There are a few icy worlds in the solar system that have the potential to host life.

Icy Water Worlds That Might Host Life

Alien life may be lurking right in Earth's cosmic backyard. Some of the icy moons of Saturn and Jupiter are known to harbor subsurface oceans that could provide habitable environments.

In the dark, cold sections of the Earth's ocean floor, communities of life-forms survive on the heat and nutrients from hydrothermal vents. Under the ice of Antarctica, scientists have found rich microbial ecosystems.

These discoveries have opened up the possibility that life could also survive in extreme environments on other worlds.

There are five icy moons in our solar system that could potentially host extraterrestrial life.

EUROPA

This icy moon of Jupiter is thought to harbor a liquid-water ocean more than twice the volume of all Earth's oceans. The subsurface sea, which lies underneath a thick layer of subsurface ice, likely remains a liquid because of tidal heating, which (similar to tides on Earth) comes from the gravitational pull of Jupiter.

Other geologic activity in the moon's rocky core could create an additional heat source for life-forms. The ice layer on Europa is more likely at least 10 to 15 miles (15 to 25 km) thick, so getting a look at those life-forms would be extremely challenging. There may be, however, isolated lakes at shallower depths.

NASA has green-lit a mission to orbit Europa and learn more about this potentially habitable world.

TITAN

Saturn's moon Titan might appear hospitable at first glance, because it is covered in rivers, lakes and oceans. Unfortunately, all of them are flowing with liquid ethane and methane, and all known life-forms need water to survive. In addition, the surface temperature on Titan is about minus 292 degrees Fahrenheit (minus 180 Celsikus) — far too cold for life as we know it.

But the active chemistry on Titan has led some scientists to hypothesize about how life could arise there. Living organisms create most of Earth's methane supply, but it's unclear where Tian's methane comes from. The source could be an underground ocean, where temperatures might be warmer.

ENCELADUS

The bluish-gray surface of Enceladus looks too frigid to host life, but under its surface lies a vast ocean. Just like on Europa, it's possible the underground ocean contains a suitable environment for life. Over 100 geysers on the moon's surface vent material from that ocean up and away from the satellite. Analysis of the plumes by the Cassini probe revealed water, ammonia, salts and organics (molecules that contain carbon, the building block for life on Earth).

A proposed mission to Enceladus would send a probe to collect samples from those plumes and analyze them in situ.

GANYMEDE & CALLISTO

Like their siblings, Europa and Enceladus, the Jovian moons Ganymede and Callisto may have subsurface, liquid oceans. But in these cases, the underground seas would be buried under at least 60 miles (100 km) of rock.

These moons are less likely to support life than icy worlds like Enceladus, according to NASA. But the European Space Agency is planning a mission to study the buried oceans of the Jupiter system, with particular emphasis on Ganymede.