Which planet could humans survive on first? Scientists have a few leading candidates

If humans ever establish a permanent home beyond Earth, the first planet is unlikely to look anything like the lush new worlds imagined in science fiction. Every planet we know well enough to consider is hostile to the human body, meaning survival would depend on sealed habitats, artificial air, radiation protection and technology that cannot afford to fail.

Mars remains the obvious front-runner, but scientists have also considered the upper atmosphere of Venus and potentially habitable planets orbiting other stars. Each candidate comes with a catch big enough to make Earth look extraordinarily difficult to replace.

There is also an important distinction between surviving somewhere and actually living there permanently. Humans may be able to build an outpost on another world long before that place becomes capable of supporting a self-sustaining population.

Mars is the strongest candidate by a wide margin

Among the planets in our solar system, Mars offers the most realistic combination of accessibility, usable resources and conditions humans might eventually learn to manage. It is still extremely hostile, but almost every alternative is worse.

A Martian day lasts about 24 hours and 39 minutes, making its day-night cycle surprisingly familiar. Mars also has seasons, accessible solid ground and large deposits of water ice that future settlers could potentially use for drinking, oxygen production and fuel.

ESA describes Mars as the most Earth-like of the other planets and treats it as a major objective for future human exploration. Its current Mars program uses robotic missions partly to prepare for eventual human missions.

Mars also has gravity equal to roughly one-third of Earth’s. That is far from normal for the human body, but it is much stronger than the microgravity astronauts experience aboard spacecraft.

Takeaway: Mars is not remotely Earth-like enough to survive on without technology, but it offers more useful resources and manageable conditions than any other nearby planet.

The Martian atmosphere would kill an unprotected human

The biggest problem is that Mars does not provide breathable air. Its atmosphere is overwhelmingly carbon dioxide and is so thin that humans could not survive outside without a pressurized spacesuit.

The low atmospheric pressure also means liquid water cannot remain stable on most of the surface under present conditions.

Temperatures add another challenge. ESA lists the average Martian temperature at about -55°C, with some locations falling dramatically lower.

Settlers would therefore need sealed habitats containing Earth-like pressure, oxygen and temperature.

Going outside would never initially resemble stepping out of a house on Earth. It would be closer to leaving a spacecraft for a carefully managed expedition.

Takeaway: Humans could potentially live on Mars only by carrying an artificial Earth-like environment with them everywhere they go.

Mars already has something settlers desperately need: water

Transporting every kilogram of material from Earth would make a permanent colony extraordinarily difficult. Mars becomes attractive partly because water already exists there in the form of ice and hydrated materials.

ESA’s ExoMars mission has detected substantial underground water in some regions, while polar ice has been known for years.

Water would provide much more than something to drink.

It can support agriculture, hygiene and industrial processes. Its hydrogen and oxygen can also potentially be separated, providing breathable oxygen and ingredients useful for rocket propellant.

Future mission planners may therefore choose settlement locations partly according to where usable ice is easiest to reach.

Takeaway: Local water could make the difference between a temporary Mars expedition and a settlement capable of reducing its dependence on supplies from Earth.

Radiation may determine where Martians live

Mars lacks the strong global magnetic protection and thick atmosphere that shield people on Earth from much of the harmful radiation arriving from space. Long-term exposure is one of the largest obstacles to permanent settlement.

ESA’s 2026 radiation research found that mission timing could substantially change astronauts’ radiation exposure during the journey.

Once people arrive, shielding would still be necessary.

Future settlers could cover habitats with Martian soil, place living areas partly underground or use natural lava tubes if suitable ones can be reached safely.

That means the first Martian cities might look surprisingly different from futuristic glass domes. Much of the safest living space could be buried beneath the surface.

Takeaway: Radiation may force humans underground on Mars, making habitat design one of the biggest differences between visiting the planet and living there for years.

Low gravity creates a problem nobody can fully answer yet

Mars has roughly 38% of Earth’s surface gravity, but scientists do not know what decades of living at that gravity would do to the human body. Nobody has ever spent years in a partial-gravity environment.

Astronauts in microgravity lose bone and muscle despite intensive exercise. Mars gravity should reduce that problem compared with weightlessness, but researchers do not know if 38% is enough to maintain normal human health.

