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First moon outside our solar system discovered, astronomers think

07 October 2018
First moon outside our solar system discovered, astronomers think

With a lot of help from the Hubble Space Telescope, astronomers now feel confident enough to publish their evidence for the first moon detected in orbit around a planet beyond our solar system.

Kipping and Teachey noticed odd anomalies in the transit data of a gas planet, Kepler 1625b, which is several times the size of Jupiter.

But a group of researchers have suggested there may be an exomoon orbiting a planet discovered by the Kepler mission, and the researchers' data was compelling enough to get them time on the Hubble Space Telescope.

This 19-hour event, known as a transit, blocked out some of the light coming from the star, which lies at a distance of 8,000 light-years from Earth.

After looking through recent data from NASA's Kepler space telescope, Alex Teachey, a graduate researcher in the department of astronomy at Columbia University, and David M. Kipping, an assistant professor in the same department, spotted evidence that an exomoon might orbit the Jupiter-sized exoplanet Kepler-1625b. They were on the lookout for a second temporary dimming of starlight.

Hubble watched the star as the planet passed in front of it, blocking some of its light. Such a scenario is unlike anything that's seen in our own solar system, of course, and it doesn't fit any of the standard theories for moon formation.

Faced with that skepticism, Teachey and Kipping are undoubtedly applying for more Hubble time during its next transit. That's why the astronomers need another look with Hubble, hopefully next spring. The first exomoon is obviously an extraordinary claim, and it requires extraordinary evidence. "Furthermore, the size we've calculated for this moon, about the size of Neptune, has hardly been anticipated and so that, too, is reason to be careful here".

But, he added: "We are excited about this result, certainly it is a tantalising result". In addition, the ideal candidate planets hosting moons are in large orbits, with long and infrequent transit times. Kipping and Teachey weren't even sure how such a moon might have formed.

This NASA photo taken on July 20, 1969 shows astronaut Edwin E. "Buzz" Aldrin, Jr. saluting the U.S. flag on the surface of the Moon during the Apollo 11 lunar mission.

To date, astronomers have discovered more than 3,500 exoplanets - worlds orbiting stars other than the Sun. But because it's so big, the object would be about twice as big in Kepler-1625b's skies as Earth's moon is in ours, Teachey and Kipping said.

The researchers identified 121 giant planets that have orbits within the habitable zones of their stars.

Another planet could cause the same gravitational nudge, the researchers noted, although Kepler observations have come up empty in that regard. They found two signs suggesting an exomoon could be in tow.

Some other object is therefore pulling on Kepler-1625b, with Teachey and Kipping reasoning that it must be a moon. He has led the field over this time, so I am delighted that his persistence has paid off.

"We are unable to find any other single hypothesis that explains all the data that we have", astronomer David Kipping told reporters during a phone call earlier this week. That makes it plausible that the new exomoon is just as off-the-menu as the "hot Jupiters" that surprised early exoplanet hunters, says Stephen Kane, an astrophysicist at the University of California, Riverside, who was not part of the research team.

A moon "is an excellent explanation" for these observations, he said. But now, "we do obviously think that the moon is the best explanation", he said, adding that "just like any other good skeptical scientist, we're saying "maybe".

Moons are kind of the next frontier when it comes to understanding alien solar systems, says Bedell: "They capture our imagination".

In our solar system, moons like Europa and Enceladus are thought to be some of the most likely places to find life outside of Earth in our cosmic neighborhood. If a gas giant exomoon is confirmed by follow-on observations, it may provide new insights into how planets and moons form and evolve across the galaxy.