“Do all astronauts fly in space with just their helmets on?”

Buzz Aldrin walks on the moon, July 20, 1969

After watching an episode of WordWorld in which Frog and three Piglets play hockey on the moon wearing nothing but a helmet, my daughter wanted to know if this behavior was typical.

“Do all astronauts fly in space with just their helmets on?”


“Why not?”

“Because space is cold.”


And just like that, it was time to Ask the iPhone. It didn’t take long for me to realize that I had fallen victim to the same sort of pop-culture misinformation campaign about outer space that I was trying to protect my daughter from. So very many writers have talked of the bitter cold of space that I just assumed it must be true, when the facts are much more nuanced. Ironic, isn’t it?

When it comes to temperature, the real answer is that once you leave the Earth’s atmosphere, your trip may be a very hot or a very cold one depending on where you go. Simply put, being warm in space requires both a source of heat (a star, for example) and matter (planets, asteroids, moons, satellites, or space debris) to absorb (or conduct) that heat.

Where there’s no matter, there can be no heat (with nothing but photon remnants from the Big Bang to warm it, space can get pretty cold, -270.7 °C).

Where there’s matter but no nearby radiation source, there’s also very little heat. This is the case for Pluto, on which temperatures range from -230 to -240 °C, depending on where it is on its orbit around the sun.

On the other hand, where there is both matter and a nearby radiation source, the heat can get pretty intense. Mercury, for example, can experience temperatures of 400 °C on the side of the planet facing the sun.

Atmospheres affect a body’s ability to keep the heat it receives. Bodies like Earth that have a defined atmosphere are protected by that atmosphere both in the amount (and type) of radiation they receive from their heat source and their ability to retain that heat, which is why we Earthlings typically don’t experience the temperature extremes found in other places.

Mercury, on the other hand, has very little by way of an atmosphere, so doesn’t keep its heat very well at all. A spot on Mercury that heats up to 400 °C during the Mercurian day can cool to -183 °C during the night.

Which brings us back to the question of those space suits. Why is Buzz Aldrin suited up so heavily for his trip to the moon? Like Mercury, our moon has very little by way of an atmosphere to protect it. As a result, temperatures on the moon can reach 107 °C during the day and plummet to -153 °C in a matter of minutes after the sun sets at night. But temperature is only part of the answer. Astronauts also rely on their suits to:

  • Protect them from radiation: With no atmosphere to protect them, an astronaut exposed to the sun’s radiation would receive a vicious sunburn in a matter of moments.
  • Protect them from very low air pressure: There’s no air pressure in space. Without a spacesuit, all the air would be quickly sucked out of an astronaut’s lungs.
  • Provide a steady supply of breathable air: Like scuba divers, astronauts carry their own oxygen in their suits, ensuring that they have a steady supply of breathable air wherever they go.

Any of those answers would have been a far better answer for my daughter. And I fully intend to give them to her, just as soon as I can reclaim her attention (she wandered off while I was still exploring Mercury).

So, what are you thinking about on this, the 42nd anniversary of the day Neil Armstrong and Buzz Aldrin first walked on the moon?

(Image Credit: Buzz Aldrin walking on the moon on July 20, 1969, courtesy of Wikipedia.)

About Shala Howell

I spent two decades helping companies like Bell Labs, Juniper Networks, and a genetic testing company that was later acquired by CVS translate some of the world’s most complicated concepts into actionable, understandable English. Now I'm working on a much harder problem -- fostering children’s curiosity and engagement in the scientific, artistic, and linguistic world that surrounds them. The first book in my Caterpickles Parenting Series, What’s That, Mom?, focuses on how to use public art to nurture children’s curiosity in the world around them. My next book, Did Dinosaurs Have Belly Buttons?, is currently planned for release in 2018. In the meantime, you can find me blogging about life with a very curious Ten-Year-Old at Caterpickles.com, chatting about books and the writing life at BostonWriters.blog, and tweeting about books, writing, science, & things that make me smile at @shalahowell.
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5 Responses to “Do all astronauts fly in space with just their helmets on?”

  1. Paul says:

    I’m thinking, “Oh crap, I am almost 42 years old.”


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