Elon Musk has big dreams for the future of human space exploration. In 2013, the SpaceX CEO said he wanted to die on Mars. In 2016, he stated publicly that in 50 years, humans could have a settlement of 1 million people on the red planet. Recently, Musk and his private rocket company moved another step closer to their dream of establishing humans as a multi-planetary species, one they believe is key to the long-term longevity of our species.

On Feb. 7, Musk announced via Twitter that the “Raptor just achieved power level needed for Starship & Super Heavy”. Starship and Super Heavy are the two components of what is known as Big Falcon Rocket (BFR), which is a pseudonym for Big F****n’ Rocket, a 387-foot behemoth capable of taking 100 passengers to Mars.

Raptor is the engine that will power both components. A video later surfaced of the engine spewing a steady stream of bright-colored flame.

BFR seeks to solve the first problem of how to get humans to Mars, but that is only the beginning of the colonizing Mars challenge. A number of planetary characteristics must be adjusted for human life to survive once it touches down: at a minimum, warmer temperature, breathable air, liquid water, and plant life.

The composition of Mars’ atmosphere is vastly different from that of Earth, so humans would have a hard time breathing. Earth’s is composed of 78 percent nitrogen, 21 percent oxygen, 1 percent argon and trace amounts of other gases, including CO2. Mars, on the other hand, has about 95 percent CO2, less than 3 percent nitrogen, less than 2 percent argon and only 0.2 percent oxygen. Lacking the levels of oxygen and nitrogen a human needs to breathe, and with far too much carbon dioxide, Martian air would quickly kill a human without proper equipment?.

"To me, when you start listing out all the services we get from our amazing planet, it starts looking pretty near impossible to generate the same thing on another planet, starting from scratch," said Jill Sohm, USC Assistant Professor of Environmental Studies. "And if we would need to transport some of those things from our planet to the other planet, then what is the point?"

Mars also has much thinner atmosphere than Earth, which would have to change for humans to live comfortably on the planet. The planet's weak magnetic field means it is unable to retain as much gas around its surface. Earth's atmosphere acts like a layer of blankets, keeping its surface at a habitable temperature, 58 degrees Fahrenheit on average. Mars has a much thinner blanket, so it rests at -81 degrees Fahrenheit.

Liquid water is also scarce on Mars. Geological evidence suggests that prolific amounts of water used to flow across the surface, carving out characteristic patterns of rivers and lakes. But today, the only water on mars is frozen in its polar caps, as well as in trace amounts as frozen clouds. Mars' weak gravity and magnetic field explain why it has not retained as much water as Earth.

The higher gravity of the Earth essentially holds on tighter to the atmospheric gases, including water vapor,” said Bruce Banerdt, Principal Investigator on JPL’s InSight mission, which is currently studying the interior of Mars. “The magnetic field of the Earth diverts the flow of the solar wind (primarily protons) from reaching the atmosphere. When a high-speed proton hits a water molecule in the upper atmosphere, the oxygen and hydrogen atoms in the molecule can be separated and the light hydrogen atoms can be swept away.”

The low gravity of Mars also poses a challenge to human colonizers. We know that long exposure to the zero gravity of space causes bones and muscles to deteriorate. Not much is known, however, about living on a planet with reduced gravity, like Mars.

Engineers constructing vehicles to carry humans to Mars attempt to account for this difference in their design.

"Astronauts have difficulty after being in space for a year adjusting to earth's gravity," said Gedi Minster, a master's candidate in Astronautical Engineering. "If you have an artificial gravity system that simulates the Mars gravity, the landing is easier."

An alternative to fully colonizing the planet is is a radical option called "terraforming Mars." In theory, it would allow humans to transform Mars into a naturally habitable planet with characteristics like Earth. The technology is still a long way from being realized.

Terraforming scenarios revolve around increasing the temperature and atmospheric density of Mars, giving it breathable air, liquid water and temperatures conducive to human and plant life, and there are three main ideas for how to do this. In the first, giant space mirrors would orbit the planet, reflecting sunlight back at Mars and heating it. They would weigh on the order of 200,000 pounds, too large to create and launch from Earth. The second is building greenhouse gas factories on the surface of Mars, using them to warm the Martian climate in a similar sense to how current fossil fuels are causing warming on Earth. The third is perhaps the most extraordinary: capturing large, nitrogen-rich asteroids, attaching engines to them, and flying them to Mars until they collide with its surface. It is estimated that four such impacts would be sufficient to create Earth-like conditions on Mars.

I think this may be a feasible long-term option, but I think it would take years, maybe hundreds or thousands of years, to accomplish,” Banerdt said. “…I do think it is worth researching the possibility, especially the basic science behind it. But we should also think about the ethical implications of drastically changing a unique planet. Some might compare this philosophically to damming up the Grand Canyon to use as a reservoir on Earth.”

Colonizing Mars — not to mention Terraforming it — is a difficult challenge. Max Donovan, a junior Astronautical Engineering major who is a member of the USC Rocket Propulsion Lab (RPL) and will be interning at SpaceX this summer, said difficulty is inherent to the fields of rocketry and space exploration.

"Space tech is the 'science of superlatives: the highest speeds, hottest hots, coldest colds, longest times,'" Donovan said. "Once [the rocket is] up there, you can't pull it back…There's no option for failure."

Donovan and USC RPL aim to become the first student-run and led group to launch a rocket to outer space. He not only enjoys the engineering challenge, but Donovan also believes rocketry has a lot to offer society.

"Space exploration is a pretty noble pursuit," Donovan said. "There is a lot of payback on the societal scale if you invest a lot of time and money. You're not losing much, and there's a lot to learn."

Some benefits include the development of new materials, economic stimulation, culture, and global partnerships. In addition, Musk and others have stated that becoming a multi-planetary species is a necessary step in ensuring the long-term survival of the human species. Skeptics, however, question whether our time, money, and brain power could be better spent tackling the survival challenges facing earth’s current inhabitants.

"Climate change is already happening on our planet, and even if we were able to stop emitting greenhouse gasses right now, we would still continue to see some effects from it," Sohm said. "I think that there are a lot of people who have the smarts, ambition and focus to solve our most difficult problems. The issue is that they don't have the resources and public platform of a person like Elon Musk."

If all goes according to Musk’s plan, humans will become a multi-planetary species in 2024, when SpaceX launches Starship to Mars.