An artist’s illustration of the exoplanet Kepler-1625b with its large hypothesized moon. The pair have a similar mass and radius ratio to the Earth-moon system, but scaled up by a factor of 11.

Scientists may have bagged the first-ever exomoon.

NASA's Kepler and Hubble space telescopes have spotted evidence of a Neptune-size satellite orbiting the Jupiter-like planet Kepler-1625b, which lies about 8,000 light-years from Earth, a new study reports.

"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 New York, told reporters earlier this week. [The Hubble Space Telescope: A 25th Anniversary Photo Celebration]

Still, he and lead author Alex Teachey, also a Columbia astronomer, stressed that the observations don't constitute a definitive detection.

"We hope to re-observe the star again in the future to verify or reject the exomoon hypothesis," Kipping said. "And 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."

Hunting for exomoons

The new results come from a concerted exomoon hunt Teachey and Kipping conducted using data from Kepler, which has discovered about 70 percent of the 3,800 known exoplanets to date. Kepler finds worlds via the "transit method," noting the tiny dips in star brightness caused by orbiting planets crossing their stars' faces.

Previous research has suggested that big (and therefore detectable) exomoons are rare around large planets that orbit very close to their parent stars. Such satellites would likely be lost during the chaos-inducing inward migration undertaken by these giants after their formation, the thinking goes.

Teachey and Kipping therefore studied Kepler observations of 284 planets with relatively wide orbits — worlds that take at least 30 Earth days to complete one lap. And they noticed weird deviations in the "light curve" generated by the 19-hour-long transit of Kepler-1625b, a planet about three times heftier than Jupiter that orbits a star about as massive as our own sun. (In 2017, the researchers reluctantly announced the discovery of these oddities in the three transits Kepler observed, after word of them leaked out on Twitter.)

One frame from an animation showing corrected images of Kepler-1625 collected by the Hubble Space Telescope’s WFC3 instrument. The star is located in the center and is spread out horizontally due to the instrument’s grism, giving color information about the source. (Image credit: Alex Teachey & David Kipping)

So the duo applied to study the planet with Hubble, and were awarded 40 hours of observation time with the iconic telescope. They succeeded in observing another transit in late October 2017 — and saw two "substantial anomalies," according to Kipping.

"The first is that the planet appears to transit one and a quarter hours too early; that’s indicative of something gravitationally tugging on the planet," he said. "The second anomaly is an additional decrease in the star’s brightness after the planetary transit has completed."

A moon orbiting Kepler-1625b is the best explanation, Teachey and Kipping said. There's no indication of another planet in the system that could be tugging on Kepler-1625b, and the secondary dimming is consistent with a moon trailing the gas giant during its transit. [7 Greatest Alien Planet Discoveries by NASA's Kepler Spacecraft (So Far)]

A very big moon

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. That latter number explains why the duo refers to the big candidate object as a satellite, Teachey said.

"When we derived the mass ratio, that's really sort of what I would say, in court, defines the difference between a planet and a moon or a binary planet," he said. "I would call that a moon, but to some extent I think this is something of semantics — what people want to define as a planet and moon or a binary system."

Indeed, the mass ratio is similar for our own Earth-moon system — 1.2 percent.

The candidate exomoon orbits 1.9 million miles (3 million kilometers) from its host planet — about eight times farther away than Earth's moon circles. 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.

Astronomers know of three major moon-formation mechanisms: There's gravitational capture (which appears to be the case with Neptune's biggest moon, Triton); powerful impacts (as happened with Earth's moon, which formed from material blasted into space by a long-ago collision); and the merging of material from a disk of material surrounding a newborn planet.

The capture and impact scenarios are implausible for such a large moon, Kipping said. So the candidate body probably coalesced from a circumplanetary disk, as the big Galilean moons of Jupiter did.

Kepler-1625b appears to orbit in its star's habitable zone, the just-right range of distances where liquid water might be stable on a world's surface. But the moon is so big that it's almost certainly gaseous, with no discernible surface, Teachey said.

So you should probably tamp down any Pandora- or Endor-related thoughts that might be running through your head, as the moon doesn't seem to be a great bet for alien life (at least not "advanced" life).

And there's another wrinkle to the habitability story. 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. So it's much farther along in its life cycle and is therefore probably quite a bit warmer than the sun.

This raises the possibility that the candidate exomoon isn't actually as massive as it may appear. Rather, it may have been puffed out relatively recently by the increased influx of stellar radiation. Indeed, some of the duo's models allow for a mass as low as that of Earth, Teachey said.

"But this is really a bit more speculative here," he stressed. "We don't have any evidence to think that directly, to prove that this is what has been happening in the past of this planet. But there's certainly interesting games that you can play when you acknowledge that this star is in this transitional phase."

Nailing it down

Again, the moon under discussion here remains a candidate, not a confirmed body. Confirmation could come quickly with further observations, however.

Indeed, it may take just a single additional transit observation that shows a "separate clean moonlike event," Kipping said.

"If we see that, then I think we're done," he said. "If we don't see it, then there is a fraction of our models which actually allow that still to happen. And it would have to go from there. It's difficult to predict exactly what the data will give us, until we actually see it in that scenario."

