# Does Jupiter protect the earth? **URL:** \ **Category:** Factual Questions\ **Created:** [January 18, 2011, 3:56am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044 "2011-01-18T03:56:32Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![automagic](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@automagic](https://boards.straightdope.com/u/automagic)\ **Post date:** [January 18, 2011, 3:56am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/1 "2011-01-18T03:56:32Z")
Some sources say that Jupiter helps to deflect potentially killer asteroids/comets while others say that Jupiter actually makes the situation worse. Which is correct? > **[Jupiter increases risk of comet strike on Earth](https://www.newscientist.com/article/dn12532-jupiter-increases-risk-of-comet-strike-on-earth/)** > > The huge planet does not act as an impact shield, a new study says – in fact its gravity attracts objects into the solar system ^^^^^That site is against Jupiter > **[Is it true that Jupiter protects Earth? | Space | EarthSky](https://earthsky.org/space/is-it-true-that-jupiter-protects-earth/)** > > Jupiter's gravity slings long-period comets out of harm's way, while nudging some asteroids closer to Earth. And, in 1770, Jupiter took aim on Earth - but missed. ^^^^^That site is for Jupiter Help. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [January 18, 2011, 4:45am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/2 "2011-01-18T04:45:28Z")
Your first link says > [@](#): > > A 1994 study showed that replacing Jupiter with a much smaller planet like Uranus or Neptune would lead to 1000 times as many long-period comets hitting Earth… > > But a new study by Jonathan Horner and Barrie Jones of Open University in Milton Keynes, UK, shows that if there were no planet at all in Jupiter’s orbit, Earth would actually be safer from impacts… > > So both the new study and the one from 1994 suggest that a smaller planet in Jupiter’s orbit would leave Earth worse off, although they disagree about how much worse. I’d put it down to further investigation is required. “Preliminary work shows that a less massive body in Jupiter’s orbit might allow for earth crossing comets to persist longer than they would otherwise. Slave wages grad student required to do more work.” ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [January 18, 2011, 4:45am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/3 "2011-01-18T04:45:43Z")
> [@automagic](#): > > Some sources say that Jupiter helps to deflect potentially killer asteroids/comets while others say that Jupiter actually makes the situation worse. Which is correct? > > [http://www.newscientist.com/article/dn12532-jupiter-increases-risk-of-comet-strike-on-earth.html](http://www.newscientist.com/article/dn12532-jupiter-increases-risk-of-comet-strike-on-earth.html) > > ^^^^^That site is against Jupiter > [Is it true that Jupiter protects Earth? | Space | EarthSky](http://earthsky.org/space/is-it-true-that-jupiter-protects-earth) > > ^^^^^That site is for Jupiter > > Help. I think the average current opinion is that it’s a net good, sucking in more debris than it deflects at us. Shoemaker-Levy is a reminder how beneficial Jupiter is. Both are possible and maybe more studies like the first one you cite will sway the standard opinion. ---
**Author:** ![ChrisBooth12](https://avatars.discourse-cdn.com/v4/letter/c/e95f7d/32.png) [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)\ **Post date:** [January 18, 2011, 5:24am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/4 "2011-01-18T05:24:17Z")
Well if Jupiter prevented at least 1 from hitting the earth the answer would have to be yes. I am going to go and assume that since Jupiter and the Earth formed Jupiter has caught/blocked at least one piece from hitting us ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [January 18, 2011, 5:38am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/5 "2011-01-18T05:38:28Z")
**ChrisBooth12** - Yes, but the point of the question is that Jupiter might draw more than one massive body towards the earth. So the effect has to be Jupiter stopping more impacts than it contributes to. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [January 18, 2011, 6:34am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/6 "2011-01-18T06:34:22Z")
My gut level geometric sense tells me that Jupiter throws things more or less at random in direction. That means that the percentage that are thrown further out from the Sun will be higher than the percentage that are thrown further in towards the sun (Resultant after all orbital mechanics are considered, that is.) The reason would be simply that there is a larger set of possibilities outward, because outward is waaaaay bigger than inward. It is not an unreasonable argument, but no way a proof. Tris ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [January 18, 2011, 7:28am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/7 "2011-01-18T07:28:44Z")
