Saturn Re-takes the Moon Crown

[BootinUp]

Prof. Sam Lawler
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MOAR MOOOOOOONS

Saturn is up to 145 discovered moons!

https://phas.ubc.ca/saturn-re-takes-mo

The work of an international team of astronomers has resulted in the announcement of 62 new moons of Saturn, catapulting it back into first place of the 'moon race' around the giant planets of our Solar System. The team is led by Edward Ashton (currently a postdoctoral fellow at Taiwan's Academia Sinica Institute of Astronomy and Astrophysics) and includes professor Brett Gladman (Department of Physics & Astronomy at the University of British Columbia), Mike Alexandersen (Harvard Smithsonian Center for Astrophysics), Jean-Marc Petit (Observatoire de Besancon), and Matthew Beaudoin (University of British Columbia).

Over the past two decades, Saturn's surroundings have been repeatedly examined for moons with increasing sensitivity. In this latest study, Dr Ashton's team used a technique known as 'shift and stack' in order to find fainter (and thus smaller) saturnian moons. This method has been used for moon searches around Neptune and Uranus, but never for Saturn. Shifting a set of sequential images at the rate that the moon is moving across the sky results in enhancement of the moon's signal when all the data is combined, allowing moons that were too faint to be seen in individual images to become visible in the `stacked' image. The team used data taken using the Canada-France-Hawaii Telescope (CFHT) on top of Mauna Kea, Hawaii between 2019 and 2021. By shifting and stacking many sequential images taken during 3 hour spans, they were able to detect moons of Saturn down to about 2.5 kilometers in diameter.

The original discovery search was done in 2019 when Ashton and Beaudoin were students at the University of British Columbia, uncovering the moons in a meticulous search of the deep CFHT imaging acquired that year. But just finding an object close to Saturn on the sky is insufficient to say for certain that it is a moon; it could in principle be an asteroid that just happened to be passing close to the planet (although this is unlikely). To be absolutely sure, the object must be tracked for several years before one can establish that it is certainly orbiting the planet. After painstakingly matching objects detected on different nights over two years, the team has managed to track 63 objects, thus confirming them as new moons. One of the new moons, designated S/2019 S 1, was announced back in 2021, with the rest being announced over the last couple of weeks. Some of the team's linked orbits were identified with past observations from many years ago that briefly glimpsed some of these moons (but were not tracked long enough to establish their orbit around Saturn).

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All of the new moons are in the class of irregular moons, which are thought to be initially captured by their host planet long ago. Irregular moons are characterized by their large, elliptical, and inclined orbits compared to regular moons. The number of known saturnian irregular moons has more than doubled to 121, with 58 previously known before the search began. Including the 24 regular moons, there is now a total of 145 recognized (by the International Astronomical Union) moons orbiting Saturn. The new discoveries have resulted in multiple milestones for the ringed planet. Saturn has not only regained its crown for having the most known moons (overtaking Jupiter with 95 recognized moons), it is also the first planet to have over 100 discovered moons in total.

https://phas.ubc.ca/saturn-re-takes-moon-crown

[rsdsharp]

1. When I was a kid, if memory serves, Saturn was thought to have 9 moons.

Of course, the solar system had 9 planets then, too.

[Warpy]

2. They'll probably discover more around Neptune and Uranus as time goes on

Not so Jupiter, it's big enough that it would keep eating the smaller ones.

[Wounded Bear]

3. If they had known this back in the day, would they have even launched Voyager?

Really, though, back then they thought the volume of space around the giant planets was much less crowded. This knowledge might have complicated their calculations. Kind of lucky neither of the Voyager craft "found" any of these satellites.

[muriel_volestrangler]

4. Though the same team have 45 new moons of Jupiter lined up too

Now, Edward Ashton, Matthew Beaudoin, and Brett Gladman (University of British Columbia, Vancouver) have detected about four dozen possible new Jovian moons that are even smaller. Extrapolating from the sky area they have searched (about one square degree), they conclude that there could be some 600 of these tiny objects orbiting the giant planet.
...
This method revealed 52 objects down to magnitude 25.7, corresponding to diameters of some 800 meters. Seven of the brighter finds turned out to be known irregular satellites of Jupiter; the others are almost certainly retrograde Jovian moons, which orbit the planet in the direction opposite its rotation. A paper describing the results has been accepted for publication in The Planetary Science Journal (full preprint available here).

If this sensitive one-square-degree “pencil-beam” search already yields 45 formerly unknown moons, the researchers estimate that the total number of satellites within this size range must be around 600. The current official number of Jovian moons is 79.

Sheppard (whose team found 20 new satellites of Saturn last year) is not surprised by the new result. “We used a similar shift and stack technique for our Jupiter moon discoveries that were announced in 2018,” he says. “In our paper, we also mentioned detections that we could not confirm as moons, because we didn’t observe them for the months and years required to reliably determine their orbits.”

https://skyandtelescope.org/astronomy-news/jupiter-could-have-600-moons/

(though some of the 45 may be the 16 Jupiter moons that Sheppard announced after that 2020 article: https://en.wikipedia.org/wiki/Timeline_of_discovery_of_Solar_System_planets_and_their_moons )