Astronomers are convinced that found the first known analogue of the Month outside of our Solar system, which orbits around the giant planet, over 8 thousand light-years from Earth. It is reportedly as big as Neptune and orbits a planet the size of Jupiter. The planet located outside our solar system is called exoplanet and its moon, that is, the satellite is called "exomoon".
Our hunt for exoplanets (planets further into the cosmos) has thrown up some truly odd and fascinating examples in recent years, with confirmed discoveries now numbering in the thousands.
Given the conditions of that planet and its potential moon are gas giants, it is impossible to think that this planet could support life.
The same is believed to have happened in the Pluto-Charon system - the largest of the five known natural satellites of the dwarf planet.
Teachey and co-author David Kipping, an assistant professor of astronomy at Columbia, published their findings in the journal Science Advances on October 3.
The team behind this intriguing discovery, researched more than 250 planets outside our solar system using the space telescope NASA Kepler. The new alien moon is roughly the size of Neptune, which has a diameter four times larger than Earth's and is 17 times as massive. The mass ratio between the exomoon and Kepler-1625b is similar to the ratio between the moon and Earth. They observed a dip in Kepler-1625's brightness when the planet and then the exomoon passed in front of it.
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It's an unlikely appointment, but one that when explored may make more sense that one might think. The tail is wagging the dog at the football club.
Fast forward a year and throw in a mix of data from the Hubble Space Telescope and older data from the Kepler Space Telescope and the results look a lot more promising. If real, Nept-moon would also be gaseous, and would appear twice as big as our moon in Kepler-1625b's sky. However, the researchers' alloted observation time ended before the planet could complete its transit. Exomoons, or moons outside of our solar system, are hard to spot due to their expected smaller size compared to planets.
In the Hubble data, they saw a moon tugging along, "trailing the planet like a dog following its owner on a leash". "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".
But Dr Kipping said: "Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it".
"Furthermore, the size we've calculated for this moon, about the size of Neptune, has hardly been anticipated, and so that, too, is reason to be careful here", Teachey said.
He said, "We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis". The problem is only large planets that orbit close to stars are detectable, and those types of planets typically don't have moons.
The James Webb Space Telescope (JWST), scheduled for launch in 2021, should make it possible for scientists to find even the smallest exomoons, Teachey said.
The researchers monitored the planet before and during its 19-hour-long transit across the face of the star. They chose to look at exoplanets with the widest orbits, or those that take about 30 days to circle their stars.