Posts Tagged planets
One of my three science fiction novels is about a group of explorers who land on a distant planet in an attempt to see if it could be colonized by people of their civilization. Many things go wrong on that planet, and that leads most of the group to consider it as dangerous and unattractive, a place to be avoided at all costs. But a couple of explorers find the planet exciting and beautiful. They are willing to look beyond the death and destruction to see the planet for what it is, a lovely and inspiring place on which they could live.
Fine. But that got me to thinking, what are we likely to find when we get into outer space and see planets and moons and asteroids and comets up close? What will we think once we land on them and take a good look around? Will we think of them as “beautiful?” Or will they be little more than desolate blobs of dust orbiting a hot, blistering sun?
Over the past fifty or so years of the US space program, we’ve seen a lot of images taken on the surface of two major celestial objects in our solar system, Mars and the moon. Astronauts on the moon (the only body outside the Earth mankind has walked on) took many spectacular photographs of their moonwalks (largely on film, mind you) and brought them back for us to wonder at. Several unmanned robotic travelers have landed on Mars and tantalized us with more vivid images, and the European Space Agency landed an unmanned probe on a comet. All three sets of images show a largely barren landscape, though to a great extent that was planned since it’s much easier and much safer to land a spacecraft on a smooth surface than on one littered with rocks. (The Russians did land a spacecraft on Venus, but its few images don’t show much.) I don’t know about you, but I found the landscapes of Mars and moon to be rather plain and not terribly lovely or “beautiful” in the usual sense of that word. They are stark, and in themselves compelling in a minimalist sense. But not “beautiful” in comparison to, say, an evening sunset on the Rocky Mountains, or an autumn landscape of the woodlands of Vermont. Just my opinion here.
Still, in our solar system are planets and moons that we haven’t landed on (and in most cases I hope we don’t), and from above they show many various mottled and unique surfaces. I imagine that the surface of Jupiter’s moon Io would be a fascinating place on which to stand. With volcanoes that spout liquid sulfur, and lava flows and what not, it might be intriguing. (Dangerous, too.) But would we characterize it as “beautiful,” especially in comparison with the Earth? I guess beauty is in the eye of the beholder. We might have to come up with new adjectives to describe the new worlds we encounter.
Nothing we’ve ever seen on any image returned from outer space even begins to compare with the beauty of the surface of the Earth. But we’ve only just begun to explore. Who knows what we will encounter when we land on planets and moons of other solar systems. Will we think of them as “beautiful?” Do you think of the moon or Mars as “beautiful?”
In the first two entries in this series of brief examinations of the difficulty of traveling in outer space to new planets and stars and worlds, I looked at how difficult it is for humans to travel in outer space (we’ve only just made it to the moon), and whether the knowledge of the ability to travel to other stars and their planets really exists at all. Is such knowledge universally available, or are we condemned to travel long distances in spacecraft at well below the speed of light?
In this post, I want to look at the development of life on a fledgling planet and ask the question, what does it take for intelligent life to develop? In fact, I want to go back not only to the development of life, but further, to the birth of the planet itself. What conditions are necessary for a planet to develop life? This will be a tricky question to ask properly because we have only one known example where such conditions have arisen, the Earth, and we can’t be sure that what happened on Earth is a reasonable example for life developing elsewhere. But what the hell, let’s take a look.
Others have tried to estimate the probability of life on other worlds, and the Drake equation is one such estimate. But the Drake equation is concerned with estimating what fraction of planets out there are broadcasting signals into space, a point in evolution we have already reached. As with any examination of the presence of life on other worlds, estimates have to be made when entering data into the Drake equation, and in reality, we have no idea how accurate those estimates are. I’m more interested in trying to find out what percentage of planets that eventually coalesce into a physical body from the dust surrounding a newly-ignited star will eventually go on to develop intelligent life that can leave the bonds of the planet and fly around. Let’s take a look at some of the factors that have to exist before this can happen.
Over the past several years I’ve jotted down a number of factors that have been proposed as essential for the development of intelligent life here on Earth, and, with a little bit of luck, might be necessary for life to develop on another heavenly body.
1. A stable sun: the star around which such a planet orbits can’t get too hot or too cold, or it could halt development of life altogether. (Earth’s sun has gone through cooling and heating phases, but never to a degree that baked or froze the planet, killing life completely.)
2. The planet has to develop at just the right distance from the star. The so-called “Goldilocks” zone.
3. There has to be water on the surface. Not just water, but liquid water, liquid because life can’t develop in steam or ice.
4. The planet has to have an oxygen/nitrogen atmosphere. Granted, life can develop in the absence of oxygen, and probably did on Earth, and those microscopic life forms did produce the oxygen in our atmosphere, but it most likely oxygen will be required for intelligent life to develop.
5. The presence of oxygen in the atmosphere implies ozone in the upper atmosphere to protect the life forms on the surface from too much ultraviolet radiation.
6. A magnetic field surrounding the planet. This implies a liquid iron core and traps cosmic rays and other injurious stuff from outer space.
7. Another planet in the same star system that is large enough to clear much of the excess debris around the star to prevent too much from bombarding the nascent planet.
8. Yet, some bombardment is essential to bring all the stuff (like water) to the new planet that life will require. Not too much, not too little.
