NASA finds signs of "exomoon" in distant solar system

Astronomers may have discovered the first “exomoon” – a moon outside our own solar system

Astronomers may have discovered the first “exomoon” – a moon outside our own solar system

The gas giants in our own solar system have rocky and icy moons, but no examples of having gas-giant moons.

"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.

Transiting planets are worlds that can be detected by a drop in light as they pass in front of their home stars. Now, two scientists from Columbia University in New York (USA) have used the incomparable capabilities of the NASA/ESA Hubble Space Telescope to study the star Kepler-1625, 8000 light-years away, and its planet in more detail. Kepler-1625b is the only planet found so far around this star.

"It's big and weird by solar system standards", Columbia University astronomy professor David Kipping said of the moon, known as an exomoon because it is outside our solar system.

Instead, it looked as if Kepler 1625b was orbited by a second body the size of Neptune - roughly four times the diameter of Earth.

"We've tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system or stellar activity, but we're unable to find any other single hypothesis which can explain all of the data we have", co-author David Kipping, an astronomer at Columbia University in NY, told reporters earlier this week.

This illustration provided by Dan Durda shows the exoplanet Kepler-1625b with a hypothesized moon. The gas giant it presumably orbits has several times the mass of Jupiter. "When we look for an Earth twin, I think one of the most obvious things you might ask is, 'Does it have a moon twin, ' because that seems to have a large influence", he notes.

At first, the researchers saw the dip in light caused by the planet passing across the face of the star, but not long afterward, they saw a second, smaller dip, likely caused by the moon transiting across the star.

Kipping and his colleague Alex Teachey made the discovery after analyzing data from almost 300 distant planets discovered using the Kepler space telescope.

"It was definitely a shocking moment to see that Hubble light curve, my heart started beating a little faster as I kept looking at that signature". Researchers aren't positive at this time that they've found an exomoon - the Hubble observations were scheduled for a set amount of time, which ended before the second transit was complete.

The Kepler results were enough for the team to get 40 hours of time with Hubble to intensively study the planet, obtaining data four times more precise than that of Kepler. The planet appeared to make its transit earlier than expected, suggesting that the gravity of something was tugging on it.

And in one instance, they found "deviations and wobbles" in the light curve representing a planet known as Kepler-1625b.

This still doesn't prove the existence of an exomoon around Kepler-1625b.

"It is an exciting reminder of how little we really know about distant planetary systems and the great spirit of discovery exoplanetary science embodies", study co-author Alex Teachey said of the discovery in a statement. Tidal forces between the two objects would rob momentum from the less massive companion and eventually pull it into a permanent orbit. Another is capture, when objects are captured and pulled into orbit around a large planet - like Neptune's moon Triton, which is believed to be a captured Kuiper Belt object. "It's exciting to see the hunt for the first exomoon continue, and with what would be a shockingly large moon", wrote Sara Seager, an astrophysicist at the Massachusetts Institute Technology in Cambridge who was not involved with the work, in an email. This could explain why the moon is 3 million kilometers from its planet; they were probably closer in the past. The planet Endor itself is a gas giant, but the Forest Moon is a habitable world, peopled by small furry sentient creatures. This is because any model of a moon must account for every transit event that has been observed (here, that included transits already observed by Kepler).

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