The Earth In A Suitcase Space colonists must carry everything they need to survive without making the ship too heavy to leave.

If you were stranded on a desert island, what three things would you want to have with you?

How about on a desert planet?

For travelers to Mars, the physical size of cargo is of utmost importance, so this question could help planners narrow down the packing list to the bare minimum. But it reaches for a deeper answer, too: Ultimately, what matters most? It turns out this is just as hard to answer for Mars as it is from the theoretical perspective of a marooned islander. Shelter, food and water are just the beginning; humans need Maslow’s entire hierarchy.

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During the space shuttle program, a team of four was responsible for packing 6,500 pounds of equipment for each mission, which was enough to fill two tractor-trailers. That was for a crew of seven for just two weeks. If governments or private companies decide to go to Mars, entire years and scores of people will be devoted to figuring out the particulars of what to bring. Boiled down to its essence, we’re talking supplies for three categories of things: Shelter, food and water, and other people. What’s on the minimalist’s packing list?

Shelter

A radiation-blocking, pressurized habitat

Humans have been living in space full time for 16 years on the biggest spaceship ever built. As a home in space, the International Space Station is far from ideal. It’s cold, loud and bright, and it lacks gravity. But it provides shielding from radiation and extreme temperatures, a place to exercise and a view that is impossible to beat.

A spacesuit with oxygen, carbon dioxide removal, water evaporation capability — and a toilet

In 2013, Italian astronaut Luca Parmitano almost drowned during a spacewalk when water flooded his helmet. A clogged filter wasn’t allowing condensation to drain properly, and it built up, collecting on Parmitano’s face. With no gravity dragging it down, the water covered his eyes and nose, and he had to feel his way back to the space station airlock to safety.

Next-generation spacesuits may also have a toilet system astronauts could use for up to six days, including during menstruation.

Exercise equipment

Crew members on the ISS spend a large chunk of their time working out, to ensure that their muscles and bones don’t atrophy. Mars travelers would have to spend even more time exercising so they could stand upon arriving at the red planet.

A sleeping bag and a dark place to sleep

Flying in space free of Earth’s gravity creates the sensation of weightlessness, so to keep from floating while sleeping, astronauts go to bed harnessed in sleeping bags attached to the space station walls. Astronauts do not sleep well in space, and studies show that disrupted circadian rhythms are one reason why. A Mars transport ship or a Martian outpost would need not just wall-mounted sleeping bags but also artificial lights in the right color hues to keep people on a natural sleep cycle.

Food and water

A balanced diet, most likely vegetarian or pescatarian

Elon Musk says his Mars Colonial Transporter, aka the BFS, would be roomy enough for a food court. But food is safer from spoilage, easier to preserve and easier to pack when freeze-dried, especially for a long journey.

Today, ISS crew members have a pretty well-rounded menu of options, from chicken and seafood to candy and nuts. Salt and pepper are available in liquid form, because you wouldn’t want the grains clogging up your air supply systems. The most popular foods on the ISS are the fresh fruit, vegetables and tortillas (because they don’t produce crumbs) supplied by Earth cargo ships. But cargo ships wouldn’t be able to restock a spacecraft en route to Mars, so what the crew takes is what the crew gets, unless they grow it themselves.

Seeds and fish eggs

Russian cosmonauts have been growing and harvesting food on the ISS since at least 2003, but NASA astronauts dined on space-grown food — freshly picked red romaine lettuce — for the first time in 2015. It’s a far cry from a full menu. Eventually, explorers might be able to raise fish, which are a good source of protein and far less resource-intensive than other animals we eat. But that means travelers will need even more …

Water

Water is dense and heavy, making it one of the biggest obstacles to space exploration. Mars has some water ice at its poles, and the mid-northern latitudes have a vast reservoir of ice, spanning an area larger than the state of New Mexico. But even if explorers could harvest that water, the amount available on Mars pales in comparison to Earth’s water cycle. Humans would therefore need to bring plenty of it — and recycle every drop they used. The ISS is already a lab for this, incidentally.

An air purification system

Plants can help, by removing carbon dioxide and producing oxygen that explorers can breathe. But settlers would still need filtration systems to catch poisonous gases, like the kinds produced by rocket fuel and cooling systems.

People

Medicine

Exposure to other people means exposure to microbes and the potential for nasty infections and illnesses. What’s more, research has shown that some species of bacteria grow more virulent in microgravity, and antibiotics don’t work as well. A medical kit will need strong antibiotics, sleeping pills, painkillers and maybe antidepressants along with lots of first-aid gear.

Entertainment — board games and movies, maybe

It’s a long trip. People are going to need something to do.

A camera

Obviously.

Psychological help

Even if space agencies and corporations figure all of this out, the most fundamental questions are still the hardest to answer. Who would colonists want with them, and why? On a trip to Mars, it will take several minutes, eventually as much as half an hour, to send and receive messages. Colonists won’t be able to have meaningful conversations with loved ones back home. And that’s saying nothing of intimacy. So a Mars mission would have to provide all these things, along with food and water.

And when we get there …

If Mars visitors become settlers and never return to Earth, it may be more practical to try to transform the planet into a watery, breathable world suitable for farming. With its rocky surface, carbon dioxide atmosphere and frozen water, Mars is one of the few places in the solar system where this may be possible. But even if we transform Mars into another blue marble, we could never replicate Earth. Colonists would surely miss our watery, rumbling world in and of itself, with its shimmering sunsets and its silvery moon and its every inch crawling with life.

There’s a scene in the movie “Interstellar” that makes an extremely profound statement about leaving Earth. Matthew McConaughey’s character is trying to console his crewmate, played by David Gyasi, and he hands him a set of earphones. As the camera zooms in on Gyasi’s face, we hear what he hears: crickets chirping amid a summer thunderstorm. Not Mozart, Beyoncé, or spoken word; not whale or birdsong; just the natural soundscapes of a random night on Earth. It’s probably what I would take, too.

Like the question posed to a marooned islander, the deeper answer of what you take with you is more profound than the packing list.