Download March 25, 2011 - RASC – Mississauga Centre

Mississauga Centre RASC
166th Meeting
Speaker's Night
Day:
Speaker:
Friday March 25, 2011
Mary Helen Armour
Search for Life in the Solar System, Where Could They be Hiding?
Mary Helen Armour teaches a course on life in the universe at York University. She spoke about
the search of life in the solar system.
Viking experiments showed us that life is hard to find. First of all, is the location livable and
secondly, is there life? Three things are required for life: an energy source, chemicals of life and
solvent. Usually, the big question is an energy source especially in the outer solar system. A star
has a habitable zone within which liquid water can exist on the surface. Besides sunlight, other
energy sources include radioactivity wherein decay produces heat especially where uranium and
thorium are abundant for long-term energy, internal heat caused by tidal heating or radioactive
decay, and chemical reactions as with deep ocean vents on Earth enabling bacteria to thrive. If
life is to be found on the surface, there needs to be an atmosphere. Other objects can have
underground environments for life but it is difficult to find this life.
Mercury and Venus are bone dry and too hot for life. Farther out, the Earth is teeming with life.
Mars is close enough to the Sun for energy but the big question is water. There is erosional
evidence as well as floodplains. The Viking lander looked for life and found chemical reactions.
Spirit and Opportunity rovers found evidence that the mineral deposits could only have been
produced by liquid water. Phoenix found frozen water and salts in solution. Images show
evidence of buried glaciers. Thus there is evidence of abundant water on Mars. The axis of Mars
wanders and in the past, with greater tilt, water could have been frozen at latitude 30 to 48. Mars
has solar energy, water, carbon dioxide, and methane. Ice on Mars is covered by a few meters of
salt and is easily accessible.
On Earth, methane is produced mainly by life. Methane is also present in the Martian atmosphere
but there it is patchy and changes and breaks down within 100,000 years. It can be formed
geologically by hot water and rock. Whether methane is formed by life or geologic activity, this
implies a dynamic subsurface on Mars. Geologic activity would form other gases but these have
not been found.
For Europa in the outer solar system, the concern for life is not water but energy due to weak
sunlight. The surface is made of ice which is breaking up and re-freezing. There has to be a
source of energy to keep the ice moving. With very few craters, the implication is for a young
surface of perhaps 10 million years. The Galileo probe found evidence of organic chemicals. The
Voyager spacecraft found that Io has more tidal heating but Europa also gets its share and the
energy could produce a liquid ocean above volcanoes similar to Earth where life may have
started in volcanic vents. Europa has a weak magnetic field and it is possible that this could be
caused by a salt water ocean with induction of the magnetic field by Jupiter. A Europa mission
is a priority for NASA and the ESA. This could take the form of an orbiter or lander or even a
drill to get below the ice. A lander could look for amino acids but there is a concern about
contamination (that is why the Galileo spacecraft crashed into Jupiter).
Ganymede is mostly covered by thick ice and has a magnetic field indicating a possible salty
ocean beneath. There is a "resurfacing pattern" but not much tidal heating although being large,
the moon can have radioactive heating. It would be difficult to go deep to look for life.
Titan, the largest moon of Saturn, is cold being far from the Sun. It has a thick atmosphere with
90% nitrogen and significant amounts of methane, argon, ethane and other carbon compounds.
The surface has liquid methane. Compared to Earth, the big difference is temperature. UV light
breaks up the methane and ethane into a soup of organic molecules. Water ice acts like rock and
produces cryovolcanoes. Because of very cold temperatures chemical reactions and evolution of
possible life would occur slowly. Radioactivity and tidal heating would produce some energy for
surface life. Titan has stable bodies of liquid (methane/ethane) on its surface and a hydro cycle as
on Earth (water). It has conditions similar to the early Earth and it is interesting to study its
composition and chemical reactions.
Enceladus is a small satellite of Saturn. The Cassini spacecraft found jets of water spewing out
containing carbon dioxide, methane ethane and salt. Various possibilities for this include an
ocean of water, ice sublimation, or water gassing through pockets in the ice and jetting out after
accumulating in pockets. There has to be a source of energy such as tidal heating, radioactivity,
or ice under high pressure. This can be an environment for life.
We are finding more and more niches in the solar system where life would be able to exist.
Chris Malicki, Secretary