In 2018, astronomers at Columbia University (USA) announced that they had evidence of the first exomoon or moon found orbiting a planet outside our solar system.

Now the same team reports Nature astronomy, from the discovery of a very large second, called Kepler-1708bi, around the planet Kepler 1708b, a Jupiter-sized world located 5,500 light years from Earth towards the constellations Swan and Lyra.


Exomoon candidate Kepler-1708 bi orbits a Jupiter-sized exoplanet, and if its discovery is confirmed, it could be the start of similar discoveries: other moons outside the solar system.

If the finding is confirmed, it could mean that exomoons are as common in the universe as exoplanets, and that, large or small, would be a feature of planetary systems. Therefore, the possibility of other similar discoveries would open up.


But the wait can be long. The first sighting of an exomoon four years ago is still pending confirmation, and verification of this new candidate can be just as long and controversial.

“Astronomers have found more than 10,000 exoplanet candidates so far, but exomoons are much more challenging: they are terra incognita”, points out one of the authors, David Kippe in Cold Worlds Laboratory from Columbia University.


This new candidate, with size of about 2.6 Earth radii, is a third smaller than the Neptune-sized moon that Kipping and his colleagues previously found orbiting a planet as large as Jupiter, Kepler 1625b.

super gas moons

Both supermoon candidates are likely composed of gas that has accumulated under the gravitational pull caused by their enormous size, explains Kipping. If the hypothesis According to some astronomers it is correct, moons could even have started life as planets, only to be pulled into the orbit of an even larger planet like Kepler 1625b or 1708b.


the two moons are located far from its host star, where there is less gravity to pull planets away from their moons. In fact, the researchers looked for cold gas giant planets in wide orbits, precisely because our solar system analogues, Jupiter and Saturn, have over a hundred moons between them.

If there are other moons out there, they are likely to be less monstrous, as the large ones are simply the easiest to detect at current sensitivity, the authors say.


If there are other moons out there, they are likely to be less monstrous, but also harder to detect, says Kipping: “The first detections in any study will usually be the rarest. The large ones are easier to detect with our limited sensitivity.”

Exomoons fascinate astronomers for the same reasons as exoplanets. They have the potential to reveal how and where the life in the universe, in addition to their scientific interest in themselves: how do they form, can they support life, what role, if any, do they play in making their host planets habitable?

Kepler Space Telescope data

In the current study, the researchers examined the sample of the coldest gas giant planets captured by the spacecraft. NASA’s Kepler to search for planets. After analyzing in depth 70 exoplanets, they found only one candidate, Kepler 1708b, with a signal similar to that of a possible moon. “It’s a difficult signal,” acknowledge Kipping and his team, who have investigated it in depth and it hasn’t disappeared.

Observations from other space telescopes, such as Hubble or Webb, will be needed to verify the discovery, a process that could take years. In fact, four years later, the first possible exomoon discovery is still hotly debated.

On a Article Recently, Kipping and his colleagues showed how a group of skeptics might have missed Kepler’s moon 1625b in their calculations. In the meantime, they continue to investigate other lines of evidence.

Just a fluctuation in the data?

Eric Agol, a professor of astronomy at the University of Washington, says he has doubts that the latter signal is real: “It could just be a fluctuation in the data, either due to the star or due to instrumental noise.”

However, others are more optimistic. “This is the best of science,” he says. Michael Hippke, an independent astronomer from Germany, “we find an intriguing object, make a prediction and confirm the exomoon candidate or rule it out with future observations.”

“I’m very excited to see a second exomoon candidate, but it’s a shame that only two transits were observed; It would be very interesting to have more data”, he adds.

transit method

Discovering a moon or even a planet hundreds or thousands of light years from Earth is not easy. Moons and planets can only be observed indirectly, since pass in front of your stars hosts, causing the starlight to dim intermittently. Catching one of these fleeting traffic signals with a telescope is tricky, as is interpreting the light curve data. the l’ssome are even harder detect because they are smaller and block less light.

But the search is worth it, emphasizes Kipping, noting how the existence of exoplanets was greeted with the same skepticism that exomoons are now: formed.

Source: columbia university


Rights: Creative Commons.