Scientists think they found the first moon outside our solar system

In the flickering light of a distant sun, scientists may have discovered the first moon outside our solar system.

In the journal Science Advances, two astronomers from Columbia University using Kepler's and Hubble's space telescopes said they discovered signs of an exomoon gas spinning around an exoplanet even more large around a star at 8000 light-years away.

This is an "extraordinary" discovery that "challenges the easy explanation," said co-author Alex Teachey – nothing like it exists in our own solar system. He and his colleague David Kipping make sure to qualify their discovery as a "moon candidate," noting that new studies are needed to confirm its existence.

But planetary scientist Kip Hodges, Associate Editor of Science Advances who did not participate in the study, described the discovery of Columbia astronomers as "convincing".

"If this finding withstands further scrutiny, it represents a major step in the field of astronomy," said Hodges.

Kepler, the powerful planet-hunter space telescope, has documented the possible moon by casting a shadow while crossing a star. Kipping and Teachey have discovered among 300 exoplanets from Kepler's catalog, all producing predictable lows in starlight that occur when a body in orbit passes in front of its sun, a phenomenon called "transit."

One star, Kepler 1625, looked promising. An aging star resembling a sun in the constellation Cygnus hosts an immense giant gas planet the size of Jupiter, known as Kepler 1625b. Yet, there were strange signatures in the flicker of this system of distant stars.

Kipping and Teachey therefore requested 40 hours of observation with the Hubble Space Telescope, four times more accurate than Kepler. These observations must be made from the space. Earth's rotation means that ground-based telescopes are turning away from their targets before they can capture a complete event.

The starlight seemed to fade more than an hour before its planet, similar to that of Jupiter, transited. And it remained dark for a moment after the passage of the planet. They determined that this was not the result of any activity on the surface of the star and that there was no evidence that another planet was firing. on Kepler 1625b and disturbed it with its orbit.

Instead, it appears that Kepler 1625b was orbited by a second body the size of Neptune – about four times the diameter of the Earth.

"A moon is an excellent explanation of the available data," said Kipping. "We can not find any other hypothesis that can explain all the data we have."

Yet astronomers have been surprised by their discovery. A body the size of Jupiter with a moon the size of Neptune is different from anything scientists have seen before. Kipping and Teachey did not even know how such a moon could have formed.

It was perhaps a lost planet captured by the largest body. Or maybe, like the moon of the Earth, it's actually a product of its planet, formed during a catastrophic collision. Or maybe its original story resembles that of Jupiter's moons, which would have merged from a ring of gas and dust that surrounded the planet.

"This raises new questions about the dynamic processes that will create planets and moons," said Teachey.

Neither Kepler 1625b, nor its moon, are likely to be habitable, scientists said, since they are mainly composed of gas. If you could stand on the surface of the planet, the moon would appear twice as big as ours and would periodically block the sun.

It is difficult to say how such worlds could be common. Teachey noted that astronomy aims to find bigger things – they are easier to spot. The first exoplanet discovered around a sun-like star, 51 Pegasi b, was a monstrous "hot Jupiter" that circled its sun every four days. It makes sense, said Teachey, that the first task of the scientists of the moon is also a giant.

Similarly, Teachey is not discouraged by the fact that only one of the nearly 300 studied planets seems to host a moon. Kepler is best able to find planets that revolve around their stars. Analyzes of orbital dynamics – not to mention the evidence of our own solar system – suggest that moons will be more common later.

"If we want to hunt the moon in the future, we will have to look at the planets further" than an astronomical unit, or the distance between the sun and the Earth, said Teachey. "We are learning new things to better make these observations."

That's what makes this job so fun, he continued – even though the existence of this moon is not confirmed.

"If we had understood everything, then we would not have much to do, we still have a lot of problems we need to work on."

© The Washington Post 2018

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