Key points from article :
Mars is a hopeful "Planet B" if Earth fails.
Terraforming is the process of changing the conditions on a planet.
It would make Mars habitable for Earth life without life-support systems.
New paper says terraforming Mars not possible with existing technologies.
Would need to raise temperatures and thicken the atmosphere.
not enough CO2 on Mars to make the planet Earth-like.
The study was published in the journal Nature Astronomy.