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Objectives
How
Does Life Begin and Develop?
Objective
1
Sources of 0rganics on Earth
Objective
2
Origin of Life's Cellular Components
Objective
3
Models for Life
Objective
4
Genomic Clues to Evolution
Objective
5
Linking Planetary and Biological Evolution
Objective
6
Microbial Ecology
Does
Life Exist Elsewhere in the Universe?
Objective
7
The Extremes of Life
Objective
8
Past and Present Life on Mars
Objective
9
Life's Precursors and Habitats in the Outer Solar System
Objective
10
Natural Migration of Life
Objective
11
Origin of Habitable Planets
Objective
12
Effects of Climate and Geology on Habitability
Objective
13
Extrasolar Biomarkers
What is Life's Future on Earth
and Beyond?
Objective
14
Ecosystem Response to Rapid Environmental Change
Objective
15
Earth's Future Habitability
Objective
16
Bringing Life with Us beyond Earth
Objective
17
Planetary Protection
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Question: Does Life Exist Elsewhere in the Universe?
Effects
of Climate and Geology on Habitability
Objective 12: Define
climatological and geological effects upon the limits of habitable zones
around the Sun and other stars to help define the frequency of habitable
planets in the universe.
The limits of a star system's
habitable zone are determined in part by the stability of liquid water
on the surface of planetary bodies, both instantaneously and over long
time periods, as the parent star luminosity changes. Planetary habitability
also depends on the stability of the planetary system, including the gravitational
effects of large (Jovian-sized) planets or nearby stars on the distribution
and dynamics of potential large impactors. Detection of habitable planets
outside of our own Solar System will rely on spectroscopic observation
of key atmospheric constituents--including water, carbon dioxide, ozone,
and possibly others. Among the factors which affect liquid water's stability
are the mass, composition, and dynamics (including effects of clouds)
of a planet's atmosphere. The development of multidimensional general
atmospheric circulation models--including the effects of clouds--for other
planets will be critical in defining the distribution of liquid water
in the universe.
Implementation
Near to mid-term:
- Conduct a theoretical research
program to model the role of clouds (both CO2 and H2O) on early Mars,
to explore cloud formation, radiative effects, and effects on atmospheric
dynamics, all of which affect the location of the outer edge of the
liquid water region, or habitable zone.
- Study the radiative effect
of water clouds in a dense, runaway greenhouse atmosphere such as may
have existed on Venus, and determine how this influences the location
of the inner edge of the habitable zone.
- Extend these models to include
a broader range of planetary sizes and orbital radii, in order to explore
more fully the role of climate in determining the extent of habitable
zones in other putative solar systems.
- Search for direct, in situ
evidence for liquid water on Mars, along with other surface minerals
(e.g., carbonates and sulfates) that may provide information about long-term
climate evolution.
- Develop better models of how
hydrogen escapes from H2-rich, primitive atmospheres and how this would
have affected atmospheric evolution on the early earth and on other,
Earth-like planets.
- Determine whether the primitive
Earth (and, by extension, other planets) could have developed an organic-rich,
atmospheric haze layer such as that found on Titan, and explore the
consequences of such haze layers for atmospheric and biological evolution.
Future Extensions:
- These models ultimately will
generate a paradigm for planetary habitability to help guide, as well
as be tested by, astronomical observations of extrasolar habitable planets.
The interplay between these climate models and the Mars sample return
analysis program will allow us to determine whether Mars is inhabited
now or whether it may have been inhabited in the past.
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