On a clear night, Mars can look close enough to touch: a bright, rusty dot hanging in the sky. Space agencies have been sending robots there for decades, and people dream of following. So how long would the trip actually take?
Usually somewhere between about six and nine months, one way. NASA's Perseverance rover spent a little more than six months traveling before it landed in February 2021, and the standard low-energy route takes about nine months. There's a catch, too: the best launch opportunities come only about every 26 months, when Earth and Mars line up just right.
Why You Can't Fly in a Straight Line
Earth and Mars are both racing around the Sun, so the distance between them keeps changing. At their closest, the planets come within roughly 34 to 64 million miles of each other. At their farthest, they can be about 249 million miles apart.
So spacecraft don't aim straight at Mars. They follow a curving path around the Sun, timed so that Mars arrives at the meeting point at the same moment. Perseverance covered about 293 million miles along its route.
The most fuel-efficient path is called a Hohmann transfer orbit. It takes about nine months from Earth to Mars, and it only works when the two planets are positioned just so. Those launch windows open about every 26 months.
Mission planners know this rhythm well. The best low-energy windows come roughly every 780 days, and the energy needed also rises and falls over a cycle of about 16 years. The 1969 and 1971 windows were especially good ones.
Faster Isn't Free
Spacecraft can get there sooner by using more energy. In 1971, the Soviet probes Mars 2 and Mars 3 reached Mars about seven months after launch. But speed costs fuel, and fuel adds weight. One proposal suggests that staging spacecraft in orbit could make a fast round trip of just 245 days possible.
For astronauts, the round trip is the real challenge. A low-energy mission might mean about nine months getting there, about 500 days waiting on Mars for the planets to line up again, and nine months coming home: a 34-month trip. Shorter plans of 400 to 450 days round trip are possible, but they need much more energy.
Long trips bring health concerns, too. Measurements taken on the way to Mars in 2011 and 2012 suggested a round-trip radiation dose of about 0.66 sieverts, compared with NASA's career limit for astronauts of 1 sievert.
Life on a Martian Schedule
Once you arrived, the days would feel familiar. A day on Mars, called a sol, lasts 24 hours, 39 minutes, and about 35 seconds, only a little longer than ours. Still, that small difference adds up over time.
The years are another story. Mars takes 687 Earth days to circle the Sun, so a Martian year is nearly twice as long as ours: 1 Earth year, 320 days, and about 18 hours. Perseverance's initial mission was planned to last at least one of those Martian years while it searched for signs of ancient life.
So a trip to Mars is a long haul, measured in months and planned years ahead around the dance of two planets. Whenever people finally make the journey, they'll need plenty of patience, and a really good playlist.
