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Astronomy 141
Life in the Universe
Prof. Scott Gaudi

Lecture 4: Search for Life on Mars


Key Ideas

Lowell saw evidence for a vast system of canals
--Subsequently shown to be spurious
--But instilled a deep-seeded belief in "Martians"

By mid-century, scientists had shown that Mars:
--Was very cold
--Had a thin CO2 atmosphere
--Had no 'canals'

Viking experiments showed no conclusive evidence for life

The Martian meteorite ALH84001 shows evidence for past biological activity on Mars

Future missions will perform additional tests and may uncover life on Mars


Canals on Mars

William Hershel (1738-1822)
English astronomer
Noted:
--Similar length of day
--Similar axial tilt
--Polar ice caps
Claimed atmosphere
Asserted there was life:

"its inhabitants probably enjoy a situation in many respects similar to our own."

Giovanni Schiaparelli

Director of Milan Observatory

In 1877 claimed to see linear features
--'Canali' = channels or canals

Percival Lowell (1855-1916)
Harvard graduate in math
Came from money

Heard about Schiaparelli's 'canali'

Thought that observations required a superior observatory
Lowell Observatory (opened 1894)

Lowell commissioned an observatory

Sought best site for astronomy

Chose Flagstaff, AZ

Lowell Observatory opened in 1894

Lowell's Canals

Spent two decades observing and mapping Mars

Published first maps in 1895
Also speculated on Martians and their civilization
Imagined canals carried water from poles to arid equator

Other scientists questioned Lowell's claims.
Canals proved to be mostly fictitious.


Lasting Effect on Popular Culture

H.G. Wells novel "War of the Worlds"

Performed on the radio on Oct 30, 1938 by Orson Wells

Many people thought the broadcast was real

Caused considerable panic


Modern Observations

Pre-Mariner (1900-1965)
Mixed opinions

Periodic Darkenings:
Seasonal vegetation?

Cold

10% Earth's atmosphere

Mariner to Viking (1965-1976)

Four missions (Mariner 4, 6, 7, and 9)

Craters, not canals

Surface similar to Moon
Cold and thin atmosphere
Ave. temp. -50 C
Ave. pressure 0.7% Earth

Cannot have liquid water
Little ozone, methane


Viking

Two missions

Each with an orbiter and lander

Viking 1: July 20, 1976

Viking 2: September 3, 1976

Tests for Life
Four tests of Martian soil:
Three direct tests for life
One test for organic material

Three tests for life:
--Pyrolitic release
--Labeled release
--Gas exchange

Looked for exchange of materials
--Photosynthesis (pyrolitic release)
--Metabolism (labeled release and gas exchange)

All three showed positive results!

Test for organic material:
--No detectable organic molecules
--In contrast, Antarctic soils show significant levels of organics (even when they fail the 'life tests')


ALH84001

Four pieces of evidence for biological activity
Existence of Polycyclic Aromatic Hydrocarbons

Carbonate grains have a layered structure similar to those produced by bacteria

Magnetite crystals identical to that found in bacteria on Earth

Small structures that look like bacteria (nanobacteria)

Source of Controversy

There may be abiological explanations for all these observations.

There is some worry about terrestrial contamination

Verdict is still out?


Methane on Mars

2004 scientists announced evidence of methane on Mars

Methane only lasts a few centuries on Mars
--Methane plus Oxygen yields water plus carbon dioxide.

Source of methane?
--Comets, Volcanoes, Life


Future Missions

Phoenix
Launch August 2007
Arrive May 25, 2008

Will land near icy northern pole

Will dig trenches up to 0.5 meters into the ground

Will example the chemical composition

Mars Science Laboratory

Launch Fall 2009
Arrival October 2010

Rover mission

Can collect rock and soil samples

Look for organic compounds and gases indicative of biological activity

And beyond?

Sample return mission

Astrobiology mission

Deep drilling mission

Manned mission?


See A Note about Graphics to learn why the graphics shown in the lectures are generally not reproduced with these notes.

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