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| . '''er, no.''' even in the ecliptic plane, the asteroid belt is sparse enough to be almost transparent. There are certainly enough "vermin of the sky" asteroids to leave light tracks through long-duration sky exposures, but a similarly long time exposure of a rural highway around 2 am would show enough headlight streaks to make the road seem bumper-to-bumper, even if cars actually only pass once every 20 minutes. The asteroid belt is vastly less bright than the full Moon, hence the steradians of the sky it occults is less than the Moon's 1e-5, so its collision cross section is vastly smaller than that fraction. A comet passing through the asteroid belt is less likely to collide with any asteroid than you are, at home in bed. In the vanishingly small chance that an asteroid /did/ hit one or two or ten asteroids, it might be smashed into small and large fragments, but the largest fragments would be potential city killers, not "harmless boulders". | . '''er, no.''' even in the ecliptic plane, the asteroid belt is sparse enough to be almost transparent. There are certainly enough "vermin of the sky" asteroids to leave light tracks through long-duration sky exposures, but a similarly long time exposure of a rural highway around 2 am would show enough headlight streaks to make the road seem bumper-to-bumper, even if cars actually only pass once every 20 minutes. The asteroid belt is vastly less bright than the full Moon, hence the steradians of the sky it occults is less than the Moon's 1e-5, so its collision cross section is vastly smaller than that fraction. A comet passing through the asteroid belt is less likely to collide with any asteroid than you are, at home in bed. In the vanishingly small chance that an asteroid /did/ hit one or two or ten asteroids, it might be smashed into small and large fragments, but the largest fragments would be potential city killers, not "harmless boulders". |
The Living Cosmos
Our Search for Life in the Universe
Chris Impey, Central 576.839 I34L 2007, Random House
A bit dated, a few howlers, skimmed.
- p151 "Slightly later, and you would have plowed into the Asteroid Belt and been ground into harmless boulders."
er, no. even in the ecliptic plane, the asteroid belt is sparse enough to be almost transparent. There are certainly enough "vermin of the sky" asteroids to leave light tracks through long-duration sky exposures, but a similarly long time exposure of a rural highway around 2 am would show enough headlight streaks to make the road seem bumper-to-bumper, even if cars actually only pass once every 20 minutes. The asteroid belt is vastly less bright than the full Moon, hence the steradians of the sky it occults is less than the Moon's 1e-5, so its collision cross section is vastly smaller than that fraction. A comet passing through the asteroid belt is less likely to collide with any asteroid than you are, at home in bed. In the vanishingly small chance that an asteroid /did/ hit one or two or ten asteroids, it might be smashed into small and large fragments, but the largest fragments would be potential city killers, not "harmless boulders".
- p160 - a graph of hypothetical radiation flux (not actual data) from solar flares and distant stellar "cataclysms" over the last 4.5 billion years, attributed to John Scalo at the University of Texas (Austin). This may have been presented at an astronomical meeting, but I cannot find it in papers by Scalo between 1995 and 2005. I'd sure like to see Scalo's methods for producing this graphe, and I would love to see a citation of a Scalo paper in Impey's book, so I can look for evaluations of that paper by others.