He and Teachey hope to make that additional observation with Hubble. Ground-based telescopes are not an option, because Earth's rotation takes Kepler-1625b and its star out of view long before the transit is complete, Teachey explained.

The new study was published online today (Oct. 3) in the journal Science Advances.

Editor's note: This story has been corrected from an earlier version that included one reference to the primary planet of the potential exomoon as WASP-1625b. The planet's name is Kepler-1625b.

Mike Wall's book about the search for alien life, "Out There," will be published on Nov. 13, 2018. Follow him on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.</s>Astronomers recognize eight major planets in our solar system, with 200 orbiting moons known so far. Much farther away, they’ve discovered nearly 4,000 exoplanets orbiting other stars, but, to date, no exomoons have conclusively been found, despite some earlier possibilities. On Wednesday, however – October 3, 2018 – astronomers announced new evidence for what could be the first true discovery of an exomoon. It appears to orbit the planet Kepler-1625b, 8,000 light-years away, in the direction of the constellation Cygnus the Swan, high in the west on October evenings.

Astronomers David Kipping and Alex Teachey, both of Columbia University, used data from both the planet-hunting Kepler spacecraft and the Hubble Space Telescope to discover the possible exomoon. It’s a saga that’s been unfolding for these astronomers over several years, and the final results still aren’t in … but the new evidence is tantalizing. If an exomoon does indeed orbit Kepler-1625b, Kipping said:

If it can be confirmed, this first known exomoon also presents astronomers with a riddle. Such large moons don’t exist in our own solar system. This discovery might require experts to revisit their theories of how moons form around planets. Thomas Zurbuchen at NASA headquarters in Washington, D.C., commented:

The scientific study of a possible exomoon for Kepler-1625b was published Wednesday in the peer-reviewed journal Science Advances.

Just as most planets outside our solar system have never been seen directly, we don’t have a direct image of this possible exomoon.

Instead, astronomers have discovered most known exoplanets – and this exomoon – during their passages in front of their stars. Such an event is called a transit, and it causes a tiny dip in the star’s light. The transit method has been used to detect most of the known exoplanets cataloged to date.

Transit signals from distant exoplanets are vanishingly small. That is why the search for exoplanets went on for decades before the first exoplanets were confirmed in the 1990s. Exomoons are even harder to detect than exoplanets because they’re smaller, and their transit signal is weaker. Exomoons also shift position with each transit because the moon is orbiting the planet.

David Kipping has spent about a decade of his career looking for exomoons. In 2017, he and his team analyzed data from 284 exoplanets discovered by the planet-hunting Kepler spacecraft. They looked at exoplanets in comparatively wide orbits, longer than 30 days, around their host stars. The researchers found one instance, in Kepler-1625b, of a transit signature with intriguing anomalies, suggesting the presence of a moon. Kipping said:

Kipping then requested time on the Hubble Space Telescope. The new Hubble results – though inconclusive – appear to confirm the earlier finding of an exomoon for Kepler-1625b. The announcement of the discovery at HubbleSite explained:

Based upon their findings, the team spent 40 hours making the observations with Hubble to study the planet intensively — also using the transit method — obtaining more precise data on the dips of light. Scientists monitored the planet before and during its 19-hour transit across the face of the star. After the transit ended, Hubble detected a second and much smaller decrease in the star’s brightness approximately 3.5 hours later. This small decrease is consistent with a gravitationally-bound moon trailing the planet, much like a dog following after its owner. Unfortunately, the scheduled Hubble observations ended before the complete transit of the candidate moon could be measured and its existence confirmed.

A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation. It was definitely a shocking moment to see that Hubble light curve; my heart started beating a little faster and I just kept looking at that signature. But we knew our job was to keep a level head and essentially assume it was bogus, testing every conceivable way in which the data could be tricking us.

Earth’s moon is known to be a major factor in the evolution, possibly even the presence, of life on our planet. This possible exomoon and its host planet lie within their star’s habitable zone, the region around a star where liquid water might exist on planetary surfaces. Could the planet, or its moon, be life supporting? The answer is: probably not. Both the exoplanet Kepler 1625b – and its possible exomoon – are gaseous, making them unsuitable for life as we know it.

These astronomers said that future searches for exomoons:

Bottom line: Astronomers at Columbia University found evidence in Kepler spacecraft data in 2017 suggesting an exomoon orbiting Kepler-1625b. They then requested time on the Hubble Space Telescope, and the new Hubble data boosts the claim – but does not prove conclusively – that this moon exists.</s>Astronomers have confirmed thousands of planets outside our Solar System, but not a single exomoon. New research is bolstering the case for a suspected exomoon first detected last year, but scientists say the evidence is still not definitive.



To date, astronomers have confirmed the existence of 3,851 exoplanets—a surprisingly big number given that the first exoplanet was discovered just 26 years ago. Yet during all this time, and after all those amazing planetary discoveries, astronomers haven’t been able to prove the existence of a single exomoon, that is, a moon in orbit around a planet in another star system.

This is a surprising result given that exomoons are guaranteed to be ubiquitous across the cosmos. Take our own Solar System, for example. Our eight planets host 185 known natural satellites. Of these, 79 belong to Jupiter and 62 to Saturn—an embarrassment of riches that showcases the potential of gas giants to harbor large collections of natural satellites. What’s more, a hefty portion of exomoons are likely to be habitable, as argued in a research paper published earlier this year.

