Atmospheric Pressure & Tempreature:
The atmospheric pressure on Mars is very thin (less than 1%) when compared to Earth and it has an average temperature of -62°C.
Mars does have polar caps, minerals, and soil that could provide sources of carbon dioxide (CO2) and water to thicken the atmosphere. And some have suggested that there is enough CO2 locked away in Mars's ice and rocks to heat the planet.
Over the years a number of ideas have been proposed on how to access these.
But in 2018, two NASA-funded scientists found that at best, accessible CO2 could only increase the surface temperature by less than 10°C. They came to the conclusion that processing all these sources found on Mars would also only increase the atmospheric pressure to 7%.
They state, "even if enough CO2 were to be available, it would not be feasible to mobilise it; doing so would require processing a major fraction of the surface to release it into the atmosphere, which is beyond present-day technology".
Low Gravity:
The surface gravity on Mars is 38% of that on Earth.
Because life on Earth has evolved over the past 3.5 billion years in an unchanging gravitational field, it shouldn't be a surprise that so much of our physiology appears to be defined by -- or dependent upon -- gravity.
At present, it is unknown what effects long-term exposure to this amount of gravity will have on the human body.
However, ongoing research into the effects of microgravity on astronauts has shown that it has a detrimental effect on health, which includes loss of muscle mass, bone density, organ function, and even eyesight.
If we wanted to terraform Mars and change it's gravity, some suggest it would mean we would have to change the overall mass of the planet itself!
Magnetic Fields:
Earth's molten core creates a magnetic field surrounding our planet that helps to protect the atmosphere from the Sun. Harmful rays from the Sun are deflected by the magnetic field, so they don't hit the atmosphere and damage it.
Billions of years ago, Mars used to have a global magnetic field, but it shut down for reasons that are still unknown, about 4 billion years ago, leaving the atmosphere unshielded to radiation and causing it to bleed over time into space.
Unfortunately, we can't just simply start it back up again. But one recent study suggests we could create an artificial one!
This study points out, if you want a good planetary magnetic field, what you really need is a strong flow of charged particles around the planet. They argue, you can create a ring of charged particles around Mars, by using its moon Phobos.
Phobos is the larger of the two Martian moons, and it orbits the planet quite closely. So, the team proposes using Phobos by ionizing particles from its surface, then accelerating them so they create a ring-shaped cloud of ions along the orbit of Phobos. They argue that this could create a magnetic field strong enough to protect a terraformed Mars.... watch this space!
