There’s a moment early in the new sci-fi film “Prometheus” where a scientist doffs his helmet on a distant alien moon.

But wait: The atmosphere is toxic, we were told. So what’s he doing? Well, the scientist has found a bubble of breathable air — which is handy, because who wants to watch pretty Hollywood faces stuffed into helmets for an entire film?

It turns out such a scenario is plausible. There could be a moon circling a faraway planet that has — in places — safe air.

The film’s director, Ridley Scott, knew this. While developing the script, he turned to one of Hollywood’s hottest science advisers, NASA astrobiologist Kevin Hand, who also consulted on “Avatar” and “Thor.”

Hand, who works at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., makes his living thinking about what alien life might look like and how we can find it. During brainstorming sessions with Scott and his team, the filmmakers said they wanted the characters to ditch their space helmets. Hand, who was detailing to Scott how alien worlds might look, feel and smell, explained how pockets of oxygen could be present.

Science saves Hollywood — again.

More than ever, writers and directors are turning to scientists to make their fantasies more plausible. In the process, they’re learning that scientists are people, too.

That’s thanks to the Science and Entertainment Exchange, which launched in Los Angeles in 2008 with a $1.1 million grant from the National Academy of Sciences. With 800 scientists on its roster, the exchange has arranged nearly 500 consultations between California creative types and scientists who can speak without jargon.

Hollywood weddings often end in disaster, but this marriage has been a hit.

“Now I’m getting big writers saying, ‘I’ve been hearing about you guys, I want to try you out,’ ” said Rick Loverd, one of the exchange’s three full-time employees. “People in the entertainment industry know about us.”

Maybe it’s just a honeymoon. After all, Hollywood has endlessly abused science in the service of story, starting in, say, 1931. That’s when moviegoers saw an obsessed scientist — a total nut job, really — stitch together dead bodies and reanimate them into Dr. Frankenstein’s monster.

A stereotype was born: Smudged lab coat. Menacing plans. Bad hair.

Not a great moment for science.

It took an unlikely character — comedy filmmaker Jerry Zucker, of “Airplane!” and “Naked Gun” fame — to flip the script.

A decade ago, Zucker and his wife, Janet, campaigned in Washington and California in favor of embryonic stem cell research. (They see such work offering a potential cure for their daughter, who has Type 1 diabetes.) While seeking funding, Jerry Zucker was disturbed by “a fear of science” among some lawmakers and the public.

“That, of course, is completely the fault of Hollywood,” Zucker said in a phone interview. “A mad scientist is an entertaining character.”

After a chance meeting between the Zuckers and Ralph J. Cicerone, president of the National Academy of Sciences — the country’s top scientific body — the exchange was born. (Jerry credits Janet for the idea.) Funding now flows from private foundations, too, with the National Academy’s contributions diminishing.

Need to know what a matter-antimatter explosion will look like, as the writers of “Angels & Demons” did? Call the exchange, and they’ll put you in touch with Sean Carroll, a physicist at the California Institute of Technology.

Carroll, who’s consulted on the TV shows “Bones” and “The Big Bang Theory,” also helped Marvel Studios with last year’s comic-book movie “Thor.” Carroll pushed the producers to change Natalie Portman’s character, Jane Foster, from a nurse, as originally written, into an astrophysicist. And not just an astrophysicist, but one searching for wormholes — you know, those plot-friendly tubes across space and time. Through which, in the film, the space god Thor happens to fall.

Ann Merchant, who works on the exchange in Washington for the National Academy of Sciences, pointed to that change as a success. She hopes strong scientists on the big screen will spark interest in youngsters.

“I’d like to think there’s a 10-year-old girl seeing Natalie Portman talking about Einstein-Rosen bridges [wormholes] and saying, ‘That’s something I might want to do, that’s a pretty cool thing,’ ” Merchant said.

At “exclusive salons” arranged by the exchange, Loverd said, top scientists hold forth in the homes of big-name filmmakers. Columbia University cosmologist Brian Greene discussed string theory with 60 writers, directors, studio executives and actors in the Zuckers’ screening room. “Family Guy” creator Seth MacFarlane and “Shrek” producer John Williams also host gatherings, with evolution, astrobiology and the neuroscience of magic on the agenda.

The exchange also drops good-talker scientists into bars with several hundred studio executives and writers.

Most Hollywood types don’t know a scientist, Loverd said, so just mingling the groups leads to richer scientist characters.

“The stereotype is shattered, because [the scientist] is not a person whose pants are too short and whose glasses are broken and who can’t form a full sentence without sounding like a big, giant nerd,” Merchant said. Filmmakers learn that “this is a normal person.”

Merging the two worlds has also sparked unexpected collaborations. MacFarlane — a big science nerd and a potty mouth — met astronomer Neil deGrasse Tyson at one mixer. The pair are now remaking Carl Sagan’s seminal 1980 PBS series “Cosmos.”

Lab tours can provide script fodder, too, said Jon Spaihts, co-writer of “Prometheus.” Through the exchange, he visited the Jet Propulsion Laboratory, home of NASA’s Mars rovers. “It was hugely inspiring,” he said. “I picked up a little bit on their mood, the vibe in the room, the way they approach the work. If you do it right, that suffuses your storytelling.”

Zucker, meanwhile, toured Verenium, a biofuels company in San Diego, for a new comedy he’s penned called “The Big O.” The script features a married couple — wait for it — trying to make fuel from algae, a hot research area. Through the exchange, Zucker — surely you can’t be serious! — found a real husband-wife team of biofuels researchers, Chris and Shauna Somerville.

“I said, ‘What would you guys talk about in the lunchroom?’ and I transcribed a bunch of that and put it in the movie,” Zucker said.

The benefit for filmmakers is clear: They get new ideas, real dialogue, fresh scenes.

So what do the scientists get out of it?

“Frankly,” Hand said, “it’s just fun,” because “Prometheus” explores the same big questions he thinks about as a scientist: Who are we, how did life arise, and are we alone in the universe? “You can let down your scientific guard a bit. You can explore a lot of ideas that would never see the light of day in a published paper.”

Scientists volunteer for the exchange. But “once or twice a year,” Loverd said, more formal, paid gigs result. Hand, for instance, was paid for his work on “Prometheus.”

There’s a fine line, Loverd said, between a friendly consultation and rank exploitation. A “few times,” Hand said, “I sort of felt like I was being used.”

Carroll has yet to get a paycheck. “I did get a sweatshirt from Marvel and a bottle of wine from Ridley Scott,” he said.

Hand dreams of a bigger benefit. Cash is tight at NASA, and a probe he has designed to search for life on one of Jupiter’s moons remains unfunded.

“Somewhat facetiously,” he said, he hopes that “these films will make enough money to someday pay us back — by funding a private mission to Europa.”

In the meantime, he’ll just have to wait for the independent film “Europa,” due next year. He was a consultant on that one, too.