First moon outside our solar system may have been found
Astronomers may have discovered the first known moon outside our solar system, orbiting a gas-giant planet 8,000 light years away. According to the finding published in the journal Science Advances, the candidate exomoon is unusual because of its large size, comparable to the diameter of Neptune. Such gargantuan moons don't exist in our solar system, said researchers from the Columbia University in the US.
"If confirmed by follow-up Hubble (telescope) 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," said David Kipping, an assistant professor of astronomy at Columbia University.
In looking for exomoons, the researchers analyzed data from 284 Kepler-discovered planets that were in comparatively wide orbits, with periods greater than 30 days, around their host star. The observations measured the momentary dimming of starlight as a planet passed in front of its star, called a transit. The researchers found one instance, in Kepler 1625b, that had intriguing anomalies.
"We saw little deviations and wobbles in the light curve that caught our attention," Kipping said. The Kepler results were enough for the team to get 40hrs of time with Hubble Telescope to intensively study the planet, obtaining data four times more precise than that of Kepler. The researchers monitored the planet before and during its 19-hour-long transit across the face of the star.
After it ended, Hubble detected a second and smaller decrease in the star's brightness 3.5hrs later, consistent with "moon trailing the planet like a dog following its owner on a leash," Kipping said, adding, "Unfortunately, it ended before the moon's complete transit could be measured."
Hubble provided supporting evidence for the moon hypothesis by measuring that the planet began its transit 1.25hrs earlier than predicted. It's consistent with the planet and moon orbiting a common center of gravity that would cause the planet to wobble from its predicted location. "An extraterrestrial civilization watching the Earth and Moon transit the Sun would note similar anomalies in Earth's transit," Kipping said.