But we still haven’t found any, despite these predictions.

Indeed, exomoons are proving to be frustratingly difficult to detect, and for obvious reasons. Unlike enormous gas giants and super-Earths, moons tend to be on the smallish side. Not only that, they’re spinning around an object that’s also spinning around an object; after a few observations, astronomers can predict when an exoplanet will pass in front of its host star, but knowing when an exoplanet’s exomoon might make an appearance is a different challenge entirely. So it makes sense that astronomers are struggling to make a definitive detection.

As some of you may recall from last year, astronomers using the Kepler Space Telescope detected a faint dip in the brightness of a star called Kepler-1625, which was interpreted to be a potential sign of an exomoon.

The data wasn’t definitive, but the observation resulted in the astronomers getting 40 hours worth of access to the Hubble Space Telescope. With Hubble, astronomers Alex Teachey and David Kipping from Columbia University were able to collect data that’s four times more precise than what Kepler was able to acquire. The results of this second survey, published today in Science Advances, is furthering the case for the existence of this exomoon, though, as before, the data is still not definitive.

“Our initial report was based on Kepler-data alone, which we always felt was not sufficient to claim a discovery,” Teaching told Gizmodo.

There are basically two features of the new data that suggest the presence of a moon.

The first of these features is an apparent dip in the brightness of the host star following the planet’s transit, which the astronomers attribute to the exomoon. The alleged exomoon is in orbit around a known exoplanet called Kepler-1625b, a large gas giant that’s several times bigger than Jupiter. It takes Kepler-1625b around 19 hours to travel across the face of its host star from our perspective here on Earth. At 8,000 light-years away, astronomers can’t actually see the planet, but they can detect a drop in the host star’s brightness when it passes in front; it’s this eclipsing effect, called a transit, that allows scientists to detect distant exoplanets.

Around 3.5 hours after Kepler-1625b performed its transit, Hubble detected a second, significantly smaller dimming of the star’s brightness. In a statement, Kipping sait it was consistent with “a moon trailing the planet like a dog following its owner on a leash.” Unfortunately, however, the scheduled Hubble observations ended before the complete transit of the supposed exomoon could be measured.



The second observation was the presence of transit timing effects, which indicate the presence of something in the system tugging on the planet gravitationally.

“Basically, when a planet has a moon, the planet is of course pulling on the moon gravitationally, but the moon is also pulling on the planet, and they’re both actually orbiting their common center of mass—a point in space along the line between the centers of the two objects,” explained Teaching. “So because the planet is orbiting this point—called the barycenter—it wobbles in its orbit around the star. What that does is, it affects the timings of the transits. Sometimes the planet transits a little earlier, sometimes a little later. Those are the transit timing variations, or TTVs.”

Teaching said the moon explanation is superior to other explanations, such as the gravitational influence of an undiscovered exoplanet in the Kepler-1625 system. The exomoon explanation also has the added benefit of being a single explanation for the two observed phenomena. But as Teaching and Kipping admit, the data is still incomplete, and something unknown may be influencing the observations.

“We would just stress that this remains an exomoon candidate,” Teaching told Gizmodo. “It’s a tantalizing result, certainly, but it really still needs to be confirmed by more observations and, hopefully, other teams replicating our results.”

Regardless, a picture of this exoplanet and moon is beginning to emerge. If this is an exomoon, it’s actually quite large—about the size of Neptune. By comparison, Jupiter’s Ganymede—the largest moon in our Solar System—is 3,270 miles (5,268 kilometers) in diameter, compared to Neptune and its 30,500-mile-wide (50,000 kilometers) diameter. This exomoon is about 1.5 percent the mass of its host planet, which, interestingly, is the same mass-ratio between the Earth and Moon, but on a far less grandiose scale. By the standards of our Solar System, this is a moon of gargantuan proportions—an attribute the researchers say is largely responsible for its discovery.

Natalie Hinkel, an astronomer at Southwest Research Institute in San Antonio who wasn’t involved with the new study, was impressed by how the authors vetted their data and analyses.

“They considered a wide variety of angles, caveats, and avenues that could render their findings null and void—but all lead them back to the likely presence of an exomoon,” Hinkel told Gizmodo. “However, because there have been no observations of this kind, I agree with their assessment that it is the ‘unknown unknowns’ which may make or break this discovery.”

University of Southern Queensland astronomer Rob Wittenmyer said the paper was thorough, and without the authors overstating their claim.



“The result is not surprising, as evidenced by the abundance of moons in our Solar system,” Wittenmyer told Gizmodo. “As moons go, this one is quite large, and hence detectable. I suspect that, like exoplanets and cockroaches, exomoons are everywhere—when you see one, there are many more you missed. As techniques are refined, we will surely find more exomoons in the coming decades.”

David Bennett, a scientist at NASA Goddard Space Flight Center, agrees that additional observations will be required to brand this a definitive discovery of an exomoon.

