Lecture of the Week: Part IV: Astrobiology

The Evolutionary Biology Lecture of the Week for June 12, 2006 is now
available at:

http://aics-research.com/lotw/

The talks center primarily around evolutionary biology, in all of its
aspects: cosmology, astronomy, planetology, geology, astrobiology,
ecology, ethology, biogeography, phylogenetics and evolutionary biology
itself, and are presented at a professional level, that of one scientist
talking to another. All of the talks were recorded live at conferences.

This is the fourth lecture in a summer-long series on the new science of
astrobiology.

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June 12, 2006

Part IV: Astrobiology

New Worlds Imager
Webster Cash, University of Colorado, Boulder
33 min.

"You have to look and be able to see things that other people looked at
and didn't see before. How do you do that? There's two ways. Either you
make a new instrument, and it gives you better eyes, like Galileo's
telescope. And that's a great way to do it, make such a nice instrument
that you don’t have to be so smart, you just look and there it is. Or
you try to internalize it is such a way that it really becomes
intuitive. Working on the right problem is only part of what it takes to
succeed."
— Stephen Chu, Nobel Laureate

Before the time of Galileo, all scientists used the unaided eye to
observe the heavens. When Galileo trained his tiny telescope on the sky,
its magnification gave him the same view as if he had traveled 90% of
the way to his target. With his 10 times improvement in angular scale,
he saw a new view of the universe, and revolutionized astronomy.

In this lecture, Webster Cash proposes a new telescope design that will
take us much further yet again, and is likely to have as revolutionary
an effect. To date, no planet has been seen around another star, even
though the gravitational effects of their presences have been measured.
The planets are fainter than their host stars by a factor of 1 to 10
billion (1:10,000,000,000). If we are ever going to directly image
exoplanets, the glare of the central stars must somehow be suppressed by
at least an equivalent amount.

Cash proposes a startlingly simple idea, The New Worlds Observer, an
orbiting telescope with an accompanying occulting starshade 50,000 km
distant.

Proposing an occulter is not new. The problem is that a simple, round
occulter can actually work to exacerbate the problem, making the central
star seem brighter than it should be through a phenomenon called
"Poisson's Spot."

By 1800, light had been shown to have both particle and wave light
natures, and each view had had its champions. Newton argued that light
acted as it were composed of particles, while Huygens argued its
wave-like nature. In 1818, Augustin Fresnel submitted a paper to a
scientific competition sponsored by the French Academy, deriving the
equations of diffraction of light as it passes around a solid object, if
it were to behave as a wave. His submission led to one of the most
famous stories in science.

Siméon-Denis Poisson, one of the judges of the competition, intensely
disliked the wave theory and quickly pointed that if Fresnel's equations
were true, then there would be conditions in which the diffracted waves
would constructively interfere to form a bright spot at the focal plane
behind the occulter. Poisson considered this result to be so
unreasonable as to disprove Fresnel's equations by itself, with no
further proof necessary. François Arago, another judge, disagreed. Arago
set up an experimental apparatus and quickly demonstrated the presence
of what has now come to be called "Poisson's Spot."

Cash solves the Poisson Spot problem by placing petals of highly
constrained shapes around the edge of his occulter. By doing this, he
breaks up the natural diffraction pattern and theoretically achieves an
astounding 1 in 100 trillion (1:100,000,000,000,000) contrast ratio,
more than enough suppression to quickly see Earth-sized planets 100
light-years distant.

More importantly perhaps, The New Worlds Observer is a simple,
error-tolerant design that could be launched now, if desired. It also
directly leads to second, more extraordinary design, The New Worlds Imager.

In its most advanced form, The New Worlds Imager would be able to
capture actual pictures of planets as far away as 100 light-years,
showing oceans, continents, polar caps and cloud banks. If
extra-terrestrial rainforests exist, they might well be distinguishable
from deserts. The New Worlds Imager gives every appearance of being an
affordable concept with a very practical technology that should allow us
to conduct direct planet imaging in the visible and other wavelengths of
light by 2018.

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