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Originally Posted by djellison
Thirded - and given that this is ATM, Jerry is obliged to respond.
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The original prediction is here:
Potential Threat to the Huygen Mission
I revised the masses of the moons of Jupiter and Saturn for Neried somewhere later, but for the rest of it, I stand by the original 'formula' prediction...at least the first two digits.
Quote:
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Originally Posted by Djellison
If our knowledge of the Mass of Mars is wrong to the tune of 14%, then the successful operation of spacecraft at and around Mars for decades is unarguably the greatest miracle of all time.
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I would reserve that title for Huygens. Incredible feat, that.
Mars landings - Mars could not possibly be 14% more massive,
unless the Newtonian equivalence principle is the root of the problem: It takes less energy to reduce momentum if you are further from objects like the sun. We can land on Mars dissipating less energy than we would have to, if Mars were at the same orbital distance from the Sun than the Earth. Even so, fighting against gravity over-time takes more energy as the rate of descent slows. It is a fact that it took both Viking probes ~5% more fuel to decelerate the last few seconds than Newtonian mechanics predicts. Mission scientists never resolved the discrepancy.
See this thread for LOTS OF evidence on how hard it has proven to land on Mars:
Mars: Hard to hit, or are Probes hitting too hard?
It remains to be seen what will happen with the
Phoenix. As always for more distant planets, the probe will fall harder and faster than Newton says it should. The nice thing is we will have both precision Doppler and radar telemetry all the way down.