Hubble data hints at first ever moon outside our moon

Gwen Vasquez
October 7, 2018

The exomoon itself is believed to be around the size of Neptune, which is about four times bigger than earth. Previous observations from NASA's Kepler space telescope suggested that the Jupiter-sized planet, known as Kepler-1625b, had a world about the size of Neptune in orbit around it. The researchers' investigations showed that the HST-recorded transit of Kepler-1625b occurred almost 80 minutes earlier than expected, a pattern suggesting the presence of transit timing variations, or TTVs, which are among the first proposed methods to confirm the presence of exomoons.

Researchers from Columbia University think that they may have found what could be the first confirmed exomoon one day.

"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.

The gas giants in our own solar system have rocky and icy moons, but no examples of having gas-giant moons. It's comparable to so-called hot Jupiters, gas giant exoplanets that are closer to their stars than Jupiter is to its own, and warmer.

It orbits its parent star at a distance similar to the distance between the Sun and Earth, which puts it - and its candidate moon - at the inner edge of the habitable zone of the star system. They observed a dip in Kepler-1625's brightness when the planet and then the exomoon passed in front of it.

It's a moon outside our solar system, which we can't see directly, but when it passes in front of a star the light from that star dims - and that how it's detected.

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.

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In the meantime, a new release of Kepler data smoothed away many of those bumps, weakening the original case for a moon search.

The first hints that there may be an exomoon in the Kepler-1625 system came in a paper by the same authors in 2017.

The Kepler and Hubble observations, along with modeling work, suggest that the moon is about the size of Neptune and 1.5 percent as massive as Kepler-1625b. The researchers were awarded with 40 hours of observation time using Hubble, and the data they gathered were four times more precise than what Kepler had captured.

The exomoon, which is a satellite that orbits a planet outside our solar system, appears to be revolving around the Jupiter-sized gas giant Kepler-1625b. In the case of the Earth-Moon system, an early collision with a larger body is hypothesised to have blasted off material that later coalesced into a moon. But because it's so big, the object would be about twice as big in Kepler-1625b's skies as Earth's moon is in ours, Teachey and Kipping said.

And in one instance, they found "deviations and wobbles" in the light curve representing a planet known as Kepler-1625b. After the transit ended, Hubble detected a second and much smaller decrease in the star's brightness approximately 3.5 hours later, consistent with the effect of a moon trailing the planet. This could explain why the moon is 3 million kilometers from its planet; they were probably closer in the past.

Based on the moon's distance from its star, its surface temperature was estimated to be 80C, which is considered just on the upper end of conditions that could support life. However, given that the existence of such a large, oddball moon had not even been predicted until now, astronomers will struggle to explain how it got there.

In our solar system, moons like Europa and Enceladus are thought to be some of the most likely places to find life outside of Earth in our cosmic neighborhood. The astronomers are uncertain how this potential moon might have formed, given its size. The research team hopes to take another look at the star next May, if there is time available on the Hubble. That would confirm that the find is an exomoon. "If they see what we see, I expect some people will be convinced and other people will be skeptical".

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