Are We Alone-Finding Life On Other Planets

Are we alone in the universe?
By Clive Cookson
Published: March 19 2010 22:18 | Last updated: March 19 2010 22:18

The Allen Telescope Array in California is used both for radio astronomy and the search for extraterrestrial intelligence
The Eerie Silence: Are We Alone in the Universe?
By Paul Davies
Allen Lane £20, 260 pages
FT Bookshop price: £16

How to Find a Habitable Planet
By James Kasting
Princeton University Press, £20.95, 326 pages
FT Bookshop price: £16.76

We Are Not Alone: Why We Have Already Found Extraterrestrial Life
By Dirk Schulze-Makuch and David Darling
OneWorld, £12.99 186 pages
FT Bookshop price: £10.39

Life, the Universe ... and the Scientific Method
By Steven Benner
FfAME Press, $35 302 pages

On a misty morning in April 1960, a young astronomer called Frank Drake pointed the Green Bank radiotelescope in West Virginia at a nearby star, Tau Ceti. He listened for signals from any alien civilisation that might inhabit its planetary system. Silence. Then Drake reoriented the 26-metre dish towards a second star, Epsilon Eridani. The startled astronomer picked up a strong radio signal that could not come from a natural source. But before he could start decoding the alien message, he learnt that it actually emanated from a secret terrestrial source: a defence radar establishment.

Fifty years later, Drake is the grand old man of the field he founded, which quickly became known as Seti, the search for extraterrestrial intelligence. The amount of data has expanded immensely but the story of Seti is still radio silence, punctuated by occasional false alarms.

Indeed, not only have astronomers failed to find evidence of alien intelligence, they still do not know for sure that any life exists beyond Earth, even simple micro-organisms. Yet, as a crop of new books shows, astrobiology – the scientific search for extraterrestrial life, simple or advanced – has never been more active. Evidence is growing that many stars in our galaxy have planets on which life might have originated. At the same time, new technology should make it easier to detect alien life if it exists – in primitive form in our solar system or more advanced on other star systems.

The authors take markedly different approaches to the subject, so there is little overlap between their four books. However they are all mainstream scientists; there is nothing here about UFOs or alien abductions. Paul Davies, a physics professor and the best-known author in the group, concentrates on Seti. James Kasting, a geoscience professor, looks at the search for habitable planets in orbit around other stars. Dirk Schulze-Makuch, an astrobiology professor, and David Darling, a science writer, focus on life within the solar system. And Steven Benner, a biochemist, takes a broader view of the scientific and philosophical issues involved in the origins and evolution of life.

Soon after beginning his search, Frank Drake formulated Seti’s key equation: N = RfpneflfifcL. To estimate N, the number of advanced civilisations with which we might communicate, you need to multiply seven terms: the number of stars in our galaxy; the fraction of stars with planets; the fraction of planets that are Earth-like and “habitable”; the fraction of habitable planets on which life gets going; the fraction of inhabited planets on which intelligent life evolves; the fraction of intelligent civilisations than can communicate over interstellar distances; and the average lifetime of a communicating civilisation. Apart from the number of stars, which can be estimated reasonably well at around 400bn, the terms in the Drake Equation remain almost as uncertain today as when it was formulated.

As Kasting shows in his technical but readable guide, How to Find a Habitable Planet, we are making rapid progress in discovering planets around distant stars – almost 500 so far. Current technology does not yet enable astronomers to detect planets similar in size and composition to Earth; all the ones found so far are much larger than Earth. But according to current theories of planetary formation, these giants must be accompanied by smaller habitable planets – 4bn of them in our galaxy, Kasting estimates. A new generation of space telescopes will narrow down that estimate. By 2013 the Kepler observatory, launched by Nasa a year ago, should give astronomers a good idea of how common Earth-like planets are.

But, as Kasting tells us, we shall have to wait another two decades – depending how generous governments are in their funding of space agencies – before telescopes are sensitive enough to detect planets that actually harbour life. An atmosphere rich in oxygen and certain other gases would be a sure sign of biology. There is even the possibility of eventually taking pictures of planets to look for an Earth-like surface of oceans and continents.

Despite the buzz about astrobiology, there is still no scientific consensus about how life started on Earth, let alone elsewhere. The general presumption is that the carbon-based (organic) compounds on which terrestrial life is based formed through abiotic chemical reactions on the hot, wet, electrically charged surface of the young planet about 3.5bn years ago. Scientists who simulate the conditions of early Earth in a laboratory can make some simple organic chemicals that may be precursors of life. But it is a huge and unknown step from there to the large, replicating and evolving molecules that might be regarded as alive.

The best account of possible origins of life on Earth and beyond appears in Life, the Universe ... and the Scientific Method. Many authors have explored the issue, and Benner valiantly read 62 previous books on the question to get a feel for scientific opinion before writing his own.

“Some books treated life as something easy to originate as an inevitable consequence of the laws of physics and chemistry,” he reports. “They viewed life as abundant in the cosmos. Reading these books, I began to believe that aliens are everywhere.” On the other side of the chasm were authors who “provided pages of reasons why life could not easily emerge by any known process. Their authors saw the emergence of life as a highly improbable event, suggesting that life in the cosmos should be scarce. Reading these books, I felt lucky to be here myself”.

