Cassini encountered Mimas. Saturday 13th February 2010.

[3488]

On Saturday 13th February 2010, the Cassini spacecraft approached Mimas & passed by at approx 9,600 KM, the closest pass of the innermost of Saturn's major moons & will be the closest during the entire mission.

Mimas is 395 KM wide & orbits Saturn at a distance of 185,500 KM once every 22 Hours & 36'. Mimas has a density of only 1.15 G/CM3 or only 15% greater than pure ice. Mimas therefore is mostly ice with a little rock.

I have consolidated all of the images I worked on & put them here in one place.

Another nice Mimas image from approx 72,000 KM. Using the UV filter.

Another view of the Herschel Crater.

Enlarged sharpened crop of the central mountain in the Herschel Crater on Mimas.

Enlarged & sharpened crop of Section of Herschel Crater wall & floor on Mimas. What is immediately obvious is the lack of small craters on the floor of Herschel Crater. Landslide debris covering the original floor perhaps? Or is Herschel Crater fairly young?

Does look like crater slumping has occured.

Another enlarged crop of the rim of Herschel Crater. It is quite apparant that material has slumped & striations visible on the crater wall.

Below, two enlarged crops of the limb of Mimas I did. I rotated them so they look like an horizon. Both crops are approx 30 KM wide & have been contrast enhanced. Looks almost like a view as if coming in to land!!!! Some of those mountains are approx 2,000 - 3,000 metres high IMO.

The 130 KM wide, 5 KM deep Herschel Crater crop during approach. It is worth bearing in mind that Mimas is only 395 KM across.

Mimas. NE of Herschel Crater rim & a curious depression.

Mimas. Northern Rim of Herschel Crater & area north. Impact melt appears to have smoothed much of the terrain.

Curious Depression on Mimas to the N E of Herschel Crater. Feature is approx 100 KM long N - S.

Mimas. Southern portion of Herschel Crater with elliptical secondaries & valleys radiating away outside to the south. The crater on the bottom right of this cropped frame also has had landslides.

Mimas. SW floor of Herschel Crater. The base of the central mountain is visible in the top right. Note how few small craters are visible here. This is quite a surprise assuming Herschel Crater is ancient.

NW limb of Mimas, showing the very cratered & rough terrain on this ice moon of Saturn.

SW limb of Mimas. Some of these larger craters appear to have been formed from double impactors?? Wayne, what do you think? Some of these craters show striations on their walls.

Andrew Brown.

 

[nimbus]

Hi Andrew,
The curious depression you're remarking is the one that's longer than wide? From your more informed perspective, what makes it curious? Is it rare to have craters and erosion coincide just right to create every now and then an elongated depression like that, or is it something else about that depression that's out of the ordinary?

 

[3488]

Hi nimbus.

Good question. The depression is certainly partly a crater chain, but the part to the south looks more like a valley. I wonder if it's a fault caused by Herschal Crater to the west??

Andrew Brown.

 

[silylene]

Andrew, thank you. Again, I really enjoyed the photos and your comments.

I also noted that the many of the craters have a greater depth:diameter ratio than is seen on the Moon. Some are even cone-like excavations. I would think this could be due to the greater velocity of the impactors, and the greater fragility of the lower-density icey matrix, compared to lunar crust.

 

[BreezyJ]

Would the impacts have a greater velocity because of the Gravity around Saturn?

 

[Fomalhautian]

I wonder if it's a fault caused by Herschal Crater to the west??

That's what I'm thinking. I was originally thinking a tributary. It almost looks like errosion from something that once "flowed" there. I can make out a mesa there in the center, but it just kinda ends there at the lower portion of the picture.

 

[EarthlingX]

More images from the fly-by data :

Ciclops : Bizarre Temperatures on Mimas

This figure illustrates the unexpected and bizarre pattern of daytime temperatures found on Saturn's small inner moon Mimas (396 kilometers, or 246 miles, in diameter). The data were obtained by the composite infrared spectrometer (CIRS) on NASA's Cassini spacecraft during the spacecraft's closest-ever look at Mimas on Feb. 13, 2010.

