Warner Bros. Pictures

Could a real-life Superman leap into outer space? Not with the humanoid body he has in the comic books and the movies - even if he was born on Krypton.

Hollywood is reviving the saga of the Man of Steel in a big way this month – and that serves to revive the debate over just how scientifically impossible Superman's powers are. As usual, there are grains of truth beneath the Hollywood hokum.

"Superman Returns" is having its invitation-only world premiere on Wednesday, leading up to the movie's nationwide release on June 28. Over the next week or so, we're likely to be inundated with articles analyzing the superhero's human side.

But what is Superman if not a Space Alien of Steel? From the start, the creators of the Superman saga clothed their hero's superpowers with an astrobiological explanation. For example, Superman is supposed to be so much stronger than mere humans because his anatomy is supposedly accustomed to the much stronger gravity of his home planet, Krypton.

That's what makes Seth Shostak eminently qualified to give the Superman saga a reality check. As senior astronomer at the SETI Institute in Mountain View, Calif., Shostak helps direct the real-life search for extraterrestrial intelligence  - and also muses on the shape of aliens to come in books such as "Sharing the Universe."

Shostak sees Superman as a great example of what not to look for in the search for alien life: "The fact that he's very humanoid in his appearance and behavior is of course a conceit that's adopted not only by the comic books, but also by Hollywood. ... If Superman looked like a typewriter, you'd end up having very little sympathy for his inner torment."

Some scientists, such as Simon Conway Morris, assert that the same basic body plan that has served so well on Earth would probably turn up on other planets where life takes root. If this sort of cosmic evolutionary convergence is the norm, it may well be that intelligent life elsewhere would look more like the fictional Superman than like Shostak's typewriter. But even then, Shostak sees plenty of reasons why Superman couldn't live up to his superpowers.

• "He still walks upright, and that suggests that the high-gravity environment wasn't too high," Shostak said. "If the gravity's really high, you're probably down on all fours, or all sixes." And obviously, there's no way a human-looking musculature would be capable of leaping tall buildings. "The only way he can do that is if he's built in fundamentally different ways."
• Then there's the energy requirements for all those feats of strength. "It takes a lot of energy to hurtle a 200-pound guy around," Shostak said. The Man of Steel would have to spend most of his time consuming some pretty high-octane fuel to run faster than a speeding bullet.
• As for Krypton, the physical factors of planet formation dictate that a planet significantly more massive than Earth would be a gas giant, with an atmosphere of methane or ammonia. "He would spend a lot of time sniffing the chemicals used for cleaning bathrooms," Shostak joked.

By now, you're probably protesting that "Superman Returns" is only a summer action movie, with no pretense of being a documentary. So there's no sense in complaining too much about fictional physics. In fact, professors such as the University of Minnesota's James Kakalios have been using superhero science as a teaching aid for years.

For example, Kakalios' students used Superman's leaping ability to calculate that Krypton would theoretically have been six times more massive than Earth. They also theorized that Krypton could have been made from the super-dense, unstable material found at the core of neutron stars - which would explain why Krypton blew up.

In a sense, Superman's creators "got the science right by accident," Kakalios said back in 2002. It turns out there's even a kernel of truth to the idea that Krypton orbited a red sun.

Similarly, Superman's powers have their parallels in real-life technologies, ranging from bulletproof vests (to stop that speeding bullet) to thermal imaging and T-ray vision (which is much more revealing than X-ray vision in real life).

And even before its official release, the new Superman movie has sparked a spirited discussion of special relativity as it applies to the Man of Steel's sojourn back to Krypton (slight spoiler alert). Anything that gets comic-book fans thinking about Einstein can't be all bad.

So go ahead and revel in the science of Superman - or have a laugh over insultingly stupid movie physics. Either way, I'd love to see your comments about the highs and lows of superhero science.