A nicer one from the Jet Propulsion Laboratory (just down the road from me):
Posted on 07/03/2002 9:03:47 AM PDT by RightWhale
Scientists estimate 30 billion Earths
By Dr David Whitehouse , BBC News Online science editor
Astronomers say there could be billions of Earths in our galaxy, the Milky Way.
Their assessment comes after the discovery of the 100th exoplanet - a planet that circles a star other than our own.
The latest find is a gas giant, just like all the other exoplanets so far detected, and orbits a Sun-like star 293 light-years away.
Scientists say they are now in a position to try to estimate how many planets may exist in the galaxy and speculate on just how many could be like the Earth. The answer in both cases is billions.
Virtually all the stars out to about 100 light-years distant have been surveyed. Of these 1,000 or so stars, about 10% have been found to possess planetary systems.
So, with about 300 billion stars in our galaxy, there could be about 30 billion planetary systems in the Milky Way alone; and a great many of these systems are very likely to include Earth-like worlds , say researchers.
Better grasp
The 100th new planet circles the star HD 2039. It was found by astronomers using the Anglo-Australian Telescope as part of the Carnegie Institution Planet Search Program.
The Jupiter-sized world circles its star every 1,210 days at a distance of about 320 million kilometres (200 million miles).
Astronomer Dr Jean Schneider, who compiles the Extrasolar Planets Catalogue, told BBC News Online: "The 100th planet is symbolic and important.
"The first discoveries concentrated on short orbital periods because of the limited timebase of observations. Now, we are learning more about the statistics of long orbital periods and know to what extent our own Jupiter is exceptional or not."
New telescopes
With the new world, astronomers say that they have just about finished surveying all the Sun-like stars out to a distance of 100 light-years from Earth.
Current planet detection technology - based on the "wobble" induced in the parent star by the gravitational pull of the orbiting planet - can only detect worlds about the mass of Saturn or larger. Earth-sized worlds are too small to be seen.
But even in this "biased" survey of giants, the smaller worlds predominate - which makes astronomers think that Earth-like worlds do exist. They may even be as common as Jupiter-sized exoplanets.
And if stellar statistics gathered in our local region of space are applied to our galaxy of 300 billion stars, then there may be 30 billion Jupiter-like worlds and perhaps as many Earth-like worlds as well.
Astronomers will have to wait for a new generation of space-based telescopes incorporating advanced detectors before they can detect Earth-sized worlds orbiting other stars.
I wonder if anyone's ever created a map showing a "Galactic Habitable Zone" (like the "habitable zone" where liquid water can exist in our own solar system).
Surely some would have interstellar travel by now.
Not really. It's pretty solid. The point is that planets are being discovered where expected, and the discoveries are coming quicker all the time. With the Kepler scope and the others in the next few years it will be possible to actually and directly see earth-size planets in other solar systems. This is a general idea of what to expect. Could be some surprises.
I understand that. My point was that they cannot logically make a guesstimate of "earth-like" planets when none have been found. Wait until some have been found, and extrapolate from numbers found per systems found.
The easy part (the volume of the Milky Way galaxy) is already on record.
I agree with you that the Torus shape would be the best bet in describing the potential for other 'Earths'. The Torus just appears too many times in nature to choose any other geometric form as a better candidate.
... At least as far as Humans see 'life-bearing' environments, that is. Arthur C. Clarke's '3001: The Final Odyssey' had an interesting take on life that may be present here in our own Solar System. Chapter 30, 'Foamscape', described the region between the gaseous atmosphere of Jupiter and it's solid core where science dictates that there must be an ocean of 'foam' that could support life.
He imagined life there to be a silicate/carbon 'worm' that would stretch from head to tail across America from West Coast to East Coast. A creature of that size would perceive the Jovian 'ocean of foam' in the same way that fish perceive water on our planet.
Now we're getting silly. :-]
There is of course only one example so far. They are looking for another solar system like this one. Within 10 years there will probably be a lot of other examples. The critics are nothing new.
