Astronomers discovered evidence of a second supermoon orbiting the sun beyond our solar system

Astronomers have discovered what looks to be a moon orbiting a planet in another solar system for the second time. This one, like the first, has characteristics that suggest such moons may be very different from those that populate our solar system.

Scientists said on Thursday that data from NASA's Kepler space telescope, which was retired in 2018, revealed the presence of a moon 2.6 times the diameter of Earth orbiting a Jupiter-sized gas giant about 5,700 light-years away from our solar system in the direction of the Cygnus and Lyra constellations.

The distance travelled by light in a year is 5.9 trillion miles (9.5 trillion km). The diameter of this moon would be greater than any of the nearly 220 moons orbiting planets in our solar system, and more than nine times that of Earth's moon.

"We don't know the mass or indeed composition. It could be a rocky core with a light fluffy envelope or a thick atmosphere all the way down to some high-density core," said Columbia University astronomy professor David Kipping, lead author of the research published in the journal Nature Astronomy.

The moons of our solar system are all stony or ice bodies. There are about 5,000 planets beyond our solar system, known as exoplanets, compared to only two such moons, known as exomoons. This is not because moons are thought to be rarer in other solar systems, but rather because planets are larger and hence simpler to discover, according to the researchers.

The first exomoon possibility, described in 2018 by the same lead researchers and currently awaiting confirmation, is considerably bigger — nearly the size of Neptune, the largest planet in our solar system. It's about 8,000 light-years away from the Earth. Its gaseous composition appears to be unlike that of any of our solar system's moons.

"Exomoons are terra incognita," Kipping said, using a Latin term meaning unknown land. "We know next to nothing about their prevalence, properties or origins. Moons may be frequent abodes for life in the cosmos and may affect the habitability of the planet their orbit. We've learned so much about exoplanets in the last few decades, but exomoons represent an outstanding challenge in modern astronomy," Kipping added.

The researchers used the "transit approach," which is commonly used to find exoplanets. When the planet and then the exomoon passed in front of the sun-like star around which the moon's planet orbits, the brightness of the star dimmed. Two such transits were observed by the Kepler space telescope.

"This is yet another tantalizing exomoon finding, suggesting again that large moons may be present in other planetary systems and that we can potentially detect them," said astronomer and study co-author Alex Teachey of the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) in Taiwan.

The researchers investigated 70 frigid, large gas exoplanets in broad orbits around their host stars, knowing that our own solar system's two such planets, Jupiter and Saturn, are orbited by multiple moons. They discovered evidence for the one new exomoon, which they described as a "mini-Neptune" due to its size.

"We will want to see follow-up observations to confirm its presence," Teachey said. "Even so, the present study goes a long way towards ruling out alternative explanations for the observed signals, leveraging more than a decade of experience in the exomoon search and pulling out all the stops. Some skepticism among the (astronomy) community is inevitable and important, but I think the paper lays out a convincing, thorough case."