It would seem to me that since comets are only a danger to us when they are incoming in the sense that they come from the outer solar system to the inner and that Jupiter might block some of them on their way in, that would be beneficial. It would throw others off course, but it might throw them in to us too. Now, as the comets come in and loop around the sun and come out, there is a danger to hit earth, but if they miss earth, then they go back out periodically to come back in and be a danger again, unless they hit another planet on the way out. So for that reason, any planets would seem to me to be other objects to stop comets. Much like a pool table makes it much harder to transfer energy to a target ball on a full table than an empty table. ---
**Author:** ![automagic](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@automagic](https://boards.straightdope.com/u/automagic)\ **Post date:** [January 18, 2011, 9:31am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/8 "2011-01-18T09:31:52Z")
I know I placed the Original Post but reading your responses made me think. I think we have been thinking about this all wrong. I do not think that objects from the outer solar system simply go in a straight line into the inner solar system. I think they spiral in towards the sun, causing them to be in the vicinity or Jupiter’s orbit for a longer period of time. Because of this Jupiter might just act like a giant vacuum. If by chance it misses Jupiter, and the other planets then it will be in the vicinity of Earths orbit making a collision, or at least a near hit likely. As for long period comets I have no idea. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [January 18, 2011, 10:09am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/9 "2011-01-18T10:09:36Z")
[QUOTE=automagic] Some sources say that Jupiter helps to deflect potentially killer asteroids/comets while others say that Jupiter actually makes the situation worse. Which is correct? [/QUOTE] Astrophysicists who study the topic have different opinions about the impact of Jupiter. > [@automagic](#): > > I do not think that objects from the outer solar system simply go in a **straight line** into the inner solar system. I think they **spiral in** towards the sun, causing them to be in the vicinity or Jupiter’s orbit for a longer period of time. Because of this Jupiter might just act like a giant vacuum. They do neither - If they are from the Kuiper Belt or Oort cloud they follow an orbital path (ellipse) with the sun at one of the foci, or a hyperbolic single pass and out of the solar system. However, the orbit is perturbed by gravity fields on the way, with Jupiter being a major player. If they are from outside the solar system, then their approach is off the planetary plane and the path is generally straight, but any intersection with the earths orbit is essentially random and Jupiter will have little impact either way. The only way to determine the impact of Jupiter on earth-intersecting orbits is by a statistical approach (you are trying to solve a [n-body](http://en.wikipedia.org/wiki/N-body_problem) orbital solution which is not mathematically feasible), running thousands of randomised simulations. Faster supercomputers and more time will give us the ability to run more of these and get better answers, but until the simulations are run, the answer is _unclear_. Si ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [January 18, 2011, 11:02am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/10 "2011-01-18T11:02:47Z")
> [@automagic](#): > > I know I placed the Original Post but reading your responses made me think. I think we have been thinking about this all wrong. I do not think that objects from the outer solar system simply go in a straight line into the inner solar system. I think they spiral in towards the sun, causing them to be in the vicinity or Jupiter’s orbit for a longer period of time. Because of this Jupiter might just act like a giant vacuum. You’re right that they don’t come straight in, at least not Kuiper Belt objects that eventually become short period comets. Neptune first perturbs an object’s orbit so it isn’t circular. It is then called a scattered disk object. Further pertubation may cause it to come near Uranus, which will also perturb the orbit. After many close encounters with the various outer planets (think of it as sort of a cosmic pinball game), it may come close to Jupiter. Jupiter could do one of three things: 1) send it out of the system, or at least to the Oort Cloud; 2) absorb it like Shoemaker-Levy 9; or 3) send it into the inner solar system where it becomes a short period comet. The whole process will take millions of years. The question is, is the last scenario more likely than the first two combined? If so, then Jupiter is more of a danger than protector. Computer simulation should tell us which it is. ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [January 18, 2011, 11:30am UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/11 "2011-01-18T11:30:17Z")
