Everything around us lies on different points of a spectrum.

Under the right conditions, the most solid things around us can be evaporated into gas, and even the atmosphere can become solid.

Can you imagine it being so cold that you could bite off a chunk of the atmosphere?

It would be possible, because the only difference between states like gasses, liquids, and solids is the closeness of their molecules. Molecules in a gas are far apart, in a solid they are close together, and in a liquid they are somewhere in-between.

When conditions change, molecules will change their state.

It is heat (i.e. the vibration of molecules), pressure, and the attraction of its molecules for each other that will determine an object’s state.

If you wanted to bite off a chunk of the atmosphere, you'd have to reduce its temperature to −219 °C (−362 °F) when almost the entire atmosphere would be solid. It would form giant glaciers on the Earth’s surface, which would gradually sink underneath the frozen oceans.

These are conditions similar to the dwarf planet Pluto, which has great frozen planes of nitrogen on its surface. When Pluto orbits closer to the warmth of the Sun some of its nitrogen evaporates, forming a thin atmosphere. Eventually, the atmosphere freezes again and falls as snow down to the dwarf planet’s surface.

But the vast majority of the universe is cold, low-pressure, empty space, which is occasionally specked with giant gas clouds called nebulae. From these nebulae come tight concentrations of matter called stars – where conditions are so extreme that everything is boiled into a unique fourth state of matter called plasma.

Plasma sounds rare and exotic but because it’s what stars are made of, it actually makes up the majority of matter in the universe.

It occurs when gas has been heated or electrified, such that its atoms turn into ions and begin to glow. They become sensitive to magnetic fields and look really cool.

It occurs on Earth in a few places, like in very hot fires, lightning strikes, and in special devices like plasma globes, plasma TVs, and in Tesla coils and neon lights like the ones below.

A unique perspective

It is interesting to think that it’s really what we see on Earth that’s rare and exotic. Every day we see a mix of gasses, liquids, and solids in the same place, and one of these is particularly interesting. Liquids.

From a cosmic perspective, it only exists within specks of dust called planets and moons. Most often it’s inside them, where geologic activity melts their insides into liquid.

For planets and moons that meet strict conditions of atmosphere and temperature, liquid can condense on their surfaces. We know that Saturn’s moon Titan has oceans of liquid methane, where it possibly rains as well.

Liquid water has even more stringent requirements. Mars has some frozen water on its surface, but as far as we know it’s only in liquid form deep inside of subterranean lakes under the southern pole of the planet.

But on Earth, it’s everywhere. We have the perfect conditions for liquid water to cover our planet, and because of the special properties of water, they are also the perfect conditions for life.

Our planet maintains this delicate balance. It’s an oasis for life like an island in a vast and empty ocean, and this is primarily because it holds everything that life needs in the right state.

When it comes to space travel, we have to artificially recreate this balance. A spacecraft’s major role is to keep a shell of heat and pressure in space, and it doesn’t always work.

During a test at a NASA facility in 1965, a leaky spacesuit exposed an astronaut to a low-pressure vacuum. He was saved and only suffered an earache, but the last thing he remembered was feeling the saliva on his tongue boiling away.

Jim le Blanc’s almost fatal test. Credit: NASA

Because liquid water can only exist in a narrow band between extremes of temperature and pressure, our search for extraterrestrial life focuses on planets and moons that meet these criteria.

But we may find that life is more varied than we expect, and based on vastly different forms of biochemistry to what we see on Earth. Astrophysicist Carl Sagan once speculated about the possibility of life using other liquids like hydrocarbons, hydrofluoric acid, or ammonia instead of water, and even of life thriving in the upper atmosphere of Jupiter.

If this is the case, then life’s narrow band is expanded considerably, so finding out more about these questions will help us discover whether or not we are alone in the universe.