The upper right image in the annotated version shows the completely different pattern that Cassini actually saw. Instead of the expected smoothly varying temperatures, this side of Mimas is divided into a warm part (on the left) and a cold part (on the right) with a sharp, v-shaped boundary between them. The warm part has typical temperatures near 92 Kelvin (minus 294 Fahrenheit), while typical temperatures on the cold part are about 77 Kelvin (minus 320 Fahrenheit). The cold part is probably colder because surface materials there have a greater thermal conductivity, so the sun's energy soaks into the subsurface instead of warming the surface itself. But why conductivity should vary so dramatically across the surface of Mimas is a mystery.

The lower two panels in the annotated version compare the temperature map to Mimas' appearance in ordinary visible light at the time of the observations. The map used to create this image is a mosaic of images taken by Cassini's imaging science subsystem cameras on previous flybys of Mimas. The cold side includes the giant Herschel Crater, which is a few degrees warmer than its surroundings. It's not yet known whether Herschel is responsible in some way for the larger region of cold temperatures that surrounds it.

The green grid shows latitudes and longitudes on Mimas at 30-degree intervals.

Another couple of interesting Ciclops articles from today : (ok, all, but 3D images of Herschel Crater)

Streaked Craters in False-Color

Examining Herschel Crater

Color Near Herschel Crater

Flying by the "Death Star" Moon

 

[nimbus]

I can't resist pointing out how that looks like pacman about to eat a pacdot.

 

[Gravity_Ray]

Man Herschel crater must have been one heck of an impact. And, what a bulls eye!

 

[EarthlingX]

I can't resist pointing out how that looks like pacman about to eat a pacdot.

Indeed, and you are not alone in this sentiment :

http://www.universetoday.com : Pacman Eats The Death Star!

Written by Nancy Atkinson
March 29th, 2010

This figure illustrates the unexpected and bizarre pattern of daytime temperatures found on Saturn's small inner moon Mimas (396 kilometers, or 246 miles, in diameter). Credit: NASA/JPL/GSFC/SWRI/SSI

Mimas has drawn a fair amount of attention with its "Death Star"-like crater, but with new images from the Cassini spacecraft, this icy moon of Saturn has just gotten a lot more interesting. The highest-resolution-yet temperature map and images of Mimas reveal surprising patterns on the surface of the small moon, including unexpected hot regions that resemble "Pac-Man" eating the Death Star crater (officially known as Herschel Crater), as well as striking bands of light and dark in crater walls. "After much deliberation, we have concluded: Mimas is NOT boring," said Carolyn Porco, Cassini imaging team leader, in an e-mail about the new images. "Who knew?!" And best of all, Porco added, "be sure you have a pair of red/green glasses handy 'cause you won't want to miss peering into gigantic Herschel crater in 3D!"

Herschel Crater in 3-D. Credit: NASA/JPL/Space Science Institute. Click for larger version.

 

[nimbus]

<<
"After much deliberation, we have concluded: Mimas is NOT boring," said Carolyn Porco.
>>

No kidding. One more moon that surprises us, like Iapetus (remember how Vogon started his first encounter thread in anticipation of something unexpected and it turned out to be even more so than expected?) and Enceladus. It's gonna be very interesting to see what the explanation is.

 

[doublehelix]

The pictures are fantastic! Thanks, Andrew!

I also thought "Death Star" when I saw the Herschel Crater!

-dh

 

[BrockG]

That crater is breathtaking. :shock:

 

[nimbus]

It kinda looks like the hot area ends right around the south west limb.

 

[3488]

Hi Breezy, welcome to SDC.

That is correct. Saturn is the third deepest gravity well in the entire solar system (Saturn does not have the third largest Hill Sphere, Neptune after the Sun does) after the Sun & Jupiter, Saturn will draw in any potential impactors very quickly. Saturn could have objects entering it's atmosphere as fast as 179,400 KPH / 129,000 MPH.

Mimas being so close to Saturn only orbiting 185,500 KM /115,200 miles above Saturn's cloudtops, any impactors will be moving pretty quickly if they hit Mimas. Wayne will probably have exact figures!!!!!

A bit more Mimas stuff I've worked on.

