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Aliens in Our Galaxy? Experts Map Possible Hotbeds

Stefan Lovgren
for National Geographic News
January 6, 2004

Scientists say a ring-shaped region in the disc of the Milky Way shows the highest potential for life in our galaxy.
But don't expect them to find extraterrestrial life anytime soon: In this region, there are some 20 billion star systems that offer the prerequisites of life.

Using computer models, astronomers have mapped star systems in our galaxy that meet basic criteria to host extraterrestrial life. The crude map includes ten percent of the stars in our galaxy, located in a ring around the center of the Milky Way. A double star cluster in a satellite galaxy of the Milky Way is pictured above.

The team of astronomers has identified stars that contain enough heavy elements to form terrestrial planets; are sufficiently distant from disastrous supernova explosions; and have existed for at least four billion years?the time it took for complex life to evolve on Earth.

Using a sophisticated computer evolution model, they found that ten percent of the stars in our galaxy, located in a ring around the center of the Milky Way, meet those criteria.

"This is a crude first map of where life could be in our galaxy," said Charles Lineweaver, an astrophysicist at the University of New South Wales in Sydney, Australia, who led the study.

The research also shows that 75 percent of the stars in this habitable zone are older than our sun; so if there is actually life there, it's probably more evolved than life on Earth.

"Metallicity"

Our galaxy, the Milky Way, contains more than 200 billion stars and countless other objects. It is one of billions of other galaxies in the universe.

The Milky Way was formed some 12 billion years ago out of a large cloud of gas, mainly hydrogen and helium, that collapsed on itself and began forming stars. Since the cloud was rotating, its spherical shape flattened into a disc.

As the formation of the new stars continued, the most massive stars exploded and enriched the gas in the cloud with new, heavier elements. The new stars that were created in these disc regions contain the heavier elements required to form terrestrial planets, which may be spinning around them.

In their search for possible life, scientists look for favorable zones of "metallicity." A star with no heavy metals can't form terrestrial planets or life.

"Anytime you can identify regions that have higher concentrations of metallicity, that's where you may find life," said Lineweaver. "In our model of the galaxy, we keep track of where and when these metals were produced. We can do that because we know how many massive stars went 'boom' as a function of time and place."

Planets in regions that are too rich in metals, meanwhile, are vulnerable to so-called Earth-killers, preferentially found in such regions. If a gas-filled, Jupiter-like planet migrates through an area that is too rich in metals, it will kill any "Earths" that are there.

Exloding Supernovae

But the right level of metallicity isn't the only prerequisite for life. The astronomers also had to look for regions that have experienced relative calm for at least four billion years, the time it took for life to evolve on Earth.

"In a high-density stellar environment, you will not have four billion years of clement, let's-sit-back-and-evolve life," said Lineweaver. "For complex life to evolve, you may need about four billion years without too many supernovae going off."

The computer model used for the study is based on local observations. Scientists can look at stars all over the galaxy and determine the metallicity at the time they were formed.

The region the researchers have concluded is the most favorable to host life is a ring that measures 21,000 to 27,000 light-years from the center of the galaxy. Created between four and eight billion years ago, this region is where 10 percent of the stars of the Milky Way were formed.

"We're not saying anything about the probability of extraterrestrial or complex life," said Lineweaver. "But if it does exist, and we're right about our prerequisites for it, this is the distribution it will have. This is where life will be."

Humans vs. Aliens

The astronomers were also able for the first time to determine the age of the stars in the habitable zone. They found that 75 percent of them are older than our sun.

"If people think that intelligent life will happen on these planets, then 75 percent of this intelligent life will have had a longer time to evolve than people or the entities that are circulating around our sun," said Lineweaver.

"We're all trying to figure out how we compare to any life-forms that may exist in the universe," he added. "This study is the closest thing I can think of to answer that question. If there are aliens, 75 percent of them will have had longer time to evolve than we have. That may be the most fundamental take-home message of this study."

Alien Life? Astronomers Predict Contact by 2025

Hillary Mayell
for National Geographic News
November 14, 2003


Earthlings could make contact with extraterrestrial beings by the year 2025, two astronomers predict in a new book.
The authors say it's unlikely space aliens look like Hollywood's ET?little, green, and hairless?and that while aliens are highly unlikely to pay Earth a visit, they may be sending radio signals across space to let us know they exist.

The book, Cosmic Company, "is an explication of why we think they're out there, how we're looking for them, what they must be like, and a little bit of what it might mean" to find life on other planets, said co-author Seth Shostak, a senior astronomer at the Search for Extraterrestrial Intelligence Institute (SETI) in Mountain View, California.

Astronomers Seth Shostak and Alexandra Barnett helped create "JO Alien," an animated character for a planetarium show at the National Space Centre in Leicester, England, to explore the question of what an alien might look like. "It's the poster child of aliens," said Shostak. "A very conventional kind of alien?grey and smooth and humanoid?very anthropomorphic. Not what we really expect."

The institute conducts research in astronomy, the planetary sciences, and evolution. Past research projects have been funded by NASA, the National Science Foundation, and numerous universities and foundations.

Beyond Our Galaxy

Shostak and co-author Alexandra Barnett, an astronomer and executive director of the Chabot Space and Science Center in Oakland, California, base their predictions on a number of factors.

They include the billions of years in which extraterrestrial life could have evolved and the abundance of planets and stars elsewhere in the universe that are likely to mimic environmental conditions found on Earth.

