In this section: Mars | EUROPA | Titan Europa is an icy moon that revolves around Jupiter The temperature on the surface is a chilly -170ºC But this inhospitable planet may harbour an underground ocean of liquid water - one of the essential ingredients for life

A frozen world?

Europa is about the same size as our Moon. At first glance, it looks like a dead, frozen wilderness. The entire surface is cloaked in a layer of ice.

Yet there may be more to Europa than meets the eye. Photographs of the moon taken by the Galileo probe revealed some unusual features in the ice. A complex web of lines criss-cross the globe.

Explore the surface of Europa further.

There is only one other place in the Solar System with similar features - the frozen Arctic seas on Earth. Could the icy surface of Europa be floating on a vast liquid ocean, just like the Arctic icebergs?

Could Europa's surface hide an underwater ocean?

Could Europa's ocean support life?

Jupiter's moon should contain all the chemicals necessary for life to begin. All that is missing is liquid water. So if there is an ocean beneath the surface of Europa, it may contain life.

What are the ingredients for life?

But in order to create life, you also need heat. If a liquid ocean exists, there must be a heat source stopping it from freezing over. The ice that covers the surface is probably too thick to allow sunlight through. So what keeps Europa warm?

Underground heating

Europa is just one of many moons that revolve around the planet Jupiter. Jupiter's huge gravity holds it in orbit. But Europa also feels a pull from the other moons around the planet. Different forces, all pulling in different directions, yank Europa's surface out of shape as it travels through space. These are called 'tidal forces'.

These tidal forces heat up the moon's core. If the forces are strong enough, then the core could heat up enough to melt the frozen water surrounding it.

It's even possible that the ocean floor may contain hotspots called 'hydrothermal vents'. These are cracks in the ground that spout warm, nutrient-rich water. Hydrothermal vents on Earth harbour many simple life-forms. Could Europa be as fertile?

Hydrobots could explore the oceans of Europa

Exploring Europa

In 2008, NASA plan to launch the Europa Orbiter - a probe that will explore this mysterious moon. It will scan the surface using radar, to locate where the ice is thinnest. This information will be used to plan the landing sites for future missions. Robotic probes will be sent to drill down through the ice to look for life in the water below.

Explore Saturn's moon Titan for signs of life