Astronomy: Why Saturn’s Moons Are So Hard to Find and What They Reveal About the History of the Solar System

Saturn thus becomes the planet with the most moons in its orbit, dethroning its giant neighbor Jupiter in what some have called the “race for the moons.”

Saturn’s moon population continues to grow, and the same team made a new discovery a few weeks later.

The location of the new moons was determined by a team led by Edward Ashton, a postdoctoral researcher at Academia Sinica’s Institute for Astronomy and Astrophysics in Taiwan.

The discovery took more than two years, thanks to a telescope installed atop the Mauna Kea volcano in Hawaii.

Astronomers have observed Saturn and its moons for more than three and a half centuries. Mankind has even sent four spacecraft to Saturn, yet these moons have yet to be discovered.

How many of Saturn’s moons are hidden? Why are distant moons so hard to find, and how many more could be waiting in the dark?

At last count, there were at least 290 “traditional” moons in our solar system.

It is not enough to observe a moon for it to be an official moon. Some of these new satellites have already been spotted, but a long process is needed before the International Astronomical Union can officially classify them as satellites. This process involves several years of continuous monitoring.

For four centuries, many of our celestial neighbors have been too far to discern.

In 1655, Dutch astronomer Christiaan Huygens discovered Saturn’s largest moon, Titan, which is larger than Mercury. It took 16 years for Jean-Dominique Cassini to discover Haptos, then Rhea, Dione and finally Thetis in 1684. It wasn’t until 1789 that German astronomer William Herschel identified Mimas and its icy moon Enceladus.

Saturn’s other 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 the direction of most of the moons.

With the advent of the space age and modern telescopes, the list of Saturn’s moons has grown exponentially. Spacecraft such as the Voyager probes and Cassini have expanded the discoveries by taking a closer look at Saturn’s complex system.

However, the vast majority of Saturn’s moons were 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 the 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 about Saturn.

“Its moons orbit in the planet’s equatorial plane, as do its rings. They are thought to have formed in orbit (a flat disk of gas and dust formed around the giant planets) in 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 stay very close and orbit around 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 the host planet’s equatorial plane. Their orbits are steeper and steeper, further away from the planet, and often follow a different direction than the planet around the sun. Also, many of them are much smaller.

For decades, lunar investigators have had to use photographic plates to try to find evidence of the solar system’s moons. The smaller they are and the more irregular their orbit, the more difficult they are to observe.

But in the 1990s and 2000s, digital photography suddenly changed the way people like Gladman could locate themselves. CCD sensors in digital cameras are much more sensitive to light than photographic plates, which makes it possible to detect even fainter objects.

However, a new problem has arisen. Because CCD sensors were small, the field of view they could capture was very limited.

“The giant planets are very big. The area around them – where you can orbit around the planets instead of around the sun – is very big,” Gladman says.

In 1997, I discovered two moons near Uranus using a camera. The planet’s relative distance from Earth means a relatively limited field of view, he adds.

Then came another breakthrough: mosaic CCD cameras, which combine several CCD sensors into an array. “It allows for a much wider field of view,” Gladman says. “When that happened, there was an explosion (in discoveries) in the late 1990s and early 2000s.

In 2000, Mr. Gladman entertained himself with this new technology. “I discovered 12 in the year 2000 with just a few telescopes,” he explains. “Large-format multiple-CCD mosaic cameras started to appear on large-aperture telescopes. Then it became possible to capture enough of the sky that you didn’t have to hunt in the dark.

Detecting moons is a delicate business. “We used to take one photo, then an hour later another photo, and then an hour later another photo,” says Gladman. These three images let us know if an object – perhaps a moon – is moving in a certain direction.

“Before, when CCD cameras weren’t so big, I’d do everything by eye. But now that data sets are huge, that’s not possible anymore. We have computer programs that take the image, find all the things, remove all that doesn’t move and look for what moves.

The as-yet-undiscovered moons are small and reflect only a tiny amount of light, forcing scientists to use new methods.

May’s discovery involved a technology called “transfer stacking,” which is similar to a camera’s multiple exposure mode.

Astronomers believe that the search for moons is an area worthy of further investigation. And recent discoveries – tiny bits of rock that barely reflect light – give tantalizing clues to the solar system’s past.

Mike Alexandersen, a postdoctoral researcher at the Minor Planet 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’s thought that the reason they are grouped together and have similar orbits is because they were once a single body that collided. Then, for billions of years, the fragments kept crashing into each other. On others.”

Gladman calls this a “collision cascade”: a series of collisions that give rise to smaller and smaller crescents.

He and his colleagues recently suggested that a relatively recent collision, during the past hundreds of millions of years, may have triggered some of Saturn’s smaller irregular moons.

Alexandersen has done extensive research on the Kuiper Belt, a huge collection of icy debris 20 times larger than the solar system’s asteroid belt.

According to him, the mapping of about 4,000 objects in the Kuiper Belt has led to some theories about how planets form and why so many small moons are scattered around the solar system.

An ancient cataclysm may have plunged these tiny 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 still exerts influence even at such enormous distances. .

The moons these astro-spys are looking for are on the order of what current technology can pick up: satellites at least a kilometer in diameter.

Artificial intelligence could be the next step. “We can use machine learning techniques from artificial intelligence to give the computer datasets and tell it to find the moons,” Gladman says.

“We’re still working on it… It’s a real challenge. But it’s only in the past few years that we’ve started to make real progress.

Either way, the revelations don’t seem like they’ll stop anytime soon.

Just weeks after the 62 new discoveries were announced, scientists were in for another surprise: They had another moon to add to the list.

“An additional satellite was announced, but it wasn’t in the press release because we didn’t get the right orbit,” Alexandersen told the BBC. But we corrected it. So not 62, but 63. That brings the total number of Saturn’s moons to 146.