First moon outside our solar system discovered, astronomers think

Gwen Vasquez
October 7, 2018

Still, he and colleague Alex Teachey say in the journal Science Advances that they have good evidence that a Neptune-size moon is orbiting a Jupiter-like planet, in a solar system about 8,000 light-years away.

Similar to the mass-ratio between our Earth and its satellite, this moon is estimated to be 1.5 percent the mass of its companion gas-giant planet, which is likely several times the mass of Jupiter.

Over the last years, astronomers kept hunting bodies that orbit distant planets and planets from the star-soaked fabric of the cosmos, using multiple techniques to find them and confirm their existence.

To date more than 3,000 exoplanets - worlds orbiting stars other than the Sun - but no "exomoons".

David Kipling, assistant professor of astronomy at Columbia University, said that this is such a case when such a moon was detected out of our solar system. Estimated to have a mass several times of Jupiter, the planet is nearly certainly gaseous and not likely to support life as we know it. This makes it the largest known satellite, which is even larger than any known in our Solar system.

To find evidence for the exomoon - dubbed Kepler-1625b-i - the team observed the planet while it was in transit in front of its parent star, causing a dimming of the starlight.

The team behind this intriguing discovery, researched more than 250 planets outside our solar system using the space telescope NASA Kepler.

"We saw little deviations and wobbles in the light curve that caught our attention", Dr. Another compelling evidence in favour of their apparent discovery was that the planet passed in front of its star one hour earlier than they had predicted. Exomoons, or moons outside of our solar system, are hard to spot due to their expected smaller size compared to planets.

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Unfortunately, the scientists' time on Hubble ended before they could completely observe the second transit. "The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence", said Teachey.

An artist's impression of the exoplanet Kepler-1625b, transiting the star, with the newly discovered exomoon in tow is shown in this image released on October 2, 2018. The moon that revolves around it, comparable in size to Neptune.

It's possible that rather than being caused by a moon this delay might be the result of another planet in the Kepler-1625 system.

The transit timing variation seen in the Kepler-1625b data could similarly be due to the presence of an unseen outer planet, perturbing the orbit of the gas giant. "But we knew our job was to keep a level head and essentially assume it was bogus, testing every conceivable way in which the data could be tricking us". If real, Nept-moon would also be gaseous, and would appear twice as big as our moon in Kepler-1625b's sky.

But Dr Kipping said: "Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it". This could explain why the moon is 3 million kilometers from its planet; they were probably closer in the past.

NASA's upcoming James Webb Space Telescope could really "clean-up" in the satellite search, .

GREENFIELDBOYCE: The researchers have requested more time on Hubble to do more observations next May.

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