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In space, no one can wash your dirty underwear. That's one of the lessons learned by late-night TV talk-show host Conan O'Brien when Canadian astronaut Chris Hadfield paid a visit on Monday night.

Hadfield — who is hitting the talk-show circuit for his newly published book, "An Astronaut's Guide to Life on Earth" — explained on TBS' "Conan" show that astronauts on the International Space Station really can't spare the water to wash clothes in orbit. Instead, when their togs get too worn or gnarly to wear, they just throw them into a disposable cargo spacecraft, such as the Russian Progress capsule or Orbital Sciences' Cygnus craft.

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Eventually, the trash-filled spaceships undock from the space station and are sent down for incineration in Earth's atmosphere. Problem solved, right?

"Wait a minute!" O'Brien told Hadfield. "You guys on the space station are throwing your dirty underwear out the window, and it's raining down on us??"

Watch the video for Hadfield's priceless response, and then check out his assessment of Sandra Bullock's space underwear in the movie "Gravity."

More about life in space:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ circles. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.