# Deep Impact - asking for trouble? **URL:** \ **Category:** Factual Questions\ **Created:** [June 30, 2005, 1:09pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502 "2005-06-30T13:09:28Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Staggerlee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/staggerlee/32/3134_2.png) [@Staggerlee](https://boards.straightdope.com/u/Staggerlee)\ **Post date:** [June 30, 2005, 1:09pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/1 "2005-06-30T13:09:28Z")
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… ---
**Author:** ![Scott\_Plaid](https://avatars.discourse-cdn.com/v4/letter/s/258eb7/32.png) [@Scott\_Plaid](https://boards.straightdope.com/u/Scott_Plaid)\ **Post date:** [June 30, 2005, 1:22pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/2 "2005-06-30T13:22:21Z")
I think it will cause harm to my “system of spiritual values”, and those of many others. For the whoosed, see [http://mosnews.com/feature/2005/04/19/deepimpact.shtml](http://mosnews.com/feature/2005/04/19/deepimpact.shtml) ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [June 30, 2005, 1:45pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/3 "2005-06-30T13:45:21Z")
Well, pretty much tosh. This [site](http://deepimpact.umd.edu/amateur/where_is2.shtml) 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](http://deepimpact.jpl.nasa.gov/science/tempel1.html). Nothing our little 370Kg probe is going to do is going to come close to the effects of a gas giant. ---
**Author:** ![Sean\_Factotum](https://avatars.discourse-cdn.com/v4/letter/s/50afbb/32.png) [@Sean\_Factotum](https://boards.straightdope.com/u/Sean_Factotum)\ **Post date:** [June 30, 2005, 1:45pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/4 "2005-06-30T13:45:28Z")
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](http://www.nasa.gov/mission_pages/deepimpact/mission/index.html). ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [June 30, 2005, 1:48pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/5 "2005-06-30T13:48:11Z")
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.](http://deepimpact.jpl.nasa.gov/science/tempel1-orbitalhist.html) ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 30, 2005, 2:15pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/6 "2005-06-30T14:15:08Z")
[Watching Comet Tempel 1](http://skyandtelescope.com/observing/highlights/article_1522_1.asp) 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. ---
**Author:** ![Staggerlee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/staggerlee/32/3134_2.png) [@Staggerlee](https://boards.straightdope.com/u/Staggerlee)\ **Post date:** [June 30, 2005, 3:37pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/7 "2005-06-30T15:37:37Z")
Well thanks for all that, and the links. I thought it unlikely, but do find myself hankering after the next cataclysm… ☹😉 ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 30, 2005, 3:47pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/8 "2005-06-30T15:47:54Z")
> [@Staggerlee](#): > > but do find myself hankering after the next cataclysm… ☹😉 We can still hope that Tempel 1 is made out of antimatter. That’d supply a big bang on the 4th. 😉 [sub](of course Tempel 1 is NOT made from antimatter, but still the collision may provide a good show)[/sub] ---
**Author:** ![acadaca](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@acadaca](https://boards.straightdope.com/u/acadaca)\ **Post date:** [July 1, 2005, 3:57pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/9 "2005-07-01T15:57:22Z")
Hmmmmm… What is it with Americans and blowing things up? ---
**Author:** ![user\_hostile](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/user_hostile/32/474_2.png) [@user\_hostile](https://boards.straightdope.com/u/user_hostile)\ **Post date:** [July 1, 2005, 4:23pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/10 "2005-07-01T16:23:21Z")
Because it’s there… ---
**Author:** ![JXJohns](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jxjohns/32/469_2.png) [@JXJohns](https://boards.straightdope.com/u/JXJohns)\ **Post date:** [July 1, 2005, 4:24pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/11 "2005-07-01T16:24:51Z")
> [@acadaca](#): > > Hmmmmm… What is it with Americans and blowing things up? Cause we can. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 1, 2005, 4:49pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/12 "2005-07-01T16:49:53Z")
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. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 1, 2005, 5:09pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/13 "2005-07-01T17:09:35Z")
