Because Mars, farther from the sun, takes longer to orbit, Earth and Mars will not be in alignment again for 26 months, in May 2018. Dr. Grunsfeld said it would take about two months to review the ramifications of the delay and the options of what to do next.

About $525 million of the mission’s $675 million budget has been spent.

CNES, the French space agency, is in charge of InSight’s seismic instrument, which is to be placed on the surface to measure the vibrations of marsquakes and the impacts of meteorites. As with sonograms, the change of velocity of sound waves passing through the planet would enable scientists to infer the depths of Mars’ crust, mantle and core.

The three seismometers in the instrument, sensitive enough to detect vibrations as slight as the width of an atom, require a near-perfect vacuum for precise measurements.

The seismometers sit within a sphere about nine inches in diameter. Bruce Banerdt, InSight’s principal investigator, said that during tests of the instrument, still in France, air was pumped out to a pressure of about one ten-millionth of a millibar, or less than a billionth of the Earth’s atmospheric pressure of about 1,000 millibars.

Over the course of the mission, the vacuum would gradually rise by a factor of 10,000, to about a thousandth of a millibar, because of gases released within the instrument. Dr. Banerdt said the instrument would still function if the pressure were 100 times higher, at a tenth of a millibar.