By Benjamin Gaul:
We live on a Rare Planet in a Special Solar System in the Unique Space of an Uncommon Galaxy in a Universe which seems designed from end to end to support Life on Earth.
“Either we are alone in the Universe or we are not. In either case, the idea is quite staggering.”
~Arthur C. Clarke~
He also said “No intelligent person can contemplate the night sky without a sense of awe. The mind-boggling vista of exploding supernovae and hurtling galaxies does seem to require a certain amount of explaining.”
Through hard work, terabytes of evidence, testable scientific reasoning and an unquenchable thirst for knowledge, we have narrowed down the Factors which are Absolutely Necessary for Life. I’m only going to hit on the top 15 or so, of the 25 or 30 Factors now known, because exploring the others would require me to use words this computer’s spell-check would choke on.
I know there are some of you out there who feel we’re rather Carbon-Centric in our assumptions of what Life can be. This article is only going to be about what we know to be certain, insofar as Life is concerned.
What it really all boils down to is how very very very virtually impossible it is -statistically speaking- to find Real Estate capable of supporting Life. I’m not going to get into how vastly complex even the simplest single celled organism is, with its hundreds of thousands of molecular machines working in perfect harmony on thousands of interdependent systems. Nor will I ask “Which came first: The dozens of molecular machines necessary to build and maintain a DNA strand, or the blueprints contained within the DNA strand necessary to build those machines?” Nope. None of that highbrow intellectual “how did life begin” Tom Foolery in THIS article; I’m simply here to talk about where Life can exist.
For reasons beyond my ability to comprehend, many people still hold on doggedly to Drake’s Equation, which he came up with in 1961, 30 years before we’d even detected a single exoplanet:
N* = the number of stars in the Milky Way galaxy: 100 Billion, give or take.
FP = fraction of stars with planets around them: As of 28 July 2010, astronomers have made confirmed detections of only 760 planets (some stars have more than one planet). Most of which are Super Jupiters whose mass and proximity to their suns preclude the possibility of a little Terrestrial planet existing along with them. So, 1 in every 1,315,789,474. (One point three billion.)
NE = number of planets per star ecologically able to sustain life: This is where Drake’s breaks down completely, with our current understanding of all the Factors necessary for Life.
FL = fraction of those planets where life actually evolves:
FI = the fraction of fl that evolves intelligent life:
FC = the fraction of fi that communicates:
FS = the fraction of the planet’s life during which the communicating civilizations survives:
Even if you plug stupid small fractions into that equation, it will pop out at least 1000 civilizations concurrent to our own, right here in the good ol’ Milky Way. Fifty years later, we have a much firmer grip on the numbers, and Drake’s is shown for what it truly was; Wishful Thinking.
Ah. Life in the suburbs. Location Location Location!
Not too close to the center, not too far out, and safely between actual spiral arms. No safer place for Life in the entire Galaxy.
Our little corner of the Galaxy has a lot going for it: In towards the center, the radiation levels are so high and concentrated that they would shrug past our Magnetic Field and scorch any possibility of Life from ever taking hold. Further out along the edge, radiation levels are lower, but so are heavy metals and minerals necessary for building rocky little Terrestrial planets.
There are also bad neighborhoods right here in the Galactic Habitable Zone: If Sol had formed inside one of the Galactic Arms, we would be subject to the same dangers the Center exhibits: Super Novae, Pulsars, Quasars, Borg… All generating radiation levels which make Life impossible. Our Sol even orbits the galactic center at exactly the same speed as the two arms we’re happily spinning between, unlike 95% of the other stars in the Milky Way. We could not have planned a better spot.
We also have to consider how awesome for Life the Milky Way is, in and of itself. One of the largest galaxies in the Known Universe, it has just the exactly right sized bulge for heavy metal creation, without excessive radiation. A rare and wonderful combination, as Galaxies go. Most have more bulge than arm, and many are too oddly shaped. It also has arms flung wide enough apart to accommodate the large open place we hold in its Habitable zone. Of all the galaxies we’ve looked at thus far, only our beautiful Milky Way displays all the “just right” measurements necessary to let a little rocky planet have complex Life. Granted, there are billions of galaxies, but to date we’ve discovered none so well suited as our own.
The right street in the right neighborhood in the right part of town.
