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Rosetta Results: Comets "Did Not Bring Water To Earth"
An anonymous reader writes with findings from the Rosetta mission which suggests water on Earth probably came from asteroids, and not comets."Scientists have dealt a blow to the theory that most water on Earth came from comets. Results from Europe's Rosetta mission, which made history by landing on Comet 67P in November, shows the water on the icy mass is unlike that on our planet. The results are published in the journal Science. The authors conclude it is more likely that the water came from asteroids, but other scientists say more data is needed before comets can be ruled out."
The theory is that the protoearth lost all its water when the impact that formed the moon happened. That impact reliquified the planet, driving off the lighter elements. Ergo we had to be reseeded somehow.
I don't read AC A human right
The more informative article from the ESA website says that the Deuterium/Hydrogen (D/H) isotope ratio is significantly higher (more than three times, in fact) than that of water found on Earth.
However, The comet in question is not of the same type and composition as *all* comets. In fact, comets (even those that generally share orbits with the one sampled) vary widely in their D/H ratios. As such, the paper does not claim that comets didn't bring water to Earth, merely that comets like the one sampled (comet 67P/Churyumov–Gerasimenko) by ROSINA did not bring water to Earth.
From the better TFA:
No, no, you're not thinking; you're just being logical. --Niels Bohr
You know we have thought of that. If you run the numbers, the atmosphere stays hot enough for long enough that much if not all escapes into space. The impact created the moon, it was really really hot for a while.
If information wants to be free, why does my internet connection cost so much?
Mass has everything to do with it. You're thinking "weight", dumbass.
No, it doesn't.
F_g = GMm/r^2
F_c = mv^2/r
Combine the two, and you get
GM/v^2 = r
So the orbital radius of an object around the sun depends only on the mass of the sun and the velocity of the object. The mass of the object doesn't matter. This is high school level physics, buddy.
Weight is defined as the force of gravity that is acting on an object. When you are in orbit, weight is serving as the centripetal force that is keeping you on a circular orbit. So if an object was weightless, it would fly off in a straight line instead of orbiting. GP is almost right. The weight of the space ship is going to be much greater than the weight of the astronaut inside simply because the spaceship is more massive (and F_g = GMm/r^2, so weight increases linearly with the mass of the orbiting object), but the astronaut feels weightless because he/she has the same acceleration as the space ship.