Science,
even by reputable practitioners, proceeds in fits, starts, and frequent excursions
down blind alleys.
As example,
in 1877 astronomers on both sides of the Atlantic observed things about Mars
that had the potential for making SETI a done deal, a fait accompli.
In that
year, the Red Planet had orbited into a particularly favorable opposition -
bringing it closer to Earth than is almost ever the case - and making it a
tempting target for new discoveries. In Italy, Giovanni Schiaparelli, director
of Milan's Brera Observatory, thought he saw linear features furrowing Mars'
russet face. His discovery was made using a telescope that is dwarfed by many
amateur instruments today: its objective lens was a modest 8 inches in
diameter. Schiaparelli provocatively referred to the features as canali,
an ambiguous word choice that would keep eyeballs enthusiastically pressed
against eyepieces for a half-century.
It was the
American astronomer, Percival Lowell, who dug Schiaparelli's work the most. He
figured that the canali were deliberate constructions, and he soon
became the most literate advocate for the existence of a globe-girdling
irrigation system on Mars. This spider web of canals was, Lowell averred, the
engineering work of advanced beings whose homes were a mere 35 million miles
from our own.
Ever since
the Mariner 4 space mission, in 1965, we've known that the "canals" mapped by
these two astronomers - every single one - were optical illusions. Nonetheless,
Lowell, who died during the First World War, remained convinced to the end that
he had charted the infrastructure of a vast, hydraulic civilization. It's
noteworthy that the public only showed intermittent interest in Lowell's claims. It's also stupefying to contemplate how different our lives would be
today had they been true.
Merely a
few weeks before Schiaparelli's work was made public, an astronomer at the
United States Naval Observatory in Washington announced a different discovery
about Mars - one that would (eventually) also suggest the presence of nearby
intelligence. Asaph Hall, using what was then the world's largest telescope -
its lens was three times the diameter of Schiaparelli's - found two midget
moons orbiting the Red Planet (they're so small, you could walk around either
one in a day). This was, of course, an interesting story, since moons
accompanying 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 Mars
was a compelling astronomical discovery. The Washington Evening Star
hailed 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 the
two bad-boy sons of Mars (Ares, in Greek tradition) and Aphrodite. Nice names
for dead rocks.
A lifetime
later, something funny happened. Long-term measurements of the inner of the
two moons, Phobos, showed that it was losing altitude, about ten feet per
century. Its orbit was gradually decaying, much the way a low Earth-orbit
satellite will gently spiral downward due to the delicate drag of residual
atmosphere several hundred miles up.
In the wake
of Sputnik, this analogy proved irresistible to some, in particular to Iosef
Shklovsky, 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 rate
of descent only if Phobos was a featherweight - a hollow, metal sphere with a
skin only a few inches thick.
That was an
astounding claim, and remember that Shklovsky was no dummy. (His book of a few
years later, Intelligent Life in the Universe, enlarged and edited by
Carl Sagan, was the first to comprehensively address the question of sentient
cosmic life. It was an early guide book for SETI research.) But what
Shklovsky was saying - and what others, including President Eisenhower's
science advisor, believed - was that Phobos wasn't dead rock at all, but a
space station welded together by advanced beings from a star system far, far
away.
The public,
to its credit, didn't riot in the streets at the prospect of an alien outpost
nearby. And indeed, a dozen years later, researchers found that the descent of
Phobos had been seriously overestimated, and its orbital change was most likely
due to tidal friction with the Red Planet, not atmospheric drag.
A credentialed
astronomer had falsely hailed a hollow world. But at least it was a mistake
with precedent. At the end of the 18th century, Edmund Halley - no
astronomical slouch himself - wrote a paper for the Royal Astronomical Society
in which he claimed that the Earth was hollow! More precisely, he
envisioned that our world consisted of three spherical shells surrounding a small,
hard central ball, a construction that he reckoned could explain the observed
changes in Earth's magnetic field. Indeed, according to Sir Edmund, not only
were there massive amounts of lebensraum beneath our feet, but he suggested
that these inner sanctums might even be inhabited. (The idea of a vasty void
within the Earth is still popular among some people. None of these are geophysicists.)
Now the
peculiar thing is that, despite the errors of the past, artificial, hollow
habitats remain a possibility for putative aliens. In 1959, only a year after
Shklovsky's speculations about Phobos, British physicist Freeman Dyson reasoned
as follows: since we seem to have an insatiable hunger for energy, it makes
sense to assume that aliens have the same. To satisfy their craving for
kilowatt-hours, extraterrestrials who are centuries more advanced than we are
will surround their sun with an orbiting flotilla of solar-cells, allowing them
to capture a large fraction of their star's energy output.
It's become
popular to envision Dyson's concept as a closed, complete energy-collecting
shell around a star, perhaps built with the materials obtained by dismantling
an outer planet - a so-called "Dyson sphere." However, a complete spherical
shell has dynamical and structural problems, and is impractical. Dyson himself
was thinking more along the lines of a very large number of individual solar
collectors.
Finding a
Dyson sphere, or more realistically, a Dyson swarm, would be just about as
exciting as learning that Phobos was built of steel plates. It would tell us
that someone out there has developed some pretty advanced technology. We can't
hope to see any of these solar-collectors-on-steroids directly, but they might
be uncovered by their waste heat, which would be radiated into space as
infrared light. In the last dozen years or so, there have been several
attempts to find such objects, usually by mining data from the Infrared
Astronomical Satellite (IRAS) that mapped the sky in the 1980s.
Living high
on the energy hog within a surrounding shell of hardware? It's an intriguing
idea, although given our limited understanding of what advanced societies will
do, it might be just another blind alley. Still, science proceeds by looking,
and some researchers have. So far, no Dyson.
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