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Life in the Universe |
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Here is a 15 billion year (give or take a few billion years) timeline: Big Bang (or some other start), subatomic particles, nucleosynthesis, atoms, large-scale structure such as galaxies, earliest stars made out of H and He, stars cook up elements in core, massive stars explode scattering elements into space, more stars form, material gets recycled for about 10 billion years, some gets put into a molecular cloud that collapses and forms our Sun and planets, you know the rest of the story.
The movie
Contact
does an okay job (for a movie) of depicting
what it is like to observe at a radio telescope and
to listen for a signal in all of the static. (Except for the earphones, and the
boyfriend.)
Funding for our searching for extraterrestrial messages is limited. Two projects are
currently underway:
Project Phoenix and
SETI@home. You should
take a few moments to visit these web sites and get a sense of what a monumental
project it is looking for the "Galactic needle in a haystack."
If another civilization were to contact us, chances are it would be much more advanced than we
are. We are but babes in arms when it comes to space technology. Walk out a door in a small town.
What will you most likely see: infants, toddlers, adolescents, adults, or senior citizens? Adults!
That is because we spend most of our lives as adults--it is a long-lived stage of our lives. It
is a sobering thought that we might be totally incapable of dealing with a much more highly evolved
civilization.
Carl Sagan once asked the question, "Who should speak for the planet Earth?" If we were to be
contacted, which people would represent us? Would we be able to put together a global welcoming
committee?
It may be too late! We've already been speaking.
We have been broadcasting our existence since the early 1950's. The TV
programs [as depicted in the movie "The Explorers" (River Phoenix and Ethan Hawke)]
that went on the air then are now 50 light years away. Since radio waves are a form
of electromagnetic radiation, they follow the inverse-square law and are now
1/(502) or 1/2500 the strength as when they left Earth. But, if a spacecraft were to
pick up that weak signal and zoom in on it, as it got closer and closer to the Earth, it would
pass through the history of the past 50 years, starting with about 1950 and ending up at the
present as it landed. Think of it: from Howdy Doody to the Simpsons.
How will the receivers know they've gotten a message rather than just noise? An alien
civilization capable of receiving radio signals and interpreting them will see
diurnal changes in the intensity of the radio signals as North America rotates into
the line-of-sight, then Japan, then Europe, then North America, then Japan......a signal that varies
with nearly a fixed cycle.
We have sent hard-copy messages into space.
Indirect messages were sent in the form of records and information on the Pioneer and voyager
spacecrafts.
National Aeronautics and Space Administration
The Pioneer 10 spacecraft, destined to be the first man-made object to escape
our solar system, carries this plaque. It is designed to show scientifically
educated inhabitants of some other star system-who might intercept it millions
of years from now-when Pioneer was launched, from where, and by what kind of
beings. The design is engraved into a gold-anodized aluminum plate, 152 by 229
millimeters (6 by 9 inches), attached to the spacecraft's antenna support
struts in a position to help shield it from erosion by interstellar dust.
At the far right, the bracketing bars (1) show the height of the woman
compared to the spacecraft. The figure indicated by (2) represents a reverse
in the direction of spin of the electron in a hydrogen atom. This transition
puts out a characteristic radio wave 21 cm long, so we are indicating that 21
cm is our base length. The horizontal and vertical ticks (3) are a
representation of the number 8 in binary form. Therefore, the woman is 8 x
21 cm = 168 cm, or about 5'5" tall. The human figures represent the type of
creature that created Pioneer. The man's hand is raised in a gesture of good
will.
The radial pattern (4) will help other scientists locate our solar system in
the galaxy. The solid bars indicate distance, with the horizontal bar (5),
denoting the distance from the Sun to the galactic center. The shorter solid
bars represent directions and distances to various pulsars from our Sun, and
the ticks following them are the periods of the pulsars in binary form.
Pulsars are known to be slowing down and if the rate of slowing is constant, an
other-world scientist should be able to roughly deduce the time Pioneer was
launched. Thus, we have placed ourselves approximately in both space and time.
The drawing at the bottom (6) indicates our solar system. The ticks
accompanying each planet are the relative distance in binary form of that
planet to the Sun. Pioneer's trajectory is shown as starting from the third
planet, Earth.
