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Extreme Life 

Does Life Exist Elsewhere in the Universe?

Hubble Space Telescope Deep Field Photograph
Photo Courtesy of Hubblesite.org

Even if only one in ten thousand stars in our Universe offer a habitable world, and even if the chances of life arising on such a world are about the same as winning the California lottery (roughly, one in two hundred million), our Universe would still host about 10 billion inhabited worlds.

What worlds in our solar system are most likely to have life?



Photo Courtesy NASA/JPL-Caltech

Enceladus, which orbits Saturn, is the brightest moon in the solar system. Almost all light that hits its surface is reflected. The surface temperature of Enceladus is -201° C (-330° F).

A partial atmosphere of water vapor has been detected over its south pole. The presence of this atmosphere suggests Enceladus may have an ocean below its icy crust. The presence of a newly discovered geyser on its surface, "Cold Faithful," lends credibility to this conclusion. Cold Faithful's power may be the result of tidal forces caused by Saturn's gravity stressing the surface of the moon while simultaneously providing enough energy to keep water liquefied.

Enceladus - Cold Faithful, Courtesy NASA/JPL



Photo Courtesy NASA/JPL-Caltech

Roughly the size of Earth, Mars has much in common with our planet. However, its surface is much colder and its atmosphere is almost nonexistent. Averaging -63 °C (-81 °F), it has a maximum temperature of 20 °C (68 °F), which is warm enough to liquefy water. If liquid water does exist, it would probably be below deep within the crust, where any potential life would be protected from radiation.



Photo Courtesy NASA/JPL-Caltech

One of Jupiter’s moons, Europa is the smoothest object in the solar system. Its surface is covered with rock hard ice, the product of an average temperature of -163.15 °C. However, scientists think it may have a vast ocean below its thick crust, because of the presence of a weak electromagnetic field.

Europa’s small size and great distance from the sun would ordinarily not result in sufficient heat to maintain a liquid ocean, but scientists believe that its motion within Jupiter’s immense gravitational field could create thermal energy.


Saturn's largest moon, Titan, is the second largest moon in the solar system. It is one of several moons in the solar system with an atmosphere. An orange hazy atmosphere makes it hard to observe the moon's surface features. However, using infrared imaging techniques, scientists have found land features that are suggestive of those found on Earth.

Because Titan is so cold, liquid water would be unlikely to exist. However, life may be able to use a solvent other than water to survive. While water would be frozen solid on Titan, there may be lakes or seas of liquid hydrocarbons.

Titan's thick atmosphere is made of 95% nitrogen, with the remainder being composed of methane and hydrogen cyanide. This primitive atmosphere is possibly similar to that found on Earth when it was in its early stages of formation.

This closeup of Titan, below, reveals two levels of atmosphere.


Photo Courtesy NASA/JPL-Caltech

Cassini recently arrived at Saturn. It sent its Huygens probe out to land on Titan's surface. On the way down it collected audio, visual and scientific data.

Nearby Saturn would not be visible from Titan, as depicted below, because the smoggy atmosphere is not transparent as this painting suggests.

Illustration: Huygens Probe descending onto Titan

Artist's Concept of Huygens Probe Courtesy NASA/JPL-Caltech

How could a probe penetrate the crust of an ice moon?

If the moons most likely to have life on them are covered in ice, how will we be able to penetrate their surface in the search for life?


Illustration of Cryobot

Courtesy NASA/JPL-Caltech

NASA's cryobot, also known as a thermal probe, harnesses the power of gravity to slice through the crust of other planets and moons. Powered by nuclear energy, a cryobot takes advantage of gravity to pull its probe down through thick sheets of ice. NASA's cryobot has already been tested in Greenland and Antarctica.


Illustration of Hydrobot
Courtesy NASA/JPL-Caltech

Cryobots could potentially carry intelligent submersibles, or hydrobots, down to subsurface lakes. The hydrobots would need to be intelligent enough to act autonomously in their search for life and return mission results to Earth. Hydrobots are not currently in a serious planning stage at NASA.

Extrasolar Planets

Illustration: Extrasolar Planets

Astronomers have discovered 156 extrasolar planets to date. Could any of them support the kind of complex life that we have here on Earth?

It's hard to say, as astronomers cannot see the planets directly. However, they know the worlds exist, because they cause nearby stars to wobble. Astronomers also know that most of the planets discovered so far are the size our own Jupiter, or larger, and orbit their stars within the orbital distance of our own Mercury. This means they are probably hot gas giants—places where the intense pressure, heat, and likely lack of liquid water would ensure life would rarely be found on them.

Exhibit Highlights


Touch a fragment of the 100 ft wide asteroid that hit Earth near Winslow, Arizona, creating a crater that is almost a mile across.

Photo Courtesy NASA/JPL-Caltech
The Huygens probe provided extensive data about conditions on Titan.