Temperature prfile of Mimas over a Cassini image. Yes the warm swathe is weirdly like PacMan. :mrgreen: Mimas appears to have a thing for the 1970's & 1980's. Looks a bit like the Death Star from Star Wars in visible image & PacMan at infrared wavelengths!!! :mrgreen: :mrgreen:

What is most odd is that Mimas is rotating left to right. so it is morning on the left side, afternoon on the right. The warm PacMan like swathe is on the morning side, not where it would be expected in early to mid afternoon.

The warmest areas here are identified at the relatively 'warm' 96 Kelvin / minus 177 Celsius, with the coldest on the dayside at around 74 Kelvin / minus 199 Celsius. Average temperatures within Herschel Crater are around 84 Kelvin / minus 189 Celsius.

A section of limb of Mimas I've cropped out & sharpened enlarged. A crater approx 30 KM wide on the limb. A much smaller, but deep crater (as silylene pointed out & I agree with his reasoning. The strange temperature profiles also support silylene's idea), in the foreground to the lower right, has very highly reflective ice walls & a dark floor, indicative of slumping.

North Polar region of Mimas I've cropped out & sharpened enlarged.

A crater approx 25 KM wide on the limb that I've cropped out & sharpened enlarged I have also rotated the image 90 deg clockwise as the crater is in Mimas's mid southern latitudes. I rotated it to make it easier to see.

An older image of Mimas I think is relevant imaged early on during the Primary Mission of Cassini. A half Mimas imaged on: Sunday 16th January 2005. I put this here to show how Herschel Crater is so deep & it's cetral mountain so high thet the crater is in shadow, but the summit of the mountain is still sunlit. This angle of Mimas to Cassini is similar to the Saturday 13th February 2010 pass, but the angle of illumination is so very different & the January 2005 observation was from much further away.

That crater is breathtaking. :shock:

Welcome to SDC BrockG. Herschel Crater is certainly a real stunner, a real breathtaking feature, who's creator nearly smashed Mimas. :shock: :shock:

Andrew Brown.

 

[3488]

It kinda looks like the hot area ends right around the south west limb.

Hi nimbus,

It does, it is really strange.

Mimas shares the same seasons as Saturn itself, so it will be Northern Spring / Southern Autumn now on Mimas, with the equinox last August, but the central part of the warmer zone does appear to be a few degrees north of the equator, too far north to account for the season alone.

On Earth, here in Britain certainly, it is warmer in Autumn than in Spring, due to the fact we're surrounded by ocean & also the land is still warm from the Summer, in Spring, still cold from the Winter.

On an airless icy world some 10 AU from the Sun, I would imagine the warm spot may just lag very slightly behind the Sun, but here, it is ahead, both diurnaly & seasonaly. Very strange indeed.

We get a very close Dione pass (one of Saturn's most interesting moons) on Wednesday 7th April 2010, the closest since October 2005, closest approach will be only 504 KM (over the night side, but Titanlit, that's a first) with some terminator imagery planned looking for potential cryovolcanic activity. I can & will post some great stuff coming up with that too. :mrgreen:

I hope Cassini will also do a similar temperature scan with CIRs alongside imagery from the cameras & see if Dione also displays this weird temperature anomaly.

Below a couple more Mimas images from the most recent pass in February.

A section of limb approx 55 KM wide on the N W limb of Mimas. This image has not been rotated. It has been cropped & sharpened enlarged.

A shadowy section approx 50 KM wide on the evening terminator, rotated Counterclockwise (north on the left, east is at top), also a crop, sharpened enlargement. I just think it has a haunting quality about it.

Andrew Brown.

 

[cgromehs]

Andrew,

Hi. Amazing photos!!! Thank you. What is your job exactly? Do you work for NASA or a University? How do you get into imagery analysis for space missions?

Chris Gromm

 

[webcalf]

Regarding the pacman shape, what's not stated in these pictures is, where is Saturn located with relation to the pacman shape? could some of the extra thermal radiation be reflected from Saturn or coming from Saturn?

 

[3488]

Andrew,

Hi. Amazing photos!!! Thank you. What is your job exactly? Do you work for NASA or a University? How do you get into imagery analysis for space missions?

Chris Gromm

Welcome to SDC Chris,

Thank you so very much for your considerate post & comments, I am very grateful. :mrgreen: :mrgreen:

I do not work for NASA or a University & I am not even American!!!!!

