Cecil’s thoughts on the sudden absence of the moon seem less well thought out than usual. I’ll refer to the numbers of his points in the column linked above.
1-2) Okay, the tides would cease, and dogs wouldn’t have anything to bay at.
3) This is intriguing, but we need more info. What species would be affected? Would any of them have a predictable direct or indirect impact on humankind?
4-8) More flippant answers. Nothing wrong with that in my book.
Second set of point:
Is the idea that the moon shields earth from meteorite strikes confined to the early universe? The news lately has contained the revelation that there are a lot more asteroids that intersect earth’s orbit than previously thought. On a geologic timescale, which includes the present, of course, how much protection does the moon give? It seems to me it might be considerable, it might not.
This is actually the most valid answer to the question. Without ocean churning, considerable amounts of plankton could die, setting off a chain reaction through all earth’s ecosystems - or at least the marine ones. However, ocean circulation is due to the Coriolis effect, not tidal forces, and the circulation may be enough to provide mixing. Is it?
Since the earth-sun system orbits about its center of mass, obviously the mass of the earth relative to the sun is important if you want to know the precise radius! I’m not an astrodynamicist, but I’d bet money that if you look up the derivation of that orbital radius equation you’d find that the earth’s mass drops out only because it is so much less than the sun’s. In other words, it’s still there someplace, we just ignore it because it only changes the answer a negligible amount. So if I’m right about that, using this equation to demonstrate the irrelevance of the earth’s mass is tautological: the irrelevance of earth’s mass has already been judged irrelevant and that fact incorporated into the form of the equation when it was written. The loss of the moon, it seems to me, WOULD change the radius of our orbit, if only slightly. Certainly, we would still be orbiting an earth-sun center of mass that is inside the sun.
-More important, the method of vaporization seems to me important: where would the angular momentum go? Would the earth’s rotation speed up? How about our orbit of the sun? Even relatively small changes in these things, if they happened suddenly, could seemingly have large effects.
-Does the orbit of the moon in the ecliptic stabilize the angle at which the rotational axis of earth intersects that ecliptic? My physical intuition says yes, but I haven’t the skills to prove it mathematically. A polar shift, or any change in precession, could have very serious consequences.
Cecil doesn’t often lead us astray, but he seems to think that the Moon’s mass would simply disappear even if it were vaporized, not simply blown to smithereens. Well, it wouldn’t disappear. Even if the Moon were transformed into a cloud of vapor, that cloud will still have the same mass and the same CG that the Moon would have, and its gravitational effect on earth would be the same. In fact, the vapor molecules would still have gravitational attraction for each other, and would eventually recoalesce into Moon 2: The Revenge.
The vapor cloud would also tend to reflect sunlight back toward Earth, much MORE brightly than at present. All of the Moon’s mass, not just the part we can now see, would be available as reflective material.
There would be a problem with the loss of the mutual tidal lock between the Earth and the Moon, though, due to the loss of the Moon’s, um, structural integrity. This is mostly seen today as the Moon keeping the same face toward the Earth, but there is a stabilizing effect on the Earth, too. The orientation of the Earth’s axis to the Ecliptic would be less stable, so would the seasons and climates, and you can imagine the rest.
He shouldn’t have blown off the effect on nocturnal animals so flippantly, either. Either way, they’re in trouble, and so is all of the food chain that depends on them.
I’m a little nervous about Cecil being so flippant also. Remember how embarrassing it was when it turned out one of Bush’s ambassadors in the Middle East had actually given Iraq the green light to invade Kuwait? What happens when Greg really does “shoot the moon” and someone points out that Cecil encouraged him. Protests of, “I was just joking for crying out loud,” are going to fall a bit flat.
It’s never good to underestimate a Greg. We’re a resourceful lot, and not all of us are sane.
I am not an astrophysicist in any way, shape or form. But reading the column on the loss of the moon made something leap out at me.
Surely, there is an axis of rotation between the earth and the moon. Sure, each spins on its own axis, but due to the gravitational pull of each one on the other, the axis of gravitation must be somewhere between the two.
This could have two effects, depending on whether vaporisation involves the whole moon just disappearing into nothingness (I seem to remember a high school science teacher saying that) or if the moon became water.
If it just disappeared, wouldn’t the orbit around the sun just stay at the level where it was when the moon disappeared (due to the sun’s massively larger mass (that sounds wierd), and our orbit would be changed by that much?
Or, if it turned into water, wouldn’t:
The Water Moon, if it reformed, be way more sphereical, with water kind of flying off from the top due to no structural integrity to hold the thing together, and the lack of gravitational attraction at the poles. This drop in mass for the moon would slowly bring the earth and the remaining water moon closer together as it lost mass, until eventually they collided on the point of axis. Or;
Being in space, and damn cold, the water immediately form into ice, and reform as a stable ice-moon. Ignoring the fact that its own gravity may heat it with friction etc. And nothing would happen, except maybe a slight gravity shudder here on earth.
