Mars has been all over the news lately, for reasons both good and bad. The big positive development was the successful launch Nov. 26 of NASA’s $2.5 billion Mars Science Laboratory, the most ambitious mission ever launched toward the red planet. If all goes well — by no means a given for a mission of this complexity — the car-sized, nuclear-powered rover will begin traversing the martian surface next summer, assessing the planet’s ability to sustain microbial life, past or present.

But the mission’s success so far — cost overruns and a two-year delay notwithstanding — cannot completely overshadow two unfolding Mars snafus: Russia’s malfunctioning Phobos-Grunt martian moon sample-return mission, still stranded in Earth orbit following its launch Nov. 8; and the turmoil surrounding ExoMars, a NASA-European Space Agency (ESA) collaboration, triggered by the U.S. budget crisis.

If Russia’s space agency, Roscosmos, is unable to fire the thrusters designed to put Phobos-Grunt on a Mars trajectory, it will be the latest in a long string of failed Russian attempts to explore the red planet. Hopes were raised Nov. 22-23, when ESA was able to briefly establish contact with the probe, but more recent attempts to call Phobos-Grunt have not been successful. Time appears to be running out for Phobos-Grunt, which also carries China’s first martian orbiter.

ESA’s commendable efforts to help — NASA says it offered similar assistance — should be taken into account as Roscosmos considers ESA’s recent invitation to participate in ExoMars. ESA has asked Roscosmos to launch a European-built communications relay orbiter in 2016 in return for full participation in the mission, which also includes a rover slated to launch in 2018.

ESA turned to Roscosmos after being told not to count on a NASA launch of the orbiter as planned under a 2009 accord between the agencies. This followed another piece of bad news delivered earlier in the year: NASA would not provide a rover for the 2018 mission — under the accord, each agency was to supply its own rover — but could contribute to a jointly built vehicle. Now, as it ponders decisions such as how to distribute the work share on its part of the mission, a task complicated by the uncertainty surrounding the 2016 launch, ESA cannot get any sort of U.S. commitment to ExoMars.

Like NASA’s moratorium on flagship-class planetary missions declared earlier this year, the prospect of a full-blown U.S. reversal on ExoMars is due to the budget crisis that shows no signs of abating. Planetary exploration advocates seem to fear the worst; a recent Washington Times op-ed piece by Mars Society founder Robert Zubrin made the alarming but highly questionable claim that NASA would stop sending probes to other worlds after the late 2013 launch of the Maven mission to Mars. U.S. lawmakers, meanwhile, complained during a Nov. 15 hearing that the White House Office of Management and Budget (OMB), by refusing to commit to ExoMars, is usurping NASA’s authority to prioritize its science program.

To suggest that OMB should have no say in major NASA investments ignores the fact that it is the White House’s prerogative to take the lead in setting overall funding levels and policy for the U.S. civil space agency. OMB has no business choosing for NASA among comparably priced science missions, but it certainly can decide whether the agency can afford to pursue a given project. The 2018 ExoMars mission would collect and cache martian soil samples that ESA and NASA hope to bring to Earth sometime in the future. With a price tag exceeding $10 billion by some estimates, a Mars sample-return mission certainly falls into a class of activities requiring direct White House approval.

So it’s possible that OMB won’t commit to ExoMars today for fear of foisting a huge Mars sample-return investment on a future administration. Or, ExoMars has gotten caught up in the larger budgetary standoff between the White House and Congress.

Either way, there can be little doubt that abandoning ExoMars would deliver a major blow to NASA’s credibility as an international partner at a time when nations are increasingly hard pressed to conquer exploration frontiers on their own. The White House’s current hesitation threatens to do the same thing, only in a way that causes even more trouble for its prospective partner. ESA needs and deserves an answer on ExoMars now.