Space habitats that produce their own gravity are ultimately better, cheaper, and much faster than terraforming a planet. Terraforming a planet takes thousands of years, probably longer. Why go to all that trouble? There is only one earth, it produced us, and it's the only planet we can live on anyway. Even in a futuristic scifi universe it's still going to be easier to manufacture space habitats than terraforming alien planets.
The problem with planetary colonization is, can we survive the journey physically and mentally intact to a new planet? If we can not do that, then any talk of colonizing a planet is moot.
The other issue would be - do we KNOW enough about said planet to say that Humans could survive and build a colony/civilization there? IMO any possible candidate world would need to be studied/mapped, etc. for decades (perhaps even a century) before you could determine the overall surviveability of a group of Human colonists sent to live there
I was listening to people's opinions about the new game "Mass Effect: Andromeda". A good point was raised. Unless you are actually at the planet or in its system, transmitting information on it back to a command center, you would not know how a planet is now or relatively now, as you are looking at it as it was, at some point in history depending on how far you are from it. (In the game, explorers, bored with exploring the Milky Way Galaxy, ventured on a 600 year journey to the Andromeda Galaxy. They were looking for habitable planets.)
Explained in-game: They converted one of the Milky Way's mass relays into an FTL telescope, which cut the time lag down to something like 100,000 years. The fact that the information was so delayed means they still had to have the Pathfinders to survey those planets and figure out what conditions were PRESENTLY. The real problem is, in the 600 years it took them to travel from the Milky Way to Andromeda, two completely different civilizations moved into the Helios Cluster, fought wars, went extinct, and left their technology behind along with a huge briar patch of dark energy that was basically tearing all of those planets apart. So it's kind of like finding a reading a five-star review for a restaurant, making a reservation for the end of the month, and then showing up for that reservation to discover that the chef has been fired, the wait staff are on strike and the owner has been on a crystal meth bender for two weeks ever since his dog got hit by a car.
According to Special Relativity, there is no objective now. Now depends on your frame of reference. Observers would agree on the order of causally-connectable events (one is within within the past light cone of the other) but not their timings. An event that appears to be simultaneous with another non-causally connected event (each one lies outside the past light cone of the other) as seen from one frame of reference might appear to be in the past or the future of the event as seen from another frame of reference
At the risk of hobby-horsing this thread, this is why I don't believe in accelerative time dilation. The concept implies that one observer is the "true time" and the other is experiencing a distortion of his clock due to high relativistic velocity. The reality is that the "stationary" observer simply OBSERVES time running slower for the traveler, because no matter how long he watches the traveler with his fictional uber telescope, it still takes light a certain amount of time to reach the lens. and that time delay is getting longer and longer as the voyage goes on. Another Andromeda reference: one of the civilizations that colonized that region of space (300 years before the humans got there) left behind a lot of automated defenses and/or robots that are kind of a pain in the ass to deal with. The second civilization (arrived 80 years before humans got there) is kind of obsessed with the first.
One bit of good news--when it comes to human influence upon worlds. Just having spaceflight seems to protect the Earth: https://link.springer.com/article/10.1007/s11214-017-0357-5 https://www.universetoday.com/135590/might-new-way-push-back-space-radiation/ https://www.extremetech.com/extreme...ficial-magnetic-field-restore-mars-atmosphere
OK so say another race can see Earth as it is now. By the time they get here assuming they can't bend space or do FTL wouldn't the world have changed to a point where it's nothing at all like they had observed? Is that what you guys are getting at?
Worlds don't change THAT fast, but yeah, you have to account for evolution and climate change (natural or otherwise) when planning interstellar voyages. A species of polar bears, for example, might arrive at Earth and angrily lament "Where the hell are all those wonderful glaciers? We can't live here, this planet is WAY too hot!"
Sadly--the planet of the Engineers we see In Alien: Covenant is, (even with the ear-infecting pods that could be vacuumed up) still better than Mars.
^ I dunno, Mark Watney managed to live over a year on Mars without getting disemboweled by xenomorphs. I'm thinking Mars might be under-rated.
Just wear the same suit--but lose the oxygen tank and carry a really good HEPA filter. Then too, a bit of indigestion on Mars won't scare you into a panic attack spiral.
If you are using science fiction as your model for reality, understand that in science fiction, they have infinite money. Economics is seldom an issue. The hurdles of sending things out into space is mass and time, and much capital you can spend to overcome them. So we use robots. It's true now, and will be in the future. Money, or the exchange of value, will always be finite. If and when humanity decides to colonize a distant world, robots go first. Humans won't follow as people or passengers, but as embryonic cargo. That may not be the method anyone favors, but it's more likely, as it is the most affordable.
And the most space saving as they wouldn't need too build much to support the ship like amenities and things that fully grown humans would need. Life support would be more compact and robust, or they'd just have onboard freezers for the embryos.