===============
In Search of the Milky Way's Habitable Zone
Our Milky Way Galaxy is structured much like billions of other spiral galaxies. The galactic disk contains a lot of interstellar matter (like dust and gas), as well as young and intermediate-age stars. While young stars can be found scattered throughout the Galaxy, the stellar population tends to be older in the bulge around the galactic center.
by Leslie Mullen
for NASA Astrobiology News
Moffett Field - May 24, 2001
Our Milky Way Galaxy is unusual in that it is one of the most massive galaxies in the nearby universe. Our Solar System also seems to have qualities that make it rather unique. According to Guillermo Gonzalez, Assistant Professor of Astronomy at the University of Washington, these qualities make the Sun one of the few stars in the Galaxy capable of supporting complex life. For one thing, the Sun is composed of the right amount of "metals." (Astronomers refer to all elements heavier than hydrogen and helium as "metals.")
Moreover, the Sun's circular orbit about the galactic center is just right; through a combination of factors it manages to keep out of the way of the Galaxy's dangerous spiral arms. Our Solar System is also far enough away from the galactic center to not have to worry about disruptive gravitational forces or too much radiation.
When all of these factors occur together, they create a region of space that Gonzalez calls a "Galactic Habitable Zone." Gonzalez believes every form of life on our planet - from the simplest bacteria to the most complex animal - owes its existence to the balance of these unique conditions.
Because of this, states Gonzalez, "I believe both simple life and complex life are very rare, but complex life, like us, is probably unique in the observable Universe."
"I think this is a very, very interesting idea," says Dr. William Borucki, a research scientist in the Planetary Studies Branch of the NASA-Ames Research Center. "I'm delighted to see this theory. I like how Gonzalez has imagined the consequences of planets existing at different parts of the Galaxy. Now scientists need to check the math to make sure it all adds up."
The Theory in Detail
Our Milky Way Galaxy is structured much like billions of other spiral galaxies. The galactic disk contains a lot of interstellar matter (like dust and gas), as well as young and intermediate-age stars. While young stars can be found scattered throughout the Galaxy, the stellar population tends to be older in the bulge around the galactic center.
Many of these older stars are gathered together into globular clusters, which orbit the nucleus of the Galaxy in a region known as the galactic "halo." Strong emissions of infrared radiation and X-rays from the galactic center indicate clouds of ionized gas rapidly moving around some sort of supermassive object, quite possibly a black hole.
There are billions of stars in the Milky Way Galaxy, and some are more metal-rich than others. Part of this is a condition of age: The older a star, the more metal-poor it tends to be. That's because the most ancient stars formed from just hydrogen, helium, and lithium.
When the most massive of these stars exploded, nuclear reactions fused these light elements into heavier ones. These heavier "metals" became part of the raw material from which a second generation of stars formed. Each stellar explosion led to a greater abundance of available metals. A metal-rich star, therefore, has material that came from many previous generations of stars.
Our Sun is unusually metal-rich for a star of its age and type. Scientists aren't sure why. It could be that the Sun formed in a part of the Galaxy that had an abundance of metals, and then migrated to its present position.
Based on studies of extrasolar planets, metal-rich stars are more likely to have planets orbiting around them. One reason for this may be that a certain minimum amount of metals is needed to form rocky bodies (including the cores of the gas giant planets). A metal-rich interstellar cloud that collapses to form a star would therefore be more likely to form planets than would a metal-poor cloud.
Besides requiring a metal-rich star, a Galactic Habitable Zone excludes stars too close to the galactic center. Our Sun is a nice distance away from the galactic center, about 28,000 light years.
Being in the outer region of the Galaxy protects our Solar System from the huge gravitational tug of stars clustered near the galactic center. If we were closer in, the combined gravity of all those stars would perturb the orbit of comets in the Oort cloud.
The Oort cloud, which circles the outer perimeter of our Solar System, contains trillions of comets. The gravitational disturbances caused by other stars would send many of those comets in our direction - increasing the rate of comet impacts and endangering - if not eventually wiping out - life on Earth.
