First alien moon discovered is gaseous

Katie Ramirez
October 6, 2018

Kipping and Teachey looked for two signals suggestive of an exomoon in the data from several transits. The Kepler outcomes were sufficient enough for the group to achieve 40 hours of time with Hubble to vehemently study the planet acquiring the data four times more accurate than that of Kepler.

In a paper published Wednesday in Science Advances magazine, researchers at Columbia University outline evidence supporting the existence of a moon orbiting the exoplanet Kepler-1625b, using data from the USA space agency NASA's Hubble Space Telescope.

GREENFIELDBOYCE: She says if this moon can't be confirmed, new telescopes mean that before too long, scientists should be in a better position to find real moons if they're out there. This apparent super-size pairing of a gaseous moon and planet is 8,000 light-years away. The planet goes around the yellow parent star every 287 days at the same distance as the Earth orbits the sun.

There are other possible explanations, but "a companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation", Kipping said in a statement. "It was definitely a shocking moment to see that light curve - my heart started beating a little faster and I just kept looking at that signature", David Kipping described his feelings.

"If confirmed by follow-up Hubble observations", said Kipping, "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".

However, before getting too excited about the prospect of finding Ewoks, it should be noted that the exomoon (formally named as Kepler-1625b-i) has a radius of around four times that of the Earth and a mass of around 16 times that of our planet, so is in fact similar in size and mass to the planet Neptune.

In addition to this dip in light, Hubble provided supporting evidence for the moon hypothesis by measuring that the planet began its transit 1.25 hours earlier than predicted. But until they have more data, this is only speculation, Kipping said.

The new study was published online today (Oct. 3) in the journal Science Advances. Though Kepler-1625b's host star is sunlike, it's thought to be about 10 billion years old - more than twice as old as Earth's star. Or perhaps, like Earth's moon, it is a product of its planet, formed in some catastrophic collision.

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He added: "We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis". The star was probably cooler in the past, so this heat could be a reason for the size of the moon, inflating the gas giant as the temperature rises.

But the research group also says there is still a possibility that they found a planet, not a satellite, so they say they will continue monitoring to confirm their findings.

It's an "extraordinary" find that "defies easy explanation" said co-author Alex Teachey - nothing like it exists in our own solar system.

Hubble's data, along with fine-tuned data from Kepler, strengthened the case for claiming Kepler-1625b had an exomoon.

Our solar system's moons all are rocky or icy objects.

The exomoon is exponentially larger than our solar system's biggest moon. A Jupiter-sized body with a Neptune-sized moon is unlike anything scientists have seen before. The exomoon's mass is about 1.5 per cent that of its planet.

Finding exoplanets is a hard task, let alone exomoons. NASA's upcoming James Webb Space Telescope could really "clean-up" in the satellite search, Kipping said. "It's sort of raising new questions and just having a moon of this size, has so far not really been anticipated much in the literature", Teachey said.

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