The League of Mars-bound Gentlemen

When National Aeronautics and Space Administration officials announced Dec. 4 that they were postponing a $1.6 billion – soon-to-be $2.2 billion to $2.3 billion – mission to put a VW Bug-sized rover on Mars, the hottest news of the moment was the delay and its contribution to the project's growing cost.

But during the press conference announcing the delay, Ed Weiler, who oversees the agency's space-science efforts, committed news of another sort – one that could have profound implications for the future of robotic space exploration.

Simply put: He and his counterpart at the European Space Agency (ESA), David Southwood, have agreed to rework their individual Mars exploration programs into a single program both agencies will follow.

This isn't just another shot at adding one agency's hardware to the other's spacecraft on a mission-by-mission basis. That can certainly work, as the highly successful Cassini-Huygens mission at Saturn shows.

Instead, ESA might become the lead agency on one Mars mission, NASA on another.  But launches would flow from a commonly agreed set of priorities for each mission, launched on a commonly agreed schedule, and the two agencies would share the costs. Ideas and instrument packages would still be welcome from researchers and space agencies outside this joint effort.

The ultimate goal: To launch a sample-return mission to the red planet (bring Martian dirt home), probably around 2020 or shortly thereafter.

In phone chats with both men, they emphasize that the details still need to be worked out. Teams from each agency are likely to be meeting over the next few months to start organizing for the effort.

Look for signs of progress at the next bilateral meeting the two agencies' science directorates regularly hold, Dr. Weiler says. The next one is scheduled for May in Plymouth, England.

"David and I would like to see significant progress" by then, Weiler says. "We should have a pretty good idea of where we're going, with groups in place and initial meetings having taken place."

So how did this come about?

Turn the clock back to July. The two top officials and their division directors gathered in Annapolis, Md., for their annual conclave.

"There's always a session where Ed and I shoot the breeze between the two of us," says Dr. Southwood, who three days before the meeting took over ESA's Mars-exploration program. "We both are a little bit skeptical about the over-optimism of some of our colleagues" in laying out how much a mission can accomplish and at what price.

In Europe, leaders were gulping at the price of ESA's ExoMars mission, estimated at 1.2 billion Euros ($1.5 billion US).  At the time, the effort faced the prospect of slipping its launch from 2013 to 2016.

In October, ESA announced it would in fact delay the mission to 2016.

This has a familiar ring.

In the United States, the Mars Science Laboratory mission – which NASA has now rescheduled for a 2011 launch, from 2009 – was dipping deeper than expected into the till and was hitting some technical snags.

As Southwood recalls it, "Basically, Ed said: 'Look, if you slip to 2016, what about putting our heads together and putting our resources together and try to do a mission we both believe in?' "

That question triggered a brainstorming session that led to what Weiler calls their "gentleman's agreement" on a more extensive, cooperative Mars exploration program.

At this stage, no formal memorandum  of understanding exists. And at least on the US side, the effort awaits the blessing of a range of stakeholders, from the US State Department to Congress, never mind a sitting or incoming president.

But Weiler suggests that the time is right for tighter cooperation on Mars exploration.

Money is one reason.

Missions are growing more expensive as they grow more ambitious. The easiest, cheapest missions are history. And even those didn't always work out.

The infamous Mars 98 missions – a lander-orbiter combo doomed by a math error – was supposed to lead to a sample-return mission in 2003, a project its proponents at the time said could be done for about $500 million, Weiler recalls.

"Obviously, the Mars 98 mission was slightly underfunded; we couldn't orbit the planet or land an it. Those missions were on cost and on schedule. I got the cheapest holes on Mars you could plan for," he quips.

With the sophisticated Mars Science Laboratory rover expected to  hit $2.2 billion or so, it's not hard to see how a sample-return mission might cost three or four times as much.

A sample-gathering lander or rover needs to reach the surface safely. It must identify and then grab the coveted samples. The system needs to launch the samples back to an orbiting "mother ship."

And the mother ship, or a smaller rocket it launches, needs to safely return the samples to Earth in a container that allows them to remain tightly quarantined to ensure that no possible Mars microbes are introduced to an Earth environment.

As with many ambitious science projects,  the cost to answer the burning questions are growing too large for one agency to bear.

Moreover, relations across the Atlantic are warming, opening the prospect of closer cooperation between the US and Europe on a range of issues.

ESA and NASA agencies have different funding horizons. And the US has tight restrictions on the books that can make international cooperation on building spacecraft difficult. But Doug McCuistion, who heads NASA's Mars exploration program, notes that both sides have found constructive ways to work around those restrictions on projects such as the James Webb Space Telescope .

Southwood and Weiler say that a joint exploration program that looks to 2016 and beyond still will need input from existing groups, such as the International Mars Exploration Working Group.

After all, the US and ESA aren't the only national space agencies with Mars in mind. Next year, for instance, a joint Chinese-Russian mission is slated for launch to the red planet. Russia will loft a pair of orbiters – one from each country – to study of Mars and its moon Phobos.

But from the standpoint of agencies with the highest success rates in orbiting and landing spacecraft at Mars, NASA and ESA are the big guns.

So, if you're a space buff, what's your take on this approach to Mars exploration? What sort of hidden (or not so hidden) gotchas do you see that might thwart the good intentions? What opportunities do you see for similar joint programs? At what point could or should countries such as Japan, China, or Russia be invited to the table for more than a contribution of an instrument or two?