Many other details remain unknown. How often does the ground shake with marsquakes? Just how big is the core? How thick is the crust? How much heat is flowing out?

“We know some, but we don’t know a lot,” Dr. Banerdt said. The new mission aims to provide “foundational information of the planet’s history and its activity,” he added. “I’m looking forward to making the first map of the inside of the planet.”

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Red Planet Redo

The 1,380-pound spacecraft is currently sitting on top of an Atlas 5 rocket at Vandenberg Air Force Base in California. Launch is scheduled at 4:05 a.m. local time on May 5, and the southward trajectory could offer a predawn light show for early risers in Los Angeles and San Diego.

Tagging along for the ride is Mars Cube One — two briefcase-size satellites which are to test communications technologies for relaying signals from InSight to Earth. This will be the first time such small satellites, known as CubeSats, have been sent on an interplanetary journey.

If weather or other issues prevent a Saturday launch, NASA has additional opportunities over the next five weeks to get InSight off the ground before Mars and Earth move too far out of alignment. Even if the launch slips, InSight’s arrival date at Mars remains the same: Nov. 26.