Scacecraft don’t get to sleep in on the weekend—and neither do their scientists. On Saturday at 5:51 a.m. Pacific, NASA’s Juno spacecraft will swing within roughly 2,500 miles of Jupiter’s cloud tops, the closest it will get to the gas giant during its planned mission.

It will also be the first time that Juno’s suite of eight scientific instruments will be on, essentially marking the beginning of the science mission, officials said.

“This is our first close look at Jupiter with our eyes wide open,” Steve Levin, Juno’s project scientist at NASA’s Jet Propulsion Laboratory, said in an interview.

After a nearly five-year journey to the outer solar system, Juno entered orbit around Jupiter on July 4, zipping close over the planet before shooting back out into space for an elongated, 53.5-day orbit. During that fast first flyby, all the science instruments were turned off, as the spacecraft focused on getting into orbit with as little potential distraction as possible.

Now, the spacecraft has come back around, with all its science instruments ready to go. Among its tasks, the spacecraft will be probing the planet’s magnetic field, taking gravity measurements and using its microwave sensors to look for water.

“What I’m really excited about is finding out how Jupiter’s going to surprise us,” Levin said. He was headed to the Southwest Research Institute on Friday night, where many team scientists would be gathering to watch the data come in early Saturday morning. (The institute is home to the mission’s principal investigator, Scott Bolton.)

This will also be the first chance Juno has to snap images of the planet’s mysterious poles, which, in spite of Jupiter’s high profile in the solar system, have not been seen up close by any spacecraft before.

The researchers will also be watching with bated breath to see how Juno handles the punishing barrage from the planet’s powerful radiation belts.

“There’s always the possibility that the radiation will affect one of our science instruments in a way we didn’t expect,” Levin said.

Juno is so far away that it will take roughly an hour for scientists to know that it successfully completed the flyby, he added.

Images from the flyby won’t be available on the same day, the scientists said, though some may be released by the end of next week. (Images taken while the spacecraft was closing in on the planet could potentially be released earlier, Levin said.)

Once it completes Saturday’s flyby, Juno will head back out into space for another 53.5-day orbit, and then settle into smaller, roughly two-week orbits thereafter.