The question becomes even harder for pregnancy and childhood.

Scientists have no human data showing how fetal development, growing bones or the cardiovascular system would respond if a person spent an entire lifetime under Martian gravity.

A permanent colony would eventually have to answer those questions rather than simply keeping adult astronauts alive for several months.

Takeaway: Mars may be survivable for visiting adults long before scientists know if humans can remain healthy there across an entire lifetime or multiple generations.

Venus sounds impossible because its surface practically is

Venus is often called Earth’s twin because the two planets are similar in size, but conditions on its surface are far more hostile than those on Mars. The temperature is around 467°C and atmospheric pressure is roughly 93 times sea-level pressure on Earth.

That combination would destroy ordinary human habitats extremely quickly.

NASA’s Venus data describes surface conditions hot enough to melt lead, beneath an atmosphere dominated by carbon dioxide and clouds containing sulfuric acid.

Building a normal settlement on the surface would therefore be dramatically more difficult than building one on Mars.

Yet Venus has one unusual characteristic that prevents scientists from dismissing it completely.

Takeaway: Venus’s surface is one of the least realistic places for humans to settle, despite the planet being remarkably similar to Earth in size.

Floating above Venus might be more realistic than standing on it

Roughly 50 kilometers above Venus’s surface, the conditions become unexpectedly Earth-like in two important ways. Temperatures can fall into a range humans can manage, and atmospheric pressure becomes similar to pressure at Earth’s surface.

That has inspired proposals for floating habitats suspended in Venus’s atmosphere rather than settlements built on the ground.

Because Venus’s atmosphere is extremely dense, a structure filled with breathable Earth-like air could even provide buoyancy, somewhat like a balloon.

The idea remains highly speculative.

Venusian clouds contain corrosive sulfuric acid, strong winds would complicate operations and every habitat would remain suspended above a surface where humans could not safely escape during an emergency.

Takeaway: Venus may be more habitable in the sky than on the ground, but floating cities remain a far more experimental concept than establishing a protected outpost on Mars.

Mercury offers solid ground but almost everything else is wrong

Mercury is relatively close to Earth compared with the outer planets and possesses a rocky surface, but its environment makes it an unlikely settlement target. Temperatures change enormously between its sunlit and dark regions.

The planet has almost no atmosphere capable of protecting settlers from radiation or micrometeoroids.

Certain permanently shadowed polar craters contain water ice, making the poles more interesting than the rest of the planet.

In theory, future humans could build deeply protected habitats near these resources.

In practice, Mercury offers few advantages over Mars while creating serious thermal, radiation and logistical problems.

Takeaway: Mercury might support specialized future outposts, but it gives humans little reason to choose it before the far more practical option of Mars.

Jupiter and Saturn are not places you can stand

The giant outer planets contain no ordinary solid surface where humans could simply land and build a settlement. Their atmospheres become progressively denser and more extreme as depth increases.

Jupiter also possesses an intense radiation environment that makes nearby operations particularly challenging.

Some of their moons are much more interesting for exploration. Europa, Callisto and Titan all offer fascinating possibilities, although none is technically a planet.

Titan stands out because it has a dense atmosphere and a solid surface. The temperature, though, is around -179°C, and its atmosphere does not contain breathable oxygen.

These worlds may eventually host research stations, but reaching and supplying them would be enormously harder than reaching Mars.

Takeaway: The giant planets themselves are poor settlement candidates, while several of their moons may eventually prove more practical than the planets they orbit.

The Moon would probably come before any planet

If the question expands beyond planets, Earth’s Moon immediately becomes the strongest candidate for humanity’s first lasting off-world settlement. It is dramatically closer than Mars and can be reached in days rather than months.

The Moon still has no breathable atmosphere, has severe temperature swings and exposes people to radiation.

Its advantage is logistics.

A crew facing an emergency on Mars may be millions of kilometers away with no rapid rescue option. A lunar settlement remains close enough for far more frequent supply missions and communication with almost no meaningful delay.

This is one reason several space programs view the Moon as a testing ground for technologies that could later be used on Mars.

Takeaway: Mars may become the first planet humans inhabit beyond Earth, but the Moon is much more likely to become our first substantial settlement beyond Earth itself.

What about planets around other stars?

