Live coverage: Atlas 5 countdown and launch journal

Scientists eager for answers to long-standing questions about the geology of Mars will get a lift Saturday with the blastoff from California of an Atlas 5 rocket with NASA’s InSight mission, a robotic landing craft that will take the pulse and temperature of the red planet.

SpaceX’s launch team ran through a traditional preflight test Monday, putting a Falcon 9 rocket through a mock countdown, loading it with propellant and briefly firing its nine engines on a launch pad in California ahead of this weekend’s liftoff with a U.S.-European oceanography satellite.

Rainy weather at the California launch site is forecast to put a damper on plans to fly an Atlas 5 rocket on Thursday evening.