Is Jupiter Earth's Cosmic Protector? 222
Hugh Pickens writes "Last Sunday, an object, probably a comet that nobody saw coming, plowed into Jupiter's colorful cloud tops, splashing up debris and leaving a black eye the size of the Pacific Ocean — the second time in 15 years that this had happened, after Comet Shoemaker-Levy 9 fell apart and its pieces crashed into Jupiter in 1994, leaving Earth-size marks that persisted up to a year. 'Better Jupiter than Earth,' say astronomers who think that part of what makes Earth such a nice place to live is that Jupiter acts as a gravitational shield, deflecting incoming space junk away from the inner solar system where it could do to humans what an asteroid apparently did for the dinosaurs 65 million years ago. 'If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hoovering up all these large pieces before they come for us,' says Australian amateur astronomer Anthony Wesley, who first noticed the mark on Jupiter. But others say the warm and fuzzy image of the King of Planets as father-protector may not be entirely accurate. In 1770, Comet Lexell whizzed by the earth, missing us by a cosmic whisker after passing close to Jupiter. The comet made two passes around the Sun and in 1779 again passed very close to Jupiter, which then threw it back out of the solar system."
A New Criteria? (Score:4, Interesting)
Is Jupiter Earth's Cosmic Protector?
If this is true, it gives us another criteria to look for in distant solar systems that we suspect may harbor life or that we would like to colonize: a large shield planet in the same system capable of leaving the smaller world to develop uninterrupted.
It is interesting to wonder if our odds increase or decrease on being hit when there is a large massive body in our solar system. Like the article and summary say, some objects that would not have come close could be put on course for earth via Jupiter's gravitational forces. Who knows, maybe massive bodies like Jupiter pull more space debris into our system and make it more hostile than if it were just the earth orbiting the Sun?
Greater benefic (Score:5, Interesting)
Just sayin'.
Luckily... (Score:2, Interesting)
The Earth has not yet faced a galaxy coming straight at it.
This reminds me of that anti-tiger rock I keep in my sock drawer?
That rock is so good, damn tigers are dieing out in India. Maybe Jupiter has similar effect on galaxies?
Probabilities are hard to calculate... (Score:3, Interesting)
Orbital Mechanics, not Conscious Intention (Score:5, Interesting)
Jupiter is the only planet in our system close enough to the sun and with a deep enough gravity well for them to have a barycenter (common orbital center) outside the sun's surface. That sort of wobbly orbital mechanics has far more effect on trajectories of small bodies than a nice, neat set of concentric circular orbits. The sun-Jupiter system will be more likely to cause fluctuations that result in small interlopers to get thrown out of the system or sucked into one of their gravity wells. Seeing the result on Jupiter is rare. Seeing it at the sun is more common. Between the two they're going to suck up far more than hit elsewhere.
But their influence is only the majority of a chaotic multi-body system. Just because they account for the most hits doesn't mean they take them all and nothing gets through elsewhere. Of course some will miss the big guys and hit (or nearly so) some of the others. That's the nature of a chaotic system of orbital mechanics. They are not exerting influence in an intentional manner, rather a deterministic but fairly unpredictable manner.
To assume a certain thing always happens because it has happened, and also to say it not accurate because there is an exception, is the sort of low caliber absolutist thinking that's common in "modern" science reporting. I have no doubt the parties credited with these viewpoints understand quite well the situation, and the apparent controversy is a function of the author of TFA.
Amazing (Score:5, Interesting)
Re:Is Jupiter Earth's Cosmic Protector? (Score:4, Interesting)
Well, kind of, but look at it this way. If the Moon was a lone planet, it'd get craters everywhere equally. But it's not a lone planet, instead it has a bigger body always on the same side of it. Therefore, that there should be more impacts on the opposite side tells you that asteroids are quite attracted to Earth and that the Moon catches a lot of the when its on their way.
Jupiter: Friend or Foe? (Score:4, Interesting)
Jonti Horner and BW Jones [jontihorner.com] have written a series of papers on this, summarized in this Astronomy and Geophysics article [jontihorner.com] The first paper deals with the Asteroids [jontihorner.com]. The second, in press, considers the Centaurs [jontihorner.com] The third, of perhaps most relevance to this discussion, considers the Oort Cloud objects.
(To simplify the simulations, Earth was inflated to one million times its actual size. A juicy target indeed)
Re:A New Criteria? (Score:3, Interesting)
Or a bisolar system, however the radiation levels and orbits may be too chaotic in such system.
