This moon candidate, which is 8,000 light-years from Earth in the Cygnus constellation, orbits a gas-giant planet that, in turn, orbits a star called Kepler-1625. We now know of thousands of planets that exist outside of our Solar System, but we also know from our own system that lots of planets have natural satellites. 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. Teachey, a third-year graduate student at Columbia University in NY, was first author of the research announcing the potential moon. Astronomers think numerous gas giants' moons are captured asteroids.
"It was a shocking moment to see that light curve, my heart started beating a little faster and I just kept looking at that signature", said lead author Teachey, NSF Graduate Fellow in astronomy at Columbia.
"If confirmed by follow-up 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", he added.
However, this moon is unusual because of its large size, which is more comparable to the diameter of 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. However, scientists know that Earth's moon is gradually moving away from our planet at a rate of about 1.5 inches (4 centimeters) per year.
Teachey and Kipping relied on the "transit" method, which is already used by researchers to discover almost 4,000 planets outside our solar system, called exoplanets.
An artist's impression of the exoplanet Kepler-1625b, transiting the star, with the newly discovered exomoon in tow is shown in this image released on October 2, 2018.
In addition to this second dip in the light curve, Hubble provided compelling supporting evidence for the moon hypothesis by detecting the planet's transit more than an hour earlier than predicted.
Kipping said "We saw little deviations and wobbles in the light curve that caught our attention". It clearly indicated a moon that was trailing behind the planet.
Kipping and Teachey combined the Kepler and Hubble data to build a model of the sun-planet-moon system.
Because their transit signals are weaker than those of planets and their positions change as they orbit their parent planets.
This is in fact a second method used to detect exoplanets, and help find planets that have a large mass (not necessarily size). 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. The problem is only large planets that orbit close to stars are detectable, and those types of planets typically don't have moons.
Even though they lie within their system's habitable zone, both the exoplanet and the exomoon are gaseous and thus unsuitable for life. "When we look for an Earth twin, I think one of the most obvious things you might ask is, 'Does it have a moon twin, ' because that seems to have a large influence", he notes".