First known moon beyond the Solar System discovered by astronomers

Astronomers may have discovered the first exomoon

Using the Hubble Space Telescope and the Kepler Space Telescope, astronomers have found the first compelling evidence for a Neptune-sized moon orbiting a giant gas planet 8,000 light-years away.

The candidate moon, with the designation Kepler-1625b-i, is unusual because of its large size; it is comparable in diameter to the planet Neptune.

According to the recent study, the object orbiting Kepler-1625b might indeed be an exomoon as the giant planet passed before its host star one hour before the astronomers predicted. Kepler-1625b, a massive planet orbiting a not-too-distant star, seems to have a friend along for the ride, and scientists are racing to confirm their findings and declare it the very first alien moon on record.

"This would be the first case of detecting a moon outside our solar system", said David Kipping, Assistant Professor at the Columbia University in NY.

The discovery, detailed by researchers on Wednesday, was a surprise, and not because it showed that moons exist elsewhere - they felt it was only a matter of time for one to be found in another star system. They will use the Hubble Space Telescope for more observations in May 2019 to confirm their finding.

Teachey and Kipping believe the moon is approximately the size of Neptune, making it larger than any moon in our solar system.

Researchers note that if this is indeed a moon, both it and its host planet lie within their star's habitable zone, where moderate temperatures allow for the existence of liquid water on any solid planetary surface.

Hubble also revealed that the planet began its transit 1.25 hours earlier than expected-consistent with the planet and moon orbiting a common center of gravity that would cause the globe to wobble from its predicted location. First, after Kepler-1625b passes by Kepler-1625, the brightness of the star dims a second time by a smaller amount, which may mean that the exoplanet had an exomoon in tow. However, using the Hubble Space Telescope more recently, Teachey and his colleagues made more detailed observations, almost confirming the existence of the first exomoon ever discovered.

But Kepler 1625b and its moon are gaseous - not rocky - so such a collision may not lead to the condensation of a satellite. "Unfortunately, the scheduled Hubble observations ended before the complete transit of the moon could be measured". "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.

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

The possible moon was documented by Kepler, the powerhouse planet-hunting space telescope, when it cast a shadow by crossing in front of a star.

In theory, this could be the result of the gravitational pull from a hypothetical second planet.

They followed up with the Hubble Space Telescope.

"If this does pan out and turn into a true discovery, it would be really revolutionary, but I don't think we're quite there yet", says Megan Bedell, an astronomer at the Flatiron Institute in NY.

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