The Voyager Interstellar Recording is attached to both the Voyager 1 and 2 spacecrafts, which were
launched on August 20 and September 5, 1977. The Recording is a gold-plated phonograph record in
an aluminum case (see picture at right). Engraved on the case are instructions on how to play the
record. Included on the record are greetings in over 50 languages, various animal noises including
the songs of the humpback whales, music from different cultures, as well as an audio representation
of the electrical activity of one person's body over the course of an hour. The recording should
last for one billion years. A cartridge and stylus are included on board.
See Voyager Recording for
the greetings and a list of the music included. (From the USA: Chuck Berry and Louis Armstrong.)
Spacecraft can go where we cannot.
We have probes in Jupiter (soon to add another one), on Venus, on the Moon, on Mars,on the asteroid
Eros, and soon will have a probe orbiting Saturn and one landing on Titan. But, sending humans is
a whole other problem. We face the tremendous distances that would need to be traveled, bringing
along all that we need (and water does not pack well), we'd suffer bone mass loss, carrying fuel
requires fuel, bombardment by cosmic rays. And, what if we were to colonize space? Can our
genes stand up toe the rigors, to the inbreeding, to the exposure to high energy particles and
radiation?
We are listening for messages from outer space, but what are the odds that there even are intelligent,
advanced, communicative civilizations out there? How many can we expect to exist in all of the
Milky Way Galaxy? Dr. Frank Drake came up with a now-famous equation that attempts to address the
odds of our being alone. Once we get past the first few factors, the rest become unknown. One more
additional sobering thought: if any of these factors are zero, then we are it--at least in our galaxy.
The Number, N, of technological, intelligent civilizations now present in the Galaxy equals
A philosophical as well as a biological question:
think about how you would define life. What does it mean to be alive?
What objects or things
here on Earth are included in your grouping of "it's alive"?
Viruses? Bacteria?
Yeast? A DNA molecule?
All life on Earth is carbon based. Carbon makes long chains with
hydrogen, oxygen, and nitrogen.
We actually find these chemical building blocks throughout our galaxy! They are in
the cold molecular clouds and elsewhere. In fact, we find some organic molecules
in space that are too fragile to exist for long here on Earth. Interstellar space
seems to be a much better laboratory in many senses than we could ever build here
on Earth because the density and temperatures are low.
Gunter Wachtershauser and Claudia Huber, German chemists, combined
chemicals that exist where molten lava boils up through fissures. They
succeeded in producing end products that were not only organic but
that also kept on producing a series of chemical reactions. Medium
was a reproduction of deep-sea vents. (Earth February
1998)
Somethings to notice when you look at the larger image linked here: 1) A large number of these planets
are closer to their star (much, much closer in some cases) than Mercury is to our Sun. 2) The derived
masses of these planets range from a small fraction of Jupiter's mass (around 25%, Saturn is about 1/3
of Jupiter's mass)to over 16 times (approaching the low-mass end of a star). 3) These stars are all
fairly close to being just like our Sun.
Before 1995, the solar system
was it. One data point. One set of planets. Then, in 1995, a team of Swiss astronomers, M. Mayor
and D. Queloz, discovered the first extrasolar planet. This planet, unseen but detected by its
gravitational influence on its parent star, knocked the astronomical world's socks off. The planet was about
1/2 the mass of Jupiter, but had less than a 5 day orbit--being a mere 0.05 AU's from its parent star.
A gaseous planet that close? Preposterous! Can't be. Astronomers all over the world got observations
using various detectors, at various wavelengths, over various lengths of time. No one could disprove
the theory that we had our first planet outside of our own system. And so, it stays.
So, how did a gaseous planet get there, so close? We must assume that the condensation temperatures for
the known elements (and all are accounted for) are the same everywhere else as
they are in our solar system. We cannot imagine that a planet-forming disk can make a metal (iron and
nickel) planet half the size of Jupiter (look how small Mercury is). Recall, we
calculated in our atmospheric escape activity that Jupiter, if somehow placed at Mercury's distance from
the Sun, would retain its hydrogen atmosphere. And so we are led to believe, and theoretical calculations
have supported this, that these giant planets formed in the outer parts of their planetary systems and
migrated inward towards their star, stopping just short of crashing by some type of braking (maybe
locking onto the magnetic field of their star--remember Jupiter's enormous magnetic field?).
