NASA's mission of space exploration:Some fine points
Roger Blandford's Reference Frame
titled "Exploring the Universe" (PHYSICS TODAY, April 2005, page 10) summarizes many of his concerns
regarding NASA's plans for astronomy and space science in the context of President Bush's vision
for space exploration. As Blandford notes, given the long list of ambitious space telescopes in
NASA's plans, clearly priorities need to be set, and some astronomers worry that "programs with
a connection to life will be favored over fundamental investigations in the inanimate, physical
sciences." The president's vision explicitly calls for NASA to "conduct advanced telescope searches
for Earth-like planets and habitable environments around other stars"1 and categorizes
future NASA missions such as the Space Interferometry Mission and the Terrestrial
Planet Finder as high-priority and life-oriented. Blandford states, "The discovery of extrasolar
planets, 150 and counting, demonstrates that our solar system is unrepresentative with immediate
consequences for the quest for extraterrestrial life." This statement would seem to weaken the
case for placing high priority on SIM and the TPF. However, Blandford draws the
incorrect conclusion that the more than 160 current extrasolar planet candidates2
imply that our solar system is unrepresentative and hence that the search for habitable planets
may be extraordinarily difficult.
Finding an exact analogue
of our planetary system is highly unlikely, given the chaotic processes involved in planet formation,
yet scientists have no reason to believe that planetary systems similar to our own are not commonplace.
The 160 known extrasolar planetary systems were nearly all discovered by Doppler spectroscopy
and photometric transits, methods that strongly favor the detection of gas-giant planets with
short-period orbits. Such planets are indeed likely to prevent the formation and stability of
habitable, Earth-like planets, but they orbit only about 10% of nearby Sun-like stars. For the
remaining 90% or so of such stars, the planetary census takers have not been collecting high-precision
data long enough to detect Jupiter-like planets on the 12-year-period orbits that would herald
the presence of exact solar-system analogues. In fact, the recent discovery of more than half a
dozen super-Earths, planets in the range of 5 to 15 Earth masses, implies that Earth-mass planets
are commonplace.
NASA's Kepler
mission, slated for launch around 2008, will determine the frequency of Earth-like planets through
an exhaustive transit survey of 100 000 stars.3
Blandford replies:
First, in remarking about the ubiquity and diversity of extrasolar planets, my (unstated) point
was that the field of astrobiology had been greatly enriched by these discoveries and that the options
for life developing elsewhere in the universe had been increased, not decreased. More important
than what I think, though, is that many young people and universities had invested in this field.
I apologize if I conveyed the opposite view.
Second, when I wrote this
piece, NASA was a very different organization from the one it is today. For example, I think its mission
statement—"to improve life here, to extend life to there, to find life beyond"—distorted
the science program. Now, NASA's stated mission is "to pioneer the future in space exploration,
scientific discovery, and aeronautics research," which, to me, is a better description of what
NASA should be doing.
Third, I stand by my assertion
that choices will have to be made between proceeding with exciting missions like the Space Interferometry
Mission and the Terrestrial Planet Finder, and with equally compelling investigations
drawn from cosmology and high-energy astrophysics. I believe the scientific community should
be heavily involved in these choices rather than sidelined as NASA has chosen to make it this past
year.
Featured Jobs
