Friday, 15 February, 2019

Thanks to help from Hubble, the first confirmed exomoon?

An illustration of the exoplanet Kepler 1625b with its large hypothesized moon An illustration of the exoplanet Kepler 1625b with its large hypothesized moon
Theresa Hayes | 06 October, 2018, 03:36

Whether confirmed or not, the subject offers insight into how rare - or how common - our own solar system might be.

A pair of Columbia University astronomers using NASA's Hubble Space Telescope and Kepler Space Telescope have assembled compelling evidence for the existence of a moon orbiting a gas-giant planet 8,000 light-years away.

The candidate moon, with the designation Kepler-1625b-i, is unusual because of its large size - comparable to the huge, icy planet Neptune in our solar system. In panel 1, the light curve begins to dip as the planet begins transiting in front of the star.

"If confirmed by follow-up observations, the finding could provide vital clues about the development of planetary systems and may cause experts to revisit theories of how moons form around planets", he added.

Kipping has spent the past decade or so working to do just that. But the results of those Hubble observations, published today in Science Advances, bring the putative moon back in play; the team finds two new lines of evidence for a moon. "We didn't think we had enough to claim a discovery", says Kipping.

However, before getting too excited about the prospect of finding Ewoks, it should be noted that the exomoon (formally named as Kepler-1625b-i) has a radius of around four times that of the Earth and a mass of around 16 times that of our planet, so is in fact similar in size and mass to the planet Neptune.

Finding moons outside of our solar system is tricky compared to finding exoplanets. The planet Endor itself is a gas giant, but the Forest Moon is a habitable world, peopled by small furry sentient creatures. And previous year, they announced that they might have found one. "To be honest, we never really anxious too much about habitability, just because they're both gas giants". They found two signs suggesting an exomoon could be in tow. Kepler-1625b is the only planet found so far around this star.

The first hints that there may be an exomoon in the Kepler-1625 system came in a paper by the same authors in 2017.

"A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation", Kipping explained.

After watching the planet, the researchers noticed that shortly after it passed in front of its star, there was a second dip of light, indicating that there was "a moon trailing the planet like a dog following its owner on a leash".

"A moon is an excellent explanation to the data at hand", Kipping said. Researchers aren't positive at this time that they've found an exomoon - the Hubble observations were scheduled for a set amount of time, which ended before the second transit was complete. This is consistent with the planet and moon orbiting a common center of gravity (barycenter) that would cause the planet to wobble from its predicted location.

Kipping said that's how the Earth and moon would appear from far away.

The researchers identified 121 giant planets that have orbits within the habitable zones of their stars. "It was a shocking moment to see that light curve".

"We're looking forward to the scrutiny of the scientific community on this work and we hope we'll have an opportunity to observe the target again before too long", Teachey said.

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

Our Moon may have formed as the result of a collision with Earth, but a collision with a gas planet like Kepler-1625b might not result in enough material to form a Neptune-sized moon.

Based on the moon's distance from its star, its surface temperature was estimated to be 80C, which is considered just on the upper end of conditions that could support life.