Our delightful little Solar System has all the latest advancements in Life Support: A Spectral type G2 dwarf Main Sequence star. Which has proven to be the right age, size, temperature and luminosity to produce a Habitable Zone far enough out that Tidal Lock didn’t slow planetary rotation down to a crawl. That would force one side of the planet to face the Sun at all times, like our Moon does the Earth. No Rotation = No Life. Only 4% of the stars in the Milky Way are that classification, and half of those are in Binary systems, which cannot sustain life-supporting planets. Two stars rotating around each other cannot have a Habitable Zone. Of the remaining 2%, how many do you think are in the “safe” spots of the Galactic Habitable Zone?
Virtually flat, relatively circular orbits for all the Key planets.
Many of the exoplanets we’ve discovered orbit their stars in elliptical, non-linear paths. Even if their stars had little rocky planets hiding in a Goldilocks zone –which we’ve yet to detect– those Big Bullies would toss them around too much. No Life. And even though our Earth has a slightly elliptical orbit, it’s closest to the Sun during the Antarctic Summer, which only serves to warm the oceans better because most of our exposed land mass is in the Northern hemisphere. (I’ll get into the importance of the size and surface percentage of our oceans in a bit.) Having all of our Gravity-well Guards in the same orbital plane keeps us safer from invaders from the Kuiper Belt. Equally as important, those massive guardians are far enough out that they do not perturb or harass our own, particularly cozy orbit.
Easily the coolest satellite in the history of the galaxy. Our Luna is far & away the most amazingly unique –and absolutely necessary for Life– Factor known. Created by the “chance” collision of a rogue planet about the size of Mars which hit the Earth at EXACTLY the right angle and speed to increase Earth’s mass, fix her rotation, and spin off EXACTLY enough debris to create a satellite which would lock all those factors in. Her gigantic size –largest in relation to her parent planet, by a wide margin– her perfect orbit and her solitude, have made her a critical Factor for Life on Earth. She stirs our oceans (critical for Life), and maintains our Axial Tilt (seasons play a vital role in Biodiversity, which is necessary for complex organisms like Us). Were the moon smaller, or not there at all, the Earth would tumble slowly instead of spin. No Life. If we had more than one moon, tides would be chaotic and our perfect 23.439281 degree axial tilt would be thrown out of kilter. No Life.
Hi-Tech Magnetic Radiation Shielding
Because the Very Best Homes demand the Very Best Protection.
Earth’s molten iron core spins out a Dynamo Effect which creates the Magnetosphere, and Life is allowed to flourish. If the Magnetosphere were too small, it wouldn’t deflect the solar radiation and cosmic rays which bombard us constantly. No Life. If it were too large or strong, it would kill us off just as effectively as the Radiation it blocks.
A “Terrestrial” planet has an interior which is composed of three basic parts: a dense metallic core, a lower density solid mantle surrounding the core and a solid outer shell called the crust. Jovian planets have a core and a fluid mantle which merges smoothly into their atmospheres. No real surface= No Life. By a wide large huge margin, mostly we only discover Jovian planets. We earnestly hope to find more Terrestrials, and I encourage the continued search.
The Earth’s Core is made of an iron-nickel alloy with a small percentage of sulfur, cobalt, and other minerals. It has a density of around 12 (water = 1). A smaller, solid component resides at the very center, with a radius of about 1300 kilometers and a density around 14. Even though the temperature of the interior increases toward the center (it’s about 6300 K at the center), the high pressures at the inner core (up to 3.64 million bars) make it solid while the outer metallic core remains liquid.
The two regions rotate at different speeds and –it is believed– not always in the same direction. This interaction creates what scientists call a “hydromagnetic dynamo.” Something like an electric motor which results in the magnetic field that surrounds our planet. Peter Olson, lead researcher on a new Johns Hopkins University study, explained that Earth’s outer core appears to rotate in the opposite direction of its inner core, generating conditions much like those that create atmospheric vortices like hurricanes.
Sol kicks out enough radiation to turn Earth into a barren little husk. There would be no Life if it weren’t for Earth’s exactly “right sized” Magnetic Field pushing it all harmlessly past us.
Liquid Water. It’s what the Goldilocks Zone is all about.
Geologists call water the Universal Solvent, because it can break down and carry every mineral you can name. It is fascinating amazing stuff, and the first thing Astronomers look for when they detect a terrestrial planet. It’s not as if Life is easy as Just Add Water, but without liquid water, No Life.
