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Artist's view of the exoplanet Kepler-1625b, transiting through the star, followed by exomoon candidate. Credit: Dan Durda
Two astronomers from Columbia University using the Hubble Space Telescope and NASA's Kepler Space Telescope have gathered compelling evidence of the existence of a moon orbiting a giant planet. aerated 8,000 light years from Earth.
In an article published on October 3 in the journal Progress of scienceAlex Teachey and David Kipping report that the detection of an exomoon candidate, ie moons revolving around planets in other star systems, is unusual because of its large size, comparable to Neptune's diameter. . These gigantic moons do not exist in our own solar system, where nearly 200 natural satellites have been cataloged.
"This would be the first case of detecting a moon outside our solar system," said Kipping, assistant professor of astronomy at Columbia. "If confirmed by Hubble's subsequent observations, the findings could provide essential clues to the development of planetary systems and lead experts to revisit theories of moon formation around planets."
In searching for exomoons, the researchers analyzed data from 284 planets discovered by Kepler that were in relatively wide orbits, with periods greater than 30 days, around their host star. The observations measured the momentary gradation of starlight as a planet passed its star, called transit. The researchers found a case in Kepler 1625b that had intriguing anomalies.
Artist's impression of the exoplanet Kepler-1625b passing through the star with the exomoon candidate. Credit: Dan Durda
"We found small deviations and oscillations in the light curve that caught our attention," Kipping said.
Kepler's results were sufficient to allow the team to have 40 hours of time with Hubble to study the planet intensively, obtaining data four times more accurate than Kepler's. The researchers monitored the planet before and during its 19-hour transit through the star's face. At the end of the conference, Hubble detected a much smaller second decrease in starlight brightness 3.5 hours later, which corresponds to "a moon tracking the planet like a dog following its owner in leave, "said Kipping. "Unfortunately, Hubble's scheduled sightings ended before the full Moon transit could be measured."
In addition to this drop in light, Hubble has provided evidence to support the moon's hypothesis by measuring that the planet had begun its transit 1.25 hours earlier than expected. This is consistent with the planet and the moon orbiting a common center of gravity (barycenter) that would flicker the planet from its predicted location.
"An extraterrestrial civilization observing the Earth and the transit of the Moon by the Sun would note similar anomalies in the synchronization of the Earth's transit," Kipping said.
The researchers point out that this anomaly could in principle be caused by the gravitational pull of a hypothetical second planet system, although Kepler has found no evidence of the existence of additional planets around of the star during his four-year mission.
"A companion moon is the simplest and most natural explanation for the second trough of the light curve and the synchronization deviation between orbit," said lead author Teachey, a NSF graduate scholar. in astronomy at Columbia. "It was a shocking moment to see this light curve, my heart started beating a little faster and I kept looking at this signature, but we knew that our job was to keep a cool head to test all the imaginable possibilities by which the data could be misleading us until we were left without further explanation ".
It is estimated that the moon represents only 1.5% of the mass of the planet that accompanies it, itself estimated several times that of Jupiter. This value is close to the mass ratio between the Earth and its moon. But in the case of the Earth-Moon system and the Pluto-Charon system – the largest of the five known natural satellites of the dwarf planet Pluto – it is assumed that an early collision with a larger body would have projected materials that have then fused moon. However, Kepler 1625b and its satellite are gaseous and non-rocky. Therefore, such a collision can not lead to the condensation of a satellite.
Exomoons are hard to find because they are smaller than their planet and their transit signal is therefore weak. they also change position at each passage because the moon is orbiting the planet. In addition, the ideal candidate planets hosting moons are in large orbits, with long and infrequent transit times. In this research, the moon of Neptune's size would have been among the easiest to detect first because of its large size.
The host planet and its moon are located in the habitable zone of solar mass star (Kepler 1625), where moderate temperatures allow the presence of liquid water on any solid surface of the planet. "However, both bodies are considered gaseous and therefore unfit for life," Kipping said.
Future research will target planets the size of Jupiter farther from their star than the Earth would be from the Sun. There is just a handful in the Kepler database. The future NASA James Webb Space Telescope could really "clean up" satellite research, Kipping said. "We can expect to see very small moons."
Explore further:
First possible appearance of an exomoon
More information:
A. Teachey el al., "Evidence of a great exomoon in orbit around Kepler-1625b," Progress of science (2018). DOI: 10.1126 / sciadv.aav1784, http://advances.sciencemag.org/content/4/10/eaav1784
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