Harnessing the Power of the Sun

Science,even by reputable practitioners, proceeds in fits, starts, and frequent excursionsdown blind alleys.

As example,in 1877 astronomers on both sides of the Atlantic observed things about Marsthat had the potential for making SETI a done deal, a fait accompli.

In thatyear, the Red Planet had orbited into a particularly favorable opposition -bringing it closer to Earth than is almost ever the case - and making it atempting target for new discoveries. In Italy, Giovanni Schiaparelli, directorof Milan's Brera Observatory, thought he saw linear features furrowing Mars'russet face. His discovery was made using a telescope that is dwarfed by manyamateur instruments today: its objective lens was a modest 8 inches indiameter. Schiaparelli provocatively referred to the features as canali,an ambiguous word choice that would keep eyeballs enthusiastically pressedagainst eyepieces for a half-century.

It was theAmerican astronomer, Percival Lowell, who dug Schiaparelli's work the most. Hefigured that the canali were deliberate constructions, and he soonbecame the most literate advocate for the existence of a globe-girdlingirrigation system on Mars. This spider web of canals was, Lowell averred, theengineering work of advanced beings whose homes were a mere 35 million milesfrom our own.

Ever sincethe Mariner 4 space mission, in 1965, we've known that the "canals" mapped bythese two astronomers - every single one - were optical illusions. Nonetheless,Lowell, who died during the First World War, remained convinced to the end thathe had charted the infrastructure of a vast, hydraulic civilization. It'snoteworthy that the public only showed intermittent interest in Lowell's claims. It's also stupefying to contemplate how different our lives would betoday had they been true.

Merely afew weeks before Schiaparelli's work was made public, an astronomer at theUnited States Naval Observatory in Washington announced a different discoveryabout Mars - one that would (eventually) also suggest the presence of nearbyintelligence. Asaph Hall, using what was then the world's largest telescope -its lens was three times the diameter of Schiaparelli's - found two midgetmoons orbiting the Red Planet (they're so small, you could walk around eitherone in a day). This was, of course, an interesting story, since moonsaccompanying planets of the inner solar system are as rare as Swiss jokes. Mercury doesn't have any, nor does Venus. So a pair of satellites around Marswas a compelling astronomical discovery. The Washington Evening Starhailed the find as "Glorious news from the skies." Following a suggestion from Eton scholar Henry Madan, Hall christened his diminutive discoveries Deimos("dread") and Phobos ("fear"). According to The Iliad, these were thetwo bad-boy sons of Mars (Ares, in Greek tradition) and Aphrodite. Nice namesfor dead rocks.

A lifetimelater, something funny happened. Long-term measurements of the inner of thetwo moons, Phobos, showed that it was losing altitude, about ten feet percentury. Its orbit was gradually decaying, much the way a low Earth-orbitsatellite will gently spiral downward due to the delicate drag of residualatmosphere several hundred miles up.

In the wakeof Sputnik, this analogy proved irresistible to some, in particular to IosefShklovsky, a Soviet astrophysicist. In 1958, Shklovsky worked the numbers,making estimates of the amount of martian atmosphere at the altitude of Phobos'orbit. He concluded that the drag on this moon could produce the observed rateof descent only if Phobos was a featherweight - a hollow, metal sphere with askin only a few inches thick.

That was anastounding claim, and remember that Shklovsky was no dummy. (His book of a fewyears later, Intelligent Life in the Universe, enlarged and edited byCarl Sagan, was the first to comprehensively address the question of sentientcosmic life. It was an early guide book for SETI research.) But whatShklovsky was saying - and what others, including President Eisenhower'sscience advisor, believed - was that Phobos wasn't dead rock at all, but aspace station welded together by advanced beings from a star system far, faraway.

The public,to its credit, didn't riot in the streets at the prospect of an alien outpostnearby. And indeed, a dozen years later, researchers found that the descent ofPhobos had been seriously overestimated, and its orbital change was most likelydue to tidal friction with the Red Planet, not atmospheric drag.

A credentialedastronomer had falsely hailed a hollow world. But at least it was a mistakewith precedent. At the end of the 18th century, Edmund Halley - noastronomical slouch himself - wrote a paper for the Royal Astronomical Societyin which he claimed that the Earth was hollow! More precisely, heenvisioned that our world consisted of three spherical shells surrounding a small,hard central ball, a construction that he reckoned could explain the observedchanges in Earth's magnetic field. Indeed, according to Sir Edmund, not onlywere there massive amounts of lebensraum beneath our feet, but he suggestedthat these inner sanctums might even be inhabited. (The idea of a vasty voidwithin the Earth is still popular among some people. None of these are geophysicists.)

Now thepeculiar thing is that, despite the errors of the past, artificial, hollowhabitats remain a possibility for putative aliens. In 1959, only a year afterShklovsky's speculations about Phobos, British physicist Freeman Dyson reasonedas follows: since we seem to have an insatiable hunger for energy, it makessense to assume that aliens have the same. To satisfy their craving forkilowatt-hours, extraterrestrials who are centuries more advanced than we arewill surround their sun with an orbiting flotilla of solar-cells, allowing themto capture a large fraction of their star's energy output.

It's becomepopular to envision Dyson's concept as a closed, complete energy-collectingshell around a star, perhaps built with the materials obtained by dismantlingan outer planet - a so-called "Dyson sphere." However, a complete sphericalshell has dynamical and structural problems, and is impractical. Dyson himselfwas thinking more along the lines of a very large number of individual solarcollectors.

Finding aDyson sphere, or more realistically, a Dyson swarm, would be just about asexciting as learning that Phobos was built of steel plates. It would tell usthat someone out there has developed some pretty advanced technology. We can'thope to see any of these solar-collectors-on-steroids directly, but they mightbe uncovered by their waste heat, which would be radiated into space asinfrared light. In the last dozen years or so, there have been severalattempts to find such objects, usually by mining data from the InfraredAstronomical Satellite (IRAS) that mapped the sky in the 1980s.

Living highon the energy hog within a surrounding shell of hardware? It's an intriguingidea, although given our limited understanding of what advanced societies willdo, it might be just another blind alley. Still, science proceeds by looking,and some researchers have. So far, no Dyson.

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