Let's make some assumptions:

  • current tech.
  • we're able to send manned missions to this exoplanet thanks to a sci-fi element (a portal for instance); I just want to obviate that we have no way of transporting there. imagine we can.
  • Planet in the habitable zone of their sun.

Some things I'd say were needed to check as pre-requisites of this "colonization protocol":

  • their sun is stable
  • Oxygen-rich atmosphere
  • gravity (close to 1G?)
  • liquid water
  • avg. temperature
  • ...

Now, if the planet passes all those tests, which would be the next step for determine if it's safe to start colonization. First drones surveys? How many surveys?

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    $\begingroup$ It seems like you are trying to ask might be closer to: what criteria should be considered to measure the habitability of a planet? $\endgroup$
    – Gillgamesh
    Nov 23 at 17:57

From space.

Check the seasons. This can be done with computer modelling and space scanning. You want a place that has warm summers, cool winters, minimal rain, and few storms. If a place is filled with storms, is too hot, is too cold, or is constantly raining colonization will be harder. This can be done with a few satellites.

Check if there are any civilizations or local competition. You can stick a few spy satellites in space and map out the planet in depth.

Check the atmospheric composition. You want to know more than the oxygen level. You want to know anything else useful.

Check the local star, local asteroids and everything nearby. You don't want to land and then have a large solar flare wipe you out, or have an asteroid hit your planet.

Next, you can land a bunch of drones in places, with curiosity style bodies.

Check the tectonics. You want to put probes in a bunch of places and check for earthquakes or disturbances. This will allow you to map out what is going on under the surface. You don't want to stick a colony down and have a volcano erupt or a massive earthquake wreck you.

Check if local organisms are edible. You'll want to send a probe down to kill a few insects or small animals and plants (or the local versions) and test if they have the right chirality, anything especially toxic.

Check if the land is able to grow earth crops. This will involve a variety of chemical tests which your probe can probably do.

Check if there are any obvious useful minerals around to build a colony from. This will involve scanning with a bunch of tools.

Check for any trees or similar things that can be used as building materials.

After this, you'll have a bunch of likely candidates for where a colony would be best. If you don't and it's a horrible planet, you might decide to not colonize it.

After this, you pick the best candidates and send a bunch of UAVs.

Unmanned aerial vehicles. These would have solar charging, and could fly around the area and scan for any local organisms, mineral deposits, signs of life, or other useful or bad things.

With the area mapped out, you can send a small human scouting force.

This will be a few humans who have a deep knowledge of biology and chemistry. They can map out any hostile insect swarms, large dangerous predators, hostile micro-organisms, and likewise any useful organisms, local compounds, local minerals. They can do more in depth scientific setting and set up any infrastructure needed for a full colony. Any dangers the previous layers didn't reveal will hopefully be exposed now.

They can also set up camera networks around the area. If there's any hidden predators or intelligent life nearby, then they may well be spotted on the cameras when they don't think they're being watched.

Or they might be killed, but that's why you send a small force first.


Send people and see if they survive.

Make sure they pack a lot of guns for negotiating with fellow Earthlings or perhaps native fauna, and maybe a dust mask, sunscreen, some rations...

In your scenario, there is a whole other planet of resources waiting to be taken. Every minute you wait is a minute someone else could be planting their silly flags and locking down control of a continent. Lives are expendable - there are always more of them. Not so with continents!

Get your tired, your poor (no refugees, we don't want any retroactive nationality debates) and promise them fabulous wealth, or at least an acre lot, once the cities are founded. Heritable in case of mishap ... provided they make sure you find out how they died.

Oh, and pack a lot of little plastic flags.


Drones and probes ad libitum.

First of all, you need to determine if there are any organisms or substances which can be directly harmful. This means you need to take and analyze samples. And for this a drone or a probe is better suited.

In parallel you need to determine if you can find anything to support the colony on site, or you need to bring everything from home, and also starting studying the weather patterns. Again, drones and probes can be more convenient for this.

Then you need to start seeing how, where and if there is the possibility to grow food on site, and how your plants and animals interact with the local environment. For this you will need to start deploying on site, in a suitable location.