"It's a matter of statistics, really," said Barnett. "Depending on who you talk to, the universe is 12 to 15 billion years old. Humans have only been around for 40,000 years. We really are the new kids on the block. It would just be too tough a pill to swallow to believe that nothing else has evolved in all that time and space."

The universe is indeed vast. In 1924 astronomer Edwin Hubble showed that there are galaxies beyond our own. "More than a half century later, the Hubble telescope has shown that there are at least 100 billion such galaxies," said Shostak. Our galaxy, the Milky Way, is home to at least 100 billion stars.

Planets are also plentiful. Since 1995, when the first Jupiter-sized planet outside of our solar system was found, astronomers have been able to identify about 100 more planets, all of them around 300 times more massive than Earth.

"Planets really are as common as phone poles," said Shostak. "Right now, we know that there are planets out there [orbiting] ten or twenty percent of the stars we look at. So far, only huge planets have been found, but it would be a big surprise if there were only big ones. I don't think anyone expects that to be the case."

Until now, the search for intelligent life has been somewhat hampered by inadequate technology?too few stars surveyed at too low a sensitivity by Earth and space-based telescopes.

But in 2007, NASA will launch the Kepler Mission, a satellite probe able to detect smaller planets the size of Mercury, Mars, or the Earth. The mission is specifically designed to look for planets in what scientists consider the habitable zone: the distance from a star where liquid water can exist on the planet's surface.

Projects like the Kepler Mission and the new Allen Telescope Array, located near Mount Lassen, California, which will enable astronomers to survey 100,000 stars by 2015, should increase the odds of finding a radio signal broadcast by alien life, say the astronomers.

"The bottom line is that there is an enormous amount of real estate, and there doesn't seem to be anything particularly special about our neighborhood. The star that's our sun is nothing special. The Earth is just a rock," said Shostak. "To think anything else is to once again put ourselves at the center of the universe, and scientists are very [wary] of doing that. We've done it before and been proven wrong."


So - was glaubt ihr - was denkt ihr - was sagt ihr dazu?

Searching for Intelligent Life

The building blocks of life on Earth?complex organic compounds and amino acids?are abundant in the universe and can be found in meteorites, comets, and interstellar gas and dust.

"There's a growing realization that there may be some other biology in our solar system," said Shostak. "There are deep oceans on the moons of Jupiter, and some evidence that Mars in its early days really should have had some life. So if there are two or maybe even three instances in this solar system alone, where life could have emerged, it's not unreasonable to consider that similar situations arose in other solar systems."

Of course, there is a difference between life and intelligent life, and scientists disagree about the likelihood of intelligence evolving on another planet.

Some believe that it takes very special conditions for intelligence to evolve. The late Stephen Jay Gould, the preeminent Harvard University evolutionary biologist and paleontologist, wrote that the creation of intelligence was a freak occurrence, requiring a number of specific events to occur that could never be replicated again.

Shostak and Barnett believe differently. They argue that there are evolutionary mechanisms that encourage intelligence, particularly among social beings.

"For instance, if you can intuit the actions of the males next to you?they're about to steal your food or your mate, say?then you're going to have increased breeding success, so the next generation is going to have more ability to live in a social environment," said Shostak. "This is very general behavior?it's not miraculous?you see it in the great apes, of course, but you also see it in dolphins, whales."

"JO Alien"

As to what an intelligent alien life-form might look like should such a thing exist, it's anyone's guess. Shostak and Barnett created "JO Alien," an animated character for a planetarium show at the National Space Centre in Leicester, England, to explore the question.

"It's the poster child of aliens," said Shostak. "A very conventional kind of alien?grey and smooth and humanoid?very anthropomorphic. Not what we really expect."

However, the genderless JO does demonstrate some of the basic principles of physics and engineering that might dictate what another life-form might look like.

"An alien would probably have to be bigger than a rat because rats have quite small brains, and an intelligent life-form would need a bigger brain," said Barnett. "So bigger than a cat, but not bigger than an elephant because there are limitations on how much weight a body can support."

JO Alien has two eyes, based on the assumption that an alien life-form would be found on a planet circling a star. Everything on Earth that lives in light has developed eyes. Why two instead of one? Two gives you the evolutionary advantage of being better able to catch your next meal, said Barnett. Why not ten eyes? It would take an enormous amount of brain-power to process all the signals, she said, with little or no extra benefit.

As far as limbs are concerned, the pair speculate that an extraterrestrial would have more than one, particularly if it's building radio telescopes, but a score would be a stretch. Again, it would require a great deal of brain-power to coordinate all 20, Barnett said.

Given the enormous distances between the stars, measured in terms of trillions of miles, Shostak doesn't expect a visit.

"There's a tremendous amount of interest in alien life, mostly from the point of view that we've been visited," he said. "I don't believe that, and I don't think most scientists do. What we'd most like to convey is that there's a possibility they exist even if they haven't visited, and we're searching for them."

Warum nicht, Zagstruk?

Da werfe ich mal eine Theorie in den Raum:

Was, wenn wir Menschen gar nicht durch Zufall entstanden sind? Sondern das ganze von jemandem beabsichtigt war? Einer Art Gott (aber nicht im biblischen Gedanken des guten, allmächtigen Schöpfers)?

Da kann ich das Buch "Gott kam von den Sternen" von Peter Krassa empfehlen. Sehr interessant zu lesen - und die Interpretationen sind durchaus logisch und ergeben Sinn!

Die Reaktionen wären wohl interessant wenn sich herausstellt, dass wir nur ein fehlgeschlagenes Experiment sind