# Say we were to bring Titan to Earth's orbit. How much would its atmospheric pressure change?

I've heard one of the reason why Titan has such a thick atmosphere is because of its really low temperature. So say that were were to magically bring Titan to the Same orbit as Earth, and the moon starts to rapidly heating up. How much of its atmosphere would it lose? Would we still be able to stand there without a pressurized suit? Is it possible to terraform Titan to the extent that we can heat up its surface while still retaining its thick atmosphere?

Thanks

• As well as temperature, Titan's lack of a global magnetic field might have long-term effects on how well the atmosphere holds. – user10106 Jun 25 '18 at 7:29
• Although Titan is more massive, its surface gravity is less than the Moon's. So my guess is that it will lose all its atmosphere, and all its water, eventually. – PM 2Ring Jun 25 '18 at 8:26
• The surface is water ice, in large part, so if you heat it up too much, you no longer have a surface. – Steve Linton Jun 25 '18 at 10:58
• Suppose one did this anyway, putting Titan at the Earth-Sun L4 or L5 points, for instance, and over millions of years, Titan started losing hydrocarbons, nitrogen and eventually water from the top of its atmosphere. Would those volatiles end up on Earth? Would you get an Earth-Titan atmospheric torus, or would the solar wind clear it out too fast. – Steve Linton Jun 25 '18 at 11:00
• @SteveLinton: The surface being mostly water ice? I think there's quite a bit of uncertainty about that. "Those data suggest a mixture of water ice, tholin-like materials, and dark neutral material with a blue slope in the near infrared; identification of water ice is suggested but inconclusive." Soderblom et al. 2009 in 'Titan from Cassini/Huygens' (Brown.. (eds.)) – AtmosphericPrisonEscape Jun 25 '18 at 21:04

As Temperature rises, so would the pressure, this would work immediately, as heat from the sun reaches Titan's surface.

The atmospheric escape (and thus, pressure loss, as you describe it) would work on a much longer timescale.
We can make a few estimates to determine this timescale: On the most simplified level, the composition if Titan's atmosphere is that of Earth's - it's mostly molecular Nitrogen.
So the mean molecular weight $\mu$ would be the same. The temperature would be similar compared to Earth by assumption of your experiment, then the only important difference is the mass and radius of the two bodies, reducing the escape speed by a factor of ~10.

Titan has 2% of the mass of Earth, so the ratio of escape speed to thermal molecular speed at the exobase, from where molecules are lost, would approximately scale like $\sim 1/\sqrt{10}\approx 3.1$
To determine escape rates, those go roughly like $\sim \exp(v_{th}/v_{esc})$ and would thus increase by $\sim \exp(3.1)\approx 22$, compared to today's level.

I don't know present estimates for the lifetime of Titan's atmosphere, but this factor would e.e. bring it down from 5 billion years to only 250 million years. That's really short, geologically speaking!

But of course it's not enough to affect you in your pressure suit on the surface. You'd rather be concerned about an overpressure than underpressure.

• There's a lot of methane and other hydrocarbons in Titan's atmosphere, and they're all excellent greenhouse gases. Also, as Titan warms up the amount of water will increase, further enhancing the greenhouse effect, but also making things more complicated due to chemical reactions. My guess is that some of the water will create photochemical smog, and the screening effect of smog will slow down surface heating a bit; Titan is already very smoggy, according to Wikipedia. – PM 2Ring Jun 25 '18 at 8:21
• @PM2Ring: True, but I state in my assumptions that I ignore those effects, for reasons of simplicity. Also what matters for atmospheric escape is mainly the exobase temperature, not the surface temperature. Surface temperature only comes in indirectly via determining the density 'support structure' upon which the exobase rests. – AtmosphericPrisonEscape Jun 25 '18 at 8:46

There's a basic problem that I don't see addressed. Titan has oceans of methane. If you warm up it's surface, those oceans will evaporate and the atmospheric pressure will increase rapidly.

In short, no, you can't warm up titan to teraform it because, at least for a while, the atmospheric pressure would become too great. In the long run it would lose it's atmosphere. It will probably lose it's atmosphere anyway given enough time and certainly as the sun goes red giant.

As far as settlements go, the cold weather of Titan is probably easier for a human colony than the near vacuum and fine/toxic dust on Mars. A vacuum requires much more technology to survive in than extreme cold. (to my limited knowledge anyway).

Mars has more metals and it's better for solar energy and its gravity is more livable. Solar energy would be basically useless on Titan and the gravity is too low for humans to maintain a good sense of up and down. There's pros and cons to both.