How much time is needed to judge an Earth-like planet to be safe?

Question

A colony ship has been sent to deep space to colonize an earth-like planet. Through astronomical spectroscopy, the atmospheric composition was found to be suitable for human life. But of course, everyone watched Alien Covenant or heard about how bad it was, and will not remove their protective equipment while on the planet without doing their due diligence first. So, once our colonists set up a few sterile bubbles to use as a base of operations, how long would it take to determine whether or not this planet is actually safe enough for one to live outside a bubble? For example, some things that need to be determined are:

• Determining whether or not bodies of water are prone to experiencing algal blooms that release large volumes of HCN into the surrounding atmosphere that would kill any human foolish enough to not wear respiratory protection
• Whether there is microbiota that would find a mobile bunch of hydrocarbons at a constant temperature to be a good place to live
• Whether limnic eruptions are a common thing with bodies of water on this planet
• Whether the native wildlife would see humans as a tasty snack, regardless of the fact that they won't actually derive nutrition from eating humans; the native predators' instincts see humans as being the right size to be food.
• Are various natural disasters more or less common here than on earth?
• Are human-toxic compounds present in the soil, local wildlife, or in the water?

Some relevant information about the colony ship:

• The ship has around 6000 people on board

• The ship has an advanced computer and a database to simulate some chemistry. Something that happens to inhibit a critical enzyme or induce protein misfolding in the human body will be determined to do so without the need to experiment. However, the technology is not good enough to fully simulate human biochemistry.

• The ship has a large complement of automated drones piloted by an intelligent AI for the purposes of sample collection and study.

So, how long would it take for some space colonists in this situation to be able to confidently say "Okay, we can live here without wearing CBRN gear all the time", "Okay, these islands are safe, but anywhere else is deadly", or "You can live here, just carry a gun at all times in case the native wildlife takes interest in you"?

Answer 1

This is a Frame Challenge: Define "safe"

Millions of people died from COVID-19 in 2020¹ and that's after billions of years of evolution, millions of years of experience, and thousands of years of technological advancement. We can't protect ourselves from (to horrendously oversimply a bit) a variant of the common cold.

So I have no idea what you mean by "safe..."

Because Earth isn't safe. That's the whole point of Will Smith's dubious movie After Earth² — humanity no longer visited Earth because everything on it had evolved to kill humans. But we live here and we thrive here anyway.

How long will it take to prove the world is "safe enough?" You don't need to analyze the whole planet for that. In fact, if the colonists didn't rely on sending a drone to plop down on the planet's surface to run a bunch of empirical tests and send a bunch of data back to Earth then they deserve to die, right? So the fact that they're there means they've done their due diligence and the planet is "safe enough" for colonization.³ So a perfectly legitimate answer to your question would be "not a single second... they had the answers before they arrived."

But there's a certain elegant paranoia in the world of science. After all, it's a fair assertion to claim the whole point of science is to answer the question, "yeah, Larry, but what if we're wrong?" So, since you have the tech to get to the planet and a pretty good computer and I assume your people had enough foresight to bring along a science lab stocked with test tubes and a compliment of medical equipment in anticipation of making absolutely sure the landing zone was safe, I should think it would take a day or two to figure out that the landing zone was (*ahem*) perfectly safe.

Besides, do you want the rest of the planet to be "perfectly safe?" Are you sure your colonists are so well adjusted that some of them wouldn't want to go hunting in some of the more secluded continents just to see what's there? Humanity requires challenges to overcome to thrive, otherwise it risks becoming a sociocultural version of Gayle Grinds. Besides, alluding to footnote #3... the cost of proving an entire planet perfectly safe is way beyond the value of doing so. Humans are the apex predator for a reason, after all.

TL;DR

1. Any extrasolar colonization program worth its salt would have sent satellites and probes to analyze the world in general and promising landing sites in particular to determine if the planet is "safe enough" to set humanity on the surface.

2. Any colonization program worth its salt would send enough scientific supplies to test and analyze the preferred landing sites to be sure the already recorded findings of the probes and satellites were acceptable. That effort would be minimal unless you can rationalize why all the tech necessary to send colonists to the world isn't enough to ensure the world safe before their arrival. So, a couple of days to be sure the unmanned satellites and probes weren't lying and we're good to go.

3. No world can be judged "safe." Earth isn't "safe." People die from everything from lightning to illness, fly bites to shark attacks, and a lot more all the time.

