That's why Massachusetts-based nonprofit group Explore Mars is urging a more aggressive strategy: launch missiles at the Martian planet to break up the upper crust and bore deep into the subsurface.
NASA and the European Space Agency both have planned missions aimed at digging a bit deeper than Curiosity: NASA's 2016 InSight lander mission will dig as deep as 16 feet and ESA's 2018 ExoMars rover will drill more than 6 feet below the surface. But NASA's mission won't be looking for life and the ExoMars mission will be limited to a small region of Mars.
Explore Mars wants astronauts to probe deeper and broaden the scope of the search for Martian life.
Last week, Explore Mars began raising money for a project called Exolance, a plan to scatter small, lightweight projectiles all across the surface of the Red Planet. Instead of warheads, the missiles would carry probes outfitted with scientific instruments and communication capabilities.
The group has already assembled a team of scientists to design such probes, but Explore Mars -- which will need to convince NASA or a private space company like SpaceX to give its probes a ride to Mars -- must prove its technology is robust enough survive such a jarring impact.
In 1999, NASA tried to slam two penetrating probes into Martian rock, but radio contact was lost upon impact.
"Penetrators result in huge shocks," ExoMars project scientist Jorge Vago told New Scientist. "Not many instruments can take this."