SETI NYT article on IDing an ETI signal

Larry Klaes (
Wed, 07 Jul 1999 11:24:26 -0400

>Date: Tue, 06 Jul 1999 23:41:20 -0400
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> . In the search for extraterrestrial intelligence, or
SETI, what kinds of
> signals would be considered evidence of transmission by
intelligent life?
> How would scientists respond?
> . Such a transmission might take many forms, but would
probably encode
> mathematical formulas. The reply would depend on the
content; it would
> not be made by scientists, but would come after extensive
> consultation.
> As for verification, according to statements on the SETI
Institute's Web site,
>, "The main feature distinguishing signals
produced by a transmitter
> from those produced by natural processes is their spectral
width," that is, how
> much room on the radio dial they take up. As far as scientists
know, any signal
> less than about 300 hertz wide is artificially produced.
> Other telltale characteristics might be coded information,
like the message beamed
> from the Arecibo telescope in 1974, which included data like
the senders' location
> (third rock from the sun, in the case of Earth). Another
important test would be a
> confirming observation of the same signal at another radio
> Once confirmed, the discovery would be announced based on a
plan set up by six
> international space agencies. First, the scientific community
would be notified
> through the International Astronomical Union and the United
Nations. Then
> international authorities would draft a reply.
> Cassini's Crucial Course
> The Cassini spacecraft has made the second of its two flybys
of Venus,
> using the planet's gravity to pick up speed on its way to
Saturn, which it
> should reach in 2004. The next planet to provide a shot
of energy to the
> spacecraft is Earth, which Cassini will approach next month.
> The craft, which is expected to spend four years exploring
Saturn from orbit and
> landing a probe on its largest moon, Titan, passed within 370
miles of Venus on
> June 24. Such a maneuver functions something like a slingshot,
boosting the
> spacecraft's speed for its long journey.
> Cassini was launched in October 1997, and a previous Venus
approach took place
> in April 1998.
> Both the flybys were right on target, a fact that might
provide some reassurance
> for critics of the project who have been concerned about the
chances for a
> catastrophic accident when the craft nears Earth on Aug. 18.
> Cassini is carrying 72 pounds of plutonium in a generator to
provide heat and
> power (the solar cells that are used by many spacecraft would
be impractical in the
> outer reaches of the solar system, so far from the Sun).
> The critics have feared that if the craft is slightly off
course, and approaches Earth
> much closer than the intended 725 miles, the atmospheric
friction could cause it to
> burn up, spreading a potentially lethal plume of plutonium.
> NASA has argued that the possibility of such a breakup is
extremely small, and
> that even if it did occur, the plutonium is in a form that
would greatly reduce any
> risks to health. But the best insurance against any problems
is a spacecraft that is
> on its intended course.
> July 6, 1999
> Sunless, Airless, and Full of Life?
> ASHINGTON -- Several Earth-like planets, created
billions of years ago
> during the formation of our solar system, may be
wandering in deep
> space harboring conditions that could sustain some
form of life,
> according to a new theory proposed by a prominent planetary
> These orphan worlds, ejected
> from the solar system by
> gravitational forces during its
> tumultuous beginnings, may
> have retained atmospheres
> rich in molecular hydrogen
> even as they were flung into
> the dark void of interstellar
> space, said Dr. David J.
> Stevenson, a professor of
> planetary science at the
> California Institute of
> Technology.
> The rogue planets, instead of
> being cold, icy masses
> meandering among the stars
> as some astronomers have
> believed, could be warm
> bodies with dense, insulating
> atmospheres that trap enough
> volcanic heat to sustain water
> oceans and some types of
> simple life forms, he said in an
> interview.
> "The idea of Earth-sized bodies being ejected when the solar
system formed is not
> new," Dr. Stevenson said. "But instead of being uninteresting
frozen balls of
> barren matter, I am proposing that they could have acquired a
dense atmosphere
> and maintained it to act as an insulating blanket to sustain
Earth-like temperatures
> in the absence of sunlight."
> The idea that life could exist in such seemingly inhospitable
conditions has been
> bolstered in recent years by the discovery of a variety of
unusual creatures living
> in lightless, sulfurous environments at the ocean floor,
warmed by heat from
> undersea vents. These discoveries have fueled speculation that
life might exist
> elsewhere in the universe, though possibly in forms that would
seem strange to
> ordinary humans.
