|
The Ages of Terrestrial Planets
A study by Charles Lineweaver of the University of New South Wales
has determined that terrestrial planets (rocky planets like the
Earth) in the Universe will on average be 1.8 billion years older
than Earth.
The Universe starts off made almost entirely of hydrogen and helium,
the only elements formed in significant quantities in the big bang.
A terrestrial planet cannot form from these elements alone. The
heavier elements (which astronomers call 'metals') are formed in
stars and thus build up slowly as generations of stars are formed
and go through their life. The metallicity must reach a high enough
value for terrestrial planets to form.
However, in cases where the metallicity is too high, it appears
to result in formation of systems with close orbiting giant planets
(hot jupiters). It seems likely that the formation of these systems
would destroy earth-like planets or preclude their formation.Combining
these constraints with estimates of the star-formation and metallicity
history of the Universe, Lineweaver is able to estimate the age
distribution of terrestrial planets. It is found that 74% of terrestrial
planets should be older than Earth.
Life on Earth appeared very soon after the formation of the planet.
If the same is true for other planets, extraterrestrial life could
have had billions of years longer to evolve than it has so far on
Earth.
|