Of all the bodies in our solar system, the sun is probably the one we want to give the widest berth. It gushes radiation, and even though its surface is the coolest part of the star, it burns at about 5,500°C, hot enough to incinerate just about any material. As such, there are no plans to send a manned mission in its direction anytime soon (Mars is much more interesting, anyway), but it can’t hurt to figure out at what distance a person would want to turn back. You can get surprisingly close. The sun is about 150 million kilometres away from Earth, and if we think of that distance as a football field, a person starting at one end could get about three quarters across without burning up.

That said, an astronaut so close to the sun is way, way out of position. “The technology in our current space suits really isn’t designed to withstand deep space,” says Ralph McNutt, an engineer working on the heat shielding for NASA’s Messenger, a new robotic Mercury probe. The standard space suit will keep an astronaut relatively comfortable at external temperatures reaching up to 120°C. Heat coming off the sun dissipates over distance, but a person drifting in space would begin encountering that kind of heat some three million miles from the sun. “It would then be a matter of time before the astronaut died,” McNutt says. Above 120°C, the suit would transform into a close-fitting sauna-the temperature would climb above 50°C and the person would become dehydrated and pass out, eventually dying of heatstroke.

Riding in the space shuttle, though, someone could get much closer to our star. The ship’s reinforced carbon-carbon heat shield is designed to withstand temperatures of up to 2,500°C to ensure that the spacecraft and its passengers can survive the friction heat generated when it reenters the atmosphere from orbit. If the shield wrapped the entire shuttle, McNutt says, astronauts could fly to within 2.1 million kilometres of the sun. But the integrity of the shield degrades rapidly above 2,500°C, and the cockpit would begin to cook. “I would advise turning away from the sun well before that point,” McNutt says. Much hotter than that, the shields would fail altogether, and the vehicle would combust in less than a minute.

Of course, just getting that close to the sun would be quite an accomplishment, says NASA radiation-health officer Eddie Semones. The constant exposure to cosmic radiation during the voyage would most likely prove fatal before the astronauts made it halfway across the ‘football field’.