Transcript U3A-Mars08 12647KB Nov 18 2013 09:49

SESSION 8
LIFE ON MARS?
LIFE ON MARS?
• The planet has long fascinated people
because of the possibility that it
harbours life
• In the 1890’s Percival Lowell suggested
either past or present intelligent life on
Mars to account for the presence of
canals and seasonal colour changes
• His beliefs had a big following for some
fifty years and imagination ran riot
Shaking hands
with a martian
soon after arrival
Flash Gordon meets with a local Martian in 1938
Martian invader meets the congregation in the
1996 Warner Brothers movie Mars Attacks!
CATCHING UP WITH FICTION
• In 1965 Mariner 4 took the first close-up
images of Mars and found a heavily
cratered landscape but no channels.
• In 1976 the twin Viking missions were
dispatched to Mars specifically to look
for life. They found no such evidence
but discovered that the planet had very
low temperatures, high radiation levels
and a thin atmosphere lacking in
oxygen
HUBBY’S SURPRISE
• In 1996 NASA scientist Everett Gibson
brought home electron micrographs of
a rock taken under high magnification
• His wife Morgan who was a biologist
took one look at the image and asked
“Why have you brought home images
of bacteria?’
• He told her that the rock in question
had come from Mars and had the label
ALH84001
What Morgan saw – a fossil from Mars?
STRANGER FROM MARS
• Gibson had many years experience in
planetary geology having directed a
programme of rock collecting on the
Moon during the lifetime of the Apollo
project
• How could NASA possess a rock from
Mars when there have not yet been any
missions to bring rock specimens back
from the surface of the red planet?
METEORITES
• About 40,000 tonnes of space debris
reaches earth every year and most of
this has come from the asteroid belt
• They date at approximately 4550 million
years, the age of formation of the solar
system
• Occasionally meteorites are found that
have younger ages and they are
believed to have come from one of the
rocky planets, especially Mars, our
nearest neighbour
IMPACTS ON MARS
• To eject Martian rock fragments into
space would require the impact of a
large meteorite powerful enough to
leave a crater at least 10 km in
diameter. Quite a few are known
• Rock types involved would have to be
massive igneous rocks such as basalts
or granites in order to survive the
impact without being pulverized
METEORITE COLLECTING
• More than 7,500 meteorites have been
collected from around the world but
only the larger ones survive passing
through the atmosphere without
burning up
• A favourite collecting place is
Antarctica where dark-coloured
meteorites are readily visible against a
white background of ice and snow
SPECIMEN ALH84001
• The catalogue number indicates that it
was the first specimen to be collected
in the Alan Hills of Antarctica in 1984
• Specimens from Mars can be identified
because compared with other
meteorites they have a high water
content, an abundance of oxygen
bearing minerals and a distinctive
oxygen isotope composition
Meteorite from Mars
METEORITES FROM MARS
• Twelve of the meteorites studied so far
are believed to have come from Mars
• They are called SNC meteorites after
the three principal discovery sites of
Shergotty, Nakhla and Chessigny
• The Nakhla meteorite from Egypt is
reputed to have killed a dog on impact
• Total weight of the many fragments was
about 10 kg
SPECIMEN ALH84001
• When found it weighed 1.9 kg and was
about the size of a large potato
• Its age was determined as 4,500 MY
indicating that it was probably part of
the original crust of Mars
• AT 3,900 MY the rock became cracked
and the fissures were filled with
carbonate, sulphide and oxide minerals
• It contained tiny pockets of trapped air
similar in composition to Mars’s
atmosphere
NASA STUDIES
• The meteorite was studied by McKay
and co-workers and they came up with
five lines of evidence of life on Mars at
the time:
• Carbonate minerals present as
globules look similar to crystal
aggregates produced by bacteria on
Earth
• Structures within globules resemble
bacterial remains found on Earth
NASA STUDIES
• Iron sulphide and oxide minerals
present in forms known to be produced
by bacteria (see next slide)
• Co-existence of minerals in cracks may
indicate non-equilibrium conditions
characteristic of life
• Organic compounds present may have
been produced by living organisms
Magnetic crystals from
the Martian meteorite
magnified a half million
times appear to be
dead-ringers of crystals
produced by bacteria
on Earth
NASA CONFERENCE
• A press conference was held in
Washington on 6 August, 1996 to
announce probable evidence of former
life on Mars
• The media had a field day but much of
the evidence has since been labeled as
inconclusive by other scientists
A field day for the media!
Some examples of front page news in
American newspapers
NAKHLA METEORITE
• It fell to Earth in Egypt 28 June, 1911
and is of basaltic composition. It broke
into many pieces together weighing
about 10kg
• Its age is approximately 1300MY and it
shows evidence of having been altered
by the presence of water at about
1100MY. It was blasted from Mars into
space about 11MY
Fragment of Nakhla meteorite
SIGNS OF LIFE?
• US geologist Fisk found tubular holes
in the meteorite that appear similar to
ones found in volcanic rocks on Earth
• They are 1 to 3 micrometers in diameter
and up to 10 micrometers long
• Norwegian geologists found similar
holes in 3500 MY old basalts and
claimed that they were the earliest
evidence for life on Earth
Tubular holes
in Earth rock
compared with
similar evidence
from the Nakhla
meteorite
METHANE – SIGN OF LIFE?
• In 2004 a German scientist using a very
sensitive spectrometer on board Mars
Express detected very low
concentrations of methane in the
Martian atmosphere
• Strong UV radiation on Mars causes
rapid breakdown of methane so there
has to be a source producing enough
gas to maintain its concentration
METHANE – SIGN OF LIFE?
• On Earth most methane found in the
atmosphere is produced by microbes
• Such microbes survive even in the
Greenland Icecap despite the frozen
state of the medium
• Geologists claim that weathering of the
mineral olivine, common in basaltic
rocks, could be responsible for
producing the levels of methane found
on Mars