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.
Presumably if you are going to use the gravitational focus for SETI, one potentially good strategy is to target old and metal-rich open clusters. While most open clusters are quite young and therefore may represent poor prospects for searching for alien civilisations, there are exceptions. Messier 67 for example has near solar age and metallicity. Another example of such a cluster is NGC 6791 in the Kepler field. There aren’t many particularly good constraints on planet abundance in such clusters: surveys to try to find hot Jupiters find them to be underabundant relative to comparable field stars, but hot Jupiters seem to be rather pickier about their environments than other types of planet.
If we were to use the gravitational lens to search for ET then it would be entirely looking for a needle in a very big haystack. If we were using the gravitational lens to look at a world of ETs that we’d already had contact with then there are two problems with this logic. The ETs should have been in existence for at least a million years already, therefore:
1) the ETs would likely have power sources sufficient to broadcast bright, easily understood carrier signal plust an info rich signal and
2) should have had plenty of time to distribute their nanoprobes throughout the galaxy thereby making their communication time to us a matter of seconds. Those communication devices should have enough information to let us look at their Google Maps in very high resolution.
But even if we don’t have an ET to look at, it would still be cool to see mountains, rivers, valleys, rifts, continents, etc.
It might be useful to perform SETI on nearby galaxies by scanning for artificial radio emissions using FOCAL. The advantage would be that you can sweep a whole galaxy, the disadvantage that you could not reply, of course.
You would then have a chance even if it turns out there is no more than one ETI per galaxy, which would be a hopeless case without FOCAL.
The gravity-lens communication enhancement is truly incredible when contemplating interstellar probes – low wattage radio sources can be received with a nice clear signal. Also means the potential for very high band-width for information return from larger probes. Imagine sending back 3-D TV signals as a probe scans an alien planet. All made possible by the 100 million-fold gain.
Also means, as John rightly observed, that ETIs can be present via tiny robotic proxies anywhere in the Galaxy – and we wouldn’t know as the signals would always be too faint for us to spy on, but clearly received by a gravity-lens based receiver back at ET’s home.
guys,yes i do think that we ought to spend some time searching for eti .either by the means you descibe above or by just going there if we are forced to! lol and thanks your friend george
With no offense to Claudio whatsoever, I think it is a bit humanocentric
to assume an ETI would have roads and cars like we do. Maybe some of
them do, but I would not bet on it.
While certain types of planets have similar characteristics, I have to wonder
if we will “get” what would could see in such powerful instruments even if we
could view alien worlds so up close? When Cassini gave humanity its first
clear views of what lay under Titan’s clouds in 2004, the general consensus
upon initial viewing was “Huh?” It took a while to figure out just what we
were looking at, because this alien moon did not bend to our preconceived
notions of what a moon should look like. This goes back to what we found
with Io from Voyager 1 in 1979.
I wonder what effect the gravitational lens of the Eath, Moon and even Jupiter have? Where are they? I suspect that for example Jupiters gravitational lens might be a lot easier to reach than 550 AU. It might even be fairly close to our neighbourhood …
ljk yes,as i said i believe last month…alien worlds will be…for want of a better term,alien.if star trek made one major mistake it was seeing everybody as huminoid just like us! no offense to trek.it is not as if i am not one of their major fans as i suspect alot of us probably are. thank you george
Luke: actually, they turn out to be located a lot further away. For comparison:
Sun = 550 AU
Jupiter = 6100 AU
Earth = 15000 AU
To get a Jupiter-radius object to have the same minimum focal distance as the Sun, it would need to have 11 times Jupiter’s mass.
Oh wow, I never would have guessed that. I would have figured a smaller gravity well would have had a smaller magnification, with a closer focal point. I guess just another example of how intuition can lead you astray.
Hmmm. That reminds me, can the gravitational lense me used for searching for brown dwarfs and other nearby dim stars?
Luke, think about it this way: if a smaller gravity well had a closer focal point, we would be using golf balls as gravity telescopes!
Tobias:
No, the magnification is very large and the ability to point extremely restricted. You have to know quite precisely where to look, surveying the sky is not an option.
Tobias and Eniac, you may find this interesting… an investigation of feasibility of detecting nearby objects through mesolensing.