“Also, the planet is 10 times more massive than Jupiter, and the predicted mass of the moon is close to that of Neptune. So, if we saw these objects in isolation, we would consider them both to be planets,” Bennett told Gizmodo. “If the observed companion to the planet is confirmed, there is a good chance that it would be considered to be a binary planet instead of a moon. It could be a Neptune mass planet that was captured by a super-Jupiter planet during the formation of the planetary system.”

Which is a good point. How is it even possible that this particular planet-moon architecture even exists? If it’s confirmed that Kepler-1625b hosts such a large moon, astronomers will have the added challenge of figuring out how this particular star system took shape.

Another neat fact about Kepler-1625b is that its orbit resides within its host star’s habitable zone. Now, it’s very unlikely that this gas giant, and its equally gassy, Neptune-like exomoon, could harbor life. But what if this purported exomoon has its own moons, and those moons are of a terrestrial nature? Could life actually emerge on the moon of a moon?



“If there is truly an exomoon around Kepler-1625b, a whole new subfield could open up, one we scientists—as well as sci-fi writers—have only speculated about, regarding the discovery and possible habitability of exomoons,” said Hinkel. “Essentially, it could be like the TV show Firefly where people live on core worlds as well as the outlying moons.”

It’ll be awhile before we can start answering these sorts of questions, but this latest observation means we can at least start to pose the questions.</s>Using NASA’s Hubble and Kepler space telescopes, astronomers have uncovered tantalizing evidence of what could be the first discovery of a moon orbiting a planet outside our solar system.

This moon candidate, which is 8,000 light-years from Earth in the Cygnus constellation, orbits a gas-giant planet that, in turn, orbits a star called Kepler-1625. Researchers caution that the moon hypothesis is tentative and must be confirmed by follow-up Hubble observations.

“This intriguing finding shows how NASA’s missions work together to uncover incredible mysteries in our cosmos,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate at Headquarters, Washington. “If confirmed, this finding could completely shake up our understanding of how moons are formed and what they can be made of.”

Since moons outside our solar system – known as exomoons – cannot be imaged directly, their presence is inferred when they pass in front of a star, momentarily dimming its light. Such an event is called a transit, and has been used to detect many of the exoplanets cataloged to date.

However, exomoons are harder to detect than exoplanets because they are smaller than their companion planet, and so their transit signal is weaker when plotted on a light curve that measures the duration of the planet crossing and the amount of momentary dimming. Exomoons also shift position with each transit because the moon is orbiting the planet.

In search of exomoons, Alex Teachey and David Kipping, astronomers at Columbia University in New York, analyzed data from 284 Kepler-discovered planets that were in comparatively wide orbits, longer than 30 days, around their host star. The researchers found one instance in planet Kepler-1625b, of a transit signature with intriguing anomalies, suggesting the presence of a moon.

“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said.



 NASA’s Hubble and Kepler space telescopes have uncovered what could be the first exomoon.

Based upon their findings, the team spent 40 hours making observations with Hubble to study the planet intensively – also using the transit method – obtaining more precise data on the dips of light. Scientists monitored the planet before and during its 19-hour transit across the face of the star. After the transit ended, Hubble detected a second, and much smaller, decrease in the star’s brightness approximately 3.5 hours later. This small decrease is consistent with a gravitationally-bound moon trailing the planet, much like a dog following after its owner. Unfortunately, the scheduled Hubble observations ended before the complete transit of the candidate moon could be measured and its existence confirmed.

In addition to this dip in light, Hubble provided supporting evidence for the moon hypothesis by finding the planet transit occurring more than an hour earlier than predicted. This is consistent with a planet and moon orbiting a common center of gravity that would cause the planet to wobble from its predicted location, much the way Earth wobbles as our Moon orbits it.

The researchers note the planetary wobble could be caused by the gravitational pull of a hypothetical second planet in the system, rather than a moon. While Kepler has not detected a second planet in the system, it could be that the planet is there, but not detectable using Kepler’s techniques.

“A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation,” Kipping explained. “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. But we knew our job was to keep a level head and essentially assume it was bogus, testing every conceivable way in which the data could be tricking us.”

In a paper published in the journal Science Advances, the scientists report the candidate moon is unusually large – potentially comparable to Neptune. Such large moons do not exist in our own solar system. The researchers say this may yield new insights into the development of planetary systems and may cause experts to revisit theories of how moons form around planets.

The moon candidate is estimated to be only 1.5 percent the mass of its companion planet, and the planet is estimated to be several times the mass of Jupiter. This mass-ratio is similar to the one between Earth and the Moon. In the case of the Earth-Moon system and the Pluto-Charon system, the moons are thought to be created through dust leftover after rocky planetary collisions. However, Kepler-1625b and its possible satellite are gaseous and not rocky, so the moon may have formed through a different process.

Researchers note that if this is indeed a moon, both it and its host planet lie within their star’s habitable zone, where moderate temperatures allow for the existence of liquid water on any solid planetary surface. However, both bodies are considered to be gaseous and, therefore, unsuitable for life as we know it.

Future searches for exomoons, in general, will target Jupiter-size planets that are farther from their star than Earth is from the Sun. The ideal candidate planets hosting moons are in wide orbits, with long and infrequent transit times. In this search, a moon would have been among the easiest to detect because of its large size. Currently, there are just a handful of such planets in the Kepler database. Whether future observations confirm the existence of the Kepler-1625b moon, NASA’s James Webb Space Telescope will be used to find candidate moons around other planets, with much greater detail than Kepler.

