Anyone remember the Little Fuzzy books by H. Beam Piper? The humans colonizing the planet Zarathustra think the little native bipeds can't pass the "talk and build a fire" test for intelligence until they start to listen in the ultrasonic range. . .
I wander whether that speed is possible vertically? Probably a bigger problem is communicating over 5km
Actually reading the information on the home page (Yes, I'm new here), I see the vertical speed is 0.5 m/sec, and they don't try to communicate with the surface, but only locally with other submersibles in a group within 6 m.
At 5km depth, the pressure is about 7000psi. The gas would have to be pressurized to more than that to expand a gas bladder. At those pressures, gasses behave far differently from ideal gasses, and change volume very little with changes in pressure. To contain the gas at the surface, you would need a thick, heavy pressure container that would weigh far more than the bouyancy you would gain from the gas.
The choice is not between two choices, one simpler and one more complex. Without a preference for a simpler explanation, there could be an endless number of explanations. A special cause could be postulated for every data point. The correct explanation would be lost among a zillion other explanations, from hitherto unknown forces to wood sprites. If you say common sense would tell you not to add endless special causes, hey, you've just applied Occam's Razor.
The thing that amazed me when I read about that collision is that even today, 500 million years later, 20 per cent of all meteorites are remnants from that collision.
First of all, one nitpick: Meteors don't move through space; a particle only becomes a meteor when it begins burning up in the atmosphere. A particle falling into earth's gravity well will build up kinetic energy equal to the potential energy it is giving up, so it will have at least escape velocity from the earth when it reaches atmosphere and becomes a meteor, 11 km/sec. Long period comets fall into the Sun's gravity well from just about the top, so its kinetic energy will be almost escape velocity from its distance from the sun at any time. At the earth's orbit, its velocity would be (um, mumble 30 km/sec times the square root of two, mumble) about 42 km/sec. Short period comets would have whatever orbital speed is determined by its orbit.
D) This is why they are looking so hard with the Mars rovers for evidence of water in the past. If Mars had been wetter billions of years ago, then life, whether native or imported, would have had a much better chance of flourishing then. And it could have evolved over time to hardier forms that could survive on or in Mars now.
things blown off mars would tend to fall inward towards the sun. . .
I don't know about that. It's not like orbits are a set of shelves where you knock something off and it falls down. A piece of rock on Mars starts off with Mars' orbital velocity. If it gets ejected in some random direction it is as likely to increase its orbital velocity (larger orbit) as to decrease it. In fact, since meteorite strikes tend to be on the leading side of the planet (the bug-on-the-windshield effect), this may favor increased orbital velocity of the ejected material.
There was a conference on asteroid defense a while back that included scientists conducting the sky searches for possible hazards and also military personnel.
The scientists' concept of asteroid defense involved detecting an asteroid in an orbit that would collide with the earth years or decades in the future. A relatively gentle nudge would change its orbit over the years enough to miss the earth. We could cobble together something from existing technology to do that if it became necessary.
The military's concept was a prepared military force that could intercept and deflect an incoming asteroid detected when it was crossing the orbit of the moon. This scenario is much less likely than one in which a dangerous asteroid is observed many years in advance.
A military force with that much power would have the capability of itself wiping out all life on earth, and it would be a greater threat than any danger from asteroids. No one can be assured that it would stay in responsible hands indefinitely into the future.
By all means we should continue and improve the search for potential hazardous asteroids, and carry out experiments on how to nudge them in their orbits, such as the one being discussed. But spending huge amounts of money to create another hazard is ridiculous.
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There are pictures and a detailed article here
Anyone remember the Little Fuzzy books by H. Beam Piper? The humans colonizing the planet Zarathustra think the little native bipeds can't pass the "talk and build a fire" test for intelligence until they start to listen in the ultrasonic range. . .
Actually reading the information on the home page (Yes, I'm new here), I see the vertical speed is 0.5 m/sec, and they don't try to communicate with the surface, but only locally with other submersibles in a group within 6 m.
At 5km depth, the pressure is about 7000psi. The gas would have to be pressurized to more than that to expand a gas bladder. At those pressures, gasses behave far differently from ideal gasses, and change volume very little with changes in pressure. To contain the gas at the surface, you would need a thick, heavy pressure container that would weigh far more than the bouyancy you would gain from the gas.
There are two meteorites that are thought to have come from Venus, see here.
The choice is not between two choices, one simpler and one more complex. Without a preference for a simpler explanation, there could be an endless number of explanations. A special cause could be postulated for every data point. The correct explanation would be lost among a zillion other explanations, from hitherto unknown forces to wood sprites. If you say common sense would tell you not to add endless special causes, hey, you've just applied Occam's Razor.
The thing that amazed me when I read about that collision is that even today, 500 million years later, 20 per cent of all meteorites are remnants from that collision.
First of all, one nitpick: Meteors don't move through space; a particle only becomes a meteor when it begins burning up in the atmosphere. A particle falling into earth's gravity well will build up kinetic energy equal to the potential energy it is giving up, so it will have at least escape velocity from the earth when it reaches atmosphere and becomes a meteor, 11 km/sec. Long period comets fall into the Sun's gravity well from just about the top, so its kinetic energy will be almost escape velocity from its distance from the sun at any time. At the earth's orbit, its velocity would be (um, mumble 30 km/sec times the square root of two, mumble) about 42 km/sec. Short period comets would have whatever orbital speed is determined by its orbit.
Reverse Polish Notation, used in calculators with push-up stacks. Here is the wikipedia article
Also important is the fine detail preserved in the fossils, down to 30 micrometers.
D) This is why they are looking so hard with the Mars rovers for evidence of water in the past. If Mars had been wetter billions of years ago, then life, whether native or imported, would have had a much better chance of flourishing then. And it could have evolved over time to hardier forms that could survive on or in Mars now.
I don't know about that. It's not like orbits are a set of shelves where you knock something off and it falls down. A piece of rock on Mars starts off with Mars' orbital velocity. If it gets ejected in some random direction it is as likely to increase its orbital velocity (larger orbit) as to decrease it. In fact, since meteorite strikes tend to be on the leading side of the planet (the bug-on-the-windshield effect), this may favor increased orbital velocity of the ejected material.
There was a conference on asteroid defense a while back that included scientists conducting the sky searches for possible hazards and also military personnel. The scientists' concept of asteroid defense involved detecting an asteroid in an orbit that would collide with the earth years or decades in the future. A relatively gentle nudge would change its orbit over the years enough to miss the earth. We could cobble together something from existing technology to do that if it became necessary. The military's concept was a prepared military force that could intercept and deflect an incoming asteroid detected when it was crossing the orbit of the moon. This scenario is much less likely than one in which a dangerous asteroid is observed many years in advance. A military force with that much power would have the capability of itself wiping out all life on earth, and it would be a greater threat than any danger from asteroids. No one can be assured that it would stay in responsible hands indefinitely into the future. By all means we should continue and improve the search for potential hazardous asteroids, and carry out experiments on how to nudge them in their orbits, such as the one being discussed. But spending huge amounts of money to create another hazard is ridiculous.