# Mars question

**URL:** <https://boards.straightdope.com/t/mars-question/453605>\
**Category:** Factual Questions\
**Created:** [June 20, 2008, 5:19pm UTC](https://boards.straightdope.com/t/mars-question/453605 "2008-06-20T17:19:49Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\
**Post date:** [June 20, 2008, 5:19pm UTC](https://boards.straightdope.com/t/mars-question/453605/1 "2008-06-20T17:19:49Z")

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Why would frozen water on Mars vaporize after it’s exposed?

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**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\
**Post date:** [June 20, 2008, 5:24pm UTC](https://boards.straightdope.com/t/mars-question/453605/2 "2008-06-20T17:24:14Z")

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Sublimimation, the same thing that makes dry ice vaporize instead of melt under Earth condition.

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**Author:** ![Jas09](https://avatars.discourse-cdn.com/v4/letter/j/d07c76/32.png) [@Jas09](https://boards.straightdope.com/u/Jas09)\
**Post date:** [June 20, 2008, 5:26pm UTC](https://boards.straightdope.com/t/mars-question/453605/3 "2008-06-20T17:26:23Z")

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I believe it is because of the extremely low atmospheric pressure (something like 1% of Earth’s pressure). At pressure and temperature below the triple point of water, it will sublimate rather than melt.

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**Author:** ![nofloyd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nofloyd/32/2870_2.png) [@nofloyd](https://boards.straightdope.com/u/nofloyd)\
**Post date:** [June 20, 2008, 5:42pm UTC](https://boards.straightdope.com/t/mars-question/453605/4 "2008-06-20T17:42:30Z")

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Don’t regular ice cubes in a standard freezer slowly sublimate? I’ve come across long, long unused ice cube trays with mini cubes in the bottom. I’m sure they didn’t go in with that little water in them.

If this is due to a different process, enlighten me.

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [June 20, 2008, 6:45pm UTC](https://boards.straightdope.com/t/mars-question/453605/5 "2008-06-20T18:45:07Z")

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[QUOTE=nofloyd]  
Don’t regular ice cubes in a standard freezer slowly sublimate?  
[/QUOTE]

Yep. Let them go long enough and they’ll disappear entirely.

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**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\
**Post date:** [June 20, 2008, 6:53pm UTC](https://boards.straightdope.com/t/mars-question/453605/6 "2008-06-20T18:53:20Z")

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Sublimation takes place much faster (than in your freezer) as you lower the pressure. That’s how they do freeze-drying. You freeze something, then pull a vacuum on it and the ice sublimes out. Mars isn’t as good as the vacuum you pull in a lab (or a freeze-dry plant), but it’s a better vacuum than your freezer, so water disappears faster from stuff left out on Mars than in your ice cube tray.

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [June 20, 2008, 8:10pm UTC](https://boards.straightdope.com/t/mars-question/453605/7 "2008-06-20T20:10:06Z")

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[QUOTE=CalMeacham]  
Mars isn’t as good as the vacuum you pull in a lab…  
[/QUOTE]  
That depends on whether the person who used the lyophilizer ahead of you bothered to fill the cold-trap. 😉