  • $\begingroup$ "First of all, you need to determine if there are any organisms or substances which can be directly harmful." That could take quite a while. A ppm aerosol made of an organic substance equivalent to ricin (but with a composition/functional structure unseen on Earth) may slip under the radar yet kill the first settlers in days (those enzymes aren't that easy to guess). $\endgroup$ Nov 23 at 16:42

For one thing, they could read a scientific discussion about what makes a planet habitable for humans in particular, instead of for liquid water using lifeforms in general. Even on Earth, there are many environments with life where unprotected humans would swiftly die.

As far as I know the main scientific discussion of the requirement for a planet to be habitable for humans is Habitable Planets for Man, Stephen H. Dole, 1964. Though they would probably also want to update some parts with the results of more recent research.


So send space probes to distant star systems first to make the most obvious choices. Like taking the spectrums of the stars to see if they belong to the right spectral calases and luminosity class to have habitable planets. And then taking the spectrums of the planets in the system to see which - if any - have oxygen rich atmopsheres. And measureing that the planets orbit their stars at the right distances to have comfortable temperatures - and actually measuring the temperatures of the planets if possible.

And maybe observing the climate regions and weather patterns on each candidate planet for at least a full plnetary year.

And then they can send robot landers or even manned landings to the surfaces of candidate planets to take soil samples and water samples and samples of the vegetation in various regions.

It is quite possible that the native vegitation might be inedible for humans,for example, which would be important to know. And many plants and animals might be edible, but some might be poisonous (a good adaptation to discourgabe being eaten) which would be good to know.

And they would have to test for microrganisms which were capableof infecting humans and causing human disease.

And there may be geological surveys looking for mineral deposits.

Any planet with is not only habitable for humans but quite similar to Earth would be worth colonizing eventually.

But the main mission would be to select the best region on a planet to start colonizing. Earth has many different regions which vary greatly in their desirability. The oceans, Antarctica, the Amazon rainforest, the Sahara desert, Tibet, and the temperate zones, for example.

If you discover several planets which are habitable and suitable for eventual colonization, the first one to be colonized would be the one which has the best region suitable for the first colony.


Its not a one way problem i.e there are two issues at play.

The first is your question. Is it safe for humans (and related Terran lifeforms) to colonize this planet. But the second question is potentially of equal importance. And that's 'is it safe for the ecology of the planet for humans it colonize it'. This second question is important only because the current ecological system on the planet (i.e. all it's plant's and animals and the related microbiome isn't what makes the planet habitable in the first place.

So if Earth based viruses, bacteria, fungi and insect pest pests etc prove lethal to the local life forms you now have the added problem having to rebuild a whole new ecology from the bottom up.

In reality? Chances are the biochemistry of Earth and planet X's life forms are so different that it would be hard if not impossible for them to infect each other. And if we could eat them they probably wouldn't provide all the required nutritional elements we need (and vice vera).

That aside arduous screening with probes as others have mentioned and samples returned to quarantined labs orbiting the planet would soon reveal if there were serious issues. We have a whole range of scientific instruments and tests that are relevant and could be applied. So many in fact you'd have to look them all up! Cell sample analysis would reveal the amino acids and proteins native life forms used and their metabolic pathways. Exposing viruses and bacteria from both planets to plant and animal tissue samples samples would also show if there was a problem.

It might take decades but then the planet is going anywhere and neither is Earth so you have the time.

  • $\begingroup$ Any Earth-like planet will have life that is fundamentally Earth-like. The phenotypes of individual organisms will be drastically different, but they will encode information on DNA and build their proteins with the same amino acids we do. The laws of physics don't change, and they have rather a lot to say about abiogenisis and selective pressures. The entire second half of this answer rests on an assumption speculative xenobiology moved past decades ago $\endgroup$
    – Dallium
    2 days ago
  • $\begingroup$ Firstly, 'fundamentally' Earth like doesn't cut it. There are numerous plants and animal life forms on Earth that are toxic to humanity if ingested and thousands of examples situations where introducing foreign life forms to local ecologies does severe damage. Secondly even slight differences in biochemistry and metabolisms could have massive ramifications for how species interact (e.g. metabolic waste products produced by one species can be toxic to another). Lastly 'any Earth like planet will (definitely) have life that is fundamentally Earth-like'. OK then - prove it! $\endgroup$
    – Mon

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