Deep Impact - asking for trouble?

I hear the ‘Deep Impact’ probe is due to crash into a comet on Monday morning - while I know that the mass of the probe is incredibly small in comparison to that of the comet, I would guess that the impact will inevitably alter the orbit of the comet to an similarly incredibly small degree. Though if this is the case, that minor change will surely be amplified by the enormous distances it travels.

Am I speculating tosh? Again?

It’s just that I’d find it grimly ironic if the ‘Deep Impact’ probe caused that comet to head earthward…

I think it will cause harm to my “system of spiritual values”, and those of many others.

For the whoosed, see

Well, pretty much tosh. This site has some very interesting detail on the comet Tempel 1, including extrapolations of its future orbit. But of the things to note, one is that the the comet’s closest approach to Earth is (I think) about 0.5 AU. That’s half the distance from the Earth to the Sun, or over 46 million miles. It would take considerable energy to perturb the orbit of the comet enough to change it’s course by that much. The energy released by the collision is 19GigaJoules or (so the site says), about the equivalent of 4.8 tons of TNT. Which sounds like a lot, but most of the energy is going to be going into making a big crater in what is probably a very massive rocky snowball. I doubt the change in its orbit will be measurable.

Another thing to note is that space is very, very big. So the probability of any random change in an orbit causing it to zero in on Earth is very, very low.

The final thing to note is that Jupiter regularly perturbs the orbit of Tempel 1. Nothing our little 370Kg probe is going to do is going to come close to the effects of a gas giant.

I would think not. NASA itself says “The impact is not forceful enough to make an appreciable change in the comet’s orbital path around the Sun.” This quote is found at the end of paragraph 5 in this article.

Tempel’s perihelion distance (closest approach to the Sun) is more than 1.5 AU. An AU (astronomical unit) is the distance form the Earth to the Sun. So that means that Tempel only comes within .5 AU of Earth, under optimal conditions. That’s quite a lot of breathing room.

Also, as you say, the impactor is of negligible mass compared to the comet. The comet’s own jets, caused by water and other volatiles that are converted to gas by the heat of the Sun, will alter its orbit far more than the impactor could, and in largely unpredictable ways.

Here are the details.

Watching Comet Tempel 1
The impact will occur at 10:52 pm Pacific Daylight Time Sunday night July 3rd.
Visible in binoculars, the comet will be easy to find because it’ll be near Jupiter, and the bright star Spica.

Well thanks for all that, and the links. I thought it unlikely, but do find myself hankering after the next cataclysm… :frowning: :wink:

We can still hope that Tempel 1 is made out of antimatter.
That’d supply a big bang on the 4th. :wink:

[sub](of course Tempel 1 is NOT made from antimatter, but still the collision may provide a good show)[/sub]

Hmmmmm… What is it with Americans and blowing things up?

Because it’s there…

Cause we can.

One of the scientists associated with the event likened it to a mosquito running into a 747. Even if the proportions are not exactly parallel, that analogy leads one to believe that the effect of the impact on its orbit should be negligible.
xo, C.

Somewhere, I read that the comet has started spewing some 730 lbs of water a second. So not only is the probe tiny compared to the comet, it’s tiny compared to what the comet’s throwing off.

If it makes you feel any better, Brian May’s convinced that it’ll blow the comet up!

Not sure I’m happy about the company I’m keeping, but I’m concerned about the possibility that the comet is just an aggregate (like some recent speculation about larger asteroids) glued together with ice, and that DI is gonna send pieces flying off in all directions. :frowning:

In any event, if the probe were to alter the comet’s course, isn’t it equally likely that it would cause the comet to MISS Earth when it otherwise would have hit it, as the other way around?

I notice that a number of largish telescopes will be ‘live casting’ the impact. Is there any chance that the impact itself will be visible? Are we expecting a huge ice cloud that will suddenly make the comet brighter or something?

As Finagle pointed out, the comet at it’s closest approach would be .5 AU from the Earth. That’s some 43 million miles (give or take a million or two), and the most likely thing that would happen if the comet did explode is that it would burst in a manner similar to the Death Star (minus the ring shockwave from the SE version), so you’d have hunks of it flying off in all directions. Most of them would probably stay in the same general area for quite some time (the impactor’s traveling at roughly 23K mi/sec.), so we’d definately miss any debris on this pass. What we would get (if anything) on the next pass depends entirely upon how long it takes the comet to complete an orbit and what (if any) celestial bodies are nearby as it makes it’s loop. If the hunks pass too close to Jupiter, they’ll no doubt get sucked in. IAC, we’ll have ample warning to prepare in the incredibly remote event that something large enough to be a concern starts heading this way.

Sam Stone, it’s supposed to get bright enough to be seen with the naked eye when it hits because the amount of material kicked up. Of course, predictions of how bright a comet’s supposed to be are notoriously off. Halley’s comet was pretty dim, IIRC, and so was one that appeared in the 1970s. I was more impressed by the comet which passed through the solar system the year before Hale-Bopp showed up than I was by Hale-Bopp.

So she’s 99% sure that it’s not 100% sure? And no, nothing is ever 100% certain.

Wait until we know more? We’re doing this to learn more!

The sheer idiocy humans are capable of is astounding. (referring to Scott Plaid’s link as well.)

Don’t you mean “visibly brighter” if looked through a telescope? The comet would have to brighten by more than 5 magnitudes before it’s literally visible to the naked eye.

Everything I’ve read indicates that there’s a chance it could become visible to the naked eye. Sample.

As I said above, comet brightness is notoriously difficult to predict, so I’m not holding my breath.