Just as NASA is on the cusp of answering the most fascinating questions about Mars — is there, was there or could there be life there? — the money needed to provide the answers is about to be abruptly withdrawn, a victim of President Obama’s budget request for 2013, scientists say.

Two ambitious missions that NASA had hoped to launch to Mars, in 2016 and 2018, will be canceled. The first would have sent an orbiter to measure gases in the Martian atmosphere — methane in particular, since methane does not last long. Its presence could suggest that Martian microbes are busy at work emitting the gas (though other explanations are also possible).

The second, in 2018, would have set the stage to fulfill the longstanding desire of scientists to bring pieces of Mars back to Earth for close-up study with the full arsenal of instruments available in their laboratories. Now the prospect of bringing Martian rocks to Earth is likely pushed to the mid- or late 2020s, all because of budget cuts.

“The pipeline is being shut off, and that’s not what anyone wants,” said Bill Nye, executive director of the Planetary Society, a nonprofit group founded by Carl Sagan and others who wanted to foster interest in outer space. “We are closer than anyone has ever been to discovering life on another world.”