By Ron Cowen of Nature magazine

The European Space Agency (ESA) will forge ahead with ExoMars, an ambitious two-part robotic mission that would look for signs of life on the Red Planet, even though NASA has reneged on its promise to provide a launch rocket for the first stage of the mission.

During a 12-13 October ESA council meeting in Paris, the agency decided to begin negotiations with Russia for a rocket that would launch the first stage of ExoMars, in 2016, in exchange for Russian participation in the mission. Already €150 million (roughly US$207 million) shy of the €1 billion it needs for the entire ExoMars project, ESA has deemed it too costly to use its own Ariane rocket for the 2016 launch, according to a senior ExoMars official who asked not to be identified.

The initial 2016 phase of the mission would carry an orbiter designed to sniff out possible sources of methane and other trace gases that might signal the presence of microbial life on Mars. The orbiter would then serve as a data relay for a rover, to be launched in 2018, that would collect Martian soil samples. A future mission would carry those eagerly awaited samples back to Earth, where scientists would examine them for signs of past or present biological activity.

Money talks

ESA officials say they were quietly informed more than a month ago that budget problems would prevent the US space agency from providing an Atlas V rocket for the 2016 launch. NASA still plans to provide a rocket for the second part of the mission in 2018.

By February, ESA aims to conclude the Russian negotiations and confirm NASA's other commitments to ExoMars, which include providing several instruments for both parts of the mission.

Because of uncertainties in NASA's proposed planetary science budget, which is expected to decline after 2012, the US agency hasn't been able to provide the assurances that ESA needs, NASA planetary science division director James Green told a NASA advisory committee on 13 October.

"It makes us look like we're a bad partner," acknowledged Green, but he said NASA hoped to firm up its commitment in the coming months. Nature 's ExoMars source says the outcome of the negotiations between ESA, Russia and NASA will be crucial to the success of the mission.

A bad sign?

NASA is asking all of its divisions, including planetary science, to come up with some of the extra money, Green noted. The agency will need to find an additional $1 billion to support the JWST from 2013 to 2016.

Some US planetary scientists are concerned that NASA's inability to provide a rocket for the 2016 ExoMars launch is a sign of a bigger problem. The space agency must find $156 million in its 2012 budget to pay the skyrocketing costs of the long-delayed James Webb Space Telescope (JWST), its flagship observatory and successor to the Hubble Space Telescope.

The cost of JWST "is obviously a factor" in the ExoMars problems, says planetary scientist Mark Sykes of the Planetary Science Institute in Tucson, Arizona. Sykes was a co-editor of a bluntly titled editorial, 'JWST Threatens Planetary Science', published on 8 September in the Planetary Exploration Newsletter. "There are important national priorities in space beyond the goals of JWST that as a country we cannot afford to sacrifice," the editors argue.

Sykes suggests that if the costs of JWST can't be contained within NASA's astrophysics budget, perhaps it should be cancelled, or funded by the US Congress as a stand-alone project. But other planetary scientists, including Jonathan Lunine of Cornell University in Ithaca, New York, note that JWST will also use its infrared eyes to peer at planets both inside the Solar System and beyond.

At a joint meeting of the European Planetary Science Conference and the American Astronomical Society's Division for Planetary Sciences held last week in Nantes, France, the session on ExoMars began not with a review of the mission's science, but with a discussion about ways to ensure its survival.

"I'm wearing black, but I hope this isn't a funeral," said Ann Carine Vandaele of the Belgian Institute for Space Aeronomy in Brussels who attended the session.

ESA's decision this week to soldier on should quell some of those concerns, at least temporarily. But they may come to the fore next February if the agency isn't able to hammer out an agreement with Russia.

This article is reprinted with permission from Nature magazine. It was first published on October 14, 2011.