate in the study, to Ars. “I think this discussion fundamentally revolves around these questions,” he added.
One of the main phenomena that need to be accurately modeled is known as the star’s limb darkening effect. Stars, including our Sun, appear dimmer at their edges than in the center due to atmospheric effects. Since this affects the apparent brightness of the star, it is clear that it is important to understand this in the context of searching for exomoons by measuring the brightness of the star.
“We have
“We have models for this, but we do not know exactly how a particular star behaves in terms of this apparent effect of stellar edge dimming,” said René Heller, the lead author of the study and an astronomer at the Max Planck Institute for Solar System Research, in an interview with Ars. The behavior of specific stars can be inferred, but this is not always an easy task. By incorporating improved models of stellar edge dimming, researchers found that they could explain signals previously linked to an exomoon.
Data processing is also critical, especially a type of processing known as “bias reduction.” This takes into account long-term variations in brightness data arising from random changes in stars and instrumental variations, among other things. New research shows that the statistical outcome, whether there is a moon or not, heavily depends on how this bias reduction is executed.
Moreover, the researchers say that the data obtained from the Hubble Space Telescope, which is primarily the source of the claim of a moon around Kepler-1625b, cannot be properly reduced and therefore should not be relied upon in the search for exomoons.
Results and Future Expectations
Until more data is obtained, this is likely to remain an ongoing scientific debate without a final conclusion. Kerins points out that Keeping and his team have been very cautious in their announcements. “They are very careful not to claim that it is a confirmed discovery. They conducted a thorough examination of the data provided to them, and indeed I think the difference here has to do with what physics you impose, how you process the data, and ultimately the fact that the Kepler dataset is really on the edge of discovering exomoons,” Kerins added.
However, Heller remains unconvinced. “My impression is that in the Kepler data, and also in other teams, we have done what is currently possible and there is nothing convincing that really stands out,” Heller said.
Moons vastly outnumber planets in our solar system—290 moons compared to 8 planets so far—so it is reasonable to assume that we will find exomoons as sky exploration continues. “It would be quite extraordinary, I think, if we continued through the next few years without finding an exomoon,” Kerins said. “I think it’s only a matter of time.”
Source: Nature Astronomy, 2023. DOI: 10.1038/s41550-023-02148-w
Ivan Paul is a freelance writer living in the UK, completing a PhD in cancer research. You can follow him on Twitter @ivan_paul_.
Source: https://arstechnica.com/science/2023/12/more-doubts-raised-over-exomoon-candidates/?comments=1
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