Published online: 01 September 2004; | doi:10.1038/news040830-4
ET write homeMark PeplowMail, not phone, might be best for interstellar messages.
| The Voyager 1 and 2 probes carry this gold-plated disc containing sounds and images from Earth.
© NASA |
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If
an extra terrestrial wanted to send a field report describing all she had
learned about Earth, she might be better off writing rather than phoning.
A new analysis has concluded that a physical object would be a more efficient
way to send a long message to the stars than a beam of radio waves.
So
while we scour the heavens for radio broadcasts from other worlds, we should
also search our planetary backyard for a parcel of alien information, says
Christopher Rose, an electrical engineer at Rutgers University, Piscataway,
New Jersey, who argues his case in this week's Nature1.
"Communication
by the transmission of matter once seemed ridiculous compared to using radiation,
but it's not, and we should be looking for both," Rose says. He thinks that
a stable orbit around Jupiter, or on the Moon or even the Earth could all
be potential mailboxes - all locations occupied by the alien monoliths in
Arthur C. Clarke's novel 2001.
There
are plenty of places in the Solar System to hide, agrees Greg Wright, a physicist
from Antiope Associates in Fair Haven, New Jersey, who worked with Rose on
the calculations. "Only parts of the Moon, Mars and a few asteroids have
been mapped carefully," he says. "We haven't launched a serious search for
these sorts of things yet," adds Rose.
 Communication
by the transmission of matter once seemed ridiculous compared to using radiation,
but it's not, and we should be looking for both  |
Christopher Rose
Rutgers University, Piscataway, New Jersey |
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You've got mail
Rose
calculated how much energy it would take to send a message to a star system
1,000 light years hence. The package, travelling at about one million kilometres
per hour, would reach its destination after about a million years. The radio
waves would be sent and received by giant radio telescopes.
For
simple messages, a radio transmission would use the least energy, Rose found.
But for a transmission of 100 terabits or more, it is easier to write.
A
message of 100 terabits could contain all the books in the US Library of
Congress five times over. Rose argues that any message worth sending would
exceed this easily - perhaps being closer to the 40 million terabits contained
in all the world's telephone calls in a year.
An
inscribed object has the advantage of remaining legible no matter how far
it travels, whereas even the narrowest beam of radio waves spreads out over
interstellar distances, eventually becoming undetectable. For long messages
over long distances, an alien civilisation is likely to send a package, says
Rose. "Energy is kind of a currency: if something costs less, it's more likely
to get done."
I hope that someone finds my...
We
have sent several inscribed messages into space. The two Voyager probes each
carry a long-playing record of "The Sounds of Earth", and both Pioneer craft,
the first manmade objects to leave our Solar System, bear plaques charting
their route, along with a picture of naked humans waving a greeting. A similar
alien salutation could be waiting on Earth for us, says Rose.
| There's room for Rose and there's room for radio. For now I'm sticking with radio |
Jill Tarter
SETI Institute, Mountain View, California |
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The
SETI Institute is already hunting the heavens for radio transmissions from
other stars. Jill Tarter, Director of the Center for SETI Research in Mountain
View, California, agrees with Rose to a point. "We should look for artifacts
of all kinds in our local neighbourhood, including packages on our doorstep,"
she says.
But
she adds that the most important contact is the first, which doesn't require
a long, complicated message. "There's room for Rose and there's room for
radio. For now I'm sticking with radio," she says.
References
- Rose C. & Wright G. Nature, 431. 47 - 49(2004). | Article |
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