Astrobiologists hope to
find life elsewhere in the universe, or possibly even in our own cosmic neighborhood, the solar system. Their efforts are usually
concentrated on worlds such as the planet Mars, or icy moons like Europa. However, there are other, less conventional
locations in the solar system where scientists think life may be found.
At
the International Society for the Study of the Origin of Life conference in
Florence, Italy, Joop Houtkooper
from the University of Giessen divulged a theory that life could have
originated on the
asteroid Ceres.
The
distant world Ceres, the smallest known dwarf planet in the solar system, lies
within the asteroid belt. It was called a planet after its discovery in 1801, then later downgraded to asteroid status. With the latest
planet definition from the International Astronomical Union, the round object
is now considered a dwarf planet. Is there a chance that this exotic world is
home to extraterrestrial organisms?
"This
idea came to me when I heard a talk about all the satellites in the solar
system that consist of a large part of ice, much of which is probably still in
a liquid state," says Houtkooper. "The total
volume of all this water is something like 40 times greater than all the
oceans on Earth."
This
reminded Houtkooper of a theory about how life
originated. Organisms may have first developed around hydrothermal vents, which
lie at the bottom of oceans and spew hot chemicals. Many icy bodies in our
solar system have rocky cores, so they may have had or still have hydrothermal
vents. Houtkooper realized, "if life is not unique to
the Earth and could exist elsewhere, then these icy bodies are the places where
life may have originated."
Looking
at the evidence
Early
in the history of the solar system was a period known as Late Heavy Bombardment,
a turbulent time when cataclysmic asteroid impacts were common. If there was
life on Earth before this dangerous era, it was most likely eradicated and had
to begin again after much of this cosmic debris had cleared out of the inner solar
system. Interestingly, evidence indicates that Ceres avoided being pummelled by
devastating impacts during this time. If it had been bombarded, it would have
completely and forever lost its water mantle, as its gravitational force is too
weak to recapture it. This is probably what happened to the asteroid Vesta, which has a very large impact crater and no water.
"The
evidence points to Ceres having remained relatively unscathed during the Late
Heavy Bombardment," states Houtkooper. He says this
means Ceres still could have "a
water ocean where life could have originated early in the history of the
solar system."
This
leads to an interesting hypothesis. If the Earth was sterilized by colossal
impacts, but Ceres hosted life which survived, could the dwarf planet have
reseeded our world with life, via rock fragments that chipped off Ceres and
then crashed into Earth? Are all organisms on Earth, including humans,
descendants of Ceres? This is an idea that Houtkooper
had to pursue.
"I
looked at the different solar system bodies which either had or currently have
oceans," he explains. "The planet Venus probably had an ocean early in its
history, but the planet's greater mass means that more force is needed to chip
off a piece of the planetary crust and propel it in the direction of the Earth.
Smaller objects like Ceres have lower escape velocities, making it easier for
parts of it to be separated."
Houtkooper then
calculated the orbital paths of candidate planets, moons and asteroids to see
which were in the best positions to have pieces successfully reach the Earth,
without being intercepted by other objects. Ceres fared favourably in these
calculations.
Life
on Ceres
Finally,
Houtkooper considered the possibility of organisms
still being present on Ceres. "In the ocean, there could be life," he suggests.
"On the surface, it would be more difficult. But there are some possibilities.
There could be hydrogen
peroxide-based life, able to withstand the low temperatures." It's not
currently known whether hydrogen peroxide is present on Ceres, but nothing
rules it out, either.
The
thought of Earth being seeded with life from Ceres and creatures existing there
today is certainly fascinating, but Houtkooper admits
that it is more science fiction than science fact until evidence can be
provided. This is naturally difficult to obtain, as Ceres is a small and
distant world. Even the best current images contain very little detail, and
just show that there are some surface features; what these features are exactly
is a mystery. Spectral analyses indicate the presence of clay-like minerals,
and Ceres' slightly flattened shape is what we would expect from a world with a
rocky core below a layer of water or ice. Ceres is a dwarf planet with many
secrets.
Fortunately,
this will soon change thanks to NASA's
Dawn mission. Launched in 2007, the probe is due to arrive at Ceres in
2015. Once there it will shed light on the mysterious world, and perhaps take
photographs of geysers of water erupting from the surface. Its close-up view
could indicate whether Ceres really does have the potential for life.
advertisement
