TPF-I SWG Report - Exoplanet Exploration Program - NASA

D ISCUSSION AND C ONCLUSION
8 Discussion and Conclusions
The goal of NASA’s Navigator program is to find terrestrial planets and to search for life. We must find
potentially habitable planets, (e.g., 0.5 to 10 Earth mass) located in or near the habitable zone of their
parent stars, characterize their physical properties in terms of our growing knowledge of conditions that
might be hospitable for the formation and stable evolution of life, and determine their atmospheric
constituents or surface composition by looking for specific biomarkers (O 2 , O 3 , chlorophyll) or, more
generally, the disequilibrium processes that might be attributable to the presence of life. As outlined in
Chapters 1 and 2, this program is an ambitious one requiring the determination of masses via astrometry
(with SIM PlanetQuest) and the detection of optical photons (with TPF-C) and mid-IR photons (with
TPF-I/Darwin). In addition, TPF-I will address the cradle-to-grave evolution of stellar systems,
specifically; the early evolution of star and planet formation, stellar and planetary death and cosmic
recycling, the formation and evolution of Black holes, and galaxy formation and evolution.
The main areas of focus for TPF-I in the past 3 years have been on architecture selection with emphasis
on reducing sources of systematic noise and on technology development in the areas of starlight nulling
and formation flying. In a 5-year mission, the X-array architecture using four 3.5-m telescopes has the
capability to:
a) Survey at least 150 F, G, K, and nearby M stars with at least three visits each;
b) Make spectroscopic observations of the planets detected around at least 10 stars looking for O 3 ,
CO 2 , H 2 O, and possibly other species that are trace constituents in the Earth’s atmosphere but
which might be abundant in alien atmospheres such as CH 4 and N 2 O;
c) Carry out a program for general astrophysics probing the 3-μm to 20-μm wavelength region with
unprecedented μJy sensitivity and milli-arcsecond angular resolution.
We have also examined in a cursory way the scientific capabilities of a reduced TPF-I mission consisting
of four 3.2-m telescopes on a 36-m boom. While this configuration would be severely limited compared
to the full TPF-I/Darwin mission, because of its limited angular resolution, it would be able to measure
the mid-IR emission of nearby terrestrial planets found with other missions (SIM and/or TPF-C) in a
number of broad-band colors and to look for the broadest spectral lines in a few of the brightest planets. If
terrestrial planets prove to be common, nearby, and bright, a reduced version of TPF-I might be worth
considering as a first probe of the infrared properties of planets.
As outlined in this report a cadre of capable scientists and engineers around the country (and in Europe)
are making steady progress on the precursor science and enabling technologies. Stable nulls deeper
than10 -4 have been achieved with a spectral bandwidth of 32%. Deeper nulls of 10 -6 have been achieved
in narrow laser bandpasses. Simulated planetary signals two million times fainter than a simulated star
have been extracted using the Planetary Detection Testbed. The formation-flying testbeds are developing
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