“We can expect to see really tiny moons with Webb,” Teachey said.

Publication: Alex Teachey and David M. Kipping, “Evidence for a large exomoon orbiting Kepler-1625b,” Science Advances 03 Oct 2018: Vol. 4, no. 10, eaav1784; DOI: 10.1126/sciadv.aav1784</s>Exoplanet Kepler-1625b might harbor a moon the size of Neptune—potentially the first confirmed exomoon—but researchers urge caution in interpreting the data.

Last year, astronomers tentatively reported that they might have found the first known moon outside our solar system. Now, those same researchers think their claim just got a little stronger.

New observations from the Hubble Space Telescope lend credence to the idea that a moon roughly the size and mass of Neptune is orbiting about 3 million kilometers (about 2 million miles) from the Jupiter-size exoplanet Kepler-1625b, about 7,800 light-years from Earth.

For some perspective, according to René Heller (Max Planck Institute for Solar System Research, Germany), that one moon is about 10 times as massive as all the moons and rocky planets in our solar system combined.

But the discoverers themselves urge caution. “The first exomoon is obviously an extraordinary claim,” said Alex Teachey (Columbia University) at an October 1st press conference. “We’re not cracking open champagne bottles just yet.”

Teachey and colleague David Kipping (Columbia University) got their first hints of an exomoon after looking through data on 284 planetary systems from the Kepler space telescope. The telescope identifies exoplanets using the transit method, which relies on dips in starlight created by a planet passing in front of its sun. The team found one system that looked promising — a gas giant that transited about every 287 days, paired with the barest hint of a second, smaller transit from a potential moon — but they needed more data to be sure. So they turned to the Hubble Space Telescope, which spent 40 hours looking for confirmation on October 28th and 29th of 2017, when the planet was expected to transit again.

They weren’t disappointed. The hoped-for second transit came a few hours after the exoplanet's. What’s more, the planet started its transit about 78 minutes earlier than expected. While that could be evidence of other planets in the system tugging on this one, it could also be caused by a planet and moon orbiting each other.

“We’ve tried our best to rule out other possibilities such as spacecraft anomalies, other planets in the system, or stellar activity,” Kipping said. “But we’re unable to find any other single hypothesis which can explain all of the data we have.”

The research is published October 3rd in Science Advances.

“I think we have to be very, very cautious,” says Stephen Kane (University of California, Riverside). “But it is very encouraging.” The Hubble data are critical, he says, because those observations were specifically targeted toward this system, as opposed to the Kepler observations, which cast a wide net to maximize the odds of finding planets.

“Alex and David did a marvelous job of examining the data from various perspectives and they are very transparent about the methods they used,” Heller says. “As to the confidence that I have in the actual existence of this exomoon, I remain skeptical.”

It’s not that exomoons are unlikely. And it’s not that the signal is too small to be reliable. Being a Neptune-size world, the moon blocks an amount of starlight that's actually on par with many planets already discovered, says Heller. The trouble is the noise in the data. Heller stresses that it is critical to understand all the potential sources of noise — the telescope, the instruments, and the star itself.

The authors do try and address these issues. One test was to look for the transit in multiple wavelengths. If the star were flickering, then red and blue starlight would dip by different amounts. But these transits look the same in all colors.

Data reliability aside, there is also the matter of the moon’s unusual size. While the ratio in masses between the moon and the planet is about the same as that of our Moon and Earth — about 1% — the entire system is roughly 1,000 times as massive as ours.

“The kind of system they found is so extraordinarily different from what we’re used to,” Kane says. “It raises a whole lot of questions about how did this come to be.”

There are three presumed ways to create a moon. It can form in the aftermath of something massive impacting a planet (such as Earth’s Moon). It can form in a disk of gas and dust encircling a planet (such as Jupiter’s Galilean satellites). Or it can be captured by wandering too close to a planet (such as Neptune’s largest moon, Triton).

All three methods are tough to reconcile with this situation. The moon’s orbit is stable, but how it got there is an open question. No one has really looked at how an impact on a gas giant planet could produce a moon, Kipping said. A disk around a Jupiter-mass world occasionally gives birth to such a moon, according to recent simulations. “It’s kind of the tip of the iceberg, but you do sometimes form moons that big,” said Kipping.

However, Heller argued in a paper earlier this year that the masses in the Kepler-1625b system are off the charts with regards to calculations of how things form in a circumplanetary disk. And capture, he finds, requires that the moon once had a mini-Neptune companion that got ejected in a close encounter with the planet — a plausible though unlikely scenario that posits two large worlds once gravitationally bound to one another.

“This moon, if confirmed, must have formed through a yet unknown astrophysical mechanism,” he says.

The next step is to get more data. To that end, Teachey and Kipping have applied for time on Hubble in May 2019, when the planet is expected to transit next. One more transit with the moon in the right position based on its predicted orbit could clinch the case. “If we see that,” Kipping said, “then I think we’re done.”

R. Heller. "The Nature of the Giant Exomoon Candidate Kepler-1625 b-i." Astronomy & Astrophysics. February 26, 2018.

M. Cilibrasi et al. "Satellites Form Fast & Late: A Population Synthesis for the Galilean Moons." Monthly Notices of the Royal Astronomical Society. August 9, 2018.</s>If confirmed, this could be the first moon ever detected outside of our solar system.

