What, or who is out there, beyond the blue sky we see at daytime, or the mysterious blackness, interspersed with a myriad of twinkling stars dazzling us at nighttimes?
Is there any life out there beyond the tiny sliver of our biosphere, any creatures, perhaps just single cell amoebas, or creatures we might recognize, or even someone else, just like us?
This question is probably as old as the rise of our conscious faculties, and must have puzzled peoples around the globe alike for millennia.
Frank Drake pioneered the search for extraterrestrial life in the early 60s when he listened for signals that might be distinguished from the known cosmic ‘noise’, and emanate from some unknown intelligent civilisation beyond our own fragile spaceship. But since then, no signal candidate has emerged which might give us hope that indeed we’re not alone.
Now the conditions for life to emerge in the vastness of the Universe appear quite stringent, we seem to be extremely lucky to live on a planet, and in a solar system which enjoys just the right conditions.
First, the star providing the necessary energy to warm a planet circling it, plus powering the required photosynthesis for plant growth, and ultimately food production for higher animals, must be of the ‘right kind’.
This means the star must fall into the right range on the HR diagram. 1.)
To keep it brief:
- A star must be: of the right spectral type, long lived, stable.
- ‘Metallicity’, the elements other than H and He in astronomers’ parlance. A star, and hence planets circling it must be born of a gas cloud with high metallicity. So its candidate planets must be similar to earth: rocky, contain Carbon, Hydrogen, Oxygen and all the other elements required for life. 1.)
Quite an ask one might contend.
Yet, we can safely assume the following:
All laws of physics are the same anywhere in the Universe.
Therefore, all the dynamics are the same throughout the Universe.
This means that the formation of stars, and solar systems with planets, follows the same dynamics as in our own.
Rocky planets form closer to the star, near the ‘Goldilock’s Zone’, and larger gaseous planets at the outer fringes.
To date some 300 plus extra solar planets around 260 individual stars have been identified, which might indicate that there should be planets circling most every star in the Universe. Though the planets identified to date are not of the terrestrial type like earth and mars, as they are too small to detect, as yet, the search for these is just intensifying.
We also know the approximate number of stars in our own Galaxy, and a (very) rough guess of the number of Galaxies in the visible Universe:
Stars in the Milky Way Galaxy: perhaps 200, maybe up to 400 billion.
Galaxies in the ‘visible’ Universe: perhaps up to many trillions, but ‘decent’ sized ones perhaps 300 billion.
Stars in the ‘visible’ Universe: perhaps 50 billion trillion, i.e. (50 sextillion) 50x1021.
One can discard a very large number of stars that would not qualify and meet the stringent criteria for life to emerge, and still be left with a rather impressive number of probable stars with solar systems that could be harbouring life!
Keep just one in a thousand and you’ll still be left with 50x1018 possible worlds.
Or keep only one in a million: That leaves 50x1015
Or even just one in a trillion: You’re left with 50x109
That is still Fifty Billion probable worlds in the visible universe as we know it.
Enough probable solar systems with planets to provide the conditions for life, one might contend.
Now even in the solar neighbourhood a probable 10 to 30 percent of stars would meet these conditions; that is the stars, as we don’t know about any planets circling them.
By comparison, in nature as we know it, maybe one in a ten, or even just one in a hundred of seeds may sprout and grow into a plant.
Or on the other end of the scale, one out of 200 to 400 Million sperms has the fortitude and good fortune to be the one to fertilize a waiting egg!
Nature’s largesse is splendid, but so is also its harshness!
Will we ever in the future, or have been in the past, be visited by extraterrestrial beings?
The distances are just too great, and time travel is, and will remain a topic for science fiction writers.
Just to travel to the nearest star system Alpha Centauri at the fastest speed of any man made object ever achieved (250,000km/h by Helios) it would take close to 20,000 years, one way.
This would men a lot of provisions to take along for the ride! And presumably a very large spaceship harbouring enough “breeding stock” to prevent inbreeding over the 1,000 generations or so it would take to get there. Of course frozen sperm could be the answer to that, but this would make the journey all the more tedious!
And as an ultimate test for human nature, would they’ve wiped each other out in the close confines during this rather lengthy journey, before they even arrive?
Will we ever communicate with extraterrestrial beings?
Again because of the vast distances and the time it takes even for signals travelling at the speed of light, communication might be rather awkward.
Conversation’ with intelligent beings on the nearest probable planet in the Alpha Centauri star system:
“Hello, is anybody there”
8 ½ years later:
ñٶ䁲1ἲŁ}ش ŀ}ش£}ش핾ñ}ش ٶ䁲1ٶ䁲1ἲŁŀ ἲ}ش Ł ش£ŀ}ش£
“Sorry Chaps, didn’t get that, can you translate that into Earth-Language”, preferably English if you don’t mind!
On a philosophical level the question is one of whether we should assume that our solar system, our planet earth, and that we, ourselves, warrant to be considered a special case in the Universe.
Now if you’re of a religious bent that may come naturally.
For as we marvel at the smooth workings of the solar system, the meticulous turning of our planet, the clockwork like appearance of the sun, moon, day and night, and the natural flow of the seasons, there seems to be the hand of superior being at play.
We might just be the chosen ones and enjoy the benevolence and generosity of this supernatural being.
Yet fortunately science has provided answers for most every question we might have asked in the past and is uncovering more and more as we search deeper and deeper into the mysteries of the Universe.
To Nature, life is cheap; it is engendered easily for its virility, and yet lost just as quickly for its fragility.
So again, our solar system could hardly be of such uniqueness that in all the vastness of probabilities no other solar system should have provided the same conditions for life to emerge and evolve to the stage of questioning beings like us.
Then yet again, should a star explode in a massive supernova nearby, or even just our own sun have some unexpected ructions before she is ‘due’ to die, and expand inexorably in about 5 to 10 billion years; we’d all be doomed in an instant!
Nature is profligate in its giving and its taking!
Or one more of those massive meteorites or comets hit our fragile spaceship, and we’d perish in a slow, agonising demise.
Not quite the fate one would expect from a benevolent provider and protector of life on a unique oasis, in an otherwise desolate expanse of an unfathomably vast Universe.
But these are the distinct possibilities we have to contend with, and that they haven’t happened to date is not proof of a superior protector, or the uniqueness of our planet.
Meteorites have struck earth and wiped out whole arrays of species, the most famous, and most recent perhaps, being the mighty Dinosaur, 60 million years ago, which is very recent, indeed in astronomical terms.
It is also no proof that things always work this way, for the numbers are just too “astronomical”, so that many worlds out there might have perished along with all its precious cargo of life, at whatever stage of evolution.
Equally, myriads of worlds must have endured for the required billions of years for life to evolve to the stage of “intelligent” beings, as we like to call ourselves, which ponder and ask questions such as these:
Why are we here, how did we get here, and is anyone else out there?
The HR diagram plots the stars according to their colour, (spectral type) versus luminosity.
The categories are classified as:O B A F G K M
Ranging from (O) the Hottest, Largest, Shortest Lived and of the colour Blue, to (M) the Coolest, Smallest, Longest Lived, and of the colour Red.
The sun is a G2 star, so placed somewhere in the lower middle range.
Metallicity is a development which comes with age of a galaxy. All matter in the universe was created in the Big Bang, mainly H and He, and that’s the same for all galaxies. Now some galaxies may be slower and some faster in developing stars which manufacture these higher elements, and then in dying contribute it to the galaxy. Larger Galaxies have an advantage over smaller ones in the formation of new stars.
Metallicity varies from older, ‘metal’ poorer stars to younger, ‘metal’ richer ones.