Martians may actually exist, but this Martian is not an alien from a science fiction movie, but a future human born and raised on Mars. Let's say, if you were born on Mars, what would you have been like? Why is your skin orange? Would you be a different species from today's humans? Will you still be able to visit Earth in the future?
If humans want to build a stable settlement on Mars and people have to start having children, how many people do we need to create a healthy rather than inbreeding population? Some people think we only need 98 people, but others say we need at least 10,000 people. In fact, no matter how big the number of reproductions is, it only takes a few generations, and we will see a huge difference between Earthlings and Martians.
Mars is the most Earth-like planet in the solar system, but not exactly like Earth, and its gravity, atmosphere and magnetic field will pose serious challenges to human life. Challenges often come with evolution, with children on Earth born with up to 120 genetic mutations, and moving these babies to Mars, they begin to produce mutations that are appropriate for life on Mars that may be passed on to their children, and by the time we settle on Mars, we may already have the ability to modify our own genes to put evolution on Mars on the fast track.
If you were a third or fourth-generation Martian, you would be very different from who you are today, and what is the reason for the huge changes in your body?
First, there is gravity. Mars' gravity is only 1/3 of that of the Earth, and your bones will not be subject to the same gravitational pull as the Earth, which will cause your bones to lose density, become more fragile, and fracture easily.
Then, there's the atmosphere. You're used to Earth's dense atmosphere of nitrogen and oxygen, but on Mars, you'll experience a thin atmosphere with the main content of carbon dioxide and only trace amounts of oxygen. You can't evolve a whole new respiratory system, but you can develop other ways to cope with hypoxia, for example, you can have denser capillaries that will more efficiently deliver blood and oxygen to each of your muscles. But even with these improvements, you still have to live in a house underground or with thick insulation to survive in the harsh atmosphere. Since life on Mars has always been confined to a very small space, Martians do not need to see far away, and you are short-sighted as soon as you are born.
Finally, there is radiation. Earth has a strong magnetic field that protects us from deadly solar radiation, but Mars has only one weak magnetic field that is scattered across the planet.
On Earth, our bodies produce melanin that protects us from radiation from Earth's magnetic field, but radiation on Mars is stronger, and melanin doesn't stop radiation from happening. Instead, your skin produces carotenoids, because this pigment can help prevent skin cancer by slowing down or stopping cell cycles, and carotenoids can even self-destruct melanoma cells. When your body undergoes these changes, your skin will naturally turn orange as well.
Since there are no bacteria and viruses of the same type on Mars as on Earth, your immune system will be much weaker than that of Earthlings, and once you return to Earth you may be in danger, even if your immune system is strong enough to resist the terrible germs distributed on Earth, the gravitational pull of The Earth will have a huge impact on your fragile bones.
If you were born on Mars, you might stay on this red planet all the time. Maybe after a long time of life, humans still look the same, but after a few generations, we may have orange, myopic humans, provided that Mars has enough oxygen above the assumption that it may hold.
Once we succeed in settling on Mars, humans won't stop there, humans will settle on a variety of planets, even outside the solar system, so that exciting and frightening aliens are just a future version of humanity.