# How long would a magnetic shield placed at the Mars L1 point take to replenish Mars's atmosphere?

This conference paper proposes placing a magnetic shield at the Mars L1 point to protect it's atmosphere. The paper reports the results of modeling the martian atmosphere at a variety of pressures (10, 50, 100, 500, and 1000 mbar).

How long will it take for the martian atmosphere to increase to these pressures, if the magnetic shield is applied?

The Wikipedia article says that

Simulations indicate that within years, the planet would be able to achieve half the atmospheric pressure of Earth

I suspect that this is too fast, and the Wikipedia article is wrong.

My back of the envelope calculation is:

• Mars loses atmosphere at 0.1kg/second
• Earth's atmosphere weighs 5x1018 kg
• Therefore it will take 5x1019 seconds or 1.6x1012 years for mars to naturally generate an atmosphere as heavy as the Earth's, if we install a magnetic shield.
• This means that it will take at least millions of years before we see a useful increase in atmospheric pressure on Mars using this approach.

How long will it take for the martian atmosphere to increase to pressures of 10, 50, 100, 500, and 1000 mbar if the magnetic shield is applied?

• Hard to tell what the author was thinking, but I suspect that line conflates the effect of the magnetic field with other terraforming activities. "Half the atmospheric pressure of Earth" roughly lines up with the pressure that would be achieved by sublimating all the polar CO2 deposits (30-60 kPa), which could indeed happen rather quickly once it reaches a certain point and greenhouse heating starts sublimating the ice. It'd do that whether there's any magnetic shield or not, though. Jun 2 at 15:34
• here is a list of questions about magnetic fields and terraforming Mars space.stackexchange.com/a/27539/12102
– uhoh
Jun 2 at 16:51
• from a highly pedantic point of view, "within years" encapsulates it taking millions of years Jun 2 at 22:46

The main mechanism for large changes in the Martian climate in response to small changes in initial conditions is that elevated temperatures results in sublimation of $$CO_2$$ in the ice caps, further increasing pressure and temperature.