In 2017, the world of astronomy was abuzz with the following events: announcement This means that the exoplanet Kepler-1625b may have its own moon, or exomoon. This was the first hint of an exomoon that anyone saw, followed five years later by another hint. another candidate Around the planet Kepler 1708b.
More than 5,000 exoplanets have been discovered so far, but it’s unclear whether any of them have moons orbiting them. This is what made this announcement so exciting. Exomoon offers a more potentially habitable region to explore for extraterrestrial life, and studying the satellite could provide a valuable window into the formation of its host planet.
However, there is much debate about these exomoon candidates, and multiple groups are scrutinizing data from the Kepler and Hubble Space Telescopes.
of latest papers A paper published on this topic by German astronomers concluded that the existence of exomoon candidates around Kepler-1625b and Kepler-1708b is unlikely. past works It also casts doubt on the exomoon candidates around Kepler-1625b.
However, this is not a clear-cut case. david kippingThe leader of the group that made both original discoveries, an assistant professor of astronomy at Columbia University, disagrees with the new analysis. He and his group are preparing a manuscript for the latest publication.
needle in a haystack
The most common method for detecting exoplanets is the transit method. This technique measures the brightness of a star and looks for small dips in brightness that correspond to planets passing in front of the star.
Stellar photometry can be extended to search for exomoons, an approach pioneered by Kipping. In addition to the main dip caused by the planet, you should also be able to see additional small dips caused by the moon blocking some of the starlight if the moon is orbiting the planet.
An example of what exomoon transit detection would look like.
The smaller the satellite, the smaller the signal it produces and the harder it is to spot. But what makes this particular case even more difficult is that the host stars Kepler-1625 and Kepler-1708 are not very bright. This makes the light drop even weaker. In fact, these systems must have large moons within detection range of the Kepler Space Telescope.
model, model, model
Until scientists get more data from James Webb, or something like a future mission. Plato of the ESA After launch, it’s all about what you can do with the existing numbers.
“The important aspects here are how the data itself is processed, what physics to introduce when modeling that data, and what kind of signals it is possible to reproduce. Is there a possibility that there is a false positive signal that you are looking for? Eamon Kerinssaid a senior lecturer in astronomy at the University of Manchester, who was not involved in the study. Ars. “I think this whole discussion essentially centers around these questions,” he added.
One important phenomenon that requires accurate modeling is known as the stellar edge darkening effect. The edges of stars, including the Sun, appear darker than the center due to the effects of the star’s atmosphere. This is clearly important to understand in the context of measuring star brightness and searching for exomoons, as it affects the star’s apparent brightness.
“We have models for this, but we don’t know exactly how a particular star will behave in terms of this star-rim darkening effect,” he said. René Hellerthe study’s lead author and an astrophysicist at the Max Planck Institute for Solar System Research, said in an interview. Ars. Although we can deduce how a particular star behaves, this is not always obvious. The authors found that incorporating an improved model of stellar edge darkening can explain signals previously thought to be caused by extrasolar satellites.
Data processing, especially a type of processing known as detrending, is also of paramount importance. This takes into account long-term fluctuations in brightness data caused by random fluctuations in stars, instrument fluctuations, etc. New research shows that the statistical outcome, whether there is a moon or not, is highly dependent on how this detrending is performed.
Additionally, the authors argue that searches for exomoons should not be relied upon because data obtained from the Hubble telescope (primarily the source of claims about the moon around Kepler-1625b) cannot be properly detrended. It has said.
both sides
Until more data is available, this is likely to remain a scientific debate without a final conclusion.
Kerins points out that Kipping and his team were very cautious in their announcement. “They’re very careful not to claim that it’s a cast-iron detection. They do comprehensive testing of the data they’re given. In fact, the difference here is I think it’s all about what kind of physics you bring in, how you process the data, and ultimately the fact that the Kepler dataset actually exists in the world.That’s the limit of exomoon discovery. ”
But Heller remains unconvinced. “My impression is that with the Kepler data, we and other teams are doing what we can currently do, and there are no particularly compelling objects that stand out.”
There are far more satellites than planets in our solar system.Two hundred and ninety to eight For now, it’s reasonable to assume that if we continue to explore the skies, we’ll encounter an exomoon. “If we continue to search for the next few years and still don’t find an exomoon, I think that would be extremely unusual,” Kerins said. “I think it’s only a matter of time.”
Natural Astronomy, 2023. DOI: 10.1038/s41550-023-02148-w
Ivan Paul is a UK-based freelance writer with a PhD in cancer research. He is on his Twitter @ivan_paul_.