I find the whole thing perturbing. Incidently, how large is Jupiter’s Hill sphere compared to Earth? ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [January 18, 2011, 1:15pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/12 "2011-01-18T13:15:41Z")
Nah. Jupiter is a complete and utter prick who victimized humanity for centuries. What…? ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [January 18, 2011, 1:28pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/13 "2011-01-18T13:28:06Z")
Let’s not leave Saturn out of the equation either. The fact that both of them have scores of smaller bodies around them attests to their ability to capture or absorb passing bodies. ---
**Author:** ![The\_Controvert](https://avatars.discourse-cdn.com/v4/letter/t/dec6dc/32.png) [@The\_Controvert](https://boards.straightdope.com/u/The_Controvert)\ **Post date:** [January 18, 2011, 2:16pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/14 "2011-01-18T14:16:35Z")
> [@Nametag](#): > > Nah. Jupiter is a complete and utter prick who victimized humanity for centuries. Nah, that’s Superman. And that makes Saturn = Batman. Both “heroes” ostensibly protect us, but they also draw in or outright create the very supervillain threats they “guard” us from. ---
**Author:** ![BobLibDem](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/boblibdem/32/3149_2.png) [@BobLibDem](https://boards.straightdope.com/u/BobLibDem)\ **Post date:** [January 18, 2011, 2:40pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/15 "2011-01-18T14:40:46Z")
> [@Alka\_Seltzer](#): > > I find the whole thing perturbing. Good one! I guess I’m in the helpful shield camp. It’s possible that Jupiter has caused objects to deflect into orbits which eventually intersect earth, but I think it’s more likely to deflect objects into orbits which don’t intersect earth. Plus Jupiter likely consumes a good many objects, eliminating their threats altogether. ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [January 18, 2011, 5:06pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/16 "2011-01-18T17:06:58Z")
> [@Alka\_Seltzer](#): > > I find the whole thing perturbing. > > Incidently, how large is Jupiter’s Hill sphere compared to Earth? Haven’t done the math, but the [wiki for Hill Sphere](http://en.wikipedia.org/wiki/Hill_sphere) lists Earth’s Hill’s radius at 1.5 million km, and Jupiter’s at 53 million km. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 18, 2011, 5:30pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/17 "2011-01-18T17:30:16Z")
Hell, our own moon has caught a fair number of things that (I’d guess) would have likely hit the earth otherwise. Sure we see craters on this side but [look at the far side](http://apod.nasa.gov/apod/image/0702/farside_apollo16.jpg)…it is a lot more chewed up. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [January 18, 2011, 11:03pm UTC](https://boards.straightdope.com/t/does-jupiter-protect-the-earth/568044/18 "2011-01-18T23:03:27Z")
> [@Chimera](#): > > Let’s not leave Saturn out of the equation either. Didn’t mean to diss Saturn. I did say “close encounters with the various outer planets” and meant to include Saturn in that. > [@](#): > > The fact that both of them have scores of smaller bodies around them attests to their ability to capture or absorb passing bodies. I don’t know for certain, but I suspect most of the small, outer, Jovian satellites are captured Trojan asteroids. Some may even wander back and forth between orbiting Jupiter and being a Trojan. When a body is in transition between being a Kuiper Belt object and a short period comet, it’s known as a [Centaur](http://en.wikipedia.org/wiki/Centaur_(planetoid)). There’s an interesting section in that Wiki page that basically says the same thing as my post above: > [@Wikipedia](#): > > Since the centaurs cross the orbits of the giant planets and are not protected by orbital resonances, their orbits are unstable within a timescale of 10[sup]6[/sup] –10[sup]7[/sup] years.[10] For example, 55576 Amycus is in an unstable orbit near the 3:4 resonance of Uranus.[1] Dynamical studies of their orbits indicate that centaurs are probably an intermediate orbital state of objects transitioning from the Kuiper Belt to the Jupiter family of short period comets. Objects may be perturbed from the Kuiper Belt, whereupon they become Neptune-crossing and interact gravitationally with that planet (see theories of origin). They then become classed as centaurs, but their orbits are chaotic, evolving relatively rapidly as the centaur makes repeated close approaches to one or more of the outer planets. Some centaurs will evolve into Jupiter-crossing orbits whereupon their perihelia may become reduced into the inner solar system and they may be reclassified as active comets in the Jupiter family if they display cometary activity. Centaurs will thus ultimately collide with the Sun or a planet or else they may be ejected into interstellar space after a close approach to one of the planets, particularly Jupiter. The same article does suggest that Saturn’s moon Phoebe may be a captured Centaur,