Scale of the Problem

By Eric M. Jones

SPACE ARTIST DON DAVIS’ dramatic impression of a planetoid impacting the Earth is often used to illustrate descriptions of the Chicxulub (CHICK-sa-loob) asteroid impact, which school science books say wiped out the dinosaurs and ended the Cretaceous period. But an impact of a planetoid as large as this would have wiped out all life on Earth and probably repaved the planet wholesale.

My purpose here is not to argue against the current theory. But there are reasons to speculate that the Chicxulub impact was not the proximate cause of the end of the dinosaurs. Walter Alvarez, Geologist, and his father Luis Alvarez, Nobel-prize winning Physicist who discovered that the K-T worldwide boundary was laced with iridium, originally believed that Iceland was a good candidate for the dinosaur ending impact crater. This was later put aside when the Mexican Chicxulub crater was discovered.

But there is a reasonable suspicion that some other impact was involved; perhaps the still speculative 500 km diameter Shiva crater off the west coast of India or others.

And there is a convincing argument that it was not an asteroid impact at all. A far more ferocious epoch-ending event might have been the truly enormous (500,000 km3 volume, 30,000-year-long) deep-mantle-plume volcanic eruption, the igneous remnants of which are the Deccan Traps in India. Oddly, India was nearly antipodal to the Chicxulub impact point at the same time as the asteroid impact. Thus, some think the Chicxulub impact shockwave went through the Earth and disrupted the crust on the other side. Too clever a theory? (See: “The Deccan Traps Volcanism-Greenhouse Dinosaur Extinction Theory” by Dewey McLean.)

Large volcanic eruptions almost certainly ended previous epochs. The Siberian Traps volcanism probably ended the Permian (Permo-Triassic or P-Tr boundary, about 245 million years ago). This was the greatest known mass extinction in Earth’s history when 95 percent of all marine species became extinct. Goodbye Trilobites. Goodbye ammonoids, blastoids, acanthodians, placoderms, and pelycosaurs. Volcanic eruptions of this sort are very hot and fluid—deriving from the core-mantle interface. They contain deep-Earth metals like iridium in economically important quantities, as do large asteroid impacts.

There are also wide gaps in our understanding of how large impacts would affect Earth. There are a great many variables ... and obviously it’s hard to run meaningful tests. But what would the actual Chicxulub asteroid have looked like? Current estimates put the asteroid diameter at about 10 km with a velocity of about 20 km/s. It is thought to have been a carbonaceous chondrite or perhaps a comet. There are many uncertainties.

The estimates of the Chicxulub asteroid’s size and velocity are pretty good because it left a huge buried crater for us to examine. So let’s look closely at this impact event. As shown, the Chicxulub asteroid would have been the size of an extremely tiny grain of sand compared to a standard soccer-ball-sized Earth. The asteroid would have made it through the Earth’s atmosphere in just a few seconds, so visions of a giant hot fireball are wild exaggerations.

It is a fairly easy exercise to calculate the energy release of such a collision, and making the sensible assumption that most of the energy would have gone into atmospheric heating yields the starkly discouraging result that the atmosphere could have broiled steaks. Still ... these numbers are based on only a partial understanding of radiative cooling, asteroid (or comet) shape and composition, the effect of the oceans, unknowns involving deep penetration of the Earth’s crust, convection of the atmosphere (then ~30 percent O2) and blast conduction on round planetary bodies, etc.

But again, my purpose is merely to discourage certainty. If you understand the scale of the problem, one might pay more attention before accepting the orthodoxy—any orthodoxy.

A good scientist must always be a skeptic.

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Thus far we have tried to illustrate how the size of things not only matters, but how our human understanding of reality is frequently plagued by faulty misconceptions. People get their ideas of the relative sizes of things from TV or graphic images which are often scaled to fit the artists’ own conceptions or the limitations of the media.

A classic visual illusion is how much larger the Moon appears when it is low on the horizon. It certainly looks like it is much bigger than the same Moon when it is high in the sky. There are common notions that the atmosphere somehow magnifies the Moon near the horizon. (But why only there?) But this notion can be dispelled by anyone with a fixed focus camera willing to do a simple experiment: Take a photo of the Moon near the horizon and then another when the Moon is high in the sky. Compare them. They’ll be identical. At either position, the Moon subtends an arc smaller than that of a dime held at adult arm length, or slightly more than 0.5 degree (32 arc-minutes). The Moon’s orbital radius does vary slightly, but only very slightly, and not because it’s near your neighborhood’s horizon.

But there is another illusion that is rarely acknowledged, and even people who should understand it almost never seem to: The Moon is so far away that editors and artists hardly ever show the image in a realistic way ... but here it is:

This shows the orbital radius of course. The Moon is 30 Earth-diameters from the Earth—and no amount of wishing will change that. The Moon’s mass is a mere 1.2 percent the mass of the Earth even though the Moon’s diameter is 27 percent that of Earth, because the Moon is much less dense.

The truth is that the Moon is very small, and very far away and that this size and distance relationship is almost never shown properly. Understanding this relationship makes many questions patently clear without resorting to long-winded arguments:

Can we economically generate solar power on the Moon and beam it back to Earth? No. It is too far away. Solar power is just barely economical on Earth. To put it on the Moon is delusional. And remember that a solar power plant on the Moon is still in the dark half of every month.

Can we economically mine minerals or helium-3 and transport it back to Earth? No. Helium-3, potentially useful in fusion reactors, is probably the only thing worth collecting on the Moon; but it’s a considerable stretch to think this is an economical possibility. On Earth helium-3 is a decay product of tritium and can be (and is) collected from many sources.

Does the Moon shield the Earth from asteroids and meteors? Not really, it’s just too small and too distant. The Moon is a tiny speck, and although its surface is covered by meteoroid and asteroid impact craters, many are billions of years old.

Does it make sense to build a moonbase? Not much. The fantasy of “building something in an inaccessible place and a purpose will be found” is what drove the construction of the International Space Station. Carl Sagan and the “Infinitely Smart” Freeman Dyson sat on a commission to evaluate projects for the ISS, and they could find no reason for 46 out of 48 proposals, the remaining two were projects to determine how people could live on space stations. Of course he was right. There are certainly few useful projects for a moonbase, other than learning how humans survive at a moonbase. But robots are better because you never have to bring them back, and they don’t eat, breath, or have loved ones back on Earth, at least until the robot revolt.

Why didn’t the US go back to the Moon? Check the map. Men never ask for directions! The NASA Apollo program was hellaciously dangerous, difficult and wildly expensive, and we learned about all we could from it. But now (sadly) not one person in ten can even tell you how many Earthlings walked on the Moon.

Final note: If you were on Mars, Phobos would appear half the diameter of our moon, orbits Mars twice a day and would be only about 10 percent as bright. But it could easily cast sharp shadows of Ray Bradbury’s abandoned Martian city’s crystal spires. Deimos orbits once a week, and would appear so much smaller than many stars that it would hardly be noticed. 

Eric M. Jones is the Contributing Editor of “Perihelion.” He is an engineer, designer, consultant, and entrepreneur, currently working in his Internet business PerihelionDesign, designing, building and selling unique products, parts and materials for people in the home-built experimental aircraft community.