NASA’s MAVEN Mars orbiter is set for Mars orbital insertion this weekend. The unmanned probe will fire its engines on Sunday at 9:37pm Eastern Time.

And then mission controllers will have to white-knuckle it for 12.5 minutes to find out whether the maneuver was successful, because that’s how long it will take a radio signal from the craft to travel the 140 million miles back to Earth.

MAVEN’s mission is to find out exactly what happened to Mar’s atmosphere, much of which seems to have escaped into space, taking with it a lot of water that use to run in rivers and pool in lakes on the surface.

MAVEN will study Mars’ upper atmosphere on a one-Earth-year science mission for clues about how atmospheric gases may have been carried off in the solar wind. It will also get a chance to observe a once-in-a-million-years Mars close encounter with a comet.

See more details in my write-up for Popular Mechanics: