Welcome to Molecular Mondays! Every other Monday, we examine the atoms and molecules that serve as the building blocks of our universe, both in reality and in science fiction. Today we continue our investigation of:

WATER

In my previous Molecular Monday post, I told you about some of the exotic forms of water ice believed to exist on other planets, where pressures and temperatures are radically different than what we’re familiar with here on Earth.

But those seventeen forms of ice were only crystalline ices, ices where the water molecules line up to form neat geometric patterns. It takes energy (heat) for water to crystallize. That may seem counterintuitive, but consider that 0º C is a whole lot hotter than absolute zero.

In the darkest depths of space, it’s too cold for water to crystallize. Instead, water molecules freeze solid in a random, haphazard way. This is called amorphous ice, or sometimes porous ice, and it is believed to be the most common form of water in the universe (even though it hardly ever appears here on Earth, except under laboratory conditions).

When handling amorphous ice, be careful. For one thing, it can react violently to changes in pressure. Here’s a brief video where samples of high density amorphous ice transition into low density amorphous ice due to lowering the pressure.

Also, because amorphous ice has a random structure, microscopic cavities often form between water molecules. That’s why it’s also called porous ice. Other chemicals can get trapped inside these internal pores. Melting the ice (or even adding heat to crystallize the ice) could accidentally release those chemicals, or allow them to mix, with unpredictable results.

In the distant Sci-Fi future where humanity has spread throughout the Solar System and beyond, interplanetary travelers will be dependent on whatever sources of water they can find in space. Appropriate safety measures should be put in place for harvesting water from comets, asteroids, or even small icy moons like Europa or Enceladus. Amorphous ice can be full of unpleasant surprises.

Links

Goddard Lab Works at Extreme Edge of Cosmic Ice from NASA’s official website.

Why Comets Are Like Deep Fried Ice Cream from JPL’s official website.

Supercooled and Glassy Water from Physics Today.

Welcome to Molecular Mondays! Every other Monday, we examine the atoms and molecules that serve as the building blocks of our universe, both in reality and in science fiction.

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At some point, you may have heard in a science documentary or something that in the vacuum of space, liquid water boils and freezes at the same time. So what the heck does that mean?

Maybe it means water behaves something like this:

The chemical in that video is called cyclohexane, but it could just as easily have been any other chemical, including water, that has been brought to its triple point.

In a previous Molecular Monday post, we talked about how water’s freezing and boiling temperatures change as you raise or lower the pressure. At a certain point, when the pressure is low enough, the freezing and boiling temperatures are the same, causing water to freak out.

Since water is trying to be all three states of matter simultaneously, we call this the triple point.

The temperature and pressure in space are well below water’s triple point, precluding any possibility of a liquid state. So if you put liquid water in space, it starts changing into something else. Anything else.  As rapidly as possible.

According to astronauts who’ve watched this happen (i.e.: astronauts who’ve looked out the window after using the space toilet), liquids tend to turn into vapor first, and then the vapor turns into ice crystals. So all those science documentaries should really say that liquid water in space boils then freezes, or rather it boils then desublimates. Although given that these changes occur in a matter of seconds, I won’t be too nitpicky.

I started writing Molecular Mondays with the goal of teaching myself a little chemistry. Chemistry was always my worst subject, but as a science fiction writer, I need to know this stuff. I’ve found that while researching and writing this series, I’ve had to unlearn much of what I learned in school.

Here’s a good example: my teachers told me that the boiling point of water is 100 ºC (212 ºF). That’s it. End of story.

Except it isn’t.

Water boils at 100 ºC if it’s under one bar of pressure (equal to normal atmospheric pressure at sea level). Also, water boils at 100 ºC if it’s pure water. Lower the pressure, and the boiling point drops. Raise the pressure, and the boiling point rises. Adding impurities like salt will also drive the boiling point up. These factors can also affect water’s freezing point.

As a science fiction writer, I spend most of my time (metaphorically speaking) on other planets, with atmospheric pressures often much higher or lower than one bar. And for those rare worlds that do possess liquid water, like Europa, Enceladus, or maybe Mars, that water undoubtedly contains loads of impurities.

As a result, water freezes and boils at very different temperatures throughout the Solar System. In many cases, due to the low or no pressure environments often found in space, water just skips its liquid phase entirely, transforming straight from ice to vapor and vice versa.

Since we live on Earth, I might be willing to forgive my old science teachers for failing to mention any of this space stuff… except even on Earth, the boiling point of water can vary greatly.

At sea level, the boiling point is 100 ºC. Go to Kansas, with a mean elevation of 2,000 feet above sea level, and the boiling point is roughly 98 ºC. That may not seem like a huge difference, but it’s a difference. Climb the Rocky Mountains, reaching a maximum elevation in excess of 14,000 feet above sea level, and the boiling point drops to 85 ºC. Climb Mt. Everest (over 29,000 feet above sea level), and water will boil at only 72 ºC. (Click here for a chart showing water’s boiling point at various altitudes.)

So while 100 ºC may be water’s boiling point under certain specific conditions, it’s hardly the universal standard I was led to believe it to be.

In the next Molecular Monday post, I’ll continue my research on water. I’m pretty sure there are a few more old science lessons I need to unlearn.