(CNN) — Astronomers may have found a moon that is completely unlike anything in our solar system.
It is only the second space object discovered that may be an exomoon or a moon outside our solar system. The giant moon was found orbiting a Jupiter-sized planet called Kepler 1708b, located 5,500 light-years from Earth.
A study detailing these findings was published Thursday in the journal Nature Astronomy.
The newly detected celestial body is 2.6 times larger than Earth. There is no analogy for such a large moon in our own system. For reference, our own moon is 3.7 times smaller than Earth.
It is the second time that David Kipping, assistant professor of astronomy and leader of the Cool Worlds Lab at Columbia University, and his team have found a candidate for an exomoon. They discovered the first, a Neptune-sized moon orbiting a giant exoplanet called Kepler-1625b, in 2018.
“Astronomers have found more than 10,000 exoplanet candidates so far, but exomoons are much more challenging,” Kipping said in a statement. “They are” terra incognita “(unknown land)”.
Understanding more about moons, for example how they form, whether they could support life, and whether they play a role in the potential habitability of planets, could lead to a greater understanding of how planetary systems form and evolve.
Hard to find objects
Kipping and his team are still working to confirm that the first candidate they found is actually an exomoon, and this latest discovery will likely face the same uphill battle.
Moons are common in our solar system, which has more than 200 natural satellites, but the long search for interstellar moons has been largely unsuccessful. Astronomers were successful in locating exoplanets around stars outside of our solar system, but exomoons are more difficult to identify due to their smaller size.
More than 4,000 confirmed exoplanets have been discovered across the galaxy, but that doesn’t mean finding them has been easy. Many of them were detected using the transit method, or by looking for dips in starlight when a planet passes in front of its star. Detecting moons, which are smaller and cause even tinier drops in starlight, is very difficult.
To find this second potential moon, Kipping and his team used data from NASA’s retired Kepler planet-hunting mission to study some of the cooler gas giant exoplanets the telescope found. The researchers used this criteria in their search because in our solar system, the gas giants Jupiter and Saturn have the most moons orbiting them.
Of the 70 planets they studied, only one revealed a companion signal that appeared to be a moon, with only a 1% chance that it was something else.
“It’s a stubborn sign,” Kipping said. “We threw the kitchen sink at this thing, but it just won’t go away.”
3 ways a moon could form
The newly discovered candidate shares similarities with the first potential exomoon discovery. Both are probably gaseous, which explains their enormous size, and they are far from their host stars.
There are three main theories about how moons form. One is when large space objects collide and the detached material turns into a moon. Another is capture, when objects are captured and put into orbit around a large planet, such as Neptune’s moon Triton, which is believed to be a captured Kuiper Belt object. And the third is the moons that are formed from the materials, such as gas and dust that swirl around the stars, that created the planets in the early days of the solar system.
It is possible that both exomoon candidates started out as planets that were eventually dragged into orbit around larger planets such as Kepler 1625b and Kepler 1708b.
Giant moons are probably an anomaly
Kipping believes that all moons outside of our solar system are unlikely to be as large as these two candidates, which may make them the weirdos, rather than the standard. “The first detections in any survey will generally be the weirdos,” he said. “The big ones that are just easier to spot with our limited sensitivity.”
To confirm that the two candidates are exomoons, follow-up observations by the Hubble Space Telescope and the James Webb Space Telescope will be required in 2023. Meanwhile, Kipping and his team continue to gather evidence in support of the exomoons.
The fact that each associated planet takes more than one Earth year to complete one orbit around its star slows down the discovery process.
“Confirmation requires lunar transits to be repeated multiple times,” Kipping said. “The long-period nature of our target planets means that we only have two transits available here, but not enough to see a series of lunar transits necessary to claim a confirmed detection.”
If confirmed, it could be the beginning of a new acceptance that exomoons are as common as exoplanets outside of our solar system.
The first exoplanet wasn’t discovered until the 1990s, and most of the exoplanets known today weren’t revealed until Kepler’s launch in 2009.
“Those planets are extraterrestrial compared to our home system,” Kipping said. “But they have revolutionized our understanding of how planetary systems form.”