by Astronomers have always known that it would be no mean feat to spot moons around planets outside the solar system – but a current debate in planetary science circles shows just how difficult it will be to detect these so-called exoplanets .
The story begins in 2018, when astronomers including David Kipping, an assistant professor of astronomy at Columbia University, believed they had made their first detection of an exomoon. The material was found around exoplanet Kepler-1625b, a Jupiter-like world located about 8,000 light-years from Earth. It was first observed with the Kepler Space Telescope.
When it was allegedly discovered, Kepler-1625b’s moon was aptly named “Kepler-1625 b I”. It was later confirmed with data from the Hubble Space Telescope. Then, in 2022, another team, including Kipping, seemed to get a second exomoon, this time only with the Kepler Space Telescope. This material is thought to have been seen orbiting Kepler-1708 b, a gas giant located about 5,400 light-years from Earth with a mass 4.6 times that of Jupiter. The second possible exomoon had a similar name to the first; it was named “Kepler-1708 b I.”
Related: That’s no moon! Scientists are skeptical that the 1st exomoons are proposed to be detected
These two moons were unlike anything found in the solar system. Both exhibited sizes larger than those of Earth, for example, making them similar in scale to a class of exoplanets known as “mini-Neptunes.” To that end, the first exomoons appeared to represent some of the first exoplanet discoveries, including things scientists never expected to see as Jupiter-sized worlds snuggled up to their stars and planets. orbiting rapidly spinning neutron stars called pulsars.
Although the discoveries of Kepler-1625 b I and Kepler-1708 b I – let’s call them the “pro-exomoon team” – kept an open mind about the existence of the moon, and still to this day they maintain a healthy skepticism, the it seemed that the situation seemed certain. mankind found its first exomoons after years of locating only exoplanets.
That was until the end of 2023, when a separate team of astronomers led by Max Planck Solar System Research scientist René Heller — a “no-exomoon team” if you like — cast doubt on the two exomoon discoveries in a paper published in Nature Astronomy magazine. .
Kipping and colleagues have now returned, producing a research paper that appears in a preprint version of the arXiv paper repository and defending their exomoon findings.
“I believe Kepler-1625b and Kepler-1708b are perfectly valid exomoon candidates, and I think we’ve demonstrated that convincingly,” Kipping told Space.com. “So what do I think is really going on, and why didn’t they find the moon?”
An exomoon discrepancy
The technique used to detect these two exoplanets is similar to the transit method, which has delivered a large number of over 5,000 planets in the exoplanet catalog to date.
The transit method relies on detecting a tiny dip of light coming from the planet’s parent star, created as that world crosses or “crosses” the face of that star from our view in space. The same principle applies to exomoons, albeit on a much smaller scale. If these moons are in precisely the right position around the planet they orbit as that planet passes across its star, that should add to the light drop, albeit insignificantly.
However, such a small pool of light is the clue that Kepler-1625 b I and Kepler-1708 b I were a team for the exomoon. However, because this reduction in light output due to exoplanet transit is so small, it cannot be observed directly. Instead, it takes powerful computer software algorithms to extract it from telescope data.
Kipping says his “pro-exomoon” team and Heller’s “no-exomoon” team took the same data from the same telescopes, but Kepler-1625 b I and Kepler-1708 b I may have disappeared because of how the teams could be. treated with that data through the algorithms used.
Kipping told Space.com that the “no-exomoon” Kepler-1708 b I team may have missed it because of the software they chose to analyze the Hubble and Kepler telescope data. Although the software is related to the one he and the “pro-exomoon” team used, it is still slightly different.
“The software packages we’ve used are almost identical. Theirs is much newer. It’s only been around for a few years, but the one we’ve been using has been around for a decade or so, b ‘maybe even longer. ,’ explained Kipping. “The real answer is that their algorithm can’t find the moon. It’s not that the moon doesn’t exist in their data.”
Kipping also points out that the “no-exomoon” team used their software, which is usually very reliable, outside of its default mode and instead in a mode that is sensitive to the number of steps used to process data. This may explain why the probes were removed during their calculations.
For Kepler-1625 b I, Heller and his “no exomoon” team suggested an effect called “stellar limb darkening,” meaning that the edges of a star are darker than its center, which affects the exomoon signal. intended. Heller’s team argues that the darkening of the star’s limb would better explain observations of the parent star than the darkening caused by the presence of an exomoon.
Kipping argues that this is not a valid case against the exomoon candidates because he and his “pro-exomoon” team were already responsible for that limbic darkness when they first proposed the existence of Kepler-1625 b I.
“For an account we darkened a limb in the original paper, so it’s not like we screwed up and forgot about it, he explained. “I think this hole point is a kind of red herring in my book; it does not affect the argument for the exomoon.”
The main researcher of the exomoon debunking team, René Heller, looked at the paper returned by Kipping and the team but he is not swayed to believe that Kepler-1625 b I and Kepler-1708 b I exist.
“I don’t see anything new in the paper that would change my opinion about Kepler-1625b and Kepler-1708b being planets without large moons. Their new paper mostly circles around our work and tries to find weaknesses in our line of reasoning. a natural and very welcome process in modern science, although in this case I do not see any significant progress,” Heller told Space.com. “I reject the idea that their rejection of our rejection of their demand. I think the debate is still undecided, and this is fine. Let’s move on!”
The idea of moving forward is something that Heller and Kipping agree on – at least for now.
Are Kepler-1625 b I and Kepler-1708 b “strange?”
The whole reason these exoplanets showed up in transit is because they are massive mini-Neptune bodies that can have diameters between 1.6 times and 4 times that of Earth. If they are there, they are enormous.
Kipping thinks that’s part of what might make them too unusual to be widely accepted as the first exomoon discoveries.
“I think there’s a lot of skepticism about Kepler-1625 b I and Kepler-1708 b I because they’re both weird. They’re both like these mini-Neptune moons, right? And everybody’s asking, ‘Who ordered. that? How does the universe do such strange things?” he said. “And then this controversy does not help at all. They are too damaged now.”
Kipping now plans to use the James Webb Space Telescope (JWST) to search for exomoons that are closer analogues to the moons we see within the solar system.
“My strategy, and it may be the wrong strategy, is to let us see if we can find some more familiar moons on the JWST, analogs to the moons we have in our solar backyard like Io and Europa, ” he said. “I hope that will instill confidence that these exomoons were seen back then and that they were very interesting, and we should go back and look at them again.”
Kipping is very clear that the disagreement between the team’s conclusions does not reflect badly on either set of scientists regardless of the final answer, “exomoon” or “no exomoon.” Instead, it simply shows how challenging it will be to detect moons around planets outside the solar system until major advances in telescope technology are made.
“It’s very challenging work, and I wouldn’t pretend otherwise. When we’re looking for exoplanets, we’re looking for a signal that none of these telescopes are designed to detect,” he said. “We think we can get that kind of science out of them. But it’s pushing these instruments, especially Kepler and Hubble, to the edge of what they can do.
“So the decisions you make and the choices you make on how, what algorithms you use, how you treat the data, can make the difference between success and failure.”
RELATED STORIES
— Exomoons are being looked for around alien planets and scientists may have just found one
—Hubble telescope reveals water around tiny, hot, steamy exoplanet with ‘exciting discovery’
— Tiny 14-inch satellite studies ‘hot Jupiter’ exoplanet evaporating into space
Kipping believes that this disagreement between the two teams gives exomoon hunting scientists an opportunity to compare methods and agree on the best approach to hunting these small, distant bodies.
It is hoped that the two sets of talented and passionate scientists could come together on exomoon detection that they can agree on one day due to a refined exomoon detection method.
