For the past two decades, astronomers have been probing Saturn's surroundings with heightened sensitivity in search of moons
06-08-2023

Saturn is now confirmed to have a total of 145 "real" moons, leading the solar system moon race

In a thrilling development that propels Saturn back to the forefront of the Solar System’s “moon race,” an international team of astronomers, including researchers from the University of British Columbia, has unveiled the discovery of 62 new moons orbiting the ringed planet. 

Saturn’s latest additions not only reclaim its title for the most known moons, surpassing Jupiter’s 95, but also make Saturn the first planet to boast over a hundred discovered moons.

Dr. Edward Ashton initiated the research project at UBC and is currently a postdoctoral fellow at Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics.

“Connecting the various appearances of these moons in our data to a viable orbit feels like playing the kid’s game Dot-to-Dot. It’s akin to playing about 100 different games on the same page, not knowing which dot belongs to which puzzle,” said Dr. Ashton.

How the discovery was made

For the past two decades, astronomers have been probing Saturn’s surroundings with heightened sensitivity in search of moons. In their latest quest, Ashton’s team employed a technique known as “shift and stack,” a first in the realm of Saturn moon searches. 

The method, previously used for moon explorations around Neptune and Uranus, involves shifting a sequence of images at the rate that the moon moves across the sky. This movement, when combined with all the data, enhances the moon’s signal, making even the faintest moons visible in the stacked image.

The team relied on data collected by the Canada-France-Hawaii Telescope (CFHT) situated atop Mauna Kea, Hawaii from 2019 to 2021. By shifting and stacking many sequential images taken over three-hour spans, they successfully detected moons around Saturn as small as about 2.5 kilometers in diameter.

Ashton’s team includes UBC professor Dr. Brett Gladman, Dr. Mike Alexandersen from the Harvard Smithsonian Centre for Astrophysics, Dr. Jean-Marc Petit from Observatoire de Besancon, and Matthew Beaudoin from UBC.

Tedious work and long hours

The initial search for these moons was conducted in 2019, when Ashton and Beaudoin, then students at UBC, meticulously scrutinized deep CFHT imaging data from that year. Yet, spotting an object close to Saturn in the sky doesn’t necessarily confirm it as a moon. It could also be an asteroid making a close pass to the planet, although that is unlikely.

Objects must be monitored for several years to definitively confirm their orbit around the planet. After diligently matching objects spotted on different nights over two years, the team tracked 63 objects, ultimately identifying them as new moons.

Interestingly, some of the team’s linked orbits matched with past observations that had briefly glimpsed some of these moons but failed to track them long enough to confirm their orbit around Saturn.

All the newly discovered moons fall into the category of irregular moons, believed to have been initially captured by their host planet long ago. These moons are distinguished by their large, elliptical, and inclined orbits compared to regular moons. 

The tally of known saturnian irregular moons now stands at 121, up from 58 before the search commenced. Counting the 24 regular moons, the International Astronomical Union now recognizes a total of 145 moons.

Irregular moons often group together based on the tilt of their orbits. In Saturn’s system, there are three such groups, each named after different mythologies: the Inuit, the Gallic, and the Norse groups. The newly discovered moons all fall into one of these three groups, with the Norse group gaining the most additions.

These groups are believed to be remnants of collisions on the originally-captured moons, giving us valuable insights into the collisional history of Saturn’s irregular moon system.

Pushing the limits of modern telescopes

“As we push the capabilities of modern telescopes to their limits, we’re uncovering increasing evidence that a moderate-sized moon, orbiting Saturn in reverse, was shattered roughly 100 million years ago,” explained Dr. Gladman.

The team’s previous investigations into these moons have led them to propose that the abundance of small moons on retrograde orbits stems from a relatively recent event. 

In astronomical terms, “recent” means within the last 100 million years. During this time, it’s believed a moderately sized irregular moon was disrupted and fragmented into the many pieces we see today.

This discovery not only reaffirms Saturn’s status as the planet with the most moons but also provides scientists with a better understanding of how irregular moons form and evolve. 

Each new moon discovered around Saturn is like a piece of a larger puzzle. They help to paint a clearer picture of the Solar System’s past and how it might evolve in the future. It’s a testament to the power of modern telescopes and the diligence of astronomers who, like children connecting dots on a page, continue to map out the seemingly infinite expanse of our universe.

More about the moons of our solar system

The planets of our solar system are accompanied by a diverse array of moons. As of my knowledge cut-off in September 2021, here’s a rundown of the known moons of each planet:

Mercury and Venus have no moons. This is likely due to their proximity to the Sun. The Sun’s powerful gravitational pull makes it difficult for these planets to capture and hold onto their own moons.

Earth has one moon, known simply as the Moon. It’s the fifth-largest moon in the solar system and is believed to have formed about 4.5 billion years ago after a Mars-sized body collided with Earth.

Mars has two small moons, Phobos and Deimos, which are thought to be captured asteroids. They were discovered in 1877 by American astronomer Asaph Hall.

Jupiter, the largest planet in our solar system, has a multitude of moons. As of 2021, Jupiter’s moon count stands at 79. The four largest are known as the Galilean moons: Io, Europa, Ganymede, and Callisto. Ganymede is the largest moon in the solar system and is even bigger than the planet Mercury.

Saturn, as of the latest update in this conversation, has over 100 moons, the most of any planet in the solar system. The largest of Saturn’s moons, Titan, is the second largest in the solar system and is even bigger than the planet Mercury. Titan is the only moon known to have a dense atmosphere and large bodies of surface liquid.

Uranus has 27 known moons as of 2021. Most of Uranus’s moons are named after characters from the works of William Shakespeare and Alexander Pope. The largest, Titania, is the eighth-largest moon in the solar system.

Neptune has 14 known moons. The largest, Triton, is unique in that it orbits Neptune in a direction opposite to the planet’s rotation (a retrograde orbit), suggesting that Triton was captured by Neptune’s gravity and didn’t form in place.

Pluto, while classified as a dwarf planet, also has five known moons. The largest, Charon, is so large relative to Pluto that they are often referred to as a binary system.

The study of moons, or natural satellites, provides scientists with valuable insights into how our solar system formed and evolved over time. As technology advances, it’s likely that the counts will continue to rise and our understanding of these celestial bodies will continue to grow.

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