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Astronomers have observed Saturn and its satellites for more than three and a half centuries.
Ever since humans began looking at the sky, our moon has been watching us from its orbit relatively close to our planet. It is the most visible natural satellite in our solar system, but not the only one.
However, it is always difficult to know how many there are.
Last May, astronomers announced they had discovered 62 new moons orbiting Saturn, one of the Solar System’s gas giants.
This increases the number of confirmed moons around this Leviathan, which is about 1.3 billion kilometers from the sun, to 145.
This will make Saturn the planet with the largest number of moons in orbit, dethroning its giant neighbor Jupiter in what some call the “race for the moons.”
The number of Saturn’s moons continues to increase, and a few weeks later the same team made a new discovery.
The new moons were located by a team led by Edward Ashton, a postdoctoral researcher at the Institute of Astronomy and Astrophysics at Academia Sinica in Taiwan.
The discovery took more than two years, thanks to a telescope installed on top of Mauna Kea, a volcano in Hawaii.
Astronomers have observed Saturn and its satellites for more than three and a half centuries. Mankind has even sent four spaceships to Saturn, and yet these moons have not yet been discovered.
How is it that so many moons of Saturn remain hidden? Why is it so hard to find distant moons and how many more might be waiting in the dark of space?
Difficult to see
Credit: NASA/JPL/SPACE SCIENCE INSTITUTE/Portal
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Image of Saturn’s moon Enceladus compiled from high-resolution photos taken by NASA’s Cassini spacecraft in 2005.
At last count, there were no fewer than 290 “traditional” moons in our solar system.
Observing a moon is not enough to officially designate it as a moon. Some of these new satellites have already been observed, but it will be a long process before the International Astronomical Union officially classifies them as moons. This process requires several years of constant observation.
For four centuries, many of our heavenly neighbors were too distant for us to distinguish.
In 1655, Dutch astronomer Christiaan Huygens discovered Saturn’s largest moon, Titan, which was larger than the planet Mercury. It was 16 years before Jean-Dominique Cassini discovered Hapetus, then Rhea, Dione, and finally Thetis in 1684. It was not until 1789 that German astronomer William Herschel identified Mimas and the icy moon Enceladus.
Other moons of Saturn have eluded human observation for much longer. The potato-shaped Hyperion was discovered in 1848. About fifty years later he was followed by Phoebe, which moves in the opposite direction to most of the moons around Saturn.
With the advent of the space age and modern telescopes, the list of Saturn’s moons has grown significantly. Spacecraft such as the Voyager and Cassini probes have expanded their discoveries by taking a closer look at the complex Saturn system.
But the vast majority of Saturn’s moons have only been discovered relatively recently, since the year 2000.
One reason is that the satellites discovered in the early days of astronomy followed certain patterns: they were relatively large and followed predictable orbits, which astronomers call regular orbits.
“All giant planets have regular moons,” says Brett Gladman, a Canadian astronomer at the University of British Columbia and one of Ashton’s colleagues involved in recent discoveries around Saturn.
“Its moons orbit the planet’s equatorial plane, as do its rings. They are thought to have formed in orbit (a flattened disk of gas and dust that formed around the giant planets) in much the same way our planets formed in orbit around the “Sun”.
According to Gladman, the conventional wisdom was that if moons formed from nearby planets, they would remain very close together, orbiting their equatorial plane as planetary rings do.
However, it turns out that some moons don’t follow these rules.
Planets also have irregular satellites whose orbits do not follow a predictable path around their parent planet’s equatorial plane. Their orbits are more elliptical and inclined, moving further away from the planet and often following a different direction than the planet’s orbit around the Sun. Also, many of them are much smaller.
The digital revolution
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Jupiter and Saturn as seen from Jersey City, New Jersey
For decades, lunar detectives have had to use photographic plates to find evidence of the existence of the solar system’s moons. The smaller they were and the more irregular their orbits, the more difficult they were to observe.
But in the 1990s and 2000s, digital photography suddenly changed the way people like Gladman could locate them. CCD sensors in digital cameras are much more sensitive to light than photo plates and can therefore detect much fainter objects.
However, a new problem has arisen. Because CCD sensors were small, the field of view they could capture was very limited.
“Giant planets are very big. The region around them — where you could orbit the planets instead of orbiting the Sun — is very large,” says Gladman.
“In 1997 I discovered two moons near Uranus with a camera. He adds that the planet’s relative distance from Earth meant a relatively limited field of view.
Then came another breakthrough: Mosaic CCD cameras, which combine multiple CCD sensors into an array. “It allows for a much larger field of view,” says Gladman. “When that happened, there was an explosion (of discoveries) in the late 1990s and early 2000s.
In 2000, Mr. Gladman was having fun using this new technique himself. “I discovered 12 in 2000 with a couple of telescopes,” he explains. “Large-format multi-CCD mosaic cameras first became available for large-aperture telescopes. Then it was possible to capture so much of the sky that you didn’t have to fish in the dark.”
Discovering the moons is meticulous work. “We used to take one picture, then another picture an hour later, and then another picture an hour later,” says Gladman. These three images tell us if an object – possibly a moon – is moving in a certain direction.
“In the past, when CCD cameras weren’t very big, I did everything by eye. But now that the datasets are huge, that’s no longer possible. We have computer programs that take the picture, find all the objects, and eliminate everything.” doesn’t move and looks for what moves.
The moons yet to be discovered are small and reflect only a tiny amount of light, forcing scientists to try new approaches.
May’s discovery involved a technique called “shift stacking,” which is similar to a camera’s multiple exposure mode.
What new moons can reveal
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Saturn’s volume is enough to hold 740 times that of Earth, but its mass is only 95 times that of Earth.
Astronomers believe that finding moons is an area that deserves further investigation. And recent discoveries—those tiny chunks of rock that barely reflect light—provide tantalizing clues about the solar system’s past.
Mike Alexandersen, a postdoctoral fellow at the Minor Planets Center who was also involved in the discovery of Saturn’s new moons, believes these discoveries will help better understand how these moons formed.
“It is believed that the reason they are grouped and have similar orbits is because they were once a single object that collided. Then the fragments continued to collide for billions of years. on others.”
Gladman calls this a “collision cascade”: a series of collisions resulting in smaller and smaller lunules.
He and his colleagues recently suggested that a relatively recent collision within the last hundreds of millions of years may have produced some of Saturn’s smaller irregular moons.
Alexandersen has conducted extensive research on the Kuiper Belt, a vast accumulation of icy debris 20 times larger than the Solar System’s asteroid belt.
According to him, the mapping of around 4,000 Kuiper Belt objects has led to some theories about how planets form and why there are so many small moons scattered about the solar system.
An ancient cataclysm may have plunged these small satellites into darkness at a time when the gravitational pull of the gas giants (Jupiter and Saturn) was greater than that of the Sun, although Alexandersen points out that the Sun continues to exert such enormous influence today distances.
The moons these astronomical detectives are looking for are on the limit of what current technology can detect: satellites at least a kilometer in diameter.
Artificial intelligence could be the next step. “We could use artificial intelligence machine learning techniques to feed the data sets to a computer and ask it to find the moons,” says Gladman.
“We’re still working on it… it’s a real challenge. But it’s only in the last few years that we’ve started to make real progress.”
Anyway, the discoveries don’t seem to stop anytime soon.
A few weeks after the announcement of the 62 new discoveries, the scientists experienced another surprise: they were able to add another moon to the list.
“An additional moon was announced but it wasn’t in the press release because we didn’t get the correct orbit,” Alexandersen told the BBC. “But we corrected it. So there are not 62, but 63. So the total number of Saturn moons is 146.”