Astronomers find signs of "exomoon" in distant solar system

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Astronomers have discovered the first moon outside our solar system with the help of Hubble and Kepler space telescopes, orbiting a giant gaseous planet, 8,000 light years away. "And if validated, the planet-moon system-a Jupiter with a Neptune-sized moon-would be a remarkable system with unanticipated properties, in many ways echoing the unexpected discovery of hot Jupiters in the early days of planet hunting". While astronomers now find these planets on a regular basis, the search for moons orbiting exoplanets wasn't successful - until today.

Since researchers first began detecting exoplanets, or worlds orbiting stars other than our Sun, in the early 1990s, we've gone on to catalogue nearly 3,800 alien planets, with thousands more sightings waiting for confirmation.

Researchers Alex Teachey and David Kipping evaluated 284 planets outside our solar system that had already been discovered by Nasa's Kepler Space Telescope. The exoplanet is a gas giant, several times more massive than Jupiter.

In the Solar system known eight major planets and their satellites about 200.

"If confirmed by follow-up Hubble 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". The object has a mass about 1.5% that of the planet - a similar mass-ratio as the Earth and moon. They noticed that after Kepler-1625B crossed in front of its star there was another decrease in measurable brightness 3.5 hours late. 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.

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. However, the researchers' alloted observation time ended before the planet could complete its transit.

An artist's conception of a star with the planet Kepler-1625b and exomoon in the foreground. "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". Beyond about 4,000 planets, and satellites - no: too hard to find them at such great distances. However, both bodies are considered to be gaseous and, therefore, unsuitable for life as we know it.

He said, "We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis".

The potential moon would be considerably larger than Earth - about the size of Neptune or Uranus. The transit blocked some of the light coming in from the star and this dip in brightness was registered as the Kepler-1625b. As detailed in the researchers' publication, the Hubble telescope picked up a smaller dimming about 3.5 hours after the first one, suggesting a second body following the first one.

In principle this anomaly could also be caused by the gravitational pull of a hypothetical second planet in the system, but the Kepler Space Telescope found no evidence for additional planets around the star during its four year mission.

"We can expect to see really tiny moons with Webb", Teachey said.

Various attempts have been made previously to confirm or deny that there is a moon outside our solar system.

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