> [@Finagle](#): > > Nothing our little 370Kg probe is going to do is going to come close to the effects of a gas giant. 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](http://www.brianmay.com/brian/brianssb/brianssbjun05a.html)’s convinced that it’ll blow the comet up! > [@](#): > > Thanks Noah … yes, I realize that it is HOPED that the whole comet will not be affected, but I am 99 per cent sure that there is no guarantee of this. Who could be that sure, when no-one even knows the interior morphology of the object. Suppose it were one giant crystalline structure ? What an irreversible mess the projectile would make in this situation. > > Sorry, I am not convinced. I think it’s a rotten idea, and should be shelved at least until we have exhausted all NON-invasive techniques. > > The very uncertainty of the crater size (“somewhere between a house and a football stadium”) indicates to me an indication that the experimenters have as much idea of what effect they’re going to have as a man with an ice-pick approaching an egg. My only question to the team behind this is … “Are you really sure you are behaving responsibly here ? Can’t you wait until we know more ? Until we can be a bit more clever and attempt a landing ?” I’m really personally outraged by this. There are those who think that even life on the Earth may have originated from micro-organisms on such a comet … ---
**Author:** ![tygerbryght](https://avatars.discourse-cdn.com/v4/letter/t/a9a28c/32.png) [@tygerbryght](https://boards.straightdope.com/u/tygerbryght)\ **Post date:** [July 2, 2005, 5:02am UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/14 "2005-07-02T05:02:53Z")
> [@Tuckerfan](#): > > … > > 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. ☹ ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [July 2, 2005, 6:25am UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/15 "2005-07-02T06:25:07Z")
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? ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [July 2, 2005, 6:35am UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/16 "2005-07-02T06:35:05Z")
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? ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 2, 2005, 6:42am UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/17 "2005-07-02T06:42:41Z")
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. ---
**Author:** ![Strinka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/strinka/32/512_2.png) [@Strinka](https://boards.straightdope.com/u/Strinka)\ **Post date:** [July 2, 2005, 8:28pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/18 "2005-07-02T20:28:49Z")
> [@](#): > > Thanks Noah … yes, I realize that it is HOPED that the whole comet will not be affected, but I am 99 per cent sure that there is no guarantee of this. Who could be that sure, when no-one even knows the interior morphology of the object. Suppose it were one giant crystalline structure ? What an irreversible mess the projectile would make in this situation. So she’s 99% sure that it’s not 100% sure? And no, nothing is ever 100% certain. > [@](#): > > Sorry, I am not convinced. I think it’s a rotten idea, and should be shelved at least until we have exhausted all NON-invasive techniques. > > The very uncertainty of the crater size (“somewhere between a house and a football stadium”) indicates to me an indication that the experimenters have as much idea of what effect they’re going to have as a man with an ice-pick approaching an egg. My only question to the team behind this is … “Are you really sure you are behaving responsibly here ? Can’t you wait until we know more ? Until we can be a bit more clever and attempt a landing ?” I’m really personally outraged by this. There are those who think that even life on the Earth may have originated from micro-organisms on such a comet … 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.) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 2, 2005, 8:54pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/19 "2005-07-02T20:54:28Z")
> [@Tuckerfan](#): > > **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… 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. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 2, 2005, 9:18pm UTC](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502/20 "2005-07-02T21:18:11Z")
> [@scr4](#): > > 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.](http://www.space.com/spacewatch/050603_deep_impact.html) > [@](#): > > For skywatchers here on Earth, it should also produce a large cloud of ejected material that should cause the comet to significantly brighten enough to become visible with binoculars and perhaps even with the unaided eye. As I said above, comet brightness is notoriously difficult to predict, so I’m not holding my breath. [Next page](https://boards.straightdope.com/t/deep-impact-asking-for-trouble/310502.md?page=2)