Hi Emily,

A friend of mine has done a similar job with the irregular moons of the Solar System. The derivative is copyright Andrzej Karon 2008:



He is also considering doing the same with asteroids.

Amazing images! What a strange shape! It reminds me of someone pushing a thumb in a play-dough ellipsoid, pushing through such that the bottom gets a lump I wonder what made Steins look like that...

About the crater chain: Gravitational disruption is not the only mechanism for cometary breakup, so it could be possible, though admittedly unlikely, that a recently disrupted comet crashed into Steins. It's also notable that the scale is much smaller than for crater chains seen elsewhere (not clear if such small comets exist).
On the other hand, contrary to other posters, I find a chance alignment unlikely. Can anyone point me to a "chance alignment" of 7 or so craters out of the largest 20 or 30 on any other asteroid or moon?
We need some more quantitative analysis here.

About the loss of NAC images, it's like Emily said. The NAC at closest approach would have given factor ~5 better resolution than the WAC, 9 minutes before it's comparable to the WAC at closest approach. A rule of thumb says that one needs of
the order of 100 pixels for a good analysis of global properties, some topography, and so on. With the NAC it would have been around 300, with the WAC it's around 60.

Michael

"Can anyone point me to a "chance alignment" of 7 or so craters out of the largest 20 or 30 on any other asteroid or moon? "

Famous example: the apparent chain of six large craters extending south from Ptolemaus on the central meridian of our moon, long touted as proof of their internal origin.

Look at the 'rivers' I mentioned above. Purely random chains you can see every day. Look at stucco. Randomness includes lots of apparent patterns.

Phil

Karol,

That is a very eye-catching comparative diagram of the moons.

A small correction. The planetary symbol for Ganymede should be Jupiter, not Saturn!

That was Alice, the UV spectrometer. Background count rates due to Jovian radiation exceeded a pre-set conservative threshold so the instrument switched itself off. The flight team was able to upload a higher threshold value during the encounter, but by then background levels had fallen anyway. So we still got a fair amount of Alice data, including a very nice Jupiter stellar occultation early in the encounter, before the background got too high.

John

The large craters south of Ptolemaus are much smaller relative to the size of the moon than the craters on Steins relative to Steins. So the likelyhood of finding some chain like this somewhere on the moon is much higher than finding what we see on Steins.

The scale problem has already been mentioned. The individual pieces of a random chain should be the same scale as the noise they emerge from. To my untrained eye, the chain on Steins seems to be made of craters of a different scale from most of the random craters.

Also, it's been mentioned that Steins does not have the strength to tear apart an impactor and that the pieces of an impactor torn apart by another body would not remain together. But what about a "rubble pile" impactor?

And that's how we come back to what I said earlier - look around long enough and you're bound to find it. I simply can't think of a plausible mechanism that would explain the crater chain as anything more than coincidence. The fact it runs perfectly along the terminator where shadows are brought up is very much ignored here. For all I know, there could be other "linear chains" waiting to be seen if you change the illumination a bit. Maybe even high speed turtles, who knows?

Frankly, I find it a bit surprising to see people still see this alignment as something telling/significant, but don't let that stop you.

Good point.



Hey. At least we don't see a face (or a high speed turtle).

It is true that I did not consider illumination conditions and that the reality of the chains is more of a "gut feeling" that may not survive detailed analysis. However, the craters in the chain are large enough to be seen anywhere on the imaged hemisphere, and the asteorid appears far from saturation with craters of that size (otherwise you could indeed easily find those chains). Also, they are of about equal size and spacing, reminiscent of the chains on the galilean moons. And that you (and I) cannot think of a plausible mechanism does not necessarily mean that there is none.

Hello? Hello? (taps microphone) Is this thing on?

Again, this is my point. More overhead illumination makes the other craters not stand out so well. For what it's worth, the images widely distributed are magnified so they are blurred and hide the actual pixel scale and make you think small details are not there (when they're actually below resolving power). Here's the actual pixel scale view, magnified 3x using the nearest-neighbor algorithm in order not to add new "details" into the image.


I'm seeing several craters of similar size across the face, but they don't poke the eye because they're not on the terminator. The chain craters you speak of do absolutely not appear of the same size to me, the lower 3 ones appear much bigger than the top 4. Yet, the top 4 have a companion off to the left side with also a hint of a fifth crater almost completely shadowed. As far as I'm concerned this case is closed.

EDIT: Mike, I didn't mean you, I meant the rest of the folks who believe this feature isn't accidental.

Misc. Steins thoughts:

1) The rotation means that the gravity along the "equator" would be about 10% less than at the "poles", assuming a density of 2 g/cm^3.

2) If Steins formed as the fragment of impacts between larger bodies, there could be craters from secondary impacts that occurred precisely at the time of origin as a lot of fragments were briefly on similar trajectories.

3) Phil's comment trumps all: The "chain" craters are not of the same age, so they don't have the same origin.

4) Is everyone pronouncing it "SHTINES" like they should? There's a hacek over that "S"!

Where did you see that?