---

_{¹ I'm not going to debate how many deaths really happened. I think history is going to have the proverbial field day analyzing everything from the science to political intrigue to public ignorance (on both sides, folks) of the 2020-2022 time period. But it's a useful statistic for the purposes of this answer.}

_{² If you want a good example of good worldbuilding combined with a bad story, go watch After Earth. I'll not bore you with my opinions about why I won't be adding the movie to my Blu-Ray collection, but it is educational.}

_{³ You'd be surprised how often worldbuilders forget about economics. They focus on "scientifically accurate" to the point of getting grey hair but it never crosses their minds that nobody will invest the money and resources required to drop 6,000 people on an alien world without running a whomping truckload of cheap tests on the planet first. There would be satellites in orbit and probes on the ground — especially around the most likely landing spots — collecting, analyzing, and reporting data in the terrabytes. The more I think about it, the less the premise of your question makes sense. Yeah... I need to edit my answer to make it a Frame Challenge.}

Answer 2

Not all risks can be accounted for, but colonists are (by self-selection) far more comfortable with risk than most people

At the end of the day, the thing about life: nobody gets out alive. Frontier living is inherently dangerous, there's going to be stuff that goes wrong. That said, for a lot of questions there's standard practice for getting at answers.

In all cases, the answer to 'how long does it take to rule out a given threat' is 'however long is necessary to gather a representative sample.'

Microbiota and Soil/Air/Water toxicity are very quick to solve:

For the former, bring a bunch of lab mice/rats; expose them to the environment of interest. Wait. This won't rule out all possible pathogenic concerns, but phasing human exposure thereafter is the true test. Because of how environments function, this process could take a year if you were particularly concerned - let a full set of seasons pass before sounding the all-clear. True promise of safety on this front will take 1-3 lifetimes.

For the toxicity, you can take assays of the relevant media from geographically dispersed, randomly selected sites. Depending on processing equipment/trained personnel available this could take a day or three to a couple of months but would begin while initial setup was happening so is likely to be finished before the sterile settlements are fully established. These results also inform how aggressively sterile those habitats need to be.

Seasonal/cyclical stuff takes multiple (ideally 20+) cycles to have scientific levels of confidence in, with that confidence asymptotically approaching 100% as time passes.

Natural disasters depends on the scale you're talking about. As mentioned in another answer 100-year floods are only expected once every century, so to have a good handle on what those look like you want about 2,000 years of flood data. This is the type of risk that colonists are signing up for, however, so there's nothing about this that would induce them to need safety equipment - it's just the case that maybe you all die of something unforeseen, welcome to the frontier.

Wildlife concerns are basically a non-issue. Humans (for example) already live among dangerous predatory animals to whom we are absolutely nutritious. This is also a risk that colonists are volunteering to accept, and it's mitigated by weapons. That said, observational studies that characterize biomes and their fauna is a major initial effort of any sensible colonization program so a lot of these will become known within the first couple of years with true confidence in the understanding emerging after 20 years (or 20 full cycles of the seasons to account for cycles in fauna's behavior.

Statistically speaking, n>20 is where you can start saying things with confidence, where n is defined as 'a complete unit of study.' For things that happen annual, that's a year. For things that are constant, that's a given sample from somewhere.

Answer 3

1 year for basic safety, 20 for high safety.

Lots of animals and insects act on some sort of cycle and only are active in certain seasons. There's certainly a risk that some sort of weird lifeform with a weird bug is hiding somewhere and only comes out in a particular season and so if you push colonists out things will get dangerous.

Some insects have very long cycles e.g. cicadas which have 17 year cicadas to emerge. 20 years is a reasonable time frame to spot any unusual insect species or migration that could impact your area.

They'll have drones going around sampling wildlife and native organisms, designing vaccinations, mapping out species and useful resource areas, and will probably start off on an island where seismic events are unlikely, resources are plentiful, and the wildlife is friendly.

After a year they should be fairly confident if the island is safe. They can then set up a base there, let people wander around with lots of sensors around for danger. They should be able to find a location which has safe zones from mega tsunamis, volcanic eruptions and other things and can build shelters to withstand other dangers. Then, after 20 years of expanding their sensor net, building fabricators, sampling the area nearby and such, they can fully unload the ship and start exploring non island areas.

Answer 4

Two or three generations.

The answer by Richard Kirk mentioned the historical example of cancer by x-rays. There could be subtle things on this planet which interfere with fertility and the germline. It took mankind many decades to become aware of many such threats, especially if it is 'merely' reducing the ability to reproduce, not eleminating it.

The answer by William Walker III points out how colonists would be more tolerant of such 'minor' threats. There would be one level of risk for getting out of suits, and another level of risk for allowing colonists return home to civilization, and yet another level to encourage mass immigration.