What, that’s my thought. Please remember that this is based on high school physics, and so liable to fundamental mistakes in understanding.
I think Cecil may have overlooked the most significant threat to Earth from the disappearance of the moon: the loss of its gravitational influence on our atmosphere (I’m presuming that not only the moon disappears, but its mass as well)
The Earth-Moon system is not typical of planet-moon pairs in the solar system. The size of nearly every other moon (with the possible exception of Pluto’s Charon) is a stable fraction of the size of its primary. Huge planets, like Jupiter and Saturn, have moons the size of ours. A planet more nearly the size of our own, Mars, has moons that are mere pebbles by comparison.
Our moon, along with Earth, constitute more of a bi-planet system. The center of gravity of the combined system is significantly offset from the center of our planet, and is in fact close to sea level. Accordingly, the moon can easily affect the escape velocity of atmospheric molecules on the side of earth farthest from the center of gravity, an effect that can be likened to an atmospheric tide. The effect, over the last five aeons has been to strip huge amounts of atmosphere away from the Earth.
If you want to know what Earth would look like without the Moon, we have a perfect example: Venus. Venus, with a mass a little smaller than Earth’s has an atmosphere that is truly crushing in density and is unbelievably hot. Earth’s fate, being the heavier planet, would be worse.
Also, it is important not to understate the effect of the “tidal-lock” the moon forces on the earth, as mentioned in a previous reply. Without it, the Earth would precess, that is “wobble,” to such a huge degree that the result would bear no resemblance to seasons, as we know them, but would be truly catastrophic to the biosphere as a whole. In fact the thesis of the recent book “Rare Earth” is that, without the Moon, life would have never evolved on Earth.
Without themoon to synchronize their reproductive cycles, coral wouldn’t spawn. Without coral, 25% of the ocean’s species would have no place to live. Islands would lose an important defense against storm surges. Beaches erode,coastal cities flood, people die. Not a good scene.
I’m going to have to respectfully disagree here. Venus atmospheric pressure is ~90 bars. The majority of that atmospheric mass is in the form of carbon dioxide, ~97%. CO2 in Earth’s atmosphere is a few dozem parts per million. Eliminate most of the CO2 from Venus’ atmosphere and you’re left with a surface pressure of ~2.5 bars (standard pressure on Earth is about 1 bar).
So, Earth is Venus with all of that CO2 stripped away, right? No, All of that CO2 is still here, 'cuz it’s soluble in water, where it combines with calcium and precipitates onto the ocean floor as CaCO3 (limestone). If you took all of the CO2 stored in limestone and put it back in the atmosphere, Earth would have a Venus-like atmosphere.
Venus can’t store CO2 in the same manner because it has no oceans in which to dissolve the gas in the first place. Proximity to the sun caused liquid water to evaporate, and the lighter gas was lost to space.
Earth may have lost a bit of atmosphere to lunar tides, but it is constantly replenished by volcanic eruptions, in which 90-95% of the gases are CO2 and H2O.
I don’t think this scenario really reflects what would happen. If the Moon were reduced to small particles or vapor, it would form a small ring around the planet. While the physics of ring formation is still unclear, I think any astrophysicist studying the production of rings would tell you that the remnants of our sattelite would spread themselves into numerous micro-orbits, until they were shaped as a torus or disk concentric with the Earth. It’s possible that clumps of moon debris would gather at the Lagrange points created by the Earth-Sun system, the Moon would never reform.
So, if Earth’s volcanoes were to all become dormant (unlikely to happen soon), it would eventually become like Mars, whose volcanoes are all dormant?
Lessee… Mars is much smaller than Earth. Assuming the internal temperatures of both planets were originally the same (or nearly so), Mars would have lost its internal heat to space much sooner. (A cup of coffee cools off much sooner that a pot of coffee because you have less coffee in the cup, assuming all other conditions are the same.) Without an internal heat source, Martian volcanoes would have gone dormant much sooner, they would not have been able to replenish the atmosphere, and what atmosphere Mars ever had would have eventually been lost to space. While it is true that Mars has two moons, Phobos and Deimos, they are too small to cause significant tides; Mars did not lose its atmosphere because of them, it lost it because its gravity is so weak.
That’s essentially right; escape velocity is proportional to the square root of (Mass/Radius). The average thermal velocity of a gas is proportional to the square root of (temperature/molar mass).
Given that molecules of a gas will have velocities that vary widely around the average, a gas with a thermal velocity of less than ~20% of the escape velocity will have an atmospheric half-life of about a billion years.
IIRC Mars has a few lava flows that are believed to be less than a few hundred million years old; but most evidence suggests that eruptions have been fewer and fewer over the past billion or so years. So it loses gases more quickly because of weak gravity, and doesn’t replenish them since it’s cooled.