In a stunning discovery, astronomers may have stumbled upon the first-ever alien moon, or “exomoon,” to be found orbiting a planet outside of our solar system, NASA announced earlier today.

The credit goes to astronomers Alex Teachey and David Kipping from Columbia University in New York, who used the Hubble Space Telescope to zero in on what seems to be a massive alien moon orbiting a giant planet 8,000 light-years away.

This is “the first compelling evidence for a moon outside our own solar system,” states the Hubble Space Telescope website, noting that scientists have long waited to make such a detection. While the first discovery of an exoplanet occurred 30 years ago, no one has ever managed to uncover strong evidence of an exomoon until now.

The remarkable find, described in a study just published in the journal Science Advances, points to a Neptune-sized exomoon around an exoplanet known as Kepler-1625b, which orbits a star codenamed Kepler-1625 located in the constellation of Cygnus (“the Swan”).

As the Inquisitr previously reported, this particular object has been an exomoon candidate since 2016, when the two astronomers came across the first clues that Kepler-1625b could be orbited by an alien moon. At the time, the researchers examined 284 planet candidates found by the Kepler Space Telescope, all of which stood a good chance of hosting a natural satellite.

The original paper, available on the arXiv server, singled out the exoplanet and its suspected exomoon, dubbed Kepler-1625b-i, as the most promising of the bunch.

Their latest research revisited the old Kepler data, taking an in-depth look at the Kepler-1625 star with the Hubble telescope. The new paper makes a strong case that the stellar system’s only known exoplanet could have its very own moon based on data recorded via the transit method.

This method searches for potential alien worlds by measuring the tiny dips in brightness they cause whenever they pass in front of (transit) a star, blocking its light.

The team logged in about 40 hours of Hubble time to take a better look at Kepler-1625 and managed to observe not one, but two dips in starlight brightness during one of the exoplanet’s 19-hour transits.

According to the video below, released by Hubble officials a few hours ago, the first dip in light brightness was seen as Kepler-1625b passed in front of its parent star. Meanwhile, the second occurrence was significantly smaller and was recorded about 3.5 hours later.

This hints at a smaller object trailing behind the exoplanet, possibly the first exomoon to ever be discovered.

“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,” Kipping said in a statement.

Another clue that signals the presence of a potential exomoon around Kepler-1625b has to do with the timing of the exoplanet’s transit. As Teachey explains in the video below, the team previously examined the exoplanet during three separate transits of its host star. The new Hubble observations recorded Kepler-1625b transiting “a full 78 minutes earlier than we anticipated,” said Teachey, suggesting a wobble in the exoplanet’s trajectory.

The wobble could be explained by the presence of an exomoon, in the same way that our moon caused Earth to wobble as it orbits the planet, shows NASA.

This extraordinary discovery is made even more exciting by the sheer size of the suspected exomoon. The gargantuan moon has a diameter comparable to that of Neptune and is nothing like the moons circling the planets in our solar system.

The parent exoplanet is equally unusual, dwarfing the planets inhabiting our own system. Kepler-1625b is a gas giant weighing several times the mass of Jupiter, our solar system’s largest planet. The potential exomoon that could be floating around it is estimated to weigh just 1.5 percent the mass of this imposing planet.

The same mass-ratio can be observed in the case of Earth and our own moon, notes NASA. But while both our planet and its natural satellite are rocky, Kepler-1625b and Kepler-1625b-i are gaseous, which means that the alien moon was born in a completely different way than the accretion of leftover planetary material that gives rise to rocky moons.

“This may yield new insights into the development of planetary systems and may cause astronomers to revisit theories of how moons form,” said Teachey.

Although the exomoon is yet to be confirmed, as the allotted Hubble time ended before the astronomers could measure the full transit of the moon candidate, this is the closest that anyone has ever gotten to detecting a moon outside of our solar system.

“If confirmed, Kepler-1625b-i will certainly provide an interesting puzzle for theorists to solve,” said Kipping.</s>CAPE CANAVERAL (CBSMiami/AP) — Plenty of planets exist outside our solar system, but astronomers may have found a first.

Using images from the Hubble Space Telescope, two Columbia University researchers believe they have discovered the first moon outside our solar system. The gaseous moon looks to be considerably larger than Earth — about the size of Neptune or Uranus. The planet it orbits is as big as mammoth Jupiter. This apparent super-size pairing is 8,000 light-years away.

Researchers Alex Teachey and David Kipping evaluated 284 planets outside our solar system that had already been discovered by NASA’s Kepler Space Telescope. Only one planet held promise for hosting a moon, one around the star known as Kepler-1625, which is about the size of our sun but older.

So last October, the pair directed the Hubble Space Telescope at the star in an attempt to verify — or rule out — the possibility of a moon orbiting the planet Kepler-1625b. They were on the lookout for a second temporary dimming of starlight. The main dip in stellar brightness would be the planet itself crossing in front of its star. Another dip could well be a moon — known as an exomoon outside our solar system.

