Transcript Search for Life in the Universe

Announcement
• NO CLASS on Thursday, October 27
• Amos Yahil (instructor) will not hold his office
hour on November 1
• Steve Gindi (TA) holds his office hours as usual
• The regular office hours are:
– Amos Yahil:
– Steve Gindi:
7/20/2015
Tu 11-12, ESS 461
Tel: (631) 632-8224
Th 3-4, Physics D-116
Tel: (631) 632-4713
AST 248, Fall 2005
1
Search for Life in the Universe
Chapter 6
Life in the Solar System
7/20/2015
AST 248, Fall 2005
2
Outline
• Environmental Requirements for Life
– Elements
– Energy
– Water
• Exploring the Solar System
– Methods of Observation
– Telescopes
– Robotic Spacecrafts
• Biological Tour of the Solar System
–
–
–
–
Moon and Mercury
Venus
Jupiter and Jovian Planets
Small Moons, Asteroids & Comets
7/20/2015
AST 248, Fall 2005
3
Elements
• Most common elements on Earth (96% total): O,
C, H & N
• After H and He, they are also the most common
in the universe
• Planetessimals cannot be formed with H (except
as H2O) and He
• C essential for long organic molecules
• Some organic compounds can only be formed in
an atmosphere or an ocean
 Atmosphere and ocean are reasonable
requirements
7/20/2015
AST 248, Fall 2005
4
Energy
• Sunlight:
– Decreases as the inverse square distance
• Electrical:
– Lightning in atmospheres
• Chemical:
– Abundant, but needs mixing in atmosphere or liquid
– Earth: plenty of water and atmosphere
– Mars and Venus: still enough internal heat for surface
or subsurface chemical reactions
– Jovian moons: plenty of ice and tidal heating in the
ones closest to the planets, e.g., Io and Europa
7/20/2015
AST 248, Fall 2005
5
7/20/2015
AST 248, Fall 2005
6
Water
• Alternative liquids at colder temperatures:
– Ammonia (NH3): -78C  -33 C
– Methane (CH4): -182C  -164 C
– Ethane (C2H6): -183C  -89 C
• Reactions slower at lower temperatures
• Density decreases with decreasing
temperature below 4C  floating Ice
• Polar molecule: dissolves chemicals better
7/20/2015
AST 248, Fall 2005
7
Methods of Observation
• Human exploration:
– Greatest benefit
– Greatest danger
• Robotic spacecraft:
– Close by observations
– Collect samples
– Leave a station
• Telescopes:
– Ground based
– In orbit around the Earth
7/20/2015
AST 248, Fall 2005
8
Telescopes
• More light
–
–
–
–
Large aperture
Longer exposure
Other wavelengths
Long-term time dependence
• Imaging
– Sensitivity
– Resolution
• Spectroscopy
– Temperature from broad-band spectroscopy
– Temperature, density, pressure, velocity from spectral
lines (absorption and emission)
7/20/2015
AST 248, Fall 2005
9
7/20/2015
AST 248, Fall 2005
10
7/20/2015
AST 248, Fall 2005
11
7/20/2015
AST 248, Fall 2005
12
7/20/2015
AST 248, Fall 2005
13
7/20/2015
AST 248, Fall 2005
14
Robotic Spacecrafts
• Flyby:
– Least energy  lowest cost
– Gravitational boost to reach other planets
– Short duration
• Orbiter:
– More energy  higher cost
– Longer duration
• Probes and landers:
– Probes: death-throe information from orbiter
– Landers: often capable of roaming
• Sample return:
– Blast-off  highest energy
– So far only from the Moon (Soviet Union)
7/20/2015
AST 248, Fall 2005
15
7/20/2015
AST 248, Fall 2005
16
7/20/2015
AST 248, Fall 2005
17
7/20/2015
AST 248, Fall 2005
18
Moon and Mercury
•
•
•
•
Small: internal heat not important
No atmosphere
No liquids
Moon: may have ice at the bottom of polar
craters that are perpetually in shadow
• Mercury:
– Close to the Sun, so little original water
– Water from bombardments hard to keep
– High density: giant early bombardment removed
mantle and crust, where most water would have been
7/20/2015
AST 248, Fall 2005
19
7/20/2015
AST 248, Fall 2005
20
Venus
• Hell of the Solar System
– Temperature: 450C (850F)
– Pressure: 90 atmospheres
– Atmosphere also contains concentrated sulfuric acid and other
harmful chemicals
• Runaway greenhouse effect
– Atmosphere: 96% CO2 because there is no way to remove it
– Oceans: too hot today for liquid water
– Plate tectonics: apparently none today
• Past life on Venus?
– Oceans around 4 byr ago?
– Maybe, but the evidence is gone
– Cratering shows the surface to be ~1 byr old (volcanism)
7/20/2015
AST 248, Fall 2005
21
Jupiter and Jovian Planets
•
•
•
•
Composition: solar
No solid surface
Water at a depth ~100 km
Strong winds and vertical circulation: no
stable life at any layer of the atmosphere
• Large buoyant creatures: could avoid
circulation, but how would they be formed?
• Other Jovian planets (Saturn, Uranus and
Neptune): same problems
7/20/2015
AST 248, Fall 2005
22
Small Moons, Asteroids & Comets
• All: too small to keep liquid water
• Comets (also Pluto and 2003 UB313, the
10th planet): in permanent freeze
• Complex organic molecules: are found in
both asteroids and comets
• Early life?: no evidence, but not ruled out
• Small moons, e.g., moons of Mars: similar
to asteroids
7/20/2015
AST 248, Fall 2005
23
7/20/2015
AST 248, Fall 2005
24