Kepler-1625b: First Exomoon Potentially Discovered Using Hubble and Kepler Telescopes

Scientists have found what could be the first confirmed exomoon—a moon orbiting a planet outside our own solar system—and it appears to be absolutely huge.

Using NASA's Hubble Space Telescope and Kepler Space Telescope, researchers discovered what appears to be a Neptune-sized object orbiting the planet Kepler-1625b. This is a Jupiter-sized planet located around 8,000 light-years from Earth. The study by Columbia University astronomers Alex Teachey and David Kipping is published in Science Advances.

During a survey of 300 Kepler exoplanets last year, Teachey and Kipping noticed a gas giant, Kepler-1625d, showing some peculiar characteristics. Kepler recorded three transits and results pointed to the presence of an object orbiting it. To better understand what was going on, they used Hubble to carry out follow-up observations.

They were looking for changes to the planet's brightness. This would indicate something was passing in front of it, blocking out some of the light. If this happens at regular intervals, it suggests something is orbiting the planet. They also watched for any gravitational effects—if the planet's transit is altered in any way, it suggests there is something there, tugging at the planet.

In a press conference about the discovery, Kipping said: "I've spent about a decade of my career working on the exomoon hunt, both in terms of developing the methodology and actually implementing the search. Last year in a large survey of nearly 300 Kepler exoplanets, we noticed that the gas giant Kepler-1625b displayed some peculiarities in the Kepler data, which led us to hypothesize the presence of a Neptune sized exomoon."

With the data from Kepler and Hubble, Kipping and Teachey found compelling evidence of an exomoon. There were dips in the planet's brightness and evidence of "transit timing variations"—anomalies that indicate something is exerting a gravitational pull on the planet. Kipping said the location, shape and depth of the observed event is consistent with a large moon orbiting Kepler-1625b, and models fit with this explanation. This, he said, led them to conclude an exomoon is the best explanation for the data in hand.

"This is not by itself a proof of an exomoon, though," he warned. "We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis. If validated, the planet moon system, a Jupiter with a Neptune sized moon, would be a remarkable system with unanticipated properties, in many ways echoing the unexpected discovery of hot Jupiters in the early days of planet hunting."

Teachey also said their findings are not conclusive proof of an exomoon. "I would point out that two of our model runs suggest that the Hubble observation ended before the exomoon's transit was completed," he said. "We are urging caution here. The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence."

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Artist’s impression of the exoplanet Kepler-1625b transiting the star with the candidate exomoon in tow. Dan Durda

The team hopes to observe the planet and possible moon again soon. This will allow them to refine their models and add more evidence for or against the hypothesis. They have put in a proposal to use Hubble again in May next year—in time for the next transit.

Justin Crepp, Associate Professor of Physics at the University of Notre Dame, who was not involved in the research, said the findings were "compelling" and that the findings are consistent with the presence of a transiting exomoon.

"Future space-based follow-up of Kepler-1625b is warranted to learn more about this first exomoon candidate," he told Newsweek. "If indeed the satellite is comparable in size to Neptune, it may challenge leading planet formation theories as the system appears to somewhat resemble a 'double planet.'

"We have so far learned that the population of exoplanets is very diverse—temperature, size, composition, orbital architecture, host star environment, etc. If confirmed through further reconnaissance observations, this discovery seems to indicate that exomoons may be just as diverse."

As of August 2018, Kepler has been used to discover 2,327 exoplanets—30 of which are less than twice the size of Earth and sitting within the habitable zone of their host star. NASA's James Webb Telescope, which is currently scheduled to launch in 2021, will provide scientists with a new tool to explore these planets—potentially allowing them to find biosignatures, which would indicate the presence of life.

Kepler-1625b: First Exomoon Potentially Discovered Using Hubble and Kepler Telescopes | Tech & Science