The more powerful and precise Hubble telescope detected a second and smaller decrease in starlight 3 ½ hours after the planet passed in front of the star — “like a dog following its owner on a leash,” as Kipping put it. The observation period, however, ended before the moon could complete its transit. That’s why the astronomers need another look with Hubble, hopefully, next spring.

Despite the evidence, Teachey stressed, “we are urging caution here.”

“The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence,” Teachey said. “Furthermore, the size we’ve calculated for this moon, about the size of Neptune, has hardly been anticipated and so that, too, is a reason to be careful here.”

He added: “We’re not cracking open Champagne bottles just yet on this one.”

If indeed a moon, it would be about 2 million miles from its planet and appear twice as big in its sky, as the moon does in ours. The astronomers are uncertain how this potential moon might have formed, given its size.

“If confirmed, this finding could completely shake up our understanding of how moons are formed and what they can be made of,” NASA’s science mission chief Thomas Zurbuchen said in a statement.

According to the researchers, another compelling piece of evidence in favor of a moon is that the planet passed in front of its star more than an hour earlier than predicted. A moon could cause that kind of an uncertain, wobbly path, they noted.

Kipping said that’s how the Earth and moon would appear from far away. This particular planet — or exoplanet — is about the same distance from its star as Earth is to the sun.

Another planet could cause the same gravitational nudge, the researchers noted, although Kepler observations have come up empty in that regard. Kepler-1625b is the only planet found so far around this star.

For Teachey and Kipping, the best and simplest explanation is that Kepler-1625b has a moon.

“We’ve tried our best to rule out other possibilities,” Kipping told reporters. “But we were unable to find any other single hypothesis which can explain all of the data we have.”

Their findings were published in the journal Science Advances. The journal’s deputy editor, Kip Hodges, praised the researchers for their cautious tone, given the difficult and complicated process of identifying an exomoon.

“If this finding stands up to further observational scrutiny, it represents a major milestone in the field of astronomy,” Hodges said.

The Columbia astronomers said they may be able to clinch this as early as next year, with more Hubble viewing. In the meantime, they’re encouraging other scientists to join in and embracing the scrutiny that’s sure to come.

Whether confirmed or not, the subject offers insight into how rare — or how common — our own solar system might be.

Moons are abundant in our own solar system, with close to 200. Of the eight planets in our solar system, only Mercury and Venus have none.

 Given that both the planet and its potential moon are gas giants, no one is suggesting conditions that might support life.

“But going forward, I think we’re opening the doors to finding worlds like that,” Teachey said.</s>A pair of Columbia University astronomers have stumbled upon a possible exomoon.

Like the exoplanets we’re so keen to uncover, these moons orbiting planets in other star systems could lead us to extraterrestrial life—or at least a deeper understanding of outer space.

Using NASA’s Hubble Space Telescope and Kepler Space Telescope, Alex Teachey and David Kipping assembled “compelling evidence” for the existence of a moon orbiting a Neptune-sized planet 8,000 light-years away.

Their findings are described in a paper published this week by the journal Science Advances.

“This would be the first case of detecting a moon outside our Solar System,” Kipping, an assistant professor of astronomy, said in a statement. “If confirmed by follow-up Hubble 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.”

The researchers analyzed data from 284 Kepler-discovered planets, measuring transit—the momentary dimming of light as a planet passes in front of its star. In exoplanet Kepler 1625b, some 4,000 light-years away, they noticed “intriguing anomalies.”

“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said.

That was enough for Kipping & Co. to snag 40 hours with the Hubble for intensive study of the planet, collecting data four times more precise than the Kepler telescope.

The session ended before the moon’s complete transit could be measured. But the team did find a second, much smaller decrease in the star’s brightness, consistent with “a moon trailing the planet like a dog following its owner on a leash,” Kipping explained.

Hubble also revealed that the planet began its transit 1.25 hours earlier than expected—consistent with the planet and moon orbiting a common center of gravity that would cause the globe to wobble from its predicted location.

In theory, this could be the result of the gravitational pull from a hypothetical second planet. But Kepler’s four-year mission found no evidence of any additional orbs in the system.

“A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation,” NSF Graduate Fellow Teachey said.

“It was a shocking moment to see that light curve, my heart started beating a little faster and I just kept looking at that signature,” he continued. “But we knew our job was to keep a level head testing every conceivable way in which the data could be tricking us until we were left with no other explanation.”

Similar to the mass-ratio between our Earth and its satellite, this moon is estimated to be 1.5 percent the mass of its companion gas-giant planet, which is likely several times the mass of Jupiter.

Both bodies lie within Kepler 1625’s habitable zone, where moderate temperatures allow for the liquid water on solid planetary surfaces. But, according to Kipping, neither gaseous object is suitable for life as we know it.

NASA’s upcoming James Webb Space Telescope is expected to “clean up” the satellite search, allowing astronomers to target larger planets that are farther from their star than Earth is from the Sun.

“We can expect to see really tiny moons,” Kipping said.

You don’t need a high-tech telescope to see beautiful images of the recent Full Harvest Moon. Scientists recently discovered an electric shell that gains power when the Moon shows its full face once a month. Read more about the planetoid here.</s>Did the Hubble Space Telescope come up with evidence of the first moon orbiting a planet outside of our solar system? If so, it's a stunning discovery which changes our knowledge of the universe around us.