Water has a few other rather unique qualities which are also worth mentioning. As a heat sink, chemical sink and temperature regulator, our oceans perform some very critical-for-Life tasks. Our huge oceans absorb massive amounts of Solar energy, and use it to regulate temperatures all over the world. Earth’s 3 to 1 water to landmass ratio is also exactly perfect for a consistent temperature regulation. Season to season, year to year.
Global atmospheric temperatures sometimes rise, usually due to solar activity literally blowing Cosmic Rays away from the Earth. Clouds form easier when they have particulates to condense on, and cosmic rays are a large source of those particulates. Fewer clouds, higher global temperatures. 800 years later (forever to you and I, a blink in Geologic Time) the oceans will catch up and release more CO2 into the air. Many Scientists believe this helps the Earth’s plant-life cope with the higher temperatures, because higher levels of CO2 in the atmosphere makes plants greener, healthier, and better able to withstand the the heat.
If atmospheric temperatures decline, 800 years later the oceans will begin to absorb more CO2.
Because 800 years is just a Geologic Blink, Al Gore was able to cite the Effect as the Cause, and claim CO2 made temperatures rise in his –now banned in England for too many blatant lies– documentary “An Inconvenient Truth.” Might as well have said Thunder causes Lightning. People who still believe the Earth is Flat will also still believe CO2 is a “”Dangerous Gas.”
Best hold your breath, because you’re exhaling CO2 at an alarming & dangerous rate!
Interestingly, if the Earth were 20% of its diameter closer to the Sun, it would be too hot for liquid water. And if the Earth were just 5% father away from the Sun, it would be too cold. CO2 clouds would form in our atmosphere, killing off any chance of Life. We are snuggled in the Just Right orbit, on a planet that is perfectly sized for Sol’s Habitable Zone.
A surprisingly thin crust
Yet another in the long list of “Must Have’s” for a planet that wants to spawn Complex Life –like my friend here (you have NO idea how complex)– is a crust that is Not Too Thick.
Earth has just the right thickness of crust to allow for plate tectonics, while still keeping the surface COOL enough for liquid water and our Absolutely Awesome Atmosphere. Our planet keeps recycling carbon and other essential elements back up to the surface.
Carbon is the best and most likely chemical basis for life, for a number of reasons. The “Carbon Bond” is unique to Carbon, and allows for Complex Macro-Molecules. Even the simplest, single cell life forms require Complex Macro-Molecules. Our little Earth has an abundance of Carbon in its make-up. So I guess we can count heavy Carbon Content as yet another prerequisite for our list of Must Haves for a Home for Life.
Even though you can’t see it, you need to know how our Perfect Atmosphere works.
I don’t need to tell you how important O2 is for Life. Our Oxygen Rich, Nitrogen atmosphere is unique, special, improbable, and like our Crust: exactly the right thickness to support Life. Just less than 1% of the diameter of the planet, it is thin enough to hold the right amount of heat in for Life to flourish, but thick enough to turn an incoming meteor the size of a Buick into so much burnt powder.
Even more incredible, you can SEE through it! And it is best suited for the warm, yellow light which our Sun produces in such great abundance. If we were parked around a Blue Giant’s Habitable Zone, this excellently breathable atmosphere would do little to hold the radiation back, liquid water or no.
NO other planet we know of so far has an atmosphere which does all the incredible things ours can, and yet still offer such an excellent opportunity for gathering information about our Universe.
In Summary, each of these Factors must obtain, in the same place at the same time on the same planet, for Life to even have a chance. Take even ONE away, and Life cannot happen. More paradoxical, even if all of these Factors DO obtain on an exoplanet, that does not mean that Life will BE on that planet.
Within the Galactic Habitable Zone
Between Arms of the Galaxy
Within the Circumstellar Habitable Zone
Orbit a Spectral Type G2 dwarf Main Sequence star
Protected by gas giants, which are too far away to perturb the orbit
Nearly circular orbit- for all planets
Oxygen rich atmosphere
Carbon rich crust
Correct mass for Goldilocks Zone and Rotation rate
Large, single moon to stabilize the angle of rotation
Moderate rate of rotation for a mild climate
Ratio of water to continents
Plate tectonic re-cycling
Magnetic field of right size
The odds of all this happening on the same planet at the same time, are roughly One in Six Trillion Trillion (A 6 with 24 zeros behind it, I do believe.) We might be finding planets, but the chances against them supporting Life like us is beyond Astronomical.
Feeling Lucky, yet?