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Mars Had an Ancient Impact Like Earth
quixote9 writes "The BBC reports on a set of Nature articles showing that Mars had an impact about four billion years ago by a huge asteroid. This was about the same time that a much bigger object slammed into the Earth, throwing material into orbit around our infant planet. This material is thought to have coalesced to form the Moon. 'It happened probably right at the end of the formation of the four terrestrial planets — Mercury, Venus, Earth and Mars,' said Craig Agnor, a co-author on the Francis Nimmo study. 'In terms of the process of the planets sweeping up the last bits of debris, this could have been one of the last big bits of debris.' There's a theory that having a big moon is important to the development of life, because the much bigger tides create a bigger intertidal zone, but people used to think having a huge Moon like ours was a once-in-a-universe event."
people used to think having a huge Moon like ours was a once-in-a-universe event.
And I should hope that they still think so, seeing as Mars does not have a huge Moon like ours... Despite evidence of an impact that COULD have created one, and yet didn't.
I reckon ther's not sucha a thing as a once-in-a-universe event!
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i understand why tidal pools can be thought of as interesting chemical incubators for life with all of the heating and cooling, wetting and drying that goes on, but a lot of other completely common and normal processes that can take place on a moonless planet can also lead to such incubators as well. waves, daily temperature variations, seasonal fluctuations, geography, etc.
the moon does make us an interesting little quasi double planet system. but i think that that uniqueness does not go hand in hand with our planet's other unique trait, life. correlation is not causation looms large in my mind on this idea that the moon gave the earth life. no, the earth's chemical makeup, temperature, and atmospheric pressure putting us near water's triple point, with a lot of water around: that gave us life. every other detail seems secondary and not mandatory
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Having a single big moon is supposed to be ultra rare? I'm really curious why that is. Given what we know of our solar system, moons are far from rare. We may only have one example of a large unitary moon, but come on, that's out of a sample size of 9 (8 now I guess) from a universe with presumably a nearly limitless number of planetoids. The argument almost strikes me as one of those arguments for Humans being the only intelligent species in the entire universe because it must be almost impossible for life to occur. Arguments that are grounded entirely in conjecture.
I read the internet for the articles.
The two colliding bodies generally merge. IE, "Earth" as we know it didn't really collide with some foreign object that went skipping off into space again. "Earth Mark I" was a somewhat different planet whose remains are still here with us, and it collided with a very large object (essentially a planet in it's own right) called Theia (or sometimes aka Orpheus). Those two would have merged and the collision throw up the debris that formed the moon (which is also made up of parts of both)
So there is no search for the object that hit Earth to form the moon. It's still here with us as part of the new Earth, and Theia/Orpheus is essentially our original planet as well; it's just easier to call the bigger planet involved in that collision "Earth" because, well, it was the bigger of the two.
The same is likely true of Mars - the object that struck it probably merged with it.
As an interesting note, it's also thought that a large impact must have struck Venus as well, and must have hit it hard enough to "flip" the planet, as Venus, compared to every other planet in the solar system, rotates "backwards". There were some BIG things floating around and colliding in the early Solar system.
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Unlikely. Pluto's orbit doesn't come close to intersecting with that of Mars, and circularizing a Pluto-sized object's orbit after the huge Mars collision event would require ... another huge collision event. [Un]fortunately, most of the debris in the Sol system has been cleared out by the current set of planets, so most of this stuff will remain speculation because the evidence is gone by now.
There are several things that our extremely large moon does for us that make life much more comfortable.
#1 is of course tides that are more extreme than the sun could generate
#2 rotational speed. The moon has kept our rotation from slowing as much as it should have. Shorter day/night cycles are important for environmental management.
#3 atmosphere. The moon helped reduce the density of proto-earth's atmosphere. Without it we probably would resemble Venus.
