09 March 2017

Cassini flew by a weird moon and I made a gif of it

Cassini, NASA's doomed mission to Saturn, is doing its best to make us sad to see it go. It recently sent back data from a flyby of one of the smaller moons, Pan - and thanks to NASA's incredible open data philosophy, you don't have to be on the Cassini science team to have access to the raw images! We paid for this data, after all. Anyway, I made a gif! It was fun and easy! And now we know that Saturn has a moon that someone threw two balls of Play-Doh at each other, and they stuck.
I am super impressed by how easy the Cassini team made it to get the raw data. Check it out for yourself here: https://saturn.jpl.nasa.gov/galleries/raw-images/


People are furiously debating what Pan looks like most: dumplings, ravioli, a mini version of Saturn?

A little legwork and some Twitter hints reveals theories about how that bulge got there that are a little more reasonable than my smooshed Play Doh idea - they were probably accreted by Pan after Saturn's rings had settled down to their 20-m width but before Pan had sucked up everything nearby and cleared out the ring gap you can see in the gif. There's a nice discussion of how this might have worked here: https://ui.adsabs.harvard.edu/#abs/2007Sci...318.1622C/abstract

Here's the key figure:
The authors contend that particles still left in the gap get sucked up into Pan's L1 and L2 Lagrange points (ESA has some nice visuals here) depending on whether they are inside or outside of Pan's orbit, but Pan's gravity is so weak relative to Saturn that by the time this happens, they are basically in top of the moon already, and there isn't any room for them to land somewhere besides the equator (especially once the ridge started being more built up). 

The authors chime on on protoplanetary disks and gap clearing (h/t ALMA):

This parting shot from the conclusion is a little more far-fetched, IMO, especially since the authors make it clear that the accretion mechanism in this case is highly dependent on the particular porous nature of the particles in Saturn's rings, which may not be true for disks in general:
But hey, that's what a parting shot is for.

As a post-script, there's another moon (Atlas) on approximately the same orbit near the A ring that also has a ridged structure, but no such dramatic flyby. It's weird and flat, and I gif'd it anyway:

Double update: this is my favorite write-up so far; amazing movies https://lightsinthedark.com/2017/03/09/our-best-ever-look-at-pan-saturns-little-ufo/

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