Just to put things in perspective, Jupiter is about 9/1000 the mass of the sun. However I would point to the multitude of our gas giants. Saturn is about 2/1000 the mass of the sun, which is also significant. The other two gas giants are significantly smaller. I'd say the existence of gas giants within the carbon--water habitable zone can provide safe harbors for life as well. But I'd say a stable environment in any case is good for any sort of life form, allowing time for them to adapt without being destroyed by physics mechanics.
Re:Amazing (Score:3, Interesting)
Except that the object isn't that massive. To create a hole the size of the Pacific Ocean in Jupiter wouldn't require a very large object at all--try flicking a pebble into a cloud created by a fog machine.
Re:A New Criteria? (Score:2, Interesting)
Of course, the truth is that we're guessing out of our hats there...
What makes you think that there could not be a life-form adapted to living in a planet/moon which gets regularly hit by various bits of artillery bombardment from space? Bacteria have proven that they can live in space. All it takes is a little weird evolution to make lifeforms that can (as a group, at least) survive such a major blow. Possibly a planet-wide organism, or at least, a planet-wide ecosystem?
Come to think of it, we already have one of those - except that the dominant life-form seems hell-bent on destroying it!
Re:Is that something we should bet our existence o (Score:3, Interesting)
I'm not sure what makes you so sure that there'll be much left by the time a space object becomes a risk or that we'll be able to spot it in the first place. Many of those meteors move pretty damn fast.
Re:A New Criteria? (Score:2, Interesting)
Jupiter is like seat belts. Seat belts save lives and that is a fact. Thousands of lives are saved every year due to them but every once in a while there is the odd exception where wearing a seat belt would have killed them. Jupiter acts the same way. There may be the odd rock thrown out way because of the planet but more often than not Jupiter will throw it out of the system or eat it up.
Re:Is Jupiter Earth's Cosmic Protector? (Score:3, Interesting)
Wrong. Both sides of the moon have had the same level of impact, and the 'far' side is not facing the asteroids any more than the 'near' side. The earth-moon system rotates in space and the moon rotates around the earth so both faces are in the direction of the asteroids all the time.
The 'near' side of the moon only looks smoother because mare lava flows have smoothed it out somewhat. It's just chance that put those flows on the side we see.
Fun fact: if the earth had no weather, it would look just like the moon in terms of impact craters. The earth is much bigger and has actually been hit more often. But our weather has eroded most of them.
Re:Luckily... (Score:4, Interesting)
> The Earth has not yet faced a galaxy coming straight at it.
The Earth is facing a galaxy coming straight at it. The Andromeda Galaxy is on a collision course with the Milky Way, and there is a very real possibility that the Sun will be ejected from our Galaxy when this happens. Fortunately, this is not going to happen for about three billion years
Re:Luckily... (Score:4, Interesting)
Actually from what I understand, getting ejected from the galaxy would probably be the best outcome.
There is also a chance of the Sun being put into an orbit that takes it through uninhabitable parts of the galaxy such as the core. Also when the collision happens it will trigger a very large spurt of star formation leading to more supernova and just large amounts of radiation from large new stars. Not to mention the chance of a close encounter with another star disrupting the orbits of the planets in the solar system.
Re:A New Criteria? (Score:2, Interesting)
It is interesting to wonder if our odds increase or decrease on being hit when there is a large massive body in our solar system. Like the article and summary say, some objects that would not have come close could be put on course for earth via Jupiter's gravitational forces. Who knows, maybe massive bodies like Jupiter pull more space debris into our system and make it more hostile than if it were just the earth orbiting the Sun?
Understanding the effects of Jupiter's gravitational field is the main thing. How close does an object of a catastrophic mass need to be before it is A) redirected to earth, versus B) sucked in to Jupiter. I think your theory is already answered by the summary:
Jupiter acts as a gravitational shield, deflecting incoming space junk away from the inner solar system where it could do to humans what an asteroid apparently did for the dinosaurs 65 million years ago.
Wonderful when sentences contradict themselves. It's pretty clear that Jupiter was there 65 million years ago too. The problems include: 1) If Earth is on one side of the solar system (with the asteroid), and Jupiter on the other; probably won't help. 2) Did it skew that old trajectory; we'll never know. 3) It's just in that instance, mammals benefited more in the long run.
