
NASA's Curiosity Rover Sharpens Paradox of Ancient Mars - daredave
http://www.jpl.nasa.gov/news/news.php?feature=6734&utm_source=iContact&utm_medium=email&utm_campaign=NASAJPL&utm_content=daily20170206-1#.WJlBs6uEyNQ.hackernews
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kijin
I've heard about a scenario where Jupiter once wreaked havoc on the orbits of
the inner planets, pushing some of them closer to the Sun and pulling others
further away. (It's not the Nice model [1] but some unorthodox variation of
it.)

Could Mars have been closer to the Sun when this lake existed (3.5 billion
years ago), or is that too late in the history of the Solar System for any
major disturbance to have happened?

[1]
[https://en.wikipedia.org/wiki/Nice_model](https://en.wikipedia.org/wiki/Nice_model)

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dr_zoidberg
I think you're refering to the Grand tack hypothesis[0], but Wikipedia is
scarce on details as to how that scenario could've affected Mars orbit.

I was trying to see if this had a timeline, because the NASA cites lack of CO2
as far as -3.5GY, but there isn't enough detail in Wikipedia and my 5 minutes
slack time is over :(

[0]
[https://en.wikipedia.org/wiki/Grand_tack_hypothesis](https://en.wikipedia.org/wiki/Grand_tack_hypothesis)

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Swizec
Is it possible that other greenhouse gasses than CO2 were present that helped
keep water liquid? Or maybe the planet produced enough internal heat to warm
up the surface beyond freezing? Or atmosphere, whatever it was, was thick
enougj to produce high pressures that kept water liquid despite freezing
temperatures?

Surely if water was liquid and CO2 was not there, those must be the only
possible scenarios? Or a combination of them, of course.

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xjwm
Methane is more potent than CO2, but fairly short lived. Maybe Mars had more
Methane in the distant past? If a 95% CO2 atmosphere isn't enough green house
gas for liquid water, I'd assume internal heat played some sort of role.

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ChuckMcM
My guess is methane as well, Mars still "breathes" out methane
occasionally[1]. Given that chunks of Mars have been kicked off the planet and
landed on Earth, I wonder if you modeled a chunk of Titan's methane ice being
kicked off Titan and hitting Mars would have the effect of filling out enough
of Mars' atmosphere to warm it.

[1]
[http://science.sciencemag.org/content/306/5702/1758](http://science.sciencemag.org/content/306/5702/1758)