There are about a dozen stars that have massive planets hovering around 1 AU away. The masses of these
planets tell us they are gaseous, but, what about their moons?
We may hope for gangly aliens with big heads and over-sized eyes, or Ewoks, Wookies, Klingons, and Yoda,
but chances are we will find microorganisms: bacteria, archaea, and maybe some we've not thought of
before. Bacteria make up the largest life mass on Earth. They outnumber everything else, and live just
about anywhere they please. If you want to be really morbid, you can think of humans as conduits for
bacteria--when they are done with us, they kill us.
An argument against the probability of an abundance of complex life was made by two University of Washington
professors: Peter Ward and Don Brownlee in their book
Rare Earth. Just some of the things that need
to "line up" for complex life to form:
The planet needs to be the right distance from the star
The star needs to have the right mass, much more massive than our Sun and its lifetime is too short.
The orbits of the planets must be stable, and not too eccentric.
The planet needs to have the right mass--too small and the atmosphere escapes--too large and the
atmosphere is made of hydrogen.
A Jupiter-like neighbor is nice, need one to catch most of the asteroids and comets that would
otherwise hit the planet
A Mars-type, a little farther out in the system, that is cool enough for complex organic molecules
to form
An ocean--deep within the ocean, life would be protected from the harmful UV rays
A large Moon to stabilize the planet and create water tides for sloshing around nutrients
The planet needs the right tilt--currents mix nutrients--a Uranus tilt would not work
Giant impacts are occasionally needed to wipe out any domineering species and allow for diversity
The atmosphere needs to be of the right mix of greenhouse gases
Carbon is needed
Biological evolution must occur
Oxygen released from primitive life must remain around long enough to enter the atmosphere and
create ozone to protect the budding life from harmful radiation from its star
The star needs to be in the right kind of galaxy, one that is undergoing consistent star formation
The star needs to be in the right part of the galaxy: too close to the center and the neighborhood
is way too crowded, too close to the edge and not enough chemical enrichment would have taken place
SETI at Home use your
PC to look for signals from outer space.
Planetary
Society
Exoplanets -- BE SURE TO VISIT THIS SITE,
EVEN IF IT'S A SHORT STAY!
Origin of Life on Earth
Scientific American FAQ
Life, Life Everywhere
Scientific American, 1996
Chemicals from Space
Shaped Earth Life? from Christian Science Monitor, including a discussion about "handedness."
Evolutionary Timeline for
Life on Earth from The Talk Origins Archive
Life on Other Planets in the Solar
System from an educational project in Michigan, with a wonderfully organized list of links.
We've been talking: Radio Station Earth
SETI (Search for Extra-Terrestrial Intelligence)
researchers have not been very interested in broadcasting because of the long
time one has to wait for a reply. If the nearest civilization is 100 light-years away,
we would have to sit around for 200 years for a reply to a deliberate broadcast.
Nonetheless, a few, mostly symbolic, intentional messages have been sent. One message,
transmitted in 1974 from the Arecibo Observatory, consisted of 1.679 bits of
information. The number is divisible by two prime numbers, 73 and 23, which suggests
laying out the message in those dimensions, revealing the image shown at the left.
This message was a simple picture describing our
solar system, the compounds important for life, the structure of the DNA molecule, and
the form of a human being, including the height.
This message, given as a binary code, was transmitted in the direction of the globular
star cluster M13, about 25,000 light years away. (from SETI web site)
Is it worth our search? The Drake Equation
Make your own calculation of the number of intelligent, communicative,
technologically advanced civilizations through these links:
For background information, and estimates for the factors,
the Drake Equation and for
the actual calculation,
Drake Equation Calculator.
The Definition(s) of "Life"
Where can you find these chemical building blocks?
There are currently a number of favored scenarios:
You have to realize that people in the origin of life field
are not very straight. This is pseud-religious field. People
behave like Grand Inquisitors. If somebody dares to propose a
new theory, s/he is put on the Index.
Why do people yell and scream so hard? Because of scant data.
The more data, the lower the volume. There's nothing like facts
to make people shut up.
Around other planets in our solar system
Life on Planets around Other Stars
Habitable zones around planets in other stellar systems
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