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Old February 19th 04, 01:18 AM
Steve Dufour
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Default Alien probes are here?

Interstellar Espionage: While We're Watching Mars, Could Someone be
Watching Us?

By Seth Shostak
Senior Astronomer
posted: 06:00 am ET
22 January 2004





Have aliens sent mechanical emissaries to our solar system -- robotic
probes on a snoopy mission to reconnoiter Earth?

It's certainly an intriguing idea: sophisticated spy satellites from
light-years away monitoring our planet, watching the slow evolution of
life, and reporting back to their alien masters. Such a scenario has
frequently appeared in the SETI literature, and Allen Tough, at the
University of Toronto, has urged that we take the idea seriously
enough to make a search for these alien "bugs."

You might question whether interstellar spying makes sense. After all,
there are several hundred billion star systems in the Galaxy, spread
across a disk 100,000 light-years in diameter. Sending billions of
probes over such daunting distances sounds like a project that no
alien congress would ever approve.

But the idea can't be dismissed that easily. Advanced societies --
even those that are only modestly beyond our own -- will have catalogs
of planets known to support life. This inventory can be assembled by
using large telescopes to collect and analyze the light reflected from
the atmospheres of other worlds; looking for "biomarkers" such as
oxygen and methane. Finding these gases on someone else's planet would
be a clue that biology is present. Surprising as it may seem, microbes
can be detected at light-years' distance using this technique.

If worlds with life are plentiful, then some of them will be
relatively close to the aliens' home planet, encouraging a close-up
look via a probe. If bio-worlds are rare, then these would be so
singular as to make the greater travel times required to reach them
worth the wait. Either way, there could be some stimulus to post a
probe. And the total number of probes need not be extraordinarily
large.

How big do the probes have to be? Allen Tough has written that these
alien bugs "could be smarter and more knowledgeable than any human
being, yet… be smaller than a basketball or baseball." Smaller is
better for two reasons: less energy is required to hurl them to other
worlds, and they would be harder to find and confiscate by any
intelligent beings on the spied-upon planet.

On the other hand, the probes are pretty useless if they don't have
the oomph required to send back data, either via a radio signal or a
tightly focused infrared laser (the latter seems more sensible to me).
So the aliens might opt for a "master-slave" setup somewhat akin to
the scheme used to retrieve data from the Mars rovers. A relatively
small probe could orbit near to Earth, making high-resolution photos
and collecting information, while a larger, more distant "mother ship"
could be hanging out in, say, the asteroid belt, where it would
process the data from the smaller probe and relay it back home.
Another approach would be to have only one probe, but on a highly
elliptical orbit (like a short-period comet). This scheme would keep
the probe largely out of sight, but bring it close to our planet for
detailed looks every few dozen years.

What about the costs? For a truly advanced society, the bill for the
hardware might be negligible. But to send a probe to the stars at even
a leisurely one-tenth light speed requires a substantial dollop of
energy. If the probe weighs 10 pounds, the minimum energy necessary to
rocket it to target and then slow it down on arrival is roughly 5,000
trillion joules. If you buy that much energy from your local electric
company, it will cost you $120 million. Frankly, although a bill that
size would probably stupefy your spouse, it's not an unthinkable
amount (a Mars Exploration Rover costs three times as much).

Still, there are some probe-o-phobes who ask, "why would the aliens
bother? After all, the probes can only telemeter their data at the
speed of light. Why wouldn't the snoopy extraterrestrials simply await
our television signals? These would reach them at the same time any
report from a probe would."

Indeed. And one could argue that the content of our broadcasts would
tell alien viewers all they might want to know about our society (I
won't lapse into the obvious…)

But there's another angle. Life on Earth has been detectable (via
atmospheric biomarkers) for two billion years. Intelligent life is
only a recent, and so far, brief, phenomenon. Very few (if any) of the
biologically active worlds investigated by probes are likely to have
brainy life. The aliens will surely know this. They will send probes,
not to find us – after all, our signals, in the end, will find them –
but to investigate, up close and personal, life that isn't ever going
to broadcast. For 500 million years, there's been a rich pantheon of
plants and creatures on this planet, making it a natural history
exhibit of enough interest to warrant a close-up look.

So probes are a possibility. And maybe one was launched our way,
sometime in the last two billion years. We might still be able to find
it, if we knew where to look. Should we make a careful investigation
of the asteroid belt? The Earth-Moon Lagrange points? Perhaps parked
in a nearby orbit, or on the Earth itself?

We just don't know, and that makes the search space dreadfully large.
Probes are not crazy, but how to find one is hazy.