HIGHLIGHTS

Ice Planets are frozen balls
of ice.
They may harbour deep,
dark oceans.
Some have volcanoes that
spew ice crystals!
Ice can have different colours:
white, pink, red, or blue.

ATLAS

Link to: ATLAS – ICE
for image ideas

Bundle up for a trip to the big chill. If you like cold winters, this place is for you. These freezing, rocky worlds are permanently covered by a thick sheet of ice. 

Ice Worlds come in various levels of iciness. Some are frozen nearly all the way through to their cores, others are enveloped by a thin shell of ice that is floating on a subsurface ocean. Whether ice worlds are solid balls of ice or ice-covered ocean worlds depends on how much heat they hold. Heat energy can radiate up from the planet’s radioactive core and keep its interior from freezing for billions of years (uranium’s half-life is 4.5 billion years – about the age of the Earth!). The larger and hotter the core, the deeper the ice world’s ocean. An effect called “tidal heating” is another way to keep water liquid. Jupiter’s moon Ganymede is an example of this process: Ganymede is sandwiched between Jupiter’s massive gravitational pull and the gravitational influence of its sister moons Io, Europa, and Callisto which orbit nearby. The constant squeezing and stretching of the competing gravitational fields heat up Ganymede’s core enough to melt its interior, resulting in an ice world that harbors a massive subsurface ocean of liquid water. 

However thick the cryosphere is (that’s what the icy shell is called), ice worlds’ oceans are excellent environments to harbour life. But what about the planet’s icy surfaces? They may be much too cold to host life, but they do offer some amazing vistas. We have quite a few ice worlds right here in our Solar System to provide us with some examples. Saturn’s moon Enceladus and Neptune’s moon Triton, for example, feature cryovolcanos. These are volcanoes that don’t spew lava into their atmosphere but massive plumes of ice crystals. On Enceladus, the cryovolcanoes eject pristine white water ice over a terrain covered with large, bright blue rifts called “tiger stripes.” Some of the ice plumes are so massive that they escape the moon’s gravity and feed Saturn’s rings. On Triton’s south pole the ejecta from massive nitrogen geysers create smudges on fields of pink ice. Jupiter’s moon Europa is covered with a crackled frozen terrain where “rafts” of ice float on a rust-coloured ocean.

The dwarf planet Pluto can also be considered to be an ice world. The New Horizons spacecraft took amazing pictures of the heart-shaped terrain that is now called Sputnik Planitia. It contains frozen nitrogen, carbon monoxide, and methane. The methane ice reacts with the Sun’s UV light creating compounds called tholins that give Pluto’s heart its reddish hue. New Horizons also discovered the “bladed terrain” that contains structures as tall as skyscrapers that are made almost entirely of methane ice.

Ice Worlds are fascinating places to explore – both above and below the ice. Here are a few real-life examples:

OGLE-2016-BLG-1195Lb:
Like Earth, but in a Freezer

This Earth-sized planet orbits a tiny, faint star at the same distance that the Earth orbits the Sun. But because the star is so dim and cool, this planet is likely to be an ice-covered, frozen world. In fact, this could be the coldest exoplanet discovered to date!
Find out more about OGLE-2016-BLG-1195Lb

Gliese 436b:
The “Burning Ice” Planet 

This strange world is enveloped by an exotic form of water-ice known as “Ice-X.” This variant of ice isn’t cold, though, it is blisteringly hot. How is this possible? Scientists suggest that the immense gravity of the planet is so strong that it keeps the water in its atmosphere from turning into steam. 
Find out more about Gliese 436b

Europa: Jupiter’s Icy Moon May Harbour Life

This frozen world is covered by a crackled, icy shell that hides a vast ocean of liquid water. In fact, Europa contains twice as much water as all of Earth’s oceans combined! The Hubble Space Telescope also found evidence of a tenuous oxygen atmosphere. Could this icy moon harbour life?
Find out more about Europa

LINK: LIFE UNDER THE ICE
VIDEO: FROZEN BUG RETURNS TO LIFE

HABITABILITY

The surface of an ice world may resemble a frozen hellscape, but the chances of life developing there are actually fairly good if you go underground. The subsurface oceans beneath an ice world’s icy crust offer an excellent chance of hosting life. Here on Earth, scientists have discovered tiny organisms like algae and diatoms in Antarctica that are perfectly happy living underneath the ice. In the depths of the Gulf of Mexico methane ice worms make their home.

However, an ice world’s frozen shell may be many kilometres thick and block out nearly all sunlight, so any organism living in a subsurface ocean could not rely on photosynthesis. Instead, they would probably absorb nutrients directly from the environment, a process called chemosynthesis. There may also be another source of light and heat: underwater volcanoes could spew lava into the frigid waters. On Earth, underwater volcanic vents are host to many ancient organisms such as tube worms and yeti crabs, which love living in the near-boiling waters. In fact, scientists propose that life on Earth may have started near such a volcanic vent.

STORY IDEAS

The heat from the volcanic vents could create tunnels in the ice. Imagine a warren of interconnected shafts, a city in the depth of the cryosphere. Who may live there? Would the inhabitants continue to burrow further? Where to?

In this dark environment, life forms would probably experience their world in the infrared and have evolved heat-sensitive organs. They may also sense their world by touch. What may these organs look like?

How would life in a subsurface ocean communicate? Sound travels very far in water, think of whale and dolphin songs. Would your lifeform sing? Eels and sharks sense electricity. Electric pulses could both be a language and a weapon. Many deep water organisms glow in the dark, this could also be a form of communication.

Inhabitants of a subsurface ocean would never have seen the sky. How would they understand the universe and the world on which they live?

The ice sheet covering the subsurface ocean may not be equally thick everywhere. What if there was a thin spot where you could poke through? What would happen if a subsurface lifeform suddenly found itself on the surface? 

What if you landed on the surface of an ice world? Would you explore its glaciers, ice caves, and endless windswept fields of snow? What would happen if you got too close to a cryovolcano? Would you drill a well and see what hides below the cryosphere?