9. A large moon that provides a gravitational tug on the planet, inducing tides in the large bodies of water, as well as on the land masses, pulling and pushing them around in just the right way.
10. The planet should be in a near circular orbit so that the radiation it receives from its sun is relatively constant. Not too hot, not too cold.
11. Other planets in the same system have to be in near circular orbits to prevent them from sending debris toward the newly-formed planet, and preventing their gravitational field from pushing the planet into an odd orbit, or even knocking it out of its solar system altogether.
12. Tectonic activity to keep the developing life in a constant state of evolution. Stagnation is the death-knell of advancing development.
13. Periodic extinctions, whether caused by an asteroid strike, volcanic activity, the cooling of the central star, or other factor, to, as in #12, keep the development of life going. Or, to put it more simply, everything has to be shaken up from time to time.
In so many of these factors, not only are they essential in an absolute or qualitative sense, but in a quantitative sense too. Not too much, not too little. Earth got just the right amount of some things—just the right amount of oxygen, a sun neither too hot or too cold, just the right size moon, and so forth. That’s just going to complicate the calculations.
Now, with all these factors in mind (and there may be more we don’t know about), can we make any reasonable calculation as to what proportion of planets in our galaxy fit this profile? Are there other planets out there that could have developed life like ours? To make that calculation, we have to ask what proportion of planets meet each characteristic. That’s impossible to do right now, so we have to estimate. Such estimates may be way off, but let’s give it a try. Let’s assume the simplest situation (and probably an overestimate), that each planet has a 1 in 100 chance of having each characteristic. This works out to 1/100 to the 13th power, or 10 to the −26 power. That says that only one planet out of 10 to the 26th has all the characteristics needed for life to develop. It is estimated that around one hundred billion planets exist in the galaxy. That’s 10 to the 11th power. Okay, make it 10 to the 12th. Clearly, even if we use a serious overestimate to the chances of any characteristic happening on a developing planet, we’ve just eliminated not only the possibility of life developing on another planet, but on our own too. We shouldn’t even exist. Yet, there’s good evidence these characteristics are essential. We can’t just drop two or three. The numbers just don’t add up.
So, where are we? Those numbers do give one possible explanation to Enrico Fermi’s famous paradox, but they are such an overestimate it’s hard to know if that’s the right explanation or not. It is possible that life could develop on other planets in situations we’re not familiar with, after all, we’re using Earth as an example and that may not be the most judicious model. Are we freaks in one way or another? Are we alone? You be the judge.
Could life ever arise on the planet Venus? That is, Venus as it exists today. Venus is a hellish place, with temperatures of around 462°C at the surface, rain composed of sulfuric acid, lava-flows over much of the surface, and an atmospheric pressure around 90 times that of Earth at sea level. It’s not a pleasant place, and a manned spacecraft would find it difficult to land there, and it might be even more difficult for humans to get out and walk around. In fact, I think we can dispense with the possibility of humans walking on Venus’s surface for the foreseeable future.
Many billions of years ago, some scientists speculate, Venus may have had a climate similar to Earth. Water may have been present in abundance, enough to fill relatively shallow oceans. An atmosphere of oxygen may have existed that could have been conducive to life. But if it did, under the influence of the heat from the sun (Venus gets about twice as much sunlight as Earth) the oceans boiled away, the water was split by ultraviolet light into hydrogen and oxygen, the hydrogen escaped into space, and the oxygen combined with carbon on the surface to form carbon dioxide, and the greenhouse effect took over. That pushed the temperature into the stratosphere. So to speak. And here we stand today.
But the presence of water making life possible on Venus in the distant past isn’t what I want to hypothesize in this post. I’m thinking about the possibility of life on Venus as it exists now. Yes, in the presence of all that heat, lava, pressure, and sulfuric acid. Earlier, on March 13, 2011, in a blog post entitled “Life–A New Definition,” I suggested that life on any arbitrary planet should be defined as “that which arises . . . under the influence of the energy from its sun over and above any other milieu . . . .” That’s without regard as to what the life forms look like, or what they’re composed of, or how they replicate, or any other limiting factor we may require to define life on Earth. We can’t think of life on other planets within the limited range we find here on Earth.
So, what would life on Venus look like now? Under the influence of that tremendous heat and pressure, chemical reactions are running wild, at least in comparison with Earth. That might be a good thing. It might be the very factor that makes “life” viable on the surface. Lava may stay liquid all the time on Venus. Possibly a life form could arise composed of lava globules that slowly creep across the surface, consuming other bits of the ground, extracting necessary elements, metabolizing them by sulfuric acid digestion, and eventually dividing into smaller globules that continue the process. And that’s just one scenario. I’m sure others could be visualized by those who are better at chemistry than I, so there’s no sense in me speculating much further here.
I certainly realize that the chance of “life” actually existing on the surface of Venus is probably very low, and that speculating about what it looks like could be a somewhat unscientific pursuit. But the real reason for looking at Venus this way (sorry about that) is that it gives us a different way of looking at life in general all across the galaxy. (Think what it would mean if we did find some sort of life on Venus.) Life certainly exists on (a few? many?) other planets somewhere in our galaxy because there are so many of them, and we should always be aware that it won’t necessarily look like us. It may be so vastly different that we may not recognize it at first, and we have to remain open to any possible physical form, and any possible metabolic form. Temperature and pressure won’t necessarily be a limiting factor.