Astronomers have discovered rocky planets occupying regions around their stars where temperatures could potentially allow liquid water. Some appear far more Earth-like on paper than anything in our own solar system besides Earth.

Proxima Centauri b is especially tempting because it is the nearest known exoplanet, only about four light-years away.

NASA says its mass is consistent with a rocky planet and it orbits within its star’s habitable zone.

Yet “habitable zone” does not mean habitable.

Scientists do not know if Proxima b possesses a suitable atmosphere, and its red dwarf star can expose the planet to intense radiation capable of stripping atmospheric gases away.

Takeaway: Some exoplanets may eventually turn out to have better natural conditions than Mars, but scientists know too little about them and humans have no practical way to reach them.

TRAPPIST-1 contains several intriguing candidates

The TRAPPIST-1 system contains seven rocky planets roughly similar to Earth in size, and three—TRAPPIST-1e, f and g—lie within the star’s conventional habitable zone.

NASA continues studying the system with the James Webb Space Telescope. Its 2026 overview still places those three worlds in the region where liquid surface water could theoretically exist under suitable atmospheric conditions.

The problem, again, is distance.

TRAPPIST-1 lies roughly 40 light-years away.

Even if scientists discovered tomorrow that TRAPPIST-1e contained oceans, breathable temperatures and an atmosphere much like Earth’s, current spacecraft technology provides no realistic way to send settlers there.

Takeaway: Finding a potentially better planet does not mean humans can reach it. Distance makes the most intriguing exoplanets irrelevant to near-term settlement.

“Habitable” does not mean humans could breathe there

The word habitable is easy to misinterpret because astronomers usually use it much more narrowly than everyday language suggests. A planet can lie in a habitable zone without having breathable air, safe radiation levels or even confirmed liquid water.

The basic habitable-zone calculation asks if a planet’s distance from its star could permit liquid water under suitable conditions.

NASA emphasizes that atmospheric composition matters enormously. A planet in the right orbit could still have no useful atmosphere or suffer extreme stellar radiation.

For human survival, the requirements are much stricter.

We need manageable temperature, pressure, accessible water, protection from radiation and an atmosphere or habitat capable of supplying oxygen.

Takeaway: A potentially habitable planet may only satisfy one of many conditions humans need. The term does not mean astronauts could land, remove their helmets and survive.

Terraforming Mars would be far harder than simply building habitats

Science fiction often solves Mars’s problems by transforming the whole planet—warming it, thickening the atmosphere and eventually creating conditions suitable for humans outdoors. Current science does not provide an easy route to doing that.

Planet-wide environmental engineering would require enormous quantities of gases and energy.

Even if technology eventually made major atmospheric changes possible, settlers would still have to deal with low gravity and radiation.

That makes localized habitats much more realistic.

Instead of transforming an entire planet into Earth, humans could create small Earth-like environments inside sealed structures.

The distinction could remain for centuries.

Related: The Quest for Life on Mars: 10 Groundbreaking Discoveries

Takeaway: The first humans living on another planet would probably adapt their habitats to the planet rather than successfully redesigning an entire world around human biology.

So which planet could humans survive on first?

Mars remains the strongest answer. It has accessible solid ground, water ice, a day close to Earth’s length and conditions that, although deadly without protection, are less extreme than those on Venus, Mercury or the giant planets.

That does not make Mars a second Earth.

Settlers would depend on sealed habitats, radiation shielding, reliable power, recycled water and artificial oxygen every day of their lives. Medical care, food production and equipment repair would need to become unusually self-sufficient because emergency help from Earth could be months away.

Venus provides an intriguing alternative only if humans live high in its atmosphere rather than on its surface. More distant exoplanets may eventually prove naturally friendlier, but they remain far beyond any realistic human journey with current technology.

So the answer depends on what “survive” means.

If humans simply need to stay alive using advanced technology, Mars is the leading planet.

If the requirement is a place where people could walk outside and live naturally without life-support equipment, scientists have not discovered another planet humans could currently call home.

Question for you. Which would you choose if given the opportunity: an underground settlement on Mars, a floating habitat high above Venus or waiting until scientists discover a truly Earth-like world? Each option reveals just how difficult replacing our home planet would be.

More articles

The post Which planet could humans survive on first? Scientists have a few leading candidates appeared first on FODMAP Everyday.