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Astronomers Discover Evidence of Super-Sized Moon Orbiting a Jupiter-Sized Planet Beyond Our Solar System

The discovery of a second exoplanet hints at the possibility that exomoons are as common as exoplanets. Credit: Helena Valenzuela Wiederström

The exomoon signal in the archival data indicates the possibility of further discoveries.

Astronomers report a second, super-sized moon orbiting a JupiterA planet the size of outside our solar system. If confirmed, the vision could mean that exomoons are as common in the universe as exoplanets, and that these large or small moons are a feature of planetary systems. But it can be a long wait. The first-ever sighting of an outer moon four years ago is still awaiting confirmation, and verification of this new candidate can be long and contentious.

The discovery was published in natural astronomyLed by David Kipping and Cool Worlds Lab at Columbia University, which reported the first exomoon candidate in 2018.

Astronomers have discovered more than 10,000 extrasolar planet So far, said Kipping, who has spent the past decade researching external satellites, presents a much bigger challenge. “They are uncharted territory.”

The team discovered the candidate giant exomoon orbiting the planet Kepler 1708b, a world 5,500 light-years from Earth in the direction of the planets Cygnus and Lyra. This new filter is about a third smaller than NeptuneA moon of its size that Kipping and colleagues found earlier orbits a similar planet the size of Jupiter, Kepler 1625b.

Both candidates for the giant moon, Kipping said, are likely made of gas accumulating under the influence of gravity from their enormous size. If an astronomer’s hypothesis is correct, the moons may have started their lives as planets, only to be pulled into the orbit of a larger planet such as Kepler 1625b or 1708b.

Both moons are located far from their host star, as there is less gravitational pull to pull the planets and remove their moons. In fact, researchers searched for cold gas giant planets in wide orbits in their search for outer moons precisely because the analogue in our solar system, Jupiter and SaturnBetween them are more than a hundred moons.

If there were other moons, Kipping said, they would likely be less monstrous, but also harder to spot. “The first discoveries in any survey will generally be rather eccentric,” he said. “Big things are easy to detect simply with our limited sensitivity.”

Exoplanets fascinate astronomers for the same reasons that exoplanets do. They have the power to reveal how and where life arose in the universe. They’re also a curiosity in their own right, and astronomers want to know how these outer moons form, whether they can sustain life, and what role, if any, they play in making the host planets habitable.

In the current study, researchers looked at a sample of the coldest gas giant planets ever captured NASAPlanetary Hunting Spacecraft, Kepler. After scanning 70 planets in depth, they found only one candidate – Kepler 1708b – with a moon-like signal. “It’s a stubborn signal,” Kipping said. “We threw the kitchen sink on this thing but it won’t go away.”

Observations from other space telescopes, such as Hubble, will be needed to verify the discovery, a process that could take years. Four years later, the first exomoon discovery of kiping is still hotly debated. In a recent paper, he and his colleagues show how a group of skeptics may have missed Kepler 1625b in their calculations. Meanwhile, Kipping and his colleagues continue to investigate other lines of evidence.

Eric Agul, Professor of Astronomy at University of WashingtonHe said he doubted this last signal was real. “It might just be fluctuation in the data, either because of the star or the noise of the machines,” he said.

Others seemed more optimistic. “This is science at its best,” said Michael Hebeck, an independent astronomer in Germany. “We find something intriguing, make the prediction, and either confirm the exomoon candidate or rule it out with future observations.”

“I am very excited to see a second candidate for an exomon, although it is unfortunate that only two crossing-overs have been observed,” he added. “More data would be very nice.”

Detecting a moon or even a planet hundreds to thousands of light-years away from Earth is no easy feat. Moons and planets can only be observed indirectly as they pass in front of their host stars, causing the star’s light to dim intermittently. Capturing one of these transiting signals with a telescope is challenging, as is the interpretation of the light curve data. Moons are more difficult to detect because they are smaller and block less light.

The research is worthwhile, Kipping said, as he recalls how the existence of exoplanets was greeted with the same skepticism as today’s exomoons. “These planets are strange compared to our home system,” he said. “But they have revolutionized our understanding of how planetary systems form.”

Reference: “Exomoon Survey of 70 Fascinating, Giant Exoplanets and the New Candidate Kepler-1708b-i” by David Kipping, Steve Bryson, Chris Burke, Jesse Christiansen, Kevin Hardegre-Ullman, Billy Karls, Brad Hansen, Judit Szolagy, Alex Teachey, 13 January 2022, natural astronomy.
DOI: 10.1038 / s41550-021-01539-1

The other authors are: Steve Bryson, NASA Ames Research Center; Chris Burke with; Jesse Christiansen and Kevin Hardegre Ullman, Caltech; Billy Quarles, Valdosta State University; Brad Hansen, University of California, Los Angeles; Judit Solagey, ETH Zurich; and Alex Tecchi, Columbia.

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