Like the best mysteries, every new discovery on Mars seems to raise more questions than it answers.
The recent discovery of methane "burps" in the Martian atmosphere, for example, could be a sign of microscopic life past or present. It could also simply result from geological processes. Or it could be a hitchhiker from Earth skewing readings. Or even a completely meaningless glitch in data.
Whatever the cause, the methane discovery, along with new evidence of organic material in Martian rocks and further confirmation that water was once much more widespread on the planet's surface, has given greater incentive for missions to send humans to Mars.
After all, some questions can only be answered by scientists on the ground. That goal might not be so far-fetched either.
NASA scientists recently announced an innovation that could make traveling to the Red Planet much easier.
Traditionally, Mars-bound spacecraft are launched from Earth during a brief window that occurs every 26 months in order to minimize the distance the vehicle will need to travel.
Then, vehicles arriving at Mars have to slam on the brakes in order to avoid slamming into the surface or overshooting it entirely. Slowing down requires burning a lot of fuel.
The new method, called ballistic interception, shoots a vehicle into Mars' path around the Sun rather than at the planet itself.
Eventually, Mars catches up and its gravity drags the spacecraft into orbit. Ballistic interception uses less fuel and allows for year-round launches, both huge advantages for sending human colonists to Mars.
And the first volunteers have been lining up for two years now. Mars One, a non-profit based in the Netherlands, started recruiting a first wave of Martian settlers in 2012 for a planned 2024 mission. The $6 billion mission would be partly funded by a reality TV show covering the one-way trip. Let's hope that "Real Housewives of Mars" is still several centuries away.
But Mars One explorers might not be the first humans to settle on another planet.
NASA recently proposed establishing a colony on Venus as a way to test important technologies for Mars exploration. Venus is much closer to Earth than Mars, but its surface is less than hospitable.
Temperatures average 900 degrees Fahrenheit and atmospheric pressure is 96 times greater than Earth's. Human visitors would be simultaneously crushed and melted - unless they stay far away from the surface.
The solution, according to NASA, is to build a floating colony not unlike the cloud city featured in "The Empire Strikes Back." It all sounds a little more glamorous than life in a desert made out of rust, although gliding endlessly over the planetary equivalent of a blast furnace could be a little unsettling.
Regardless of whether humans aim for Mars or Venus - or both - it's an exciting time for space exploration.
Stepping out into space satisfies a human yearning to test boundaries and tackle frontiers, and the more we learn about our cosmic neighbors, the more we learn about ourselves.