Without coming down firmly on either side of the argument, Benner describes a plausible chemical scenario for the formation of life, in which minerals could act as a template for molecules of RNA (ribonucleic acid) to form and replicate themselves. Today RNA acts as an intermediate between DNA (deoxyribonucleic acid), the store of genetic information, and proteins, the molecules that do most of the work in living organisms. According to the “RNA world” hypothesis, simple life on Earth began with self-replicating RNA, which evolved into cellular microbes as proteins and DNA were added to the equation. So far, scientists have assumed that life on Earth started once only. Certainly the biochemical evidence, notably the existence of a single genetic code, suggests that all creatures great and small are descended from a common ancestor.

But Paul Davies suspects that a second genesis may have given rise to a “shadow biosphere” consisting of microbes with distinctly different biochemistry, which could be still lurking in some extreme environments – such as deep within rock strata.

A shadow terrestrial biosphere is certainly worth a scientific search. As Davies writes in The Eerie Silence: Are We Alone in the Universe?: “If life started more than once on Earth, we could be virtually certain that the universe is teeming with it. Unless there is something very peculiar about our planet, it is inconceivable that life would have begun twice on one Earth-like planet but hardly ever on all the rest.”

Some extraterrestrial life enthusiasts, however, feel they already have convincing evidence for its existence. They include Dirk Schulze-Makuch and David Darling, as the title of their provocative – but not wholly convincing – book makes clear. We Are Not Alone concentrates on our own solar system. The authors conclude that three sources of evidence prove the existence of microbial life on Mars. One is the experiments carried out on the Martian surface in 1976 by the US Viking Landers; at the time Nasa said the intriguing soil chemistry could be explained by non-biological processes but Schulze-Makuch and Darling make a good case for microbial involvement. They also believe that methane gas, recently detected in the Martian atmosphere, is a sign of life – and that fossilised microbial remains exist in Martian meteorites, chunks of rock blasted off the planet by asteroid impacts that ended up on Earth.

Because the planets can exchange material via meteorites, the discovery of life on Mars would not necessarily require a second genesis. Earth could have seeded Mars or vice versa. But Schulze-Makuch and Darling are also confident – without any firm evidence, it must be said – that life of a very different kind exists in the outer solar system, on moons of Jupiter and Saturn, where it could not have realistically travelled from Earth or Mars.

Once life does get started, what are the chances that intelligence will evolve? On Earth it took around 3.5bn years, in what appear by galactic standards to have been remarkably benign conditions. Both Kasting and Davies discuss many special factors that may have made Earth a uniquely stable environment for complex life to develop. These include plate tectonics – a geological mixing process that plays a vital role in the development of a life-friendly atmosphere – and the stabilisation of Earth’s spin axis by the moon. Sheer luck must have played a role, too, in preventing a life-ending impact with an asteroid or comet larger than the one that put paid to the dinosaurs 65m years ago.

In the end Kasting rejects what has become known as the Rare Earth hypothesis, which holds that complex life is extremely scarce throughout the galaxy. Davies, however, concludes “as a scientist” that “we are probably the only intelligent beings in the universe ... I arrive at this dismal conclusion because I see so many contingent features involved in the origin and evolution of life, and because I have yet to see a convincing theoretical argument for a universal principle of increasing organised complexity”.

On the other hand, Davies “as a philosopher and human being” takes a very different view. He strongly supports Seti – though he wants it to move beyond ever more powerful searches for extraterrestrial radio signals and laser flashes to look for other signs of aliens in the galaxy – and he even has an official role, as chairman of the Seti Post-Detection Taskforce, which decides how astronomers should respond to an alien message. Davies is the most engaging of writers and his contradictory views encapsulate those in the field.

Today, enthusiasts can still argue that we just have not looked hard enough for extraterrestrial life. But data and analysis are accumulating at an exponential rate. After another 50 years we should know enough to choose between the three current possibilities. Most exhilarating would be to find a universe full of intelligence, promising a bright future for mankind. The most depressing finding would be that complex life is widespread but intelligence is confined to Earth, because this would imply that advanced civilisations got snuffed out quite quickly by warfare, environmental destruction or technological accidents. The third possibility, that Earth is a unique oasis of life, might be quite uplifting. Davies says: “It would provide us with the truly cosmological mission of perpetuating a precious phenomenon – the flame of reason.”

The Best Place To Look For Life On Other Planets

Starring Intelligent Aliens



Alien Life
Posted: 11/05/09
Author: Clara Moskowitz
Summary: The most probable place to find intelligent life in the galaxy is around stars very similar to our sun, a new study has found.


Artist's visualization of one kind of habitable planet that might exist in the galaxy - a "water world" with a creature living it its vast, planet-covering ocean.
Credit: Nahks Tr'Enhl
When scientists search the heavens for habitable worlds beyond Earth, they don't necessarily know what to look for. A new study has found that the most probable place to find intelligent life in the galaxy is around stars with roughly the mass of the sun, and surface temperatures between 5,300 and 6,000 Kelvin (9,100 and 10,300 degrees Fahrenheit) - in fact, stars very similar to our own sun.