> Dr. Stevenson described his theories in the current issue of
the journal Nature. He
> said that if planetary systems around other stars formed in
similar ways, then there
> could be billions of such interstellar planets flung into
space. If life can develop
> and be sustained without sunlight on these planets, he wrote,
"it is conceivable
> that these are the most common sites of life in the universe."
> Dr. Stevenson said his idea of dark, life-sustaining planets
moving among the stars
> is drawn from linking several accepted concepts of planetary
theory and his own
> calculations. "This is just an idea, but it comes together
plausibly," he said.
> Dr. Jack J. Lissauer, a specialist in planet formation at the
National Aeronautics
> and Space Administration's Ames Research Center in California,
said Dr.
> Stevenson's idea is an interesting one that extends other
scientists' work.
> "Stevenson put all these parts together and has raised the
possibility of
> something that is really far out, but not ridiculous," he
said. "It makes some
> sense."
> Dr. Alan P. Boss, a solar system specialist at the Carnegie
Institution of
> Washington's Department of Terrestrial Magnetism, said the new
theory "is a
> logical extension of what people have proposed for a long time
about the early
> solar system."
> When the solar system was formed about 4.5 billion years ago
from primal gases
> and dust coming together, Dr. Boss said, the process produced
multiple cores that
> tried to become planets near the orbits of Jupiter and Saturn.
Some of these bodies
> became parts of the giant planets when drawn in by their
gravity, he said, while
> others passed nearby and were flung away in a slingshot effect
that propelled
> them out of the solar system.
> This process was responsible for knocking about a trillion
small bodies out of the
> infant solar system, causing them to form a giant sphere of
debris in deep space
> that surrounds the sun and its planets. This debris, called
the Oort cloud, is
> believed to be the source of most comets that enter the solar
> "If the Oort cloud was formed by many small bodies being
knocked out of the
> solar system, it is not a great leap to imagine losing a few
Earth-sized bodies the
> same way," Dr. Boss said.
> According to Dr. Stevenson, there were about a half-dozen
Earth-like planets in
> Jupiter-crossing orbits in the early days of the solar system.
Planets with masses
> one-half to two-and-a-half times that of the Earth could
gather and retain some of
> the dense hydrogen gas that permeated the solar system at the
time. This gas
> could collapse to the surface of the planet under enough
pressure to become an
> opaque, heat-retaining blanket, he said.
> Without sunlight to provide energy, the planets' heat would
come from volcanic
> activity and natural radioactive elements. Because of the
thick hydrogen
> atmosphere, exerting pressures 100 to 1,000 times greater than
that at sea level on
> Earth, temperatures on the dark planets could reach more than
60 degrees
> Fahrenheit, Dr. Stevenson said.
> The surface of such a planet would be almost totally dark, he
said, except for the
> occasional illumination of lightning or a volcanic eruption,
and the sky would be
> covered with layers of clouds made up of methane, ammonia and
perhaps water.
> Even under these conditions, he said, water, temperature
variations and other
> factors might foster life and sustain it. However, because
available energy is
> thousands of times less than that found on Earth, he said, any
life that developed
> there would probably be very simple and scarce.
> Dr. Stevenson said interstellar planets produced during the
formation of our solar
> system would be hundreds of trillion of miles away by now.
Similar planets created
> by other star systems billions of years ago could be closer to
Earth and its
> neighbor planets than those created by our solar system, he
> Because these planets are so dark and give off relatively
little energy, they cannot
> be seen with present technology, he said. The best hope of
demonstrating the
> existence of interstellar planets, scientists said, would be a
programmed search of
> the sky for the events called occultations, which occur when a
body passes
> between the Earth and a star, causing the starlight to flicker
or fade.
> Dr. Harold F. Levison, an astronomer with the Southwest
Research Institute in
> Boulder, Colo., said a good place to look might be the Oort
cloud, where one or
> more of these tossed-off planets might be trapped with other
debris of solar
> system formation. Although this area is far away -- equal to
100,000 times the
> distance from the Earth to the sun -- it is closer than nearby
stars, he said.
> "They may be more easy to find in the Oort cloud," Dr. Levison
said, "But it still
> will be hard to find something Earth-sized that far out."
> Copyright 1999 The New York Times Company
>Jay Respler
>Sky Views:
> Satellite Tracker * Early Typewriter Collector
> Freehold, New Jersey

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