A team of astronomers from Columbia University (USA) has found consistent evidence – thanks to the instruments of the Hubble space telescope and old data from the Kepler telescope – of the first moon outside our solar system. It is 8,000 light years distant from Earth and nothing like this has ever been observed before.
This moon candidate is comparable in size to Neptune and orbits a planet slightly larger than Jupiter.
In the study by astronomers Alex Teachey and David Kipping in the journal Science Advances , they explain that the detection of an exomoon candidate, that is, moons orbiting planets in other star systems, is unusual due to its large size (remember that it is comparable to Neptune and Neptune is 49,244 km in diameter). These gigantic moons do not exist in our solar system, where almost 200 natural satellites have been cataloged.
“This would be the first case of detection of a moon outside our solar system,” Kipping said, “If confirmed by follow-up Hubble observations, the finding could provide vital clues about the development of planetary systems and could make experts review theories of how moons form around planets. “
The researchers analyzed data from 284 planets discovered by Kepler that were in comparatively wide orbits, with periods of more than 30 days, around their host star. The observations measured the transit to the stars, finding that Kepler 1625 had intriguing anomalies. “We saw small deviations and oscillations in the light curve that caught our attention,” says Kipping.
An exomoon the size of Neptune
With Hubble they had the opportunity to study the planet in depth, obtaining data four times more accurate than Kepler’s. The researchers monitored the planet before and during its 19-hour transit across the face of the star, detecting a second, much smaller decrease in the star’s brightness, which would be consistent with “a moon that follows the planet as a dog that follows its owner on a leash , “Kipping said. “Unfortunately, the scheduled Hubble observations ended before the full transit of the Moon could be measured.”
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 of additional planets around the star during its four-year mission.
“A companion moon is the simplest and most natural explanation for the second dip in the light curve and orbit deviation,” said lead author Teachey. “It was a shocking moment to see that curve of light; my heart started beating a little faster and I kept looking at that signature.”
The moon is estimated to be just 1.5% the mass of its companion planet, which in turn is estimated to be several times the mass of Jupiter. This value is close to the mass ratio between Earth and its moon, but Kepler 1625b and its satellite, however, are gaseous , not rocky.
The host planet and its moon lie within the habitable zone of the star Kepler 1625, where moderate temperatures allow liquid water to exist on any solid planetary surface. “However, both bodies are considered to be gaseous and therefore not suitable for life as we know it ,” Kipping explained.
Future searches will target Jupiter-sized planets that are farther from their star than Earth is from the Sun. There are only a handful of such planets in Kepler’s database. When the time comes for NASA’s James Webb Space Telescope “we will be able to see really small moons.”
Reference: A. Teachey el al., “Evidence for a large exomoon orbiting Kepler-1625b,” Science Advances (2018). DOI: 10.1126 / sciadv.aav1784, http://advances.sciencemag.org/content/4/10/eaav1784
