Human colonization of Mars has long been a subject of science-fiction, but it might not be too long before the first astronaut sets foot on the Red Planet. The Martian atmosphere is inhospitable for life currently, but some evidence suggests that it might have harbored life in the past. Probes have found the presence of frozen water and other evidence that suggests the planet could have had a life-supporting habitable environment.

The first spacecraft to successfully land on Mars was the Soviet Mars 3 space probe, which touched down on the Martian surface in 1971 before failing within the next few seconds. The first fully-successful Mars lander was the Viking 1, which touched down on the Red Planet in 1976. It was part of a NASA mission to investigate the Red Planet and search for signs of life. Since then, there have been multiple successful unmanned missions to the Red Planet, including the Curiosity rover, which landed back in 2012, and the Perseverance rover that landed last year.

Related: Why Is Mars Red? Understanding The Planet’s Unique Color

Various space agencies are aiming to land humans on Mars in the coming decades. NASA is said to be optimistic that it will be successful in sending the first manned mission to Mars in the 2030s, although long-term missions might take a whole lot longer. In 2015, NASA Administrator Charles Bolden, Jr. said that the first crewed flight to mars might happen in 2030, according to MarsDaily, with the Perseverance rover supporting the human mission. He further claimed that the astronauts won’t have to build their own base on the planet because robots sent from earth would have already done the job for them in advance.

Elon Musk Wants To Send Humans To Mars This Decade

Photo of Mars, showing the planet's red appearance

Photo credit: ESA/MediaLab

Private space exploration companies are also working on Mars missions and aiming to send crewed flights to the Red Planet in the coming decade. SpaceX is taking the lead in this regard, with the company’s founder and CEO Elon Musk recently saying humans will likely land on the Red Planet by 2029 at the earliest. Musk had earlier said that SpaceX was aiming to land a crewed mission to Mars in five to ten years.

While space enthusiasts are excited about a possible manned mission to Mars, there are real challenges ahead. Firstly, with current technology, it takes about nine months to reach the Red Planet, so a round-trip might take between two to three years, including the time needed for on-site research. Throughout that time, the astronauts would need food, water and oxygen, as well as protection from radiation. As there’s no known technology to harvest Martian resources for water, fuel, and building materials, everything will have to be taken from earth, which will also be a major impediment for the space tourists. Overall, the promise of a trip to Mars sounds enticing, but many loose ends will have to be tied up before it becomes a reality.