Kosh

In honor of my niece (now in college!), I propose we call it.... "boo boo planet".

Tom Sawyer

I like this "Eris theory". It's always struck me as a little strange why all the mass formed into planets most everywhere in the solar system, yet there was this big belt of asteroids that didn't form into a planet sitting right in the middle of them.

The idea that it might have once been a planet that broke up would give a good answer to why it seems to differ from everything around it. I don't think it has anything to do with Mars's atmosphere - as Valentine Pontifex pointed out, the planet only has 10% of the mass of Earth to explain that - but I think Eris's being so close to the massive gravity of Jupiter could cause it to rip apart or not form properly in the first place.

This is a really interesting theory. I'd like to give some thanks to lpetrich for bringing it to my attention.

Shadowy Man

There are definitely some strong orbital resonances with Jupiter in the asteroid belt.

This may have affected any planet's ability to form there - assuming that Jupiter formed in its current orbit.

beausoleil

Some general comments...

LPS abstracts are a great place to float whacky ideas - the conference can be a venue for brainstorming. I've done it myself. So don't get too carried away with this model.

This model isn't that the asteroid belt is the remains of a broken up planet (there isn't that much mass in the asteroid belt anyway). The fifth planet is supposed to have perturbed the asteroid belt directing some asteroids towards the inner planets. The fifth planet then disappeared as its evolving orbit led it to collide with the sun, perhaps.

The present martian atmosphere is lost as it is sputtered by the solar wind - not strictly because it has low gravity. If the Earth didn't have a magnetic field the atmosphere would suffer the same fate. One model of atmospheric collapse on Mars involves precipitation of carbonates in an early ocean. The same thing happens on the Earth, but the CO2 is recycled by subduction. No plate tectonics on Mars - no subduction - no recycling.

It's still not settled whether the late heavy bombardment was a spike or the tailing off of accretion. I've seen it suggested that plastic deformation of Oceanus Procellarum might suggest that it formed while the crust was more 'malleable' than later impacts such as Imbrium.

Shadowy Man

If this is true then why does Venus still have an atmosphere? A thick one at that!

beausoleil

And it's being sputtered by the solar wind. The rate depends on the gravitational field of the planet. I was just illustrating the process and that low gravity isn't enough in itself to explain the current low atmospheric pressure on Mars.

Shadowy Man

Maybe, but which is the dominant process? Is the extra gravity of Venus enough to account for its thick atmosphere even though it is being sputtered by the solar wind?

If the timescale for the loss of a thick atmosphere by sputtering is even longer than the current age of the Solar system, is it even appropriate to suggest this as a mechanism?

Do you know the answer to this? I'm sure some planetary scientists have studied this and published some answers. I know a few planetary scientists (my dissertation advisor was one) so I will ask when I get the chance.

beausoleil

All I said was that the present atmosphere is being lost through sputtering as distinct from simple gravitational escape.

Loss of the proposed original thick martian atmosphere comes down to a number of mechanisms, people are still arguing about which if any dominates. Among them are...

impact sputtering by asteroids greater than ~few km diameter
hydrodynamic escape
sputtering/ pick-up ions
CO2 precipitation as carbonates (As I mentioned above)

None of them are just loss due to insufficient gravity, though gravity plays a role in the first three.

It would take ~10^8 years to remove the existing oxygen budget in the martian atmosphere

From my point of view, precipitation of CO2 in an early ocean seems likely to have played a significant role. The same mechanism is part of the wet-greenhouse model for Venus atmospheric evolution - which tries to explain where the water has gone. A simple greenhouse can't get dry enough.

In simple terms, when there's water around a CO2 atmosphere's fate is governed by weathering and precipitation of carbonates from an ocean. On the Earth the carbonates are recycled by plate tectonics leading to a feedback mechanism keeping the greenhouse intact. If it gets hotter weathering rates increase and the CO2 level goes down. If it gets colder they decrease and CO2 goes up.

In contrast, Mars has no recycling from the crust so the atmosphere collapsed. Most of the CO2 ended up in the crust (in some models)

Venus (it's proposed) had a saturated atmosphere and a very hot ocean. Water vapour was lost from the atmosphere by uv dissociation and escape of hydrogen (people plan to look for haematite in the crust to trace where the oxygen went) and the oceans 'boiled' away over 100s of millions of years. Because they'd precipitated carbonate the atmospheric pressure was low enought to allow water escape to go close to completion (escape from the current atmosphere couldn't be sufficiently efficient.)

When the oceans were gone the CO2 was recycled to the atmosphere as the carbonates decomposed. Hence a relatively dry CO2 rich atmosphere.

I hope that makes sense! It's not exactly my field but I've tried to summarise current thinking as I understand it. Apologies if I've misrepresented anyone's research!

Shadowy Man

So, how long would it take for the Earth to lose its atmosphere through sputtering without its magnetic field?

beausoleil

A longer time than we need to worry about. I'm not sure I've seen a figure anywhere.