#4 plate tectonics. The tidal influence on the crust heats up the mantel and keeps the plates from sealing
#5 protection. The moon intercepts a large percentage of the impacts destined for earth. This reduces the disruptions caused my meteor impacts. This was more pronounced earlier, when the moon was closer and when it was even more important (more meteors around)
#6 increased metal content. Since the moon is almost entirely light minerals, most of the metals that were in the original impact were left on earth which artificially increased the concentration of metal in the crust.
While I can think of other things that could help with one or two of these, I can't think of something that would satisfy all of these consistently for a few billion years.
What do you suggest as an alternative?
Yeah, Venus must have had some fairly...unique event to make it rotate backwards, cause that's just flatly impossible to happen by itself. Debris further away from the sun is moving faster than debris closer, and hence when they merge they're always going to rotating in the same direction. At least on average of the billions of collisions that make the planet. So something really big must have hit the mostly-formed Venus and done something near the end.
Whether things brushed it 'the wrong way' enough to make it spin backwards, or if they hit the top or bottom of it and actually rotated it 180 degrees so its north became south, is unknown. I, like you, suspect the latter, that Venus was essentially flipped over like grabbing a spinning gyroscope and flipping it...which obviously takes a lot of force, even more than it would normally take because of gyroscopic action.
The first option is that it was bombarded with enough debris on the 'inside' and not on the 'outside'. But that's just sorta implausible, whereas the 'flip' theory just requires one really big hit.
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From the article
According to one group of researchers, the rock struck with an energy equivalent to one million billion atomic bombs like the one dropped on Nagasaki in 1945.I think after the first billion Nagasaki bombs, you just say "energy equivalent to being struck by the Moon".
Nit picking, I know, but how can you even wrap your mind around that number of atomic bombs?
Here will be an old abusing of God's patience and the king's English.
Mars Had an Ancient Impact Like Earth
No it didn't. Like Earth, Mars had an ancient impact, but the impact itself was decidedly NOT like the impact Earth experienced.
Earth's impact obliterated the Mars-sized object that impacted earth, leaving a ring of ejects circling the Earth. The ring coalesced into the moon. This didn't happen on Mars; Mars has no giant satellite, only two small moons.
Also, I saw a few different accounts, and not everyone is yet convinced that the disparity between Mars' poles was caused by a giant impact. The San Fransisco Chrinicle, for instance, says "Huge impact may have divided Mars surface".
An interesting, yet probably non-answerable question occurred to me - If an object did smash into Mars, rather than hitting pole-on as the theory says (and I'm no astrophysicist and can't even spell it properly), which seems improbable to mee, seeing as how all the orbits of all the crap circling the sun seem to lie on a plane, could it have struck Mars' pole and then hit the next planet in (Earth), causing its moon?If this could have happened, could life have been on Mars at he time but completely wiped out, with its remnant chemicals starting life over on Earth?
There have been meteorites that are Martians.
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Or crossing Neptune very closely. And since we suspect that Triton was captured by Neptune as it was forming a couple with a similar body which got ejected away when Triton was captured, we can imagine that Mars' hypothetical Moon was that other body. Now who knows, Mars probably caught that asteroid that made this moon to protect its beloved Phaeton, who was ultimately destroyed by the mighty gravitational pull of the ruthless and jealous Jupiter who failed to capture Phaeton in the past despite his numerous attempts, and thus pulverized it to make Mars miserable in retaliation.
Meanwhile, in the solar system. Will Jupiter find out which of the other gas planets threw a Shoemaker-Levy 9 at him? What surprise lurks in the confines of the solar system for Mars' old moon? Are Pluto and Charon about to divorce? Find out in the next episode of Desperate Planets!
You just got troll'd!
If this is true (a glancing blow by a huge object), I'm confused as to where the debris ejected from the collision would have ended up? Certainly not everything would have ended up melding with the main planet, especially (again) if this was a glancing blow. I'd expect some sizable amount of mass to be blown into orbit, as happened in the Earth-Moon formation event.
Mars's two moons are incredibly tiny - IIRC more like smallish asteroids - so no coalescence of debris into a larger satellite as we have.
Someone more awake in astrophysics class maybe can help with this.