The Frantic Determination of Some Scientists to Discover Life Elsewhere
We often hear exciting news about ‘habitable planets’ that might have life, or at least the ‘building blocks of life.’ Are these reports based on sound thinking about the requirements?
I am constantly amused by the ongoing vigorous efforts to find some sort of life at places other than the earth. Daily I see conjectures about microbes in deep oceans in the Saturnian moons Titan or Enceladus (e.g., Space.com, July 5th). Excited reporters announce organic compounds on Mars. On and on it goes.
Let me approach this from two angles: how does life originate? And what are the requirements for life to survive, advance and propagate?
Requirements for Assembling and Jump-Starting Life
If life starts from some sort of single cell, how could that cell form, and how could it get life? Even the simplest cell is an indescribably complex object, like a factory. It is suggested that a cell, over the course of extremely long time frames, could just “come together” from ‘building blocks of life’ in some sort of primordial soup – a liquid containing a host of organic compounds. Is that reasonable?
A cell consists of a number of indispensable parts. It needs a membrane to contain the internal parts and to gather nutrients and expel waste products. It needs a genetic code which controls the operations of the cell. It needs enzymes and proteins to move and control operations. These are at the very least crucial elements. Each constituent element consists of thousands of molecules all attached to each other properly. How could millions upon trillions of atoms slam together, attach at the right places and orientation, and create all these structures, all at one time?
And, if they did, what jump-starts this process which we call life? Life implies that all these mechanisms start working, producing energy, metabolizing, growing, taking in nutrients, expelling waste products. The accidental production of a complex cell would be an outstanding miracle, but starting it operating is even a greater miracle. We can consider two cells—identical in structure and composition—one alive and one that died. What was lost to cause the second cell to die? Why can’t it jump-start again? It does not happen.
Requirements for Viability
But putting this aside, imagining that somehow a live cell came together somewhere in the universe, what conditions are necessary to allow it to survive, to propagate, and to expand its functions further (i.e., to evolve)? We can examine the one case we know about, and that is spacecraft earth. We know a great deal about the earth, and know many features, conditions, and elemental substances available to allow life.
In searching for life elsewhere, it is necessary to identify all the enabling conditions and raw materials required, before jumping to the conclusion that just because some organic molecules are found, that life must exist there.
In their search, astrobiologists start looking for and hypothesizing about simple microbial organisms. SETI researchers are dedicated to looking for higher (intelligent) forms of life. What conditions and substances must be there for life to exist? To answer that question, we can ask: what about the earth do we know to be essential for life to exist? And not just a few of these conditions, but ALL of them must be present simultaneously.
David Coppedge and I spend a good part of a chapter of our book Spacecraft Earth: A Guide for Passengers, examining the earth and identifying necessary features. I agree with most astrobiologists that life needs to be carbon-based to have all the different organic molecules and compounds available for life forms. We know of no other element that has all the features and versatility that carbon has. Some have suggested a silicon-based ecology, but although there are some silicon compounds that duplicate the carbon ones, the selection is very limited. Carbon has literally millions of compounds available.
Many carbon compounds, however, are fragile, susceptible to damage from heat, cold, energetic particles, ultraviolet light, chemical attacks, etc. This is particularly true of organic compounds in life forms, particularly DNA. So considerations of the survival of life forms centers on protections against damaging forces. The other main consideration is the availability of beneficial compounds and chemicals to allow and promote growth. A number of carbon atoms are needed to form proteins, amino acids, esters, alcohols, enzymes, fats, carbohydrates, and so on. To interact in the ways we see in cells, they need a solvent. I also agree with astrobiologists that water is the best candidate for a solvent—which means that a habitable planet must at least have liquid water.
Requirements for Habitability
A planet would need to have an abundance of the elements required for carbon-based life, not just carbon itself. And those elements must be available at the surface, or in the proposed oceans under the ice that scientists believe exist at Europa and Enceladus. For the required elements and molecules to be available, though, numerous other factors would also have to be satisfied. Some scientists think that just having water and heat is enough, with some organic molecules mixed in.
Many people have heard of a “habitable zone” around a star where liquid water can exist. As we show in the book, that’s just one of the factors in the “cosmic lottery” that life has to win. The Earth, of course, won that lottery. But more thinking about habitable zones has added further requirements. From the literature of astrobiology, we can identify ten or more other “zones” required for habitability, in addition to circumstellar distance. We list these in the book:
- Galactic Habitable Zone: the solar system must be localized in a narrow band within the galaxy.
- Continuously Habitable Zone: the habitable zone must not vary significantly.
- Temporal Habitable Zone: the habitable zone must last long enough for life to persist.
- Chemical and Thermodynamic Habitable Zone: the planet’s chemistry and heat transfer mechanisms must permit liquid water to persist.
- Ultraviolet Habitable Zone: the planet must filter out ionizing radiation from its star.
- Tidal Habitable Zone: the star must not tidally “lock” its habitable planet to force one hemisphere to always face the star (this rules out most stars).
- Obliquity Habitable Zone: the star must not “erase” its habitable planet’s tilt through tidal forces. (While not eliminating the possibility of life, a planet without a tilt would have no seasons, drastically reducing its habitable surface area.)
- Eccentricity Habitable Zone: the planet must have a nearly circular orbit so that it stays in the proper place in the zone.
- Stellar Chemistry Habitable Zone: the star must have the right chemical composition to remain quiet and well-behaved. A G2 main-sequence star like our sun is ideal.
- Stellar Wind Habitable Zone: the star must not be given to extreme “space weather” that might strip off a habitable planet’s atmosphere.
- Inhabited Zone: recently, two astrobiologists suggested that to be habitable, a planet needs inhabitants! “…there is a growing amount of evidence supporting the idea that our Planet will not be the same if we remove every single form of life from its surface,” a news report said.
A planetary scientist at the University of Arizona said, “Habitability is very difficult to quantify because it depends on a huge number of variables, some of which we have yet to identify.” It’s likely, therefore, that this is only a partial list.
Requirements Are Not Enough
As we show in the book, when you use reasonable probability estimates of 1 in 10 for each factor to calculate how many planets might meet all the requirements, the result is less than one! Obviously there is one, which we are living on right now. But is it reasonable to think the universe is filled with other planets as ‘lucky’ as the earth? I think not.
Another planet could meet all these requirements, though, and still be lifeless. What physical process could organize the ingredients into cells? And what force could endow the cells with life? And could we expect undirected evolution to once again bring about anything on the level of the beauty and complexity of life we find here on Spacecraft Earth? I maintain that it could not have happened once by accidental means here, much less than a second time elsewhere.
My conclusion: there are a lot of wishful thinkers out there who have not thought this through. And there is a lot of money being poured into a life search against all odds.
Dr Henry Richter, manager of Explorer 1 (America’s first satellite) at JPL in 1958, is a contributing science writer to Creation-Evolution Headlines. Dr Richter was a key player at NASA/JPL in the early days of the American space program. With a PhD in Chemistry, Physics and Electrical Engineering from Caltech, Dr Richter brings a perspective about science with the wisdom of years of personal involvement. His book America’s Leap Into Space: My Time at JPL and the First Explorer Satellites (2015), chronicles the beginnings of the space program based on his own records and careful research into rare NASA documents, providing unequaled glimpses into events and personnel in the early days of rocketry that only an insider can give. His second book, Spacecraft Earth: A Guide for Passengers was printed by CMI in November, 2017. For more about Dr Richter and a list of his articles, see his Author Profile.