For much of the past two decades, the Mars science community in the United States has enjoyed special treatment. It had its own programme office at NASA, with a budget equal to almost half of that given to all planetary science. It had its own line of small missions, called Mars Scout, that would fly every few years. Even in the decadal survey, the planetary community's consensus list of prioritized missions last published in 2003, Mars had its own special pecking order.

All of that is changing. Now, Mars scientists will have to compete with everybody else.

MAVEN may be the last of the Mars Scout missions. Credit: NASA

Steven Squyres of Cornell University in Ithaca, New York, says that in the decadal survey for 2011, which he chairs, Mars missions will be evaluated alongside missions to other planets. And this week, NASA planetary science division director Jim Green told Nature that he has opened up the mission competition called Discovery, worth $425 million, to all solar system destinations.

The decision was made in part because a future Mars Scout opportunity, one that many had hoped for in 2016, is unlikely to happen. "There was no future Mars Scout opportunity if it wasn't a part of Discovery," says Green. "We're treating the solar system as a unified set of science opportunities."

Some Mars scientists are worried about the future of the overall Mars programme office at NASA, which is coming down off of historic budgetary highs of $600 million in 2008. "The decadal survey is key to determining what the fate of the Mars programme is going to be," says geologist Phil Christensen of Arizona State University in Tempe.

Space consolidation

Green says that NASA wants to use a 2016 launch window to partner with the European Space Agency (ESA). ESA plans to send its ExoMars lander while NASA wants to build a gas-sniffing orbiter, but both are short on the necessary cash. If the collaboration fails, Green says, the NASA money could still be used for a Mars Scout mission costing about $450 million. Phoenix, which landed last year on the Martian polar plains, was the first Scout.

Before the Mars programme office was set up in 1994, individual missions had to round up Congressional support — the reason, says Christensen, why no Mars missions flew between the 1976 Viking landers and the 1992 Mars Observer, which failed to reach Mars.

With a dedicated programme, missions can plan for the future in smaller steps. As an example, Christensen mentions a mission concept he proposed for the last Scout competition in 2006: to slam a projectile into the surface and measure the gases tossed up, which would set the stage for a future rover to explore the impact crater. The winner of that Scout competition was Mars Atmosphere and Volatile Evolution (MAVEN), an atmospheric mission scheduled for launch in 2013.

Christensen estimates that there were 30 proposals in the 2006 Scout competition, and he expects at least that many non-Mars proposals will be submitted to the Discovery competition when it is announced later this fall. Many Mars scientists, including Christensen, won't bother submitting proposals. "The Mars community is somewhat sceptical as to whether Mars has a real chance in Discovery," he says.

But the Mars community might have itself to blame for the tight budgets that have led to the current quandaries. The $2.3-billion Mars Science Laboratory — the super-sized rover scheduled for launch in 2011 — ended up being the mammoth, bells-and-whistles mission that a stepwise Mars programme was supposed to help avoid. The mission also ended up chewing through hundreds of millions of dollars in its budget overruns — more than enough to fund a Mars Scout.

"In hindsight, many people would say that was probably too big of a step," Christensen says. "The programme got a little carried away."