How Does Life Begin and Develop?
Objective
1
Sources of 0rganics on Earth
Objective
2
Origin of Life's Cellular Components
Objective
4
Genomic Clues to Evolution
Objective
5
Linking Planetary and Biological Evolution
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
Question: Does Life Exist Elsewhere in the Universe?
Origin
of Habitable Planets
Objective 11: Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars, especially the habitable ones.
Because of our working assumption that life is a planetary phenomenon, we must understand the planet formation process. Astronomers must determine, in a statistically valid manner, the distribution of planets and planetary orbits and masses -- around a range of star types having a range of ages. Specifically, astrobiology is most concerned with habitable planets, defined as those where liquid water can exist on the surface. Other types of bodies, for example Jupiter's moon, Europa, might have subsurface liquid water and perhaps subsurface life as well, but the life zones on such bodies cannot be examined remotely in the way that surface biospheres can. The size and location of this zone varies with the type of star and its age. A multi-pronged program should be mounted to detect habitable planets in sufficient numbers so as to understand their distribution, and help guide the development of future large spaceborne interferometers -- the technique of choice for finding (and, perhaps, characterizing) distant planetary bodies.
Astrobiologists must also create theoretical models of the processes that lead to the origins of habitable planets, to understand the provenance of the water, minerals, and organics that permit the origin and early evolution of life. Analyses of meteorites will continue to help us constrain these models.
Implementation
Near to mid-term:
- Conduct theoretical modeling
of the planetary formation process, and catalog the conditions that
lead to habitable planets. Incorporate meteoritical studies of aqueous
alteration of primitive bodies as in-situ boundary conditions on these
models.
- Conduct ground based studies
to search for the smallest planets that can be detected around a variety
of stellar types. Utilize a variety of techniques, including astrometry
(Keck and Large Binocular Telescope interferometers, plus others), radial
velocity searches, and eclipse photometry, to carry out sustained searches
for habitable planets. This will lead to solutions for key technological,
and data analysis problems facing larger spaceborne systems.
- Carry out eclipse photometry
or alternative techniques that will characterize the distribution, sizes,
and orbits, of planets surrounding a wide variety of star types, with
adequate statistics to establish the properties of the planet forming
process, down to and including terrestrial size planets in the habitable
zones of their stars.
- Coordinate efforts with existing
and planned facilities to study the process of planetary system formation:
SIRTF and SOFIA to inventory the number and composition of small bodies
in the Solar System, and to study protoplanetary disks in the Galaxy;
SIM to accurately characterize the dynamics of planetary systems identified
by the survey mission. o Simulate in the laboratory the formation, growth,
and evolution of interplanetary grains and organics that contribute
directly to planet formation.
- Develop the criteria for, and a catalog of potentially habitable systems.
Future extensions:
- Construct coupled cosmochemical/astrophysical
evolution models of growing planetesimals and early planets that can
serve as boundary conditions for the origin of life. This will lead
to understanding aspects such as the influence of early core formation
and metal segregation, and giant impacts (as perhaps controlled by different
configurations of giant planets) on thermal, oxidation, and atmospheric
state.
- Contribute these research findings to the development and flight of TPF to image nearby planetary systems and take global spectra of planets in the habitable zones.