Learning that sun-like stars are good candidates for life may not sound surprising, but it isn't always what scientists have thought.

"The principle of mediocrity says that, barring any evidence to the contrary, our observations should be typical among those of all intelligent observers,” said researcher Daniel Whitmire, a physicist at the University of Louisiana at Lafayette. "But the typical star is not like the sun - the typical star is a low mass star. We don’t find ourselves around a typical star and we show the reason why in this paper. Our results confirm the principle of mediocrity as applied to the sun."

Sun-like stars are actually a minority in the galaxy - 93 percent of stars in the Milky Way are less massive, less luminous and cooler than the sun. Though the typical star in the galaxy weighs between one-tenth and half the mass of the sun, life is more likely to be found around the more unusual variety of stars like our own, the researchers found.


Distributions of mass and orbit size for the extrasolar planets so far discovered. The habitable zone is marked in green.
Credit: NASA
To make their calculation, Whitmire and colleague John Matese combined models of how planets form with data on the distribution of stars in the galaxy as a function of mass. The planet models show when worlds are most likely to form in the habitable zone - a Goldilocks region around a star in which a planet would be just right for life - not too close that its surface would be boiling, and not too far that it would be frigid either. Planets in the habitable zone are the best candidates for having liquid water, which is thought to be a prerequisite of life. In general, the planet-formation theories predict that more massive stars are the most likely to have planets in the habitable zone. So the larger a parent star is, the more likely its planets will have environments conducive to life.

But this advantage of larger stars is counteracted by the fact that more massive stars are less abundant - there are fewer big stars out there. In addition, the more massive a star is, the shorter its lifetime. That makes it hard to find very massive stars that have lived long enough for complex life to develop.

The researchers weighed these factors against each other to calculate the distribution of stars most likely to host thinking, living creatures. "It's a tradeoff between the numbers of stars out there and the probability of habitable planet formation increasing with mass." Whitmire said. "We show it's no accident we find ourselves around a star like the sun." The distinction between habitable planets and planets harboring intelligent life is based on the fact that intelligent life requires stars with lifetimes greater than the time required for intelligence to evolve. For example, in the case of this solar system, we could not find ourselves around a star with a lifetime less than 4.5 billion years.


Stars like our sun may be the most likely to harbor intelligent life in the galaxy.
Credit: NASA/SOHO
Indeed, sun-like stars seem to have the right balance: They are of high enough mass that they are more likely to host habitable planets, but they are of low enough mass that they live long enough for intelligent life to develop, and are not extremely scarce. Whitmire estimates that 10 percent of the Milky Way's stars might fall into the category they've outlined. This would still leave over 10 billion candidate stars in the Milky Way alone.

The results mitigate the most commonly used argument that intelligent life must be extremely rare, Whitmire said. This idea, based on the anthropic principle, was outlined by astrophysicist Brandon Carter. There is an approximate coincidence between the time it took intelligence to evolve on Earth and the lifetime of the sun. Assuming these two timescales are independent, this coincidence makes sense if intelligent life is extremely improbable, Carter argued. In most cases, he claimed, the time it takes for intelligent life to emerge is much longer than the portion of a star's existence that is conducive to such life.

"In the paper we explain one number in the coincidence – why the lifetime of the sun is what it is," Whitmire said. "The additional assumption necessary to counter the Carter argument is that intelligent life requires at least a few billion years to evolve, as expected if we are typical."

Renowned Astronomer Dr. Frank Drake Says Life On Other Planets A Certainty

http://www.seattlepi.com/local/405707_drake30.html?source=mypi

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Galaxy Has Billions Of Earths

Galaxy has 'billions of Earths'


The number of stars points to there being many rocky planets
There could be one hundred billion Earth-like planets in our galaxy, a US conference has heard.
Dr Alan Boss of the Carnegie Institution of Science said many of these worlds could be inhabited by simple lifeforms.
He was speaking at the annual meeting of the American Association for the Advancement of Science in Chicago.
So far, telescopes have been able to detect just over 300 planets outside our Solar System.
Very few of these would be capable of supporting life, however. Most are gas giants like our Jupiter, and many orbit so close to their parent stars that any microbes would have to survive roasting temperatures.
But, based on the limited numbers of planets found so far, Dr Boss has estimated that each Sun-like star has on average one "Earth-like" planet.
This simple calculation means there would be huge numbers capable of supporting life.
"Not only are they probably habitable but they probably are also going to be inhabited," Dr Boss told BBC News. "But I think that most likely the nearby 'Earths' are going to be inhabited with things which are perhaps more common to what Earth was like three or four billion years ago." That means bacterial lifeforms.
Dr Boss estimates that Nasa's Kepler mission, due for launch in March, should begin finding some of these Earth-like planets within the next few years.
Recent work at Edinburgh University tried to quantify how many intelligent civilisations might be out there. The research suggested there could be thousands of them.