There may be a planet out there that has an Earth-like moon friend.
Since the early 1990s, scientists have cataloged thousands of exoplanets drifting beyond our solar system. One showers glass instead of water, the other is wrapped in one, not one two There are atmospheres, and even some without anchor stars, that alone are traversing the universe.
Nevertheless, we have yet to confirm an exoplanet with an exomoon companion, similar to the friendship between our Moon and Earth. “Exomoons are far more challenging,” David Kipping, an astronomer at Columbia University and leader of the institute’s Cool Worlds Lab, said in a statement. “They’re Terra Secret.”
But after studying the appearance of these cosmic objects over the past decade, Kipping has made some progress in the discovery. In a paper published Thursday in Nature Astronomy, he and his team found evidence of a supersized exomoon orbiting the exoplanet Kepler 1708b, a Jupiter-sized giant that floats 5,500 light-years away from Earth.
The discovery, made using NASA’s planet-hunting spacecraft, Kepler, comes a few years after Kepling saw the first exomoon candidate in 2017. They observed a Neptune-sized moon, possibly orbiting the planet Kepler 1625 b, which is as massive as Kepler 1708 b. However, its formal exomoon classification is awaited, so the field of astronomy is technically still exomoon-less.
Despite the extensive vetting process required for all possible exoplanet signals, which includes observations from the space telescope from Hubble, Kiping says the discovery is well worth it. He recalls the skepticism that once surrounded the quest to find exoplanets before their earlier confirmation.
“Those planets are alien compared to our home system,” he said. “But they have revolutionized our understanding of how planetary systems form.” In the same way, finally proving the existence of exomoons could help scientists understand the dynamics of planet-moon systems, and one day, even explain the Moon’s role in supporting and sustaining life. There may also be an unveiling.
Returning to Kipping’s newly documented possible exomoon: it’s about a third smaller than his first contender. However, both are likely made of gas that piles up with their heft under the gravitational pull, he says. They are each located relatively far from their respective host stars, another reason why Kipping believes they are so massive. Such a distance means that there is less gravity for their layers to come off.
“The first detections in any given survey will generally be strange, large ones that are easy to detect with our limited sensitivity,” Kipping said.
Detecting exoplanets, let alone exomoons, is very difficult because their signals reach astronomers only when the globes intersect the light of their home star. Think of it like Morse code is visible in space from Earth’s point of view, with each dot representing a star blocking the planet.
Since the moons are so much smaller than the planets, it is inherently difficult to see when they block out starlight. Morse code is, in a sense, unconscious. In fact, that’s why Kiping’s discovery has garnered some scrutiny—seeing these rare, exotic jewels isn’t every day.
“This data may fluctuate, either due to star or instrumental noise,” Eric Egol, an astronomer at the University of Washington, said in a statement.
Others, however, are hopeful about Kipping’s exomoon data. “This is science at best,” said Michael Hippke, an independent astronomer in Germany who was not involved in the research. “We find an intriguing object, make a prediction, and either confirm the exomoon candidate or rule it out with future observations.”