4.10.2018
Astronomers may have found the first moon outside our solar system, a gas behemoth the size of Neptune.
Plenty of planets exist beyond our solar system, but a moon around one of those worlds has yet to be confirmed. Two Columbia University researchers presented their tantalizing evidence for a moon Wednesday.
The potential moon would 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 of a gaseous moon and planet 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 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 (3 million kilometers) 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.
Quelle: abcNews
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First 'exomoon' may have been found
Astronomers have announced the possible discovery of the first known moon outside our Solar System.
This "exomoon" is not like any in our cosmic neighbourhood: it's the size of Neptune and orbits a planet the size of Jupiter - but with 10 times the mass.
The object was spotted in data from Nasa's Kepler spacecraft, and later observed using the Hubble telescope.
Astronomers David Kipping and Alex Teachey have published their results in Science Advances journal.
But they say that further observations are needed to understand the distant planetary system.
"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," said Dr Kipping, from Columbia University in New York.
To date, astronomers have discovered more than 3,500 exoplanets - worlds orbiting stars other than the Sun.
A hunt for exomoons - bodies that orbit these distant planets - has proceeded in parallel. But so far, these natural satellites have lingered at the limits of detection with current techniques.
The researchers monitored a planet known as Kepler 1625b as it passed in front of its parent star.
This 19-hour event, known as a transit, blocked out some of the light coming from the star, which lies at a distance of 8,000 light-years from Earth.
Kipping and Teachey looked for two signals suggestive of an exomoon in the data from several transits.
The first of these signals was a dip in the parent star's brightness as the exomoon passed in front. The second was a delay in the planet passing in front of its star.
This is exactly what the researchers saw: "The location, shape and depth of this event appear consistent with a Neptune-sized moon transiting in front of the star," said Dr Kipping.
Both objects are gas giants and the apparent moon, known as Kepler 1625b-i, orbits some three million kilometres from the planet.
About 3.5 hours after the planet's transit ended, the Hubble telescope recorded a second smaller dimming of the star's brightness, which indicated a moon "trailing the planet like a dog following its owner on a leash," according to Dr Kipping.
In addition, the transit occurred about one-and-a-quarter hours earlier than predicted.
"That's indicative of something gravitationally tugging on the planet," explained Dr Kipping.
The researchers also had to remove artefacts from the Hubble data and used computer models to work out how different scenarios fit with the observed data.
"The moon model emerges as the best explanation for the data, and it has the added benefit of being a single explanation for both the timing effects and the dimming of the star that we see in the data," said Alex Teachey.
"Still we are urging caution here. The first exomoon is obviously an extraordinary claim and it requires extraordinary evidence."
But, he added: "We are excited about this result, certainly it is a tantalising result."
The astronomers were allocated 40 hours of observation time on the Hubble telescope. These observations ended before a full transit of the moon could be measured.
However, the evidence provides the most compelling evidence yet for the first known planetary satellite around an exoplanet.
David Kipping has spent about a decade of his career searching for these distant and elusive planetary companions.
Several promising exomoon candidates have cropped up in the past, only to be debunked as further data became available.
Dr Kipping, along with colleagues Alex Teachey and Allan Schmitt, announced that they were studying this candidate moon in July 2017.
At the time, he told me it was "the best candidate we've had".
They had already dubbed the candidate satellite a "Nept-moon", because of its large size.
The researchers could find no predictions of a Neptune-sized moon in the literature, but Dr Kipping notes that nothing in physics prevents one.
A current theory of planetary formation suggests that objects like this are unlikely to have formed in place with their Jupiter-mass planets, but would instead be objects captured by the gravity of the planet later on in the evolution of a planetary system.
Quelle: BBC
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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.
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.
Quelle: NASA
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Columbia Astronomers Find First Compelling Evidence for a Moon Outside Our Solar System
In a paper published Oct. 3 in the journal Science Advances, Alex Teachey and David Kipping report that the detection of a candidate exomoon – that is, moons orbiting planets in other star systems – is unusual because of its large size, comparable to the diameter of Neptune. Such gargantuan moons do not exist in our own solar system, where nearly 200 natural satellites have been cataloged.
“This would be the first case of detecting a moon outside our solar system,” said Kipping, an assistant professor of astronomy at Columbia. “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.”
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. The observations measured the momentary dimming of starlight as a planet passed in front of its star, called a transit. The researchers found one instance, in Kepler 1625b, that had intriguing anomalies.
“We saw little deviations and wobbles in the light curve that caught our attention,” Kipping said.
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 researchers monitored the planet before and during its 19-hour-long transit across the face of the star. After it ended, Hubble detected a second and much smaller decrease in the star’s brightness 3.5 hours later, consistent with “a moon trailing the planet like a dog following its owner on a leash,” Kipping said. “Unfortunately, the scheduled Hubble observations ended before the complete transit of the moon could be measured.”
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. This is consistent with the planet and moon orbiting a common center of gravity (barycenter) that would cause the planet to wobble from its predicted location.
“An extraterrestrial civilization watching the Earth and Moon transit the Sun would note similar anomalies in the timing of Earth’s transit,” Kipping said.
The researchers note that in principle this anomaly could be caused by the gravitational pull of a hypothetical second planet in the system, although Kepler found no evidence for additional planets around the star during its four-year mission.
“A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation,” said lead author Teachey, NSF Graduate Fellow in astronomy at Columbia. “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. 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.”
An animation depicting images of Kepler-1625. The star is located in the center and is spread out horizontally due to the instrument’s grating prism, giving the observer’s color information about the source. Animation Courtesy of Alex Teachey & David Teachey
The moon is estimated to be only 1.5 percent the mass of its companion planet, which itself estimated to be several times the mass of Jupiter. This value is close to the mass-ratio between the Earth and its moon. But in the case of the Earth-Moon system and the Pluto-Charon system – the largest of the five known natural satellites of the dwarf planet Pluto – an early collision with a larger body is hypothesized to have blasted off material that later coalesced into a moon. Kepler 1625b and its satellite, however, are gaseous, not rocky, and, therefore, such a collision may not lead to the condensation of a satellite.
Exomoons are difficult to find because they are smaller than their companion planet and so their transit signal is weak; they also shift position with each transit because the moon is orbiting the planet. In addition, the ideal candidate planets hosting moons are in large orbits, with long and infrequent transit times. In this search, the Neptune-sized moon would have been among the easiest to first detect because of its large size.
The host planet and its moon lie within the solar mass star’s (Kepler 1625) habitable zone, where moderate temperatures allow for the existence of liquid water on any solid planetary surface. “Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it,” Kipping said.
Future searches will target Jupiter-sized planets that are farther from their star than Earth is from the Sun. There are just a handful of these in the Kepler database. NASA’s upcoming James Webb Space Telescope could really “clean-up” in the satellite search, Kipping said. “We can expect to see really tiny moons.”
Quelle: Columbia University