Life can exist even in total darkness - study shows

Astronomers have long known about the existence of "stray" planets - worlds ejected from their systems and travelling in total darkness.

Such objects were thought to be too cold for life. But a new study shows: their satellites can maintain suitable conditions.

Details

When a planet is out of its system, the orbits of its satellites can become elongated. Because of this, they constantly experience gravitational "compression and stretching".

This produces internal heat - similar to that seen in Jupiter's satellites, such as Europa.

But on its own, this heat would quickly dissipate into space. The atmosphere plays a key role.

If a satellite has a dense, hydrogen-rich atmosphere, it can effectively trap heat.

At high pressures, hydrogen begins to absorb infrared radiation and prevents the surface from cooling.

As a result:

• heat is retained
• temperature stays stable
• water can exist in liquid form

According to models, such conditions can persist for up to 4.3 billion years - comparable to the age of the Earth.

The main problem is that such objects are extremely difficult to detect.

Even if such a satellite could be found, it would probably not be possible to study its atmosphere any time soon.

Why it matters

The study changes a key idea about the "habitable zone":

• that life can exist without a star
• suitable conditions are possible in total darkness
• there could be many more potential habitable worlds in the Universe

The work also provides new insights into Earth's early atmosphere, which may have contained more hydrogen.

Background

"Wandering" planets are objects ejected from their systems by gravitational interactions. Hundreds of such worlds are now known.

Source

The study by scientists from the Max Planck Institute for Extraterrestrial Physics and the European Space Agency is published in the journal Monthly Notices of the Royal Astronomical Society.