Staying away from the galactic center has an additional advantage. The center of the Galaxy is awash in harmful radiation. Solar systems near the center would experience increased exposure to gamma rays, X-rays, and cosmic rays, which would destroy any life trying to evolve on a planet.
"Large, complex organisms are much more sensitive to environmental perturbations than simple life," says Gonzalez. "Our hypothesis deals exclusively with complex life, more specifically, aerobic macroscopic metazoan life. The effects of radiation would damage the ozone layer, as well as increase radiation levels at the surface of a planet from secondary particle cascades in the atmosphere."
Keeping out of the way of the Galaxy's spiral arms is another requirement of the Galactic Habitable Zone.
The density of gases and interstellar matter in the spiral arms leads to the formation of new stars. Although these spiral arms are the birthplaces of stars, it would be dangerous for our solar system to cross through one of them.
The intense radiation and gravitation of a spiral arm would cause disruptions in our Solar System just as surely as if we were closer to the center of the Galaxy.
Luckily, our Sun revolves at the same rate as the Galaxy's spiral-arm rotation. This synchronization prevents our Solar System from crossing a spiral arm too often.
"At our location, our orbital period is very similar to that of the pattern speed of the spiral arms," says Gonzalez. "This means that the time interval between spiral arm crossings will be a maximum, which is a good thing, since spiral arms are dangerous places. Massive star supernovae are concentrated there, and giant molecular clouds can perturb the Oort cloud comets leading to more comets showers in the inner solar system."
The unusually circular orbit of our Sun around the galactic center also tends to keep it clear of the spiral arms. Most stars the same age as our Sun have more elliptical orbits.
"If the Sun's orbit about the galactic center were less circular," says Gonzalez, "the Sun would be more likely to cross spiral arms."
Thus, thanks to a lot of unusual characteristics of our Sun, our Solar System is lucky enough to lie in a Galactic Habitable Zone. Gonzalez argues that these characteristics made it possible for complex life to emerge on Earth.
More than 95 percent of stars in the Galaxy, says Gonzalez, wouldn't be able to support habitable planets simply because their rotation is not synchronized with the rotation of the galaxy's spiral arms.
Add all the other factors involved in keeping a solar system habitable, and it seems that the odds of finding another solar system in a Galactic Habitable Zone are close to impossible.
"This is a good theory," says Borucki. "I think this idea is a spark that will initiate similar research. Like a spark plug, it can't drive the car, but it provides the necessary impetus to get the car moving."
What's Next?
Gonzalez says he plans to continue his studies on the limitations of life in the Universe. He and his colleagues are working on a paper that discusses such dangers from space as transient radiation sources and large comet or asteroid impacts.
===============
There you have it: Detecting extraterrestrial life is a hopeless endeavor.
Who's got a beer?
A nicer one from the Jet Propulsion Laboratory (just down the road from me):
1.) They know about commie/social/facists trying to run this planet and since the key word is "intelligent", they're staying away.
2.) They have commie/social/facists running their planet, and can't be considered "intelligent".
3.) Played God with the wrong genome.
4.) Got hit by a really big object.
5.) Their sun became really big and red.
6.) Too close to a supernova.
7.) Too close to a black hole.
8.) They were in the way of a Vogon Constructer Fleet.
9.) Deported all of their telephone sanitizers.
GSA(P)
GSA(P)
They certainly CAN make logical deductions based on existing knowledge and theory, they have to use the only example they have, "our" solar system to determine the ratio of rocky planets to gaseous ones and then extrapolate that to other systems. They may NEVER be able to actually SEE the other planets optical or radio imaging at those distances are quite limiting. As new telescopes come online, like the wide baseline optical interferometer, they will be able to refine the technique for wobble measurement to include ALL bodies orbiting a particular star and knowing where an object is orbiting they can then calculate a rough idea of it's temperature, gravity, etc. and come pretty darn close to determining if it's almost earthlike.
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