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An awful waste of space
“THERE are four hundred billion stars out there, just in our galaxy alone. If only one out of a million of those had planets . . . if just one out of a million of those had life… and if just one out of a million of those had intelligent life,” says astronomer Allinore Arroway “there would be literally millions of civilizations out there.”
“If there wasn’t,” says Palmer Joss “it’d be an awful waste of space.” With these simple dialogues in the movie Contact, writer Carl Sagan put his ambitious dreams and worst nightmares together.
Everyone who is looking for extraterrestrial (ET) intelligence is hopeful about the existence of intelligent life beyond Earth. At the same time, no one is sure whether ET will contact us. For the last hundred years or so, ET has been a popular subject of debate among the astronomers, cosmologists, creationists and science fiction writers as well. And, if Martin Beer and his colleagues at the University of Leicester are correct, we can easily consider ourselves an exception, rather than a routine of the universe.
In a recent online preprint, published on Arxiv
We, the earthlings, are so familiar with life that we don’t even bother about how rare and precious it can be at a cosmic level. Along with other revolutions in science and technology, the twentieth century has also broadened our cosmic vision.
Equipped with better, deeper theories and increasingly sensitive instruments of observation, modern day astronomers discovered numerous galaxies like the one we live in. Such findings gave rise to the thinking that as there are countless Sun-like stars in the universe, so there might be billions upon billions of Earth-like planets orbiting such stars.
This led to the idea that, if there is a greater probability of an Earth-like planet orbiting a Sun-like star, then life can also emerge on such a planet.
Furthermore, primordial life may also evolve to become intelligent like human beings. That intelligent life might form a civilization like humans and, after a dozen or so millennia of continuous progress in science, technology, politics and other disciplines, it may reach the “radio communication age.”
That is, an extraterrestrial civilization might become advanced enough to use radio waves as a tool for communication. If interested in finding out another civilization in outer space, that civilization may broadcast radio signals to contact “someone” like itself, beyond its own planet.
Keeping this idea in mind, astronomers Frank Drake and Carl Sagan attempted to approximate intelligent, developed and “capable of radio communication” civilizations in the universe, considering a number of factors. This approximation is now known as the “Sagan-Drake equation.”
Sagan, in his bestseller Cosmos, carefully estimated that there might be around ten technologically advanced civilizations in our galaxy. In 1960’s, astronomers’ passion for ET resulted in “Search for Extra-Terrestrial Intelligence” (SETI). With increasingly advanced and sensitive instruments, SETI people have scanned a good portion of the sky at various radio frequencies, but in vain.
Perhaps ET has recently transmitted radio signals towards the Earth and, perhaps, it is thousands of light years away from us. As such, the radio signals from ET may take a couple of thousand years to reach the Earth. With this hope, the SETI people continue to look and listen.
Diminishing hopes of finding life were rekindled once again in 1996, when Geoffrey Marcy and Paul Butler from San Francisco State University announced the discovery of two Jupiter-like planets, orbiting the stars 47-Ursae Majoris and 70 Virginis respectively.
Having masses of 2- 6 times of Jupiter, the planetary systems of these extra-solar planets did not seem to harbor life. But their discovery fuelled a long standing debate regarding ET, since if Jupiter-like planets are out there, then, soon or later, we should be able to find a planetary system identical to the one we have. It’s just the matter of more sensitive and advanced instruments.
Since then, 110 extra-solar planets have been discovered (astronomers have announced the discovery of two or three more extra-solar planets last month).
Right now, there are no telescopes powerful enough to directly observe extra-solar planets. Therefore, observable irregularities in the movements of distant stars are used. If a star is accompanied by a Jupiter-like planet, gravitational pull of that massive planet will cause wobbling in the motion of its star.
By carefully observing the wobbling in a particular star, astronomers utilize sophisticated equations of gravitation to calculate the probable mass, orbital velocity and orbital eccentricity of the planet. All extra-solar planets have been discovered by using this technique.
If planetary systems with Jupiter-like planets are common place, then why can’t there be earth-like planets, argue ET enthusiasts. Martin Beer and colleagues don’t seem to agree with this presumption. They counter-argue that the mass of a planet isn’t everything.
Although the masses of extra-solar planets discovered thus far are one-tenth to ten times that of Jupiter, most other properties are very different. For example, almost all of the Jupiter-like extra-solar planets are found to be much closer to their parent stars than Jupiter is to our sun. That is why they are also called “hot Jupiters.”
Furthermore, their orbits are far more elliptical, while Jupiter has an almost circular orbit.
According to modern astronomy, planets in our solar system formed when small pieces of rock and dust merged. About 4.5 billion years ago, our newborn sun was surrounded by a huge cloud of dust and gas. Gravity squeezed dust particles into pebbles. Those countless pebbles collided together and formed larger rocks. And, finally, those rocks merged further to form very small planets or “planetesimals.”
Collisions among planetesimals continued and resulted in Mercury, Venus, Earth and Mars — now collectively known as “rocky dwarves.”
On the other hand, a greater number of planetesimals merged and formed even bigger balls of rocks.
Being more massive than dwarves, those giants attracted most of the remaining gas from around the sun and turned it into their denser atmospheres. These “gas giants” are now called Jupiter, Saturn and Uranus.
But there can be another scenario for a planetary system to form. Known standard laws of nature suggest that Jupiter-like planets can form directly. Gaseous clouds around a star may condense into huge balls of gas, which can collapse under its own gravity to form Jupiter-like planets.
The net result might be a planetary system having giant planets only. Though such giants can have a wide range of orbital radii and eccentricities, no earth-like planet would be present. No one denies the validity of this scenario.
However, a solar system is supposed to be the most common case in point, and astronomers estimated that the direct method of planetary system formation is so rare that it can be safely kept out of consideration.
Beer and his colleagues suggest that we should rethink about the process responsible for a greater number of planetary systems.
They think that, perhaps, all the extra-solar planets discovered by now are a result of another process that is considered least probable for a planetary system.
With more powerful space-based telescopes and vast networks of earth-based telescopes, astronomers expect to directly observe extra-solar planets within a decade or so.
After discovering even more planetary systems, we should be better able to figure out whether we can hope for a large number of civilizations out there, or if it really is an awful waste of space.
The author
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