Asteroids

Internet Poster's Question:

I understand (drag etc) why the asteroid would disintegrate, but that is something different from actually exploding which, to me at least, implies that there is some kind of internal energy reserve which is released causing the asteroid to fragment violently from the inside. This is different from breaking up due to external forces (equivalent to the difference between how a bomb exlodes on hitting the ground and how a china teapot disintegrates on hitting the ground).

If I hit the water at 100 miles an hour I would, indeed, splatter quite unhappily, but I would not actually explode.

The Siberian example given by the speaker features an asteroid actively exploding, not just burning up. How does that happen?

My Answer:

The explosion is not a chemical explosion but a pressure-wave induced explosion. Take a look at this high-speed camera footage of a bullet going through an apple and a banana:


Inside the apple and banana, if the bullet were traveling slowly, it would just enter and exit leaving a hole-shaped burrow, much like slowly jabbing a pencil through chocolate cake. Because of the bullet's speed relative to the resistance of the medium, the bullet creates a pressure wave as it passes through.

This space.com article talks some more about asteroids exploding in the atmosphere.

An explosion can be triggered by expanding gas, as with nuclear bombs that heat the air and cause it to expand, or with TNT which chemically combusts to create CO2 and O2 gases that expand from denser, solid matter (and heats the air since it's exothermic). But an explosion can be any shock wave moving outward from the center.

When an asteroid hits the hard rocky surface of the earth, an explosion occurs as the kinetic energy is transferred to the surrounding rock as shock wave energy. That's why a room-sized asteroid can leave a mile-wide crater.

Similarly, if an asteroid is moving fast enough, the atmosphere will seem "hard" enough for much of its kinetic energy to be converted into shock wave energy (and heat from friction). When a smooth asteroid fractures and breaks off into numerous jagged non-aerodynamically shaped objects, further shock waves are created as these non-aerodynamic objects suddenly transfer even more kinetic energy into shock wave energy.

P.S. Regarding your teapot v bomb analogy: If your teapot were moving at 3,000m/s, it'd have the explosive power of a kilogram of TNT (4.1 megajoules). Remember, kinetic energy = 0.5mv^2, so something moving 100 times faster has 10,000 times the energy.

parallax

I was reading a certain xkcd comic talking about how large the clouds in the sky are and yet how difficult it is for us as humans to recognize their size. In the comic, the feat was accomplished through a marvelous use of technology, utilizing HD cameras kept 100 feet apart to achieve the depth perception needed to appreciate the true scale of these giants floating above us.

Well, that started cranking some of my now aged and beleaguered neurons into remembering an epiphany I had as a small child.

I was four years old and it was my first night out, literally. I had until then never experienced the night's sky, the stars, or the moon in all their splendor for any more than a glimpse, courtesy of getting tucked into bed each night. Well, this particular night was different; I was ushered into a car and, as per usual, wasn't told anything. Not being told anything actually had its advantages -- it meant I grew savvy at eavesdropping, though listening at that age generally led to more confusion than clarity. From bits of conversation, I gleaned that this was a long road trip. I disliked confined spaces, and I especially disliked confined spaces that so nauseatingly hurtled down the monotonous roads.

It was late, I was tired, but I was too excited to sleep. The night was so mysterious. My nose was practically pressed against the car window as I tried to soak in the strange new world. A bright glowing creature seemed to be hovering and following us, though. At first I wondered if this was some new insect or animal I hadn't known. None of the adults seemed to pay it any heed. It behaved very strangely for an insect, though. It seemed to follow and keep pace however fast we went, yet if we stopped, so did it and it seemed to keep its distance. It didn't seem like an insect; if it were interested, why did it not fly straight into the car? If it were not interested, why did it follow? Why did it not chase any other cars; why was it fixated on us? Moreover, insects fly forward, and thus would chase us from behind; this creature seemed just as content to fly sideways, hovering outside my side window. Then, something strange happened; we turned at an intersection and this creature rather than hovering to our side was hovering in front of us! This was either some devilishly clever creature trying to play tricks on me, or, as was made increasingly likely as we turned at more intersections, it was a fixture in the sky!

I marveled at it. It seemed so near and tangible like a firefly but now so very distant. I trained my gaze to probe it, to study it. It was the most inspiring object I had seen in that short little life I led. After some time we meandered through the small streets and intersections and hit a large, straight, road. The glowing orb was still outside. The car picked up speed, the pavement whizzed by in a blur, the grass across the shoulder of the road sped by as well. The trees in a distance danced along, and even the faint outlines of mountains in the extreme distance crept. The glowing ball stood still -- it stood perfectly still! This was astonishing to me. A tree was large, and a mountain gigantic; what did that say about this glowing ball? Well, it was no ball at all, it was a planet!

And for the next four years I believed the moon was the largest object in the universe, bigger than Earth or anything else that had ever existed.

Patriarchy, Patrilineality, and Primogeniture

With movies such as the King's Speech recently out on DVD, and the media showering attention at the wedding of a bald bloke named Willy and his air hostess bride Katy, one can't help but be cognizant of the English hereditary system.

In my case, I was additionally reminiscent of conversations I had in college regarding the distinctions between the English and French systems of heredity. The English system confers all status and privilege to the eldest male born; by contrast, the French system distributed status and privilege among all male born. Both systems employed patriarchy and patrilineality, but only the English system additionally employed primogeniture. It seems like an inconsequential difference, but, as with mathematical fractals and chaos, any iterative rule-based system takes subtle deviations and manifests them into mammoth ones.

With the English and French rules of heredity, the English fiefdoms were never divided upon inheritance, whereas the French fiefdoms were continually divided and subdivided leaving a patchwork of ineffective plots of land ultimately conquered by another, not to mention the severe inflation French titles underwent as a result. This ultimately led to the French lords losing their grasp on power, as there were simply too many of them trying to uphold the standard of living meant for a much smaller group of their ancestors.

Well, my train of thought continued along this line, and yesterday I pondered, is there an even better iterative rule-based system for consolidating power? I envisioned the Medieval society, so it had to conform to patriarchy and patrilineality. However, I decided to bend the definition of patrilineality to non-contiguous patrilineality. That is, instead of a father bequeathing to his eldest son, let him bequeath to his eldest grandson. Seems like a subtle difference, doesn't it? But, as was demonstrated earlier, subtle differences in the rules can lead to large scale differences in impact.

Let's play it out, shall we? Suppose a man from the Montague family and a woman from the Capulet family form a union. If their son is the eldest among all his male cousins, on his Montague side as well as his Capulet side, then he would be twice-inherited, creating a merged Montague-Capulet colossus!

If the English system proved superior to the French system because estates were preserved rather than divided across inheritance, this new hypothetical system may have proven even more potent in this Medieval society by actually consolidating estates across inheritance. Noble families often intermarried to form alliances, but under the proposed hereditary system, you wouldn't get a mere alliance, but an actual consolidation of two families' estates into a single heir.

In fact, this phenomenon did occasionally happen in English noble society, but more by accident than by systematic forethought. Every so often, a couple was left with no male heirs, and in such cases their son-in-law or grandson could become twice-inherited. This happened with rarity, however, and was generally avoided because the maternal grandfather had the unenvious distinction of generally not being accorded by English society any influential role over either his son-in-law or his matrilineal grandson. In fact, much of the fortune in such circumstances was afforded to charity. By contrast, a hereditary system that specifically inherited across a more removed relation — from a grandfather to his eldest grandson — would confer far greater influence to such a grandfather over such a grandson.