This discovery was made by two of NASA’s most celebrated telescopes, Hubble and Kepler, which were used by two astronomers, Alex Teachey and David Kipping, from Columbia University. The two spent hundreds of hours analyzing data from 284 planets discovered by Kepler, which had orbits longer than 30 days around their host star.

One of those, Kepler 1625b, was intriguing enough to warrant getting time on the Hubble Space Telescope to investigate it in detail because its characteristics suggested a moon.

The data they uncovered indicates an exomoon the size of Neptune, in a stellar system 8,000 light years from Earth. While this is an exciting discovery, it's still not confirmed -- it will take more time on the Hubble Space Telescope to confirm this remarkable find.

Astrophysicist Hakeem Oluseyi says this really could change the way we look at our solar system.

Now, the big question: Is there anyone else out there?

“The discovery of all these planets and understanding how they were formed opens up a whole new avenue for finding life out there,” Oluseyi told ABC News.

What is an exomoon?

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.

What Hubble was able to do was provide evidence by tracking the planet and proving it had crossed an hour earlier than expected, which like earth and its moon shows a planet and moon orbiting a common center of gravity, with a bit of a wobble -- just like earth.</s>Given the abundance of moons in our own Solar System, you'd think there are heaps orbiting exoplanets, too. Such exomoons have been elusive until now - but it looks like that has finally changed.

Last year, astronomers Alex Teachey and David Kipping of Columbia University announced they'd spotted the very first exomoon candidate in data from the Kepler telescope.

Now they've conducted follow-up observations with the powerful Hubble Space Telescope. Those observations point even more strongly to the discovery of the very first exomoon.

"This would be the first case of detecting a moon outside our Solar System," Kipping said.

"If confirmed by follow-up Hubble 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."

Kepler-1625b-i, as the candidate exomoon has been named, orbits an exoplanet called Kepler-1625b, which in turn orbits a yellow, Sun-like star called Kepler-1625. The entire system is located around 8,000 light-years away, a distance recently revised with the aid of Gaia data.

The planet, Kepler-1625-b, is a Jupiter-sized gas giant, just over 11 times the radius of Earth, but with considerably more mass than Jupiter.

The candidate moon is also a whopper - according to the astronomers' calculations, it's roughly the size of Neptune, and therefore also a gas body, orbiting its planet at a distance of about 3 million kilometres.

The astronomers first got a hint of Kepler-1625b-i when they studied Kepler data on 284 exoplanets in search of an exomoon - what they describe as "little deviations and wobbles" beyond the normal transit dips in the light curve coming from the star as the planet moves across it. But it wasn't enough information.

"Kepler recorded just three transits of the planet in front of her star, and that's largely because the planet takes almost a year to complete an orbit. Three transits was tantalising, but not conclusive. Because Kepler can no longer observe the same field, we asked for some follow up observations with Hubble. Our analysis of the new light curve reveals two substantial anomalies," Kipping explained during a press briefing.

"The first is that the planet appears to transit one and a quarter hours too early; that's indicative of something gravitationally tugging on the planet. The second anomaly is an additional decrease in the star's brightness after the planetary transit has completed."

Sadly, Hubble's time is in high demand, which means the time Teachey and Kipping had with the telescope was limited to 40 hours. This time ran out before the moon's complete transit could be measured.

While these observations mount further evidence for the existence of Kepler-1625b-i, they are not, as yet, conclusive.

Other explanations for the signals observed by Teachey and Kipping could include a second planet orbiting Kepler-1625 - although, they note, so far Kepler has found no evidence of a second planet.

Another potential explanation is that one or more of the signals they observed were noise from the star itself. However, the star itself, as the team have ascertained from Kepler data, is so quiet they can't even detect its rotation. So stellar noise is possible, but Teachey and Kipping found no evidence for it.

It's reasonable to start getting excited about the possibility of a brand new discovery - a first of its kind that hopefully heralds many more in the future.

"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," Kipping said.

An artist's impression of exoplanet Kepelr-1625b and its moon. (Dan Durda)

It will certainly raise some questions about moon formation.

Kepler-1625b-i is about 1.5 percent of the mass of the planet, similar to the mass-ratio of Earth and the Moon. But because both bodies are gaseous (which means neither are habitable as we understand it, in case you were wondering), and because of the moon's size, that raises questions about how it got there.

Our Moon may have formed as the result of a collision with Earth, but a collision with a gas planet like Kepler-1625b might not result in enough material to form a Neptune-sized moon.

Jupiter's moons are believed to have formed from a ring of material; but again, none of Jupiter's moons are the size of Neptune. Or it could have been an object that was captured by the planet's gravity from elsewhere.

For now, we can't get any answers to those questions, but we can at least hope the moon discovery will be confirmed, hopefully by future Hubble and James Webb Space Telescope Observations.

"We're looking forward to the scrutiny of the scientific community on this work and we hope we'll have an opportunity to observe the target again before too long," Teachey said.

The research has been published in the journal Science Advances.
Kepler-1625b, an exoplanet proposed in 2017 to be orbited by an exomoon, the first possible example of a moon orbiting a planet in another stellar system, is confirmed with observations from the Hubble Space Telescope.