NASA has suspended its next mission to Mars after problems with a French-built seismological instrument could not be fixed in time for the scheduled launch. The mission, a lander called InSight that was to listen for tremors on Mars as a way of understanding the planet’s interior, will not launch in March 2016, the agency said today. NASA has not announced a new launch date, but because of the relative orbits of Mars and Earth, the agency will have to wait at least 26 months before it can try to launch again.

A new launch date is not a forgone conclusion. The agency will review designs to fix the problem with the instrument, and also estimate the cost of putting the mission on ice for 2 years—and whether that can be paid for. It could take a couple months to reach that decision point, NASA science chief John Grunsfeld said during a teleconference today. “We either decide to go forward, or we don’t.”

On 3 December, the Jet Propulsion Laboratory (JPL) in Pasadena, California, which is managing the mission, confirmed that there was a leak in a vacuum-sealed metal sphere that holds three seismometers. The instrument, called Seismic Experiment for Interior Structure (SEIS), was one of two main science probes, along with a German-built thermometer that would be sent down a small bored hole. SEIS, supplied by the French space agency CNES, would have been placed on the surface of Mars, where it would have listened for faint rumblings through the planet’s crust: marsquakes.

Although CNES had been working overtime to try and repair the vacuum seal, those efforts were not sufficient. New welds, tested on 20 December in France under the extreme cold that the instrument would experience on Mars, did not hold the vacuum. Bruce Banerdt, the principal investigator for the mission at JPL, says the vacuum must be better than a tenth of a millibar, or a ten-thousandth of Earth’s atmosphere, for the instrument to work. The slow leak resulted in a vacuum of two-tenths of a millibar, he says. “The problem has been in this vacuum enclosure,” he says. “It’s not that exotic a technology.”

The Mars community was dismayed by the decision. “We’re all just pretty disappointed right now. Devastated would be a better word,” says Lisa Pratt, a biogeochemist at Indiana University in Bloomington and chair of a Mars advisory committee for NASA. “Everyone has been waiting to get a seismic instrument on Mars after Viking.”

Pratt was referring to NASA’s twin Viking landers of 1976, which also carried seismometers, but on top of the lander decks, where they were subject to background noise from martian winds. The seismometer on Viking 1 failed, and the one on Viking 2 became a better wind detector than anything else. Pratt says a properly insulated seismometer, like the one InSight has, is the key to pinning down the thicknesses of the crust, mantle, and core boundaries on Mars.

Pratt adds that the delay also speaks to the extra challenges of trying to support international collaborations. “‘International’ is so built into all of NASA’s language for the path to humans at Mars,” she says. “You don’t want any vibrant international collaboration to suffer a setback like this.”

The $425 million mission was the most recent selection in NASA’s Discovery program, a line of low-cost, competitive missions led by a single principal investigator. InSight was selected over a comet hopper mission, and one that would have landed a boat on Saturn’s moon Titan.

Total life-cycle mission costs, including the launch rocket, are $675 million, planetary science division director Jim Green said. Of that, $525 million has been spent already, he said.

*Update, 22 December, 12:11 p.m.: This story has been updated to include reaction to NASA’s announcement and other information about the mission.

*Update, 22 December, 5:07 p.m.: This story has been updated to include comments from the NASA teleconference.