First Results From Deep Impact Mission

jdoire wrote to mention a Physicsweb piece revealing some of the first bits of data from the Deep Impact mission. From the article: "Based on data from the flyby spacecraft and the impactor, Michael O'Hearn of the University of Maryland and colleagues say that Tempel 1 belongs to the Jupiter family of comets, although its overall shape and surface features are quite different from the nuclei of the two other comets that have been studied in detail -- Wild 2 and Borelly. They also report that Tempel 1 consists largely of extremely fine particles that seem to be very loosely bound together: in other words, the comet is more like a pile of powder than a solid rock." Looks like the Electric Universe folks were a bit off.

Comments

Re:Sorry

[smooth wombat]

When I saw the article (YESTERDAY!!) I thought about this also but came up with what I hope is a good analogy.

If you have ever been to the beach or played in a really deep sandbox, you know that the top layer of sand moves about easily. You can dig your toes in without any effort. The sand is loosely bound together.

However, if you drop a bucket (or anything else) onto the sand, that object will only sink in a small bit. Why? Other than the fact that there isn't much force behind dropping whatever onto the surface of the sand the sand itself compresses slightly from the impact.

'But Deep Impact was the size of a washing machine and travelling at a bajillion miles an hour when it hit. You can't compare that to dropping a bucket on the beach!' I hear you say.

Actually, you can compare the two. If you take the size of a bucket compared to the size of the beach, there is a huge difference. Even if you were to take a replica of Deep Impact and fire directly onto the beach at a speed approximating the impact speed on the comet I can guarantee you would get a similar result.

The impact would produce a nice big explosion of particles and the copper impactor would probably disintegrate. However, the beach would still be there albeit with a nice big hole in it.

Hope this long-winded explanation helps.

Mining

[SumDog]

I think its cool that we are all ready at the point where we can crash probes into comets and examine them. I wonder how long it will be until we can actually pull a comet into earth orbit and mine it for resources.

Question

[Dutchmaan]

Does this mean that using an significantly large explosive device is almost a feasible scenario for specific types of comets.

I mean, I can understand not using that approach for something make of rock and ice, but with fine particles one would think that sufficient force would break it apart like a cue ball.

Obiviously this is just fuzzy thinking, but does anyone have any scientific input to why this would or would not be an emergency solution to be put on the table for this specfic type of comet?

Re:Question

[Anonymous Coward]

My instinct here is that trying to detonate a comet is not a great solution no matter the composition.

You do not have quite the same threat of calving (i.e. splitting into two big chunks instead of one big chunk), but there is the possibility that either a) the explosion would just shove it (the beach/sand analogy above is good), or b) that you would face a sandblasting from billions of tiny particles.

That might not seem so bad - hey, no impact crater! But the simultaneous atmospheric entry of that much material can generate so much heat as to start mass fires on the ground below (this is a normal side effect of debris reentry in a lot of impact models).