Nasa has said it is not giving up on Mars - but it will have to get there later and at a lower price.
President Barack Obama's budget announced this month cancelled joint US-European robotic missions to Mars in 2016 and 2018. Now top science officials say they are scrambling to come up with a plan by the end of the summer for a cut-rate journey to the red planet in 2018.
Nasa sciences chief John Grunsfeld said he thought there was a better than even chance that Nasa would not miss the 2018 opportunity. That is when Mars passes closest to Earth, which happens only once every 15 years. It offers a chance at fuel cost-savings and the ability to send up more equipment.
Space agency officials who met upset scientists seemed intent on salvaging a programme that took some of the deepest science spending hits in the president's budget. Until this month, Nasa had been ramping up its Martian ambitions.
Meanwhile, in the middle of this year, the most high-tech rover yet, Curiosity, will land near the Martian equator in search of the chemical building blocks of life. The more scientists study Mars, the closer they get to answering whether microbial life once existed there, a clue to the ultimate question: are we alone?
Two years ago, Mr Obama stood at Kennedy Space Centre and said it was more of a priority than going to the moon. He wanted astronauts there by the mid-2030s.
But the two coming missions were then cancelled along with the most ambitious Mars flight yet planned, which the National Academy of Sciences endorsed as the number one solar system priority. That was a plan to grab Martian rocks and soil and bring them back to Earth. Now that is "not an option" given the current budget, Mr Grunsfeld said.
Mars researcher Steve Squyres, of Cornell University, who headed the national academy panel, said if Nasa could not make progress on a Mars sample return, the space agency should think about moving on to the next priorities, such as visiting Jupiter's moon Europa.
"We're really at a crossroads," Nasa planetary sciences chief Jim Green said.
Nasa said it does not quite know what a reconfigured 2018 mission would look like, but it would be cost-capped at 700 million dollars (£443m) and it will not be landing. If it is lucky, it may orbit Mars.