APOD: Herschel Crater on Mimas of Saturn (2010 May 11)

[APOD Robot]

Herschel Crater on Mimas of Saturn

Explanation: Why is this giant crater on Mimas oddly colored? Mimas, one of the smaller round moons of Saturn, sports Herschel crater, one of the larger impact craters in the entire Solar System. The robotic Cassini spacecraft now orbiting Saturn took the above image of Herschel crater in unprecedented detail while making a 10,000-kilometer record close pass by the icy world just over one month ago. Shown in contrast-enhanced false color, the above image includes color information from older Mimas images that together show more clearly that Herschel's landscape is colored slightly differently from more heavily cratered terrain nearby. The color difference could yield surface composition clues to the violent history of Mimas. An impact on Mimas much larger than the one that created the 130-kilometer Herschel would likely have destroyed the entire world.

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[tesla]

If this is an impact crater it would of destroyed the moon or left it in a sorry state. It would of hit at a high velocity. Also you would find major destruction at the antipode site on the opposite side of the crater. Nothing there.

[Chris Peterson]

If this is an impact crater it would of destroyed the moon or left it in a sorry state. It would of hit at a high velocity. Also you would find major destruction at the antipode site on the opposite side of the crater. Nothing there.

This is a moon made of water ice. The dynamics of a collision are quite different than for rock. Also, there are fractures and deformations directly opposite the crater.

People have looked at the energy dissipated in a collision producing a crater of this size, and concluded it wasn't great enough to destroy the moon. Perhaps you could share your calculations- the ones that make you certain otherwise. (What the heck else could it be besides an impact crater, anyway? It looks just like thousands of others all over the Solar System.)

[CuDubh]

It would take a MUCH larger impact to "destroy" Mimas. 4 Vesta has a crater nearly its own diameter, and the Earth (now the Earth-moon system) seems to have survived a Mars-size impactor quite nicely. To destroy such a large body, you need to inject enough energy that at least a majority of the materials comprising it (plus the impactor) exceed escape velocity. A tall order, but probably the asteroid belt and maybe the moons of Saturn are examples of where it works.

[CuDubh]

Also, the impact is not really "oddly colored". The interior of the crater seems quite similar to the areas near the limb of the moon in this image. Rather more interesting are the thick layer of light material exposed in the upper walls of the crater, and the prominent dark layer exposed around much of the base of the walls.

[Sunit]

The extent of the colored area seems too large compared to the size of the crater.

This image suggests that the meteor that crashed on Mimas was itself composed of materials of low density. A mixture of ice and rocks, for example (the fertile mind could imagine a comet - and why not).

This could also explain the "color" that extends as far from the impact zone. Perhaps the meteor was vaporized on impact, or perhaps there were materials that followed the meteor (like a comet's tail) that have naturally covered Mimas, after impact, on a wider area than the crater itself.

Regards,

[wonderboy]

We all know and believe that star wars was real. This is the death star in disguise, its not a crater. Its the eye of doom that can cause the destruction of any planet in the universe. Lets not disturb it from its icy sleep. lol.

(Its an impact crater, end of)

Paul.

[Sunit]

Paul

I hope this is not my post that you "loled". I'm really sorry if so.
I am far from any inclination within the science fiction or mysticism ... Yes, it is an impact crater, it is not necessary to argue about.

The photo caption asks why there is this particular color. So long as there is no objective answer but only speculation, I believe that imagination deserves his place.
Without imagination, no thesis. No thesis, no research.

Regards.


nb : Perhaps some terms I use could be confusing, I'm not an English native speaker.

[Guest]

Looks very much like some granite boulders I have broken with a sledge hammer making a direct hit. A region of the outer layer frgments and a harder interior floor remains. When granite weathers, the outer layer has some of its minerals leached out. It is softer than the interior and fragments a bit easier.

The look of the cratering is very similar.

In granite the interior has a different coloring because its composition is unlike the weathered surface layer.

[wonderboy]

Paul

I hope this is not my post that you "loled". I'm really sorry if so.
I am far from any inclination within the science fiction or mysticism ... Yes, it is an impact crater, it is not necessary to argue about.

The photo caption asks why there is this particular color. So long as there is no objective answer but only speculation, I believe that imagination deserves his place.
Without imagination, no thesis. No thesis, no research.

Regards.


nb : Perhaps some terms I use could be confusing, I'm not an English native speaker.

Since it appears that we are taking ourselves seriously now Sunit, I will do the same.

Firstly, your English is very good so do not worry about your terms being confusing, because if you write as eloquently as this at all times
then you have nothing to worry about. This is as far as my compliments go.

Secondly, I never "loled" at your post, I merely "loled" at the ridiculousness of my own post.

Thirdly, I never brought into question your inclinations towards science fiction or mysticism and I was not arguing with whether or not it was
an impact crater as my post above shows:

We all know and believe that star wars was real. This is the death star in disguise, its not a crater. Its the eye of doom that can cause the destruction of any planet in the universe. Lets not disturb it from its icy sleep. lol.

(Its an impact crater, end of)

Paul.

Fourthly, you are right about the photo caption, it does question why

...this giant crater on Mimas is oddly colored...

, however, as is often the case with forums, the discussion changed its direction and started discussing the origin of the crater and why the moon was not destroyed. Perhaps my post never tickled your funny bone, but it was at most a jovial attempt at injecting fun into the forums discussions. If you have seen Star Wars then you will understand that the moon in question looks similar to that of the death star:

If my post offended you in some way then for this I apologise, but for trying to inject a little humor into a subject where an element of humor makes itself apparent, I do not apologise and stand by my ridiculous post.


