Will some readers of this article walk on Mars? I hope so indeed. I think it is very likely that they will. It will be dangerous perhaps the most exciting exploration of all time. In earlier centuries pioneer explorers discovered new continents, went to the jungles of Africa and South America, reached the North and South Poles and scaled the summits of the highest mountains. Those who traveled to Mars will go in the same spirit of adventure.
It would be wonderful to traverse the mountains, canyons and craters of Mars, or perhaps fly over them in a balloon. But no body would go to Mars for a comfortable life. It will be harder to live there than at the top of the Everest or at the South Pole.
But the greatest hope of these pioneers would be to find something on Mars that was alive.
Here on Earth, there are literally millions of species of life - slime, moulds, mushrooms, trees, frogs, monkeys and humans as well. Life survives in the most remote corners of our planet-in the dark caves where sunlight has been blocked for thousands of years, on arid desert rocks, around the hot springs where water is at the boiling point, deep underground and high in the atmosphere.
Everywhere you find life on Earth, you find water. There is water on Mars and life of some kind could have emerged there. The red planet is much colder than the Earth and has a thinner atmosphere. Nobody expects green goggle-eyed Martians like those that feature in so many cartoons. If any advanced intelligent aliens existed on Mars, we would already know about them and they might even have visited us by now!
Our Earth teems with extraordinary range of life forms. But there constrains on shape and size. Big animals have fat legs but still cannot jump like insects. The largest animals float in water. Far greater variety could exist on other planets. For instance, if gravity is weaker, animals could be larger and creatures our size could have legs as thin as insects.
Mercury and Venus are nearer the Sun than the Earth is. Both are very much hotter. Earth is a Goldilocks planet i.e. not too hot or not too cold. If the Earth were too hot, even the most tenacious would fry. Mars is bit too cold but not absolutely frigid. The outer planets are colder still.
What about Jupiter, the biggest planet in our solar system? If life had evolved on this huge planet, where the force of gravity is far stronger than on Earth, it could be very strange indeed - for instance huge balloon like creatures floating in the dense atmosphere.
Jupiter has four large moons which could, perhaps, harbour life. One of these, Europa, is covered in thick ice. Beneath that there lies an ocean. Perhaps there are creatures swimming in this ocean? To search for them, there are plans to send a robot in a submarine.
But the second biggest moon in the solar system is Titan, one of Saturn's many moons. Scientists have already landed a probe on Titan's surface, revealing rivers, lakes and rocks. But the temperature is about minus 170 degrees Celsius, where any water is frozen solid. It is not water but liquid methane that flows in these rivers and lakes - not a good place for life.
Lets now widen our gaze beyond our solar system to other stars. There are tens of billions of these suns in our galaxy. Even the nearest of these is so far away that, at the speed of a present day rocket, it would take millions of years to reach it. Equally if clever aliens existed on a planet orbiting other star, it would be difficult for them to visit us. It would be far easier to send a radio or laser signal than to traverse the mind boggling distances in the interstellar space.
If there was a signal back, it might come from aliens very different from us. Indeed, it would come from machines whose creators have long ago been usurped or become extinct. And, of course, there may be aliens who exist and have big 'brains' but are so different from us that we wouldn't recognize them or be able to communicate with them. Some may not want to reveal that they exist even if they are actually watching us! There may be some super-intelligent dolphins, happily thinking profound thoughts deep under some alien ocean, doing nothing to reveal their presence. Still other 'brains' could actually be swarm of insects, acting together like a single intelligent being. There may be a lot more out there than we could ever detect. Absence of evidence isn't evidence of absence.
There are billions of planets in our galaxy and our galaxy itself is only one of billion. Most people would guess that the cosmos is teeming with life but that would be no more than a guess. We still know too little about how life began, and how it evolves, to be able to say whether simple life is common. We know even less about how likely it would be for simple life to evolve in the way it did here on Earth. My bet is that simple life is indeed very common but intelligent life is much rarer.
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This was the plaque that was carried by Voyager 1 and
Voyager 2 spacecrafts which digitally stored all sorts of
sounds, music, pictures, greetings in different languages
on the Earth. In case some extraterrestrial intelligence finds
this they may soon contact us.
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Indeed, there may not be any intelligent life out there at all. Earth's intricate biosphere could be unique. Perhaps we really are alone. If that's true, it is a disappointment for those who are looking far alien signals or who even hope that some day aliens may visit us. Bur the failure of searches need not depress us. Indeed it is perhaps a reason to be cheerful because we can ten be less modest about our place in the great scheme of things. Our Earth could be the most interesting place in the cosmos.
If life in unique to the earth, it could be seen as just a cosmic sideshow though it needn't be. That is because evolution isn't over indeed, it could be nearer its beginning than its end. Our solar system is barely middle aged and it will be 6 billion years before the Sun swells up, engulfs the inner planets and vaporises any life that still remains on Earth. Far future life and intelligence could be as different from us as we are from a Galaxy, evolving into a teeming complexity far beyond what we can imagine. If so our tiny planet, this pale blue dot floating in space could be the most important place in the entire cosmos.
(Extracted from 'George's cosmic treasure hunt' by Lucy Hawking)
Unlike our Sun, these did not form planets. The early solar system was filled with collisions due to high density of dust, lumps and gases. Several bits of matter gradually formed one or two big masses. In this way many big bodies are formed and still there were many remnants left over such as asteroids and at far off the disk, these formed what now we call comets. The ones which have nearly circular orbits around the Sun sustained collisions and avoided bumping into each other to form today's planets.
As earlier discussed, due to the arrangement of gases in the solar nebula formed on the basis of the molecular weights of the respective gases. This caused the lighter gases such as hydrogen and methane to go near the disk whereas the heavier elements come near the Sun, thus forming the gas giants and rocky balls. Since the formation, the probability of inter-planetary bumping reduced gradually.
So, as we discussed there were many remnants in the 'now' solar system. But there is still some probability of the 'tiny' bits of rocks hitting any planet and if these hit our home planet .................. it would be a disaster for the human race......... to be continued.............