Considering the long-term effects, a totally clean bill of health could come only when the first planet-born generation has reached a mature age.

Answer 5

Months

It depends largely on the organization culture and if individuals are allowed to decide for themselves. As others have said 'safe' is very subjective.

Assuming they can send out scout drones and observe multiple locations for toxic substances, life forms and geological activity. Equipped with mass spectrometers and other sensors. They will send out many and create a short list of candidate landing places.

Then assuming the planet is generally safe and they will find nothing surprising or concerning. Also assuming this is not the first studied planet, they will have a database with profiles of other planets and their risk factors to compare these landing spots against. This will take maybe a week or two, to generate a basic risk profile.

Tectonic activity can be observed with telescopes from large distances. So short term disasters are foreseeable. And if there is a big once in a thousands years eruption, then a bubble or safety gear wont help you. So trace toxic substances and alien life forms are the remaining risk factors.

There is a big difference in approach between sampling, mapping and modeling all environmental factors and the waiting game, where you just put some test subjects outside (bacteria, rats, humans) and wait until something happens. The reason for this is that modeling can be done in reasonably short time (weeks), if you're well prepared, but waiting cost a lot of time.

So nobody will go outside unprotected during the modeling phase, but during the waiting phase it becomes a matter of preference. How safe do you want to be? There are places on Earth, that are not known to be safe for humans and still humans go there for various reasons.

So my intuition is that as soon as the waiting game starts, there will be some of those 6000 who are willing to 'try' it. Assuming that the sampling, mapping and modeling phase didn't reveal anything concerning.

Then it depends upon two things, the decision structure and whether those going outside can pose a risk to those staying protected.

Are individuals allowed to decide for themselves? Do they have the information? What incentive would they have? Are they not allowed to decide for themselves? What is the moral of the leadership? Is everybody equally valuable? What is the public (the 6000 crew) perception of the decisions made by the leadership, and what information do they have?

There is one interesting dynamic, and that is the possibility of an alien 'infection'. That means, that the ones who try first do not only risk themselves, but also risk the others and the whole mission if they are allowed to come back inside. For Earth bound infections a week or two of quarantine is enough for diseases to manifest or at least be detectable in the blood. For alien life, this is a big unknown. So it might be possible that a policy of once outside, always outside is established and that the colony effectively splits in two.

All this is not a conclusive answer, but my guess is that it would not take more than a few months before some will consider waiting longer to be endless and pointless. But it depends.

Answer 6

As every single other answer already points out: What do you mean by "safe"?

There is no absolute safety. Not on Earth, not anywhere else. People will inevitably die. From accidents, disease, and eventually from old age.

The important thing is that the colony survives.

So how do you do that? By spreading the risk. Don't let everybody take the same risk. First only a few people take off their helmets, while everybody else keeps theirs on while carefully monitoring the effect of the local ecosystem on those people who take their helmet off.

Even if you have a computer that can predict chemical interactions for you, you're on a planet full of billions of new chemical combinations that you've never seen before. And to calculate what they do, you first need to detect them and examine them. You know how long we've been doing that on Earth? And we're not done yet. So understanding everything is going to take forever. You're not going to wait for that. You're going to take risks, because on a trip like this, everything is inherently risky.

The main thing you want to know is whether the atmosphere is poisonous, whether there's anything common in the atmosphere that could make people sick. And after that, you're just going to have to experience it. But not everybody at once.

They'll probably spend a few days carefully examining the atmosphere and some flora and fauna in the immediate vicinity of the landing site. At first, people will go out in space suits, but if all analysis of the atmosphere shows it to be safe, wearing those bulky suits is going to feel stupid and pointless soon enough. Make sure not everybody takes them off all at once; first a hand full of people. Examine them to see the effect the planet has on them. but if they're not getting sick, within a week or two, most people will want to go without their suit.

Hopefully there are a few cowards that will want to keep a bit more protection or stay behind in the safety of the ship. Maybe there should be a quarantine barrier splitting the crew in half, with one half free to move around without protection, and the other half as backup to learn in case something happens to the first half.

But for how long do you want to keep that arrangement? If after a month nobody is getting sick, more crew members will want to enjoy that freedom too. And I wouldn't want to condemn anyone to stay locked up inside. But could deadly diseases, germs or wildlife show up after months? Absolutely. Ideally I'd keep the split for a couple of years, but that might be hard on the half that doesn't get to enjoy the beautiful new planet directly. If it's an unpleasant planet, it would be a lot easier.

Answer 7

I assume the risk is something quite unexpected. They have not landed on something looking like a massive lava flow that feels still warm in parts, and seems to come from the distinctly conical mountain nearby. They will know what is in the air and in the soil.