I am British & just process & examine NASA planetary imagery, because:

1) I'm insanely curious.

2) I love Planetary & Earth sciences.

3) I think as many people as possible should see these, to educate.

If NASA took me on it would probably be for toilet cleaning or sweeping car parks, etc!!!!!!!!!!!

Regarding the pacman shape, what's not stated in these pictures is, where is Saturn located with relation to the pacman shape? could some of the extra thermal radiation be reflected from Saturn or coming from Saturn?

Hi webcalf,

Welcome to SDC to you too.

Great question & great reasoning too.

Saturn is only just off to the right of the frame, so the unexpectedly warm terrain is pointing towards interplanetary space. It is really a weird temperature profile we are seeing here.

Below a crop of the N E portion of Mimas I've cropped, enlarged & sharpened. Increased the contrast a bit also, to bring out the features a bit more!!!!. On the terminator, some pretty lofty mountains approx 3,000 metres tall are catching the distant setting Sun.

Also what is noticeable, is that the frozen impact melt from Herschel Crater is visible to the lower left & towards upper right, many more smaller craters & a rougher surface are apparent.

130 KM wide 5 KM deep Herschel Crater on Mimas.

An area approx 80 KM across in the southern hemisphere of Mimas, cropped out & sharpened enlarged. Some craters appear multilobed, also many show landslides & are quite deep, some appear to be between 2,000- 3,000 metres deep. Some like Herschel Crater have darker lower walls.

Andrew Brown.

 

[3488]

Below is a copy of the post submitted by EarthlingX in the Cassini thread in M & L. I thought it belonged here also.

All thanks to EarthlingX. :mrgreen:

http://www.ciclops.org : The Mimas Atlas

Presented here is a complete set of cartographic map sheets from a high-resolution atlas of Saturn's moon Mimas. The atlas is a product of the imaging team working with NASA's Cassini spacecraft.

Mimas, as imaged by NASA's Voyager spacecraft in the early 1980s, has a very large, distinguishing crater that makes it look like the "Death Star." As shown in this map, that crater is named Herschel.

The map sheets form a three-quadrangle series covering the entire surface of Mimas at a nominal scale of 1:1,500,000. The map data were acquired by the Cassini imaging cameras. The mean radius of Mimas used for projection of the maps is 198.2 kilometers (123.2 miles). Image scale is 216.2 meters per pixel. The resolution of the map is 16 pixels per degree.

Thumbs :

saturn.jpl.nasa.gov : The Mimas Atlas

July 28, 2010

saturn.jpl.nasa.gov : The Mimas Atlas -- Accolon

July 28, 2010

saturn.jpl.nasa.gov : The Mimas Atlas -- Arthur

July 28, 2010

saturn.jpl.nasa.gov : The Mimas Atlas -- Herschel

July 28, 2010

Andrew Brown on behalf of EarthlingX.

 

[3488]

What appears to be apparent to me is that there appears to be no antipodal disturbances to Herschel Crater, much like opposite the Valhalla Basin on the Jupiter moon Callisto, but unlike opposite the Caloris Basin on Mercury (where there is hilly terrain antipodal to Caloris Basin). Mimas other than Herschel Crater & impact melt from thereof appears fairly uniformly cratered, I cannot see any evidence unlike Enceladus or Dione that Mimas has rolled.

As maybe expected Herschel Crater is on the equator on the leading hemisphere as Mimas orbits Saturn, so it was a head on impact (Wayne will know more than me on this, but this is my own opinion).

Also these maps show that Mimas is now well mapped with the exception of a tiny area near the north pole, that may be filled in during the Solstice Mission. Not all of Mimas has been seen at the same resolution, but certainly enough has been to show us clearly cratering densities, general morphology & geological processes or lack thereof in the case of Mimas.

Andrew Brown.

 

[SteveCNC]

For such a small thing it sure has a very round appearence which leads me to think it is mostly ice . That crater is awsome , but when I was reading the information on that moon the whole time I was thinking what a perfect place to park a robot to churn out rocket fuel , how odd . More and more I am thinking when I retire I need to take all the info I gather about places like this and use it to write a science fiction series based on fact .