Published: Sat, October 06, 2018
Sci-tech | By Carrie Guzman

Kepler 1625b Has Neptune-Sized Moon, Astronomers Say | Astronomy

Kepler 1625b Has Neptune-Sized Moon, Astronomers Say | Astronomy

Astronomers have pinpointed what appears to be the first moon detected outside our solar system, a large gaseous world the size of Neptune that is unlike any other known moon and orbits a gas planet much more massive than Jupiter. Researchers caution that the moon hypothesis is tentative and must be confirmed by follow-up Hubble observations. "It tells a lot about how unique or how common, in fact, that our solar system is-that the setup of having planets with moons may be something quite common", says Andrew Fazekas, an astronomy columnist with National Geographic. Such an event is called a transit, and has been used to detect numerous exoplanets cataloged to date.

Compelling evidence have been found on the existence of the moon, orbiting a gas-giant planet, 8,000 light-years away from Earth.

In a new paper published in Science Advances, Alex Teachey and David Kipping of Columbia University present their case for the first "exomoon", and it's some pretty wild stuff.

The astronomers found one instance, in Kepler 1625b, that had intriguing anomalies.

Researchers have been studying Kepler-1625b as part of their hunt for exomoons and, out of a pool of 284 exoplanets, Kipping and Teachey found that Kepler-1625b was the best candidate.

So last October, the pair directed the Hubble Space Telescope at the star in an attempt to verify - or rule out - the possibility of a moon orbiting the planet Kepler-1625b. But Kepler didn't find any other planets around this star. They noticed that after Kepler-1625B crossed in front of its star there was another decrease in measurable brightness 3.5 hours late.

In the Hubble data, they saw a moon tugging along, "trailing the planet like a dog following its owner on a leash". It's though this occurred as a moon passed across the face of the star blocking its light.

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This is consistent with the planet and moon orbiting a common centre of gravity (barycentre) that would cause the planet to wobble from its predicted location. The second was a delay in the planet passing in front of its star. "It was definitely a shocking moment to see that light curve-my heart started beating a little faster, and I just kept looking at that signature", Kipping said.

The potential moon would be considerably larger than Earth - about the size of Neptune or Uranus.

Such gargantuan moons do not exist in our own solar system, where almost 200 natural satellites have been catalogued, said researchers from the Columbia University in the US.

The moon is estimated to be only 1.5 percent the mass of its companion planet - which itself is estimated to be several times bigger than Jupiter. However, scientists know that Earth's moon is gradually moving away from our planet at a rate of about 1.5 inches (4 centimeters) per year. Such gargantuan moons are unknown in our own Solar System.

Astronomers call the moon Kepler-1625b-i.

"To be honest, we never really anxious much about habitability, just because they're both gas giants, so it really wasn't something we spent any effort or time worrying about", Kipping said during Monday's teleconference.

In the Kepler exoplanet catalog, there are only a few Jupiter-size planets that are farther from their star than Earth is from the sun - good candidates for moons due to the distance. It is therefore unlikely to have a solid surface and is most likely a largely gaseous body, like the planet which it orbits every 22 days. Two Columbia University researchers presented their tantalising evidence for a moon Wednesday. They're hoping to complete a second Hubble observation next year to either prove or disprove Kepler-1625b-i's existence.

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