The weather here on Earth is ideal for life because this is where it evolved. Choosing the right planet in our Solar System to terraform in order for it to sustain is going to be a difficult task no matter the circumstances as there are so many limits as well as possible things that can go wrong and act as pushbacks. One of these limits is the weather, this includes the overall climate on a given planet and also the range of temperature. Temperature is arguably the most important factor when we consider the weather conditions for a planet that could be colonised as it would be very difficult for a very cold planet to be terraformed successfully. For example, cooling down Venus would require advanced technology which we do not possess at the moment but which we could be in the next twenty years.
Warming up Mars on the other hand could be done with our current technology. Earth’s average temperature is around 14°C, whereas in Mars the mean temperature is -63°C, which is far below freezing.This is partly because Mars has a much thinner atmosphere, which is in fact only 1% the thickness of Earth’s atmosphere. If we want life to survive sustainably on Mars we will have to make it thicker and change its composition. One strategy that could do this is triggering a greenhouse effect, meaning any heat from the Sun’s radiation is trapped, heating Mars all over. There are multiple ways to do this, like using methane mined from the rocks on Mars, carbon dioxide depending on if there is enough or ammonia. Using ammonia is the most likely way to do this. We can get the amount of ammonia needed by smashing ice-rich comets from the outer Solar System.
Ammonia is mostly nitrogen by weight, once we get to the point of releasing oxygen on Mars through plantlife, an atmosphere similar to Earth’s could be formed like it was millions of years ago. This would result in a thicker overall atmosphere, meaning a higher atmospheric pressure that would allow humans to possibly live there. As a result, the atmosphere will warm the planet and allow for a colony to be built. This can sound like quite an insane plan but, warming up Mars will be the hardest part of terraforming it and so far it is the best one scientists have come up with. After warming up Mars, the next step of terraforming it would be to melt its polar ice caps. By melting them we will have a large liquid water supply. Therefore, by having water on Mars, the source of life, we can have the environment for all life. We can for example, make changes to the Martian soil and make it suitable and fertile which will allow us to grow plants and produce abundant crops and vegetation. This will not only biologically terraform Mars, but also visually as all sorts of life will be able to live there.
However, it is a known scientific fact that Mars does not have a magnetosphere, it was a major factor of why Mars lost its Earth-like atmosphere. Mars’ global magnetic field shut down around 4.2 billion years ago. This meant that it had no protection from solar wind and powerful Sun explosions. These events resulted in Mars’ losing most of its atmosphere.This is a big disadvantage as it means there isn’t an abundance of carbon dioxide in Mars’ rocks to be released. Carbon dioxide is a vital substance in order for us to trigger a greenhouse effect on Mars. Unfortunately, this means that any atmosphere we do manage to kickstart will have a limited lifetime. Eventually, it will be stripped away exactly like it did billions of years ago.