Saturn's moon Titan may be the best bet for life in the solar system outside Earth, a panel of U.S. scientists said Friday.

A composite view of Titan based on images taken in October 2006.
(NASA/JPL/University of Arizona)

Titan is thought to have methane lakes, methane rain, and a mostly nitrogen atmosphere. So if there is life on the moon, it will be what scientists call "weird," with a very different biochemistry from Earth life, a committee from the U.S. National Research Council said in a release.

"The recent evidence that liquid water-ammonia mixtures may exist in the interior of Saturn's moon Titan suggests that increased priority be given to a follow-on mission to probe Titan, a locale the committee considers the solar system's most likely home for weird life," the Committee on the Limits of Organic Life in Planetary Systems said.

The committee also said that another moon of Saturn, Enceladus, has active water geysers, "raising the prospect that habitable environments may exist there and greatly increasing the priority of additional studies of this body."

Scientists have been too narrow in thinking about the possibility of life in the solar system, and need to consider the potential for life outside the parameters established on Earth, the committee said.

Those parameters include:

• A liquid water biosolvent.
• A carbon-based metabolism.
• A molecular system capable of evolution.
• The ability to exchange energy with the environment. 

This radar image taken in July 2006 shows dark shapes thought to be lakes containing liquid methane.
(NASA)

But studies have suggested that weird life could use different energy sources and have different DNA arrangements from life found on Earth.

"Advances throughout the last decade in biology and biochemistry show that the basic requirements for life might not be as concrete as we thought," said committee chair John Baross, a professor of oceanography at the University of Washington, Seattle.

"The search so far has focused on Earth-like life because that's all we know, but life that may have originated elsewhere could be unrecognizable compared with life here."

Scientists usually assume that life requires water, so Mars — where there's evidence that water was once present — is a favourite planet when there's speculation about extraterrestrial life.  

But ammonia or formamide could also work as biosolvents, the liquids that dissolve substances within an organism, the committee suggested. 

It called for more research into variations in the requirements for life, especially studies to determine if water is necessary for life. "Research should also focus on how organisms break down key elements, as even non-carbon-based life would need elements for energy, structure and chemical reactions," the committee said.

Looking at life in extreme environments on Earth — deserts or the ocean depths — will help in the hunt for Earth-like life in places like subsurface Mars.

"No discovery that we can make in our exploration of the solar system would have greater impact on our view of our position in the cosmos, or be more inspiring, than the discovery of an alien life form, even a primitive one. At the same time, it is clear that nothing would be more tragic in the American exploration of space than to encounter alien life without recognizing it," the report said.

NASA sponsored the report.