How it would work

Mars 2020 is based on the Curiosity rover, and is equipped with upgraded versions of many of Curiosity's instruments. It launches in July or August 2020, and lands on Mars in February 2021. Three landing sites are currently being considered.

The rover's prime mission will last one Mars year—687 Earth days—though that is likely to be extended. During that time, Mars 2020 will use a drill to collect rock and regolith samples from various locations, focusing on rocks that formed in or were altered by water. Such rocks could contain signs of ancient organic life.

The samples will be deposited in easily accessible spots throughout Mars 2020's traverse path. No earlier than 2026, NASA would launch a retrieval mission to land in the same general area. The lander would either deploy a "fetch" rover, or rely on the Mars 2020 rover itself, to collect the samples and place them into a rocket on the lander's deck called the Mars Ascent Vehicle, or MAV. The sample-laden MAV would then blast off into Martian orbit.

High above Mars, the MAV-launched samples would rendezvous with another orbiter, which would pick up the samples for return to Earth.

Zurbuchen said NASA is considering international or even commercial partners to build the orbiter, providing necessary precautions are taken to prevent the cross-contamination of Earth and possible Mars microbes.

"The planetary protection piece is absolutely essential. Whoever the partner is, needs to share our values on this one—no compromise," he said.

The samples would either return directly to Earth or ease into the region around Earth's Moon known as cislunar space. NASA plans to start launching astronauts to cislunar space no later than 2023, using the Space Launch System and Orion crew capsule. The agency is also working on a small, Moon-orbiting space station known as the Deep Space Gateway.

That means the last leg of the sample return could involve astronauts.

"One of the tradable elements that will be really interesting to look at is that cislunar infrastructure, as that landing point or kind-of handover point for … these samples," Zurbuchen said.