They are explorers. They would not take stupid risks but a certain amount of risk goes with the job. So you might imagine someone spending half a day outside without special clothing. If they seem to have no ill effects, they will try for a day, then maybe two days. Take how long they have been there and double it.

The early history of X-Rays had radiographers developing cancers. Dentists got cancer in the fingers they used to hold the film in place in a patient's mouth. If the cumulative rise is 20 years, it seems to take 20 years to become aware of the risk because you have no model for it. The early history of nuclear physics is much the same. They were explorers, though explorers of a different sort.

My answer would be that there is no point where they say 'this planet is completely safe'. If they had to wear special clothing or carry a gun, they might resent the precautions, where if the precaution was an injection once a year, it would be routine. If they have been there for years without problems, they may become confident.

Answer 8

How safe do you want it to be?

I will assume that "safe" means "it is no more likely to kill you prematurely than Earth is."

There is a reason why there are discussions of "hundred-year floods" in safety management. Many of the most dangerous disasters are on very irregular schedules.

It's unlikely that all your people are equally risk-adverse. Furthermore, the degree of safety precautions ranges widely. So there would probably be people foregoing (some) precautions after a year, and people who will die of old age never leaving the bubble, possibly even born on this planet.

Another factor is that all these precautions take time and effort which could be expended on something else. Breakdown may force them out.

Answer 9

Never

Remember Deathworld? Or SMAC/X storyline? Either consisted of a sentient planetmind, that in case of Deathworld decided to oppose the base with everything it could, and in case of SMAC/X humanity managed to interfere with its thinking for long enough to "Transcend", but anyway it took hundreds of years, and with super-advanced tech SMAC/X developers came up with. (Non-overheating reactors of arbitrary power - who doesn't want them?) If your target planet would happen to have such a planetmind, it's possible to alienate it for good, so hard that it will never allow humans outside their safety domes.

If the planet is "normal", several years

As colonists, people at first won't put their noses outside at all, but if the planet is not initially hostile, they could release animals to try to survive outside, controlled by robots and high bio-security measures in place, and anything past that depends on how do the animals fare - do they eat local grass and not die of hunger, do they catch local flu and perish due to having no immunity, how hard was that flu, how many of different flu viruses were detected postmortem, etc etc, and finally, how hard would it be to create a vaccine or palliative med for those animals to eventually resist all of them. In case of "everything went smoothly", about several years would pass until a polyvaccine would be ready for colonists to try to live outside of biohazard protection with reliance on their own immunity. Some would still die of course, but colonists are people that are expected to die in numbers, they need to just not die off entirely.

If the planet turns up bio-hostile, but without being sentient, several generations on average

There is a possibility that initial experiments would determine that some of the mechanisms used by local flu directly employ a "bug" in genetic code of earthly animals so hard that inhibiting or suppressing it would kill them outright; then the answer might also become "never". Or, in case of ever-supplying animals and induced genetic corrections (HIGHLY advanced, although possible with enough time and energy), some future generation of them might survive for long enough to breed, past that a reverse-engineered genome correction could be done to a selected group of future generation of colonists themselves to attempt survival in wildlife, exposed to all the biohazards of the planet. Even the optimistic scenario, when the biohazard breaches never happened and the colony didn't die off due to aboriginal virus outbreaks, it will take more than one generation to first prepare such a genetic correction, then test it somehow (screw ethics, we're in a "do or die" mode), then IF it went right and the altered populace is viable and can still breed, test if it was enough, repeat, retro-apply if deemed successful to people living inside, allow breeding of mixed offspring - it's a heck of a genetic programme to adapt the colonists to such conditions, had to be carried in a newborn colony, they might not have the resources to fully carry it out and might rely on natural selection and (maybe controlled) mutations to actually incorporate the required genome changes to at least the volunteers or selected party over shorter time. Then it would come to living and watching, until they successfully raise their children outside without constantly relying on the base's medical support (resources and facilities would still be needed; you don't want your outisde colonists to drop down to stone age or below, although some elements could be incorporated). But then only their children would be "safe enough" to live outside, any "clean" populace inside the base would likely still not be safe enough.

Answer 10

If life on the other planet is based on DNA there could potentially be microbial dangers, but even on earth microbes tend to be very specialized, normally infecting a single species. If the life is not based on DNA then any likely sources of danger potentially would be readily observable. But what if life there operates at speeds much faster than we can easily perceive, or has evolved camoflauge much like our aircraft (memetically) evolved stealth. So there is no easy or obvious answer to this question, which is what makes the book intersting.