Scientists Think They’ve Found the First Moon Outside Our Solar System

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Astronomers have possibly discovered the first known moon outside our Solar System, using NASA’s Hubble and Kepler space telescopes. Compelling evidence have been found on the existence of the moon, orbiting a gas-giant planet, 8,000 light-years away from Earth.

According to the findings published in the journal ‘Science Advances’, the exomoon is unusual because of its large size, comparable to the diameter of Neptune.

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. Kipping and Teachey discovered it among 300 exoplanets in Kepler’s catalogue, all producing predictable dips in starlight that occur as an orbiting body passes in front of its sun – a phenomenon called a “transit.” Just one star, Kepler 1625, looked promising. An ageing sun-like star in the constellation Cygnus is known to host a huge, gas giant planet the size of Jupiter, known as Kepler 1625b.

Such gargantuan moons do not exist in our own solar system, where nearly 200 natural satellites have been catalogued, said researchers from the Columbia University in the US. Researchers caution that the moon hypothesis is tentative and must be confirmed by follow-up Hubble observations, according to NASA’s website. This would be the first case of detecting a moon outside our solar system.

Kipping and Teachey asked for 40 hours of observing time with the Hubble Space Telescope, which is four times as precise as Kepler. These observations have to be done from space; the rotation of Earth means that ground-based telescopes spin away from their targets before they can capture a whole event. The star’s light appeared to fade more than an hour before its Jupiter-like planet transited. A moon is an excellent explanation to the data at hand.

An extraterrestrial civilization watching the Earth and Moon transit the Sun would note similar anomalies in the timing of Earth’s transit. The researchers note that in principle, this anomaly could be caused by the gravitational pull of a hypothetical second planet in the system, although Kepler found no evidence for additional planets around the star during its four-year mission.

The moon is estimated to be only 1.5% the mass of its companion planet, which itself estimated to be several times the mass of Jupiter. This value is close to the mass-ratio between the Earth and its moon.