Published: Sun, October 07, 2018
Science | By Celia Watts

Scientists think they've found the first Moon outside our solar system

Scientists think they've found the first Moon outside our solar system

Astronomers may have found the first compelling evidence of a moon outside of our Solar System - orbiting a very big planet, over 8,000 light years away from Earth.

It had all the right numbers: It was several times bigger than Jupiter, orbited a host star that is similar in mass to the sun, and is located at the same distance as the earth from sun.

The hunt for exoplanets - planets outside our own Solar System - provided its first results only 30 years ago.

Now, Columbia University astronomers Alex Teachey and David Kipping have used the incomparable capabilities of Hubble to study the planet and its host star, Kepler 1625. The planet Endor itself is a gas giant, but the Forest Moon is a habitable world, peopled by small furry sentient creatures. Kepler 1625b began its star-crossing passage 77.8 minutes early, according to Dr Kipping, 3.5 hours after the planet's transit ended, the Hubble telescope recorded some gravitationally dragging as the second smaller dimming of the star's brightness happened again which the team ascribed to the gravitational nudging of a large satellite. Another is capture, when objects are captured and pulled into orbit around a large planet - like Neptune's moon Triton, which is believed to be a captured Kuiper Belt object. They noticed that after Kepler-1625B crossed in front of its star there was another decrease in measurable brightness 3.5 hours late. This occurs when the exoplanet passes in front of the star, and the method is therefore called the "transit method".

"We saw little deviations and wobbles in the light curve that caught our attention", Kipping stated. The team held a 40-hour surveillance on the Hubble Space telescope for further study. This is consistent with a model of the system in which the planet and its moon orbit a common centre of gravity, causing the planet to wobble away from its predicted location [4]. Not because it showed that moons exist outside the solar system, but also because they felt it was only a matter of time for professionals to find another solar system. It was like "a moon trailing the planet like a dog following its owner on a leash", Kipping said. It will take more observation with the Hubble to confirm it. The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence.

That planet, called Kepler-1625b, is one of thousands that scientists have recently detected around distant stars.

The Columbia astronomers said they may be able to clinch this as early as next year, with more Hubble viewing.

In a paper published in the journal Science Advances, the scientists report the candidate moon is unusually large - potentially comparable to Neptune.

Scientists have never had enough evidence to confirm that any exoplanet has a moon orbiting it, but that might be about to change. "But we knew our job was to keep a level head testing every conceivable way in which the data could be tricking us until we were left with no other explanation".

But Kepler 1625b and its moon are gaseous - not rocky - so such a collision may not lead to the condensation of a satellite. These observations have to be done from space; the rotation of Earth means that ground-based telescopes spin away from their targets before they can capture a whole event. Beyond about 4,000 planets, and satellites - no: too hard to find them at such great distances.

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