Enceladus, Image courtesy of NASA, public domain.
Joel Kontinen
When the creation account in Genesis is discarded, scientists have a find novel ways to discover where life came from. The Earth's biosphere contains all the known ingredients necessary for life for instance liquid water, at least one source of energy, and an inventory of biologically useful elements and molecules.
But the recent discovery of
possibly biogenic phosphine in the clouds of Venus,
Reminds us that at least some of these ingredients exist elsewhere in the solar system too. Here are the other most promising locations for extraterrestrial life.
Mars
Mars is one of the most Earth-like worlds in the solar
system. It has a 24.5-hour day, polar ice caps that expand and contract with
the seasons, and a large array of surface features that were sculpted by water
during the planet's history.
The detection of a lake
beneath the southern polar ice cap and methane in the Martian atmosphere (which
varies with the seasons and even the time of day) make Mars a very interesting candidate for life.
Methane is significant as it can be produced by biological processes. But the
actual source for the methane on Mars is not yet known.
It is possible that life may
have gained a foothold, given the evidence that the planet once had a much more benign environment. Today, Mars
has a very thin, dry atmosphere comprised almost entirely of carbon dioxide.
OUND
Europa
Europa is
slightly smaller than Earth's moon and orbits the gas giant at a distance of
some 670,000km once every 3.5 days. Europa is constantly squeezed and stretched by the competing
gravitational fields of Jupiter and the other Galilean moons, a process known as tidal
flexing.
The moon is believed to be a geologically active world, like the Earth,
because the strong tidal flexing heats its rocky, metallic interior and keeps
it partially molten.
The surface of Europa is a vast expanse of water ice. Many scientists think
that beneath the frozen surface is a layer of liquid water — a global ocean —
which is prevented from freezing by the heat from flexing and which maybe over
100km deep.
At
the bottom of this ocean world it is conceivable that we might find hydrothermal vents and ocean floor
volcanoes. On Earth, such features often support very rich and diverse
ecosystems.
Like
Europa, Enceladus is an ice-covered moon with a subsurface ocean
of liquid water. Enceladus orbits Saturn and first came to the attention of scientists
as a potentially habitable world following the surprise discovery of enormous geysers near the moon's south pole.
These jets of
water escape from large cracks on the surface and, given Enceladus' weak
gravitational field, spray out into space. They are clear evidence of an
underground store of liquid water.
Not only was water detected in
these geysers but also an array of organic molecules and, crucially, tiny
grains of rocky silicate particles that can only be present if the subsurface
ocean water was in physical contact with the rocky ocean floor at a temperature of at least 90˚C. This is very strong evidence for the existence of
hydrothermal vents on the ocean floor, providing the chemistry needed for life
and localized sources of energy.
Titan
Titan is the largest moon of Saturn and the only moon
in the solar system with a substantial atmosphere. It contains a thick orange
haze of complex organic molecules and a methane weather system in place of
water — complete with seasonal rains, dry periods and surface sand dunes
created by wind.
The atmosphere consists mostly
of nitrogen, an important chemical element used in the construction of proteins
in all known forms of life. Radar observations have detected the presence of
rivers and lakes s of liquid methane and ethane and possibly the
presence of cryovolcanoes — volcano-like features that erupt liquid water
rather than lava. This suggests that Titan, like Europa and Enceladus, has a
subsurface reserve of liquid water.
At such an enormous distance
from the Sun, the surface temperatures on Titan are a frigid -180˚C — way too
cold for liquid water. However, the bountiful chemicals available on Titan has
raised speculation that lifeforms — potentially with fundamentally different
chemistry to terrestrial organisms — could according to
evolutionists exist there.
Dorrian, Gareth. 2020. The four most promising worlds for alien life in the solar system. Live Science. 18 September.
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