Paul

[neufer]

<<Mimas was one of the Gigantes of Greek mythology. Like the other giant sons of Gaia,
Mimas had serpents for legs and was born fully armoured.
Mimas was slain by Hephaestus during the war against the Olympian Gods.>>

Code: Select all

1) Titan      1655    Huygens
2) Iapetus    1671    Cassini
3) Rhea       1672    Cassini
4) Dione      1684    Cassini
5) Tethys     1684    Cassini
6) Enceladus  1789    William Herschel
7) Mimas      1789    William Herschel

<<Mimas was discovered by the astronomer William Herschel on 17 September 1789. He recorded his discovery as follows: "The great light of my forty-foot telescope was so useful that on the 17th of September, 1789, I remarked the seventh satellite, then situated at its greatest western elongation." Mimas is named after one of the Titans in Greek mythology, Mimas. The names of all seven then-known satellites of Saturn, including Mimas, were suggested by William Herschel's son John in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope. He named them after Titans specifically because Saturn (the Roman equivalent of Kronos in Greek mythology), was the leader of the Titans.

According to Liddell and Scott's Greek-English Lexicon, the adjectival form of Mimas would be Mimantean (the genitive case is Latin Mimantis, Greek Μῑμάντος). In practice, anglicisms such as Mimasian and Mimian are very occasionally seen, but more commonly writers simply use the phrase 'of Mimas'.

Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn's two widest rings, A ring and B ring. Particles at the inner edge of the Cassini division are in a 2:1 resonance with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. Other resonances with Mimas are also responsible for other features in Saturn's rings: the boundary between the C and B ring is at the 3:1 resonance and the outer F ring shepherd, Pandora, is at the 3:2 resonance. More recently, a 7:6 co-rotation eccentricity resonance has been discovered with the G ring, whose inner edge is about 15,000 kilometres (9,300 mi) inside the orbit of Mimas.>>

[Astronut]

That nice big crater has a nice compression bump in it. I could only find two more compression bumps - one in a small crater at 7:30 o'clock and one with a bump that seems to be toooooo big at 12 o'clock.
Maybe some of that white dust has smoothed them out - maybe not.

Perhaps someone thats "crater savy" could shed some light on this?

[Sunit]

Paul.
Thank you for your clarification and sorry to have imposed a return to serious ;)

I didn't detect the subtlety in your first post and I misunderstood "Its an impact crater, end of".
In fact, it was a pretty good humour and I like the self-mockery... I regret to not have understood it.

I think the most ridiculous of the two is me.

[wonderboy]

Don't be crazy Sunit.

The matter has ended. But you have to admit it does resemble the death star!


Paul.

[The Code]

Any body got a red shirt going spare?

Brilliant photo. What did this impact do to the moons orbit? Or spin? To be left intact, did the energy go elsewhere?

Mark

[Chris Peterson]

What did this impact do to the moons orbit? Or spin? To be left intact, did the energy go elsewhere?

It probably had minimal effect on the orbit or spin. The impacting body had only a tiny fraction of the mass of Mimas, and the kinetic energy of the impact would be released as heat and symmetrically distributed mechanical energy inside the moon.

FWIW, a good rule of thumb relating crater size to impactor size for hypervelocity impacts is to assume the impactor is 1/10 the diameter of the crater. Assuming in this case a rocky impactor, with a density about double that of Mimas, you get a mass for the impactor equal to about 0.008% of Mimas itself. Even with a high velocity, we are talking about a small transfer of momentum.

[The Code]

Thanks for your time Chris.

Do you think the impact is consistent with an orbital body or an incoming commit? And does the crater give any sort of time period of when, how long ago it happened?

Mark

[Chris Peterson]

Do you think the impact is consistent with an orbital body or an incoming commit? And does the crater give any sort of time period of when, how long ago it happened?

Comets are also orbiting bodies, so I don't think there is much distinction. All I can say looking at the image is that the crater was produced by a hypervelocity impact, probably no shallower than about 15°; any speculation about the origin of the body would be just that- speculation. I'm sure people who study crater morphology would look at this crater in relation to other craters, and from that could come up with plausible estimates for the crater age. I don't know how to do that, though.

[cmflyer]

I've had a question for my students to identify the "Death Star Moon" for as long as I've been teaching Earth and Space Science. But anyway, in this picture I get the impression that the ice in the crater is transparent, like seeing into a green ice cube.

[DavidLeodis]

Fascinating image. It reminded me of the image in http://antwrp.gsfc.nasa.gov/apod/ap070520.html, though admittedly the 'crater' in that image is on a very very much smaller scale.

I wonder just how huge the largest crater is on a planet or moon in our galaxy (the Milky Way) and the Universe. Probably mind-bogglingly big I suspect.

[MarkusMaximus]

"That's no moon....IT'S A SPACE STATION!"

[GaryR]

This is a moon made of water ice...

I am always puzzled how it is possible that there could be such a concentration of some chemical compound, in this case water ice, that would condensed into a large body composing mostly of that chemical compound. I would think that following a supernova, most elements produced by it would be so dispersed into interstellar space that there would be no chance of any element or compound clumping into concentrations.

Gary

[wonderboy]

could it not be the case that this is a comet captured by the planet. so instead of being "blootered" by a supernova (blootered being a scottish word for battered, drunk, smashed, hit, etc etc) in our solar system, it may have travelled for absolutely bloody miles and ended up captured.

Just an idea.


Paul