Maybe it will be avians (evolved dinosaurs) next time. So long and thanks for all the bread.
Talk about a Dyson sphere... (Score:4, Interesting)
The point is that not only does Jupiter protect the terrestrial planets now, but that Jupiter has protected Earth from the birth of the solar system. This is one reason that Earth isn't yet another gas giant.
The recent controversial redefinition of the word "planet" (http://en.wikipedia.org/wiki/IAU_definition_of_planet [wikipedia.org]) discusses this "vacuum cleaner" effect as the third of three criteria:
Jupiter is by far the largest planet and has by far the largest such effect. A lot of the reasoning in the comments has caused one to question how well Astro 100 courses are being taught, but perhaps it is ok to venture one simple statement for why Jupiter preferentially protects the inner solar system. The comets that threaten us originate in the distant Oort Cloud (http://en.wikipedia.org/wiki/Oort_cloud [wikipedia.org]). They visit the inner solar system, but their orbits all begin far outside. It is thought that external perturbations play a role in causing them to plunge inwards. Jupiter (to oversimplify outrageously) stands between us and the bombardment.
Fundamentally this is the famous "three body problem". The equations describing Newtonian gravity are straightforward to solve for two bodies, and impossible to solve precisely for three or more. Relativistic corrections add a bit of spice. As a result planetary mechanics requires numerical integration.
The solar system is full of neat resonances and points of stability such as the Lagrangian points. Jupiter's Trojan asteroids (http://en.wikipedia.org/wiki/Trojan_(astronomy) [wikipedia.org]) cluster at L4 and L5 and are thought to be as numerous as those in the main belt. Our Moon's tidal locking is a) imperfect (since the orbit is rapidly growing (http://en.wikipedia.org/wiki/Moon#Orbit_and_relationship_to_Earth [wikipedia.org]), and b) simple compared to resonances (http://en.wikipedia.org/wiki/Orbital_resonance [wikipedia.org]) between other bodies.
Re:A good reason for manned exploration... (Score:4, Interesting)
... is the fact that eventually we have to get off earth and learn how to survive in the hostile universe anyway.
With all due respect, as much as I want mankind to go into space there's nothing to suggest earth will become uninhabitable in the next few million years. Not unless we destroy it, but in that case there's not much hope we'll be capable of interstellar travel either. On that angle, who cares if that happens this century or this millennium? We could easily have spent another million years on the ape stadium, shaving off a few centuries means nothing.
The odds that any interstellar "manned" spacecraft would be anything like today's manned mission is highly unlikely. More likely what we're doing now is like testing the extreme conditions of cross-continent horse-and-buggy rides when the solution is a jet plane. I'm guessing we'll send something like space probes that'll thaw or build embryos on site with nursing robots to form new colonies, sending fully grown people is just insanely inefficient in so many ways.
You may think that's inhumane, but I think it's the only humane thing. Imagine being second generation plus on a ship in the dark void of space, only seeing pictures and videos of earth while you're trapped on a tin can because your ancenstors decided to make you a pawn in colonizing a new planet. Plus, then they'd also be real people that quite possibly, or even probably, will die at some point from ship failure. A probe on the other hand may only produce humans if all flags are green.
Jupiter's core (Score:3, Interesting)
Last Sunday, an object, probably a comet that nobody saw coming, plowed into Jupiter
First, I'd like to apologize for being slightly off-topic.
I wonder why pretty much all astronomy sources are unwilling to state with certainty that Jupiter has a rocky core. It's only natural that more solid material has fallen into the atmosphere than has been captured in orbit. It's not like the comets and meteorites will 'orbit' for very long within friction of the atmosphere, so the only place for solid matter to go is the center.
Re:Luckily... (Score:3, Interesting)
Looking at it, seems like either outcome means lights out (well, probably more like lights on one hundred million times more powerful) but whatever happens, here is where we don't want to be.
Re:Jupiter's core (Score:3, Interesting)
The heat and pressures are so intense at the center of Jupiter there's really no way to say definitively what's there. It may be a spongy form of matter (semi-metallic hydrogen). It could be super-heated slurry of materials like our core. Or it could be a solid heated sphere of materials.
It depends on what the core is made of, the densities of the materials, the convection, etc. . That's a lot of unknowns to deal with to make the assumption that it has some sort of rocky core.
The point being, we're still getting a handle on the "likely" geophysical processes in our own core, let alone a gas giant like Jupiter.
~X~