Why Mars is Often Cited as the Next Destination for Humankind

From Earth to Mars

The Red Planet has generated a lot of news in the last decade or so. Starting with the Mars Rover Pathfinder, in 1997, and continuing with Spirit and Opportunity in 2004, NASA has stepped up its missions to Mars.

In recent years, many in the scientific community have put forth the proposition that mankind should once again move beyond Earth's orbit and visit another world. The planet most often cited as the perfect destination is Mars. 

Perhaps the most outspoken proponent of a manned mission to Mars is the aerospace engineer and author Robert Zubrin. Zubrin collaborated with David Baker in the late 1980's and the duo crafted a proposal for a cost-effective mission to Mars called, Mars Direct.

Mars Direct required two modules and it proposed launching them in stages. The first stage would be the Earth Return Vehicle (ERV) and the second stage (26 months later) would be the Mars Habitat Unit. The ERV would be responsible for converting the CO2 found in the thin Martian atmosphere into methane and oxygen propellant. This was an ingenious solution to one of the major hurdles to a manned mission to Mars: the rocket fuel required to get the crew to Mars and back again would have rendered the craft too heavy to launch.

But why Mars?

Why Mars indeed. Venus is half the distance from the Earth that Mars is, why not target Venus?

Well, Venus is a most hostile environment. The average surface temperature is about 855 degrees Fahrenheit, and the atmosphere is primarily sulfuric acid. Not a pleasant place to be sure, but also not a very easy place to survive.

This leaves us with Earth's next closest neighbor: Mars.

Although Mars is on average twice as far from the Earth as is Venus, it is reachable in 6 months due to the apparent retrograde of its orbit. This retrograde is most easily understood if one thinks of Mars and Earth as race cars circling the sun. Each planet is in a different track and since the Earth is closer to the sun, its track is shorter. Because it's shorter, the Earth passes Mars every 26 months or so. It is when Earth passes Mars that the two planets are typically at their closest.