First evidence of moon outside our solar system: Astronomers

Mindy Sparks
October 6, 2018

It will take more observation with the Hubble to confirm it.

The detection of the candidate exomoon - moons orbiting planets in other star systems - is unusual because of its large size, comparable to the diameter of Neptune. Meanwhile, they encourage other researchers and astronomers to join because the course offers to understand how rare our solar system.

Astronomers may have just found the very first moon outside of our solar system. This phenomenon astronomers call a "transit".

To find evidence for the existence of the exomoon, the team observed the planet while it was in transit in front of its parent star, causing a dimming of the starlight. Unlike some notable space discoveries, this find wasn't random; Mike Wall at reports that Columbia University astronomers David Kipping and Alex Teachey were doggedly hunting for exomoons-a truly challenging feat-when they found the beast.

The so-called exomoon, estimated to be the size of Neptune, was found in orbit around a huge gas planet 8,000 light-years from Earth.

"We saw little deviations and wobbles in the light curve that caught our attention", Kipping said.

NASA's upcoming James Webb Space Telescope could really "clean-up" in the satellite search, . This shift in the planet's predicted transit was also picked up by Hubble, adding more weight to the theory that an exomoon was behind the changes. First, Kepler 1625b begins its transit of the star over an hour early, an indicator that something with relatively strong gravity is tugging on it, alternating its center of gravity and affecting its orbit. They noticed that after Kepler-1625B crossed in front of its star there was another decrease in measurable brightness 3.5 hours late. And finding future moons will require looking at planets much further out from their stars, something that is hard now, but should possible once the powerful but long-delayed James Webb Space Telescope finally begins scanning the skies. This is further complicated by the fact that the moon signal will also be in a different location with respect to the host planet at each epoch, so the moon transits will not be strictly repeatable, and multiple moons around a single planet may wash out any observable signal anyway. Imagine then, the work that needs doing in order to find a moon orbiting a planet that is itself orbiting around an average-sized star in a far-off system thousands of light years away. While Kepler has not detected a second planet in the system, it could be that the planet is there, but not detectable using Kepler's techniques.

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

The study was published Wednesday in the peer-reviewed journal Science Advances.

The exomoon is exponentially larger than our solar system's biggest moon. They will use the Hubble Space Telescope for more observations in May 2019 to confirm their finding.

However, given that both the planet and its potential moon are gas giants, no one is suggesting conditions that might support life. They estimate it to be 1.5 percent the mass of its planet and the mass ratio between planet and moon to be close to that of the Earth-Moon system. After combing through it, they focussed on the exoplanet Kepler-1625b, about 4,000 light years away from earth.

The host planet and its moon lie within the solar mass star's (Kepler 1625) habitable zone, where moderate temperatures should allow for the existence of liquid water on any solid planetary surface. But, according to Kipping, neither gaseous object is suitable for life as we know it. That could have produced a rocky moon with a bloated atmosphere that looks like a Neptune-size object.

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