2023-07-13 11:48:39
24 minutes ago
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Astronomers have observed Saturn and its satellites for more than three and a half centuries.
Since man began to look at the sky, our moon has been watching us from its orbit at a relatively short distance from our planet. It is the most visible natural satellite in our solar system, but it is not the only one.
However, it is always difficult to know how many there are.
Last May, astronomers announced that they had discovered 62 new moons orbiting Saturn, one of the solar system’s gas giants.
This brings to 145 the number of confirmed moons around this leviathan located some 1.3 billion kilometers from the Sun.
Saturn thus becomes the planet with the greatest number of moons in orbit, dethroning its giant neighbor Jupiter in what some have called the “race for the moons”.
Saturn’s moon count keeps growing, and the same team made a new discovery a few weeks later.
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 at the top of Mauna Kea, a volcano in Hawaii.
Astronomers have observed Saturn and its satellites for more than three and a half centuries. Humanity has even sent four spacecraft to Saturn, and yet these moons have not been discovered.
How come so many of Saturn’s moons stay hidden? Why is it so hard to find distant moons, and how many more might be waiting in the dark of space?
Difficult to detect
Crédit photo, NASA/JPL/SPACE SCIENCE INSTITUTE/REUTERS
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Image of Saturn’s moon Enceladus, composited from high-resolution photos taken by NASA’s Cassini spacecraft in 2005.
When last counted, there were no less than 290 “traditional” moons in our solar system.
It is not enough to observe a moon for it to be officially a moon. Some of these new satellites have already been observed, but a long process is needed before the International Astronomical Union officially classifies them as moons. This process involves several years of constant observation.
For four centuries, many of our celestial neighbors were too distant for us to distinguish.
In 1655, Dutch astronomer Christiaan Huygens discovered the largest of Saturn’s moons, Titan, larger than the planet Mercury. It took 16 years for Jean-Dominique Cassini to discover Hapetus, then Rhea, Dione and finally Thetis in 1684. It was not until 1789 that the German astronomer William Herschel identified Mimas and the icy moon Enceladus.
Other Saturn moons have escaped human observation for much longer. Hyperion, which has the shape of a potato, was discovered in 1848. It was followed, some fifty years later, by Phoebe, which moves around Saturn in the opposite direction to that of most moons.
With the advent of the space age and modern telescopes, the list of Saturn’s moons has grown considerably. Spacecraft such as the Voyager and Cassini probes have expanded discoveries by taking a closer look at Saturn’s complex system.
Yet the vast majority of Saturn’s moons have 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, what 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 in 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 the same way that our planets formed in orbit around the sun”.
According to Gladman, the conventional wisdom was that if moons formed from nearby planets, they would stay very close and orbit around their equatorial plane, like planetary rings do.
However, it turns out that some moons do not follow these rules.
Planets also have irregular satellites whose orbits do not follow a predictable path around the equatorial plane of their host planet. Their orbits are more elliptical and inclined, move further away from the planet, and often follow a different direction than the planet around the sun. Also, many of them are much smaller.
The digital revolution
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Jupiter and Saturn seen from Jersey City, New Jersey
For decades, lunar sleuths have had to use photographic plates to try to find evidence for the existence of the solar system’s moons. The smaller they were and the more irregular their orbit, the more difficult it was to observe them.
But in the 1990s and 2000s, digital photography suddenly changed the way people like Gladman might locate them. CCD sensors in digital cameras are much more sensitive to light than photographic plates, allowing them to detect much fainter objects.
However, a new problem has arisen. Since CCD sensors were small, the field of view they might capture was very limited.
“Giant planets are very large. The region around them – where you might orbit the planets instead of orbiting the sun – is very large,” says Gladman.
“In 1997, I discovered two moons near Uranus using 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 several CCD sensors into an array. “It allows for a much wider 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 himself had fun using this new technique. “I discovered 12 in 2000 with a few telescopes,” he explains. “Large-format multi-CCD mosaic cameras began to be available on large-aperture telescopes. It was then possible to capture enough of the sky that you didn’t have to fish in the dark.
The detection of the moons is a meticulous work. “We used to take one image, then an hour later another image, and then another hour later another image,” says Gladman. These three images let us know if an object – possibly a moon – was moving in a particular direction.
“Before, when the CCD cameras were not very big, I did everything by eye. But now that the data sets are huge, this is no longer possible. We have computer programs that take the image, find all the objects, eliminate all that does not move and look for what moves.
The moons that remain to be discovered are small and reflect only a tiny amount of light, which has forced scientists to use new approaches.
May’s discovery involved a technique called “shift stacking,” which is akin to a camera’s multiple exposure mode.
What New Moons Can Reveal
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Saturn’s volume is enough to contain 740 times the Earth, but its mass is only 95 times that of the Earth.
Astronomers believe that the search for moons is an area that deserves further investigation. And recent discoveries – those little chunks of rock that barely reflect light – give tantalizing clues to the solar system’s past.
Mike Alexandersen, postdoctoral researcher at the Minor Planets Center, who was also involved in the discovery of Saturn’s new moons, believes that these discoveries will help to better understand how these moons formed.
“It is believed that the reason they are grouped together and have similar orbits is that they were once a single object that collided. Then, for billions of years, the fragments continued to crash into each other. on others”.
Gladman calls this a “collisional cascade”: a series of collisions that give rise to 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 created some of Saturn’s smaller irregular moons.
Alexandersen has done extensive research on the Kuiper Belt, a vast conglomeration of icy debris 20 times larger than the Solar System’s asteroid belt.
According to him, the mapping of some 4,000 Kuiper Belt objects has led to some theories regarding how planets form and why so many small moons are scattered around 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 a influence even at such enormous distances.
The moons these astronomical sleuths are looking for are at the limit of what current technology can capture: satellites at least a kilometer in diameter.
Artificial intelligence might be the next step. “We might use machine learning techniques from artificial intelligence to feed the datasets 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.
Either way, the discoveries don’t seem to be stopping anytime soon.
A few weeks following the announcement of the 62 new discoveries, scientists had another surprise: they had one more moon to add to the list.
“An extra 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 it’s not 62, but 63. That brings the total number of moons of Saturn to 146.
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