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Wednesday July 6th 2011


SETI: The Solar Sail Perspective

I love what Dan Wertheimer, a Berkeley astronomer and one of the powers behind the SETI@Home distributed computing project, told a session at the recent AAAS meeting in San Diego. Wertheimer was talking about the possibility of using the Sun’s gravitational lens for SETI purposes, and as quoted by Alan Boyle, said that such an observatory could “read the license plates on an extrasolar planet.” That reminded me of Claudio Maccone’s whimsical but mind-boggling remark at the interstellar conference in Aosta last July, which went in much the same direction. What could lensing do? “We could see the roads of their cities. We could see the cars they are driving.”

Drake has made the case for using the Sun’s gravitational lens for SETI purposes for a long time now, and he repeated it at the TED 2010 conference in Long Beach. As to Maccone, he has long championed the FOCAL mission to the gravitational lens that would exploit the fantastic magnifications available at 550 AU and beyond. But it was Drake who first acquainted him with the topic back in 1987 at a conference on Lake Balaton in Hungary. Maccone then worked hard on both the equations and the mission possibilities, submitting a proposal to the European Space Agency in 2000 that the agency chose not to finance, although he was complimented for his vision.

Image: IAA Secretary General Jean-Michel Contant (left) with Frank Drake (center) and Claudio Maccone. Taken in London at the Royal Society Meeting of January 25-26, 2010. Credit: Claudio Maccone.

SETI and the gravitational lens make for fascinating possibilities. The 1992 Conference on Space Missions and Astrodynamics which Maccone led in Turin was the first time I am aware of that scientists and engineers began to study the possibilities of a mission. Solar sails were the propulsion method of choice, and Italy was the home of considerable work on sail concepts at the time, beginning with Quasat, a concept coming out of aerospace firm Alenia Spazio which would have been an inflatable radio telescope in Earth orbit. Quasat was never launched, but Maccone continued studying inflatable technologies with applications to extrasolar studies.

At one point, working with Jean Heidmann, Maccone suggested two kinds of FOCAL mission, one that would target astrophysical objects of interest, to be called ASTROsail, the other to study suspected artificial radio signals and to be called SETIsail. The later Aurora Project was conceived as a somewhat less ambitious solar sail attempt to reach the heliopause, with results of preliminary studies being presented at the International Academy of Astronautics meeting in Turin in 1996. Both Giovanni Vulpetti and Giancarlo Genta offered up impressive analyses of Aurora.

But back to Drake, who as the first SETI experimentalist (through his Project Ozma efforts in 1960) can be considered the godfather of the discipline. He and Nathan Cohen (Boston University) presented the case for using the gravitational lens for SETI at the 1987 bioastronomy conference in Hungary referenced above, and both have gone on to write non-technical accounts of lensing and its possibilities for SETI. SETIsail, meanwhile, grew from a targeted SETI mission to the lens to the ongoing FOCAL study, which could be used for many observations besides those involved in SETI itself.

For a look at this bit of solar sail and SETI history in context, see Heidmann and Maccone, “AstroSail and FOCAL: Two extrasolar system missions to the Sun’s gravitational focuses,” Acta Astronautica, Vol. 35 (1994), pp. 409-410. Maccone’s book on the mission is Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer/Praxis, 2009). And if you really want to dig, read A. Einstein, “Lens-like Action of a Star by the Deviation of Light in the Gravitational Field,” Science Vol. 84, (1936), pp. 506-507.

It’s fascinating to speculate on how a SETI mission to the gravitational lens might actually be used. As Drake says, a kind of galactic Internet might be built up using lenses in different systems, but given the cost and time involved in reaching lensing distances, when would a mission be contemplated? Surely it would be after the reception of signals so promising that they left little doubt of their origin in another civilization. At that point, the prospect of using the lens to examine the system in question might prove irresistible, driving mission design and advancing our propulsion technologies. A FOCAL-style SETI mission could take us from the simple knowledge that we are not alone to a rich understanding of a culture on another world.


This article was originally posted on Centauri Dreams