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."

Comments

Hopefully.

[pclminion]

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.

Re:Hopefully.

[MBGMorden]

IF you RTFA then you'll find no mention of some freaking 'Huge' moon being necessary to life. While it didn't appear in the article, I've seen quite a bit of stuff suggesting that a big moon could be a necessity. While the tidal issue is news to me, the most common thing I've heard quoted as that a large moon serves as an anchor for a planet, significantly reducing the amount of wobble in it's orbit. A wobble of less than 1 degrees can have serious climate impacts on Earth (the Sahara was once a jungle . . .), but we generally don't wobble much because of the moon anchoring us down. Other rocky planets like Mars or Venus wobble MUCH more, which would make climate conditions that would be difficult for life to spring up.

IIRC, one special that I saw suggested that while life might have formed in the absence of the Moon, it probably would have been confined to the oceans only.

Re:Hopefully.

[Bombula]

A wobble of less than 1 degrees can have serious climate impacts on Earth (the Sahara was once a jungle . . .), but we generally don't wobble much because of the moon anchoring us down. Other rocky planets like Mars or Venus wobble MUCH more, which would make climate conditions that would be difficult for life to spring up.

Depends on where in the timeline you're talking about. In the first 500 million years after the moon formed, it was so close to the Earth that the tides were 1 MILE high. Can you imagine a wall of water a mile high rolling tens or in some cases hundreds of kilometers inland several times a day? I think that probably had a signficant impact on the weather too, don't you? But who knows, maybe that was good for aiding the formation and establishment of simple life.

Re:Hopefully.

[dreamchaser]

Extreme tides like that may well have helped spur the evolution of life. Proto-microbes washed onto shore and other materials washed back in. Think of it as a big huge mixing bowl.

Some of those microbes may just have gotten stranded. Most probably died. A few probably adapted, living in shallow pools or clinging to rocks.

lots of things can lead to fluctuations in pools

[circletimessquare]

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

Re:Maybe it was the same collision

[Gewalt]

Well, considering the earth is actually very liquid and quite soft inside (and uh.. I "think" mars is as well), I have a hard time believing that the two celestial bodies would have had an elastic collision. Unless they were coming from very opposite directions and just barely nicked each other, they should have become one.

Now I wonder tho... just how close would they have to come to each other in order to have mingling gravity completely tear apart the surface of each... Mayhaps a collision isn't necessary after all.

Re:Once in a universe?

[spacemandave]

Pluto and Charon aren't formed the same way.

It is actually quite possible that Charon formed in exactly the same way as the Earth-Moon system. See this abstract. Most modern planet formation simulations show that the end stage of formation involves collisions between large proto-planets. Whether or not any particular giant collision results in a satellite or not depends on the details such as impact velocities and angles. Double bodies such as Earth-Moon and Pluto-Charon are likely to be relatively common outcomes given what we know of planet formation.

Not exactly

[sm62704]

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".

In the past some scientists have held that the great divide on Mars was caused by the upwelling of semi-molten material from the planet's interior, or perhaps by several smaller meteorite impacts. But now the theory of a single giant impact has gained major support. It's an intriguing theory - most of it derived from computer calculations and NASA spacecraft. But one scientist expressed some modest reservations about it in a separate commentary in Nature.

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.

Re:Not exactly

[jd]

It seems much more likely that it was a single body that split up into multiple smaller bodies, much as Shoemaker-Levy did, where one hit Mars and a much larger one hit Earth. The timing (both about the same time) does make for a strong case that the collisions are related, but a game of astral pinball, with the object riccocheting off Mars to hit Earth, seems unlikely to me. Given that, then, what are the possibilities? Well, one, as I said, is that the object simply fragmented (say by passing too close to Jupiter) and different sized fragments hit the different planets.

A second option, though this seems much less likely, is that the object striking the Earth partially survived. The Earth had been pretty much mulched and a moon thrown off from outer crust materials (which is why it has such a low density), but it's possible to imagine a dense core surviving from the original object. Provided it was on an outward trajectory, this body, having passed through Earth in effect, could have gone on to strike Mars. This has the same problems as an object striking Mars then Earth.

Third up would be a double planetoid (similar to Pluto/Charon) or a planet with a large moon having its orbit disturbed, where one sruck Earth and the other struck Pluto. This retains the basic idea of #1 without needing as large of a force to get the same results.

Not new

[Thelasko]

From Wikipedia:

the Sun oscillates up and down relative to the galactic plane approximately 2.7 times per orbit. This is very similar to how a simple harmonic oscillator works with no drag force (damping) term. Due to the higher density of stars close to the galactic plane, these oscillations often coincide with mass extinction periods on earth, presumably due to increased impact events.

That explains it right there.

Life? Don't talk to ME about life!

[sm62704]

If there were no moon it would have happened differently.

There is no proof or even indication that it would or wouldn't have happened at all. Life must be pretty damned special* because we've found no indication of it elsewhere. We've had probes to most of our star's planets and not found any hint of life anywhere yet, we've had SETI running for a long time and no indication at all that there's anybody out there.

We don't even know how life started on earth. So far, we DO know that life is unique to Earth in our solar system. I don't think it's likely, but it is possible, no matter how improbable, that this little rock is the only repository of life in the universe.

-mcgrew

*Marvin says life rode the short bus to school.

Re:Life? Don't talk to ME about life!

[sm62704]

True, but the point stands that there is no indication whatever that there's any life anywhere but earth.

Personally, I'm of the opinion that we most likely will find life of some sort. I also suspect that we may run across sentient life and not only not realise it's sentient, but even that it's alive.

The late Chief Dan George's character in Little Big Man had an observation (that I'm surely not quoting exactly since it's been years since I've seen that movie): "The Indian thinks everything is alive; the people, the buffalo, the trees, the rocks. The white man thinks nothing is alive, and if he suspects something is alive he'll kill it."

There was a STNG episode where they did, in fact, come across a sentient silicone-based life sentient form that they neither realized was sentient nor alive.

But currently there is no evidence of life anywhere but here.

Where's the ejecta?

[thatseattleguy]

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.

Re:Maybe it was the same collision

[Strider-]

Debris further away from the sun is moving faster than debris closer, Really? Kepler's laws of planetary motion (specifically the third law) state that the closer an object is to the sun, the faster the orbit. Only if you consider angular velocity. In strict distance traveled per unit time, the further away you are, faster you are moving.

This is why in orbital mechanics you add velocity to allow something to catch up to you, and reduce velocity if you want to catch up to something. It's totally counter-intuitive, but in the grand scheme, that's how it works.