How smart are SETI@homers?

In infinite wisdom Gary Heston answered:
In article , wrote:

From: Joe Strout
After we've used the materials in the asteroid belt, and dismantled
the moons of the giant planets, the obvious next targets are the Kuiper
belt and the Oort cloud. Our Oort cloud extends about three light
years out from the Sun. If Alpha Centauri has a similar Oort cloud,
then its cloud overlaps with ours. So by colonizing the Oort cloud,
you're already starting to colonize the next star.


Where do farcomet homesteaders get a supply of energy? [ ... ]

Breeder reactors should work fine.

I thought they would use everready batteries. That bunny just keeps
going and going... :-)

BTW, hwo do you get reacors to breed? Hell, how do you tell the males
and females apart?

Rich


Gary

"R" == Rich writes:

R In infinite wisdom Joseph Lazio answered:

R Statistics if properly done are descriptive of group distributions,
R they are not predictive.

This seems a bit extreme.

R The simple truth is extreme? How so?

I can use the known statistics of a group to predict the likely
properties of a new member that is discovered.

R You can 'predict' that the new member is average. [...]

R The only cases where you can make reasonably accurate predictions
R are when the thing being predicted is not random. You can
R reasonably predict that the next NAACP president will be black, and
R indeed this probably applies to the membership. But this is not
R much of a prediction.

I think your choice of examples illustrates a crucial difference
(between physical and social sciences).

Pick a star at random in the Milky Way. I predict that that star is
likely to be an M dwarf. Indeed, if you'd like me to be more
specific, I can quote the odds that the star will be of any given
spectral type.

Pick a pulsar at random in the Milky Way. I predict that its velocity
is likely to be around 500 km/s. More specifically, the odds are
roughly 95% that its velocity will be between 0 and 1100 km/s.

Similarly, as Louis says, finding more members of a group improves
my estimates of the group statistics.

R Estimates? It does indeed give you more information about the
R group. But the fact remains, stats are descriptive, not
R predictive. Will more information allow you to predict the mass of
R the next planet discovered (...)? No, it will not.

This sounds to me to be a semantic difference. Given the current mass
distribution, the next planet to be discovered via the radial Doppler
technique is more likely to have a mass less than that of Jupiter.

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"R" == Rich writes:

R In infinite wisdom Joseph Lazio answered:
[I thought this exchange on the number of terrestrial mass planets
to be getting to the point where a followup was not necessary.
However, I've since realized that there is an important point.]

This may once again be reaching the point where no reply is
necessary. For the benefit of any other readers though....

R Almost exclusively gas giants, only a few oddball terrestrial
R planets. I don't see how you can derive that there are "more
R lower-mass planets than Jupiter-mass planets" from the data at
R hand.

From Marcy et al. (2003, "Properties of Extrasolar Planets," ...)

The distribution of masses rises rapidly toward the lower masses,
dN/dM ~ M^{-0.7} ....
R Where M is 1 jupiter mass.
This is both incorrect and highlights an important point. The mass
distribution I write above is a function.

R It's not a function as such, it's more of a relationship. A
R function takes one input and produces one output. Even if M is
R defined, and it does not appear to be, you relate any N to any M,
R or vice verse.

From the data, the mass distribution function above is valid over the
range of roughly 0.1 M_J to 10 M_J. As to your distinction between
"relationships" and "functions," you don't define it and it doesn't
seem to be important. (Call it a relationship if you'd like, that
doesn't change the mathematical expression.)


To make this point more explicit, we can use this mass distribution
to compare the number of planets of different masses. Suppose we
want to know how many more 0.5 Jupiter mass planets there are
compared to the number of 2 Jupiter mass planets. Then dN/dM(2M_J)
~ (2M_J)^{-0.7} and dN/dM(0.5M_J) ~ (0.5M_J)^{-0.7}, and their
ratio is (0.5M_J/2M_J)^{-0.7} = 2.6. That is, there are about 3
times as many 0.5 Jupiter mass planets as there are 2 Jupiter mass
planets.

R Are there? I don't see any planets with 2 jupiter masses
R hereabouts.

Hmm. Chinese speakers are claimed to be approximately 20% of the
planet's population. There were no Chinese speakers in my high
school. Ergo, the statistic is wrong.


R If you claim the relationship has universal validity, perhaps you
R can show me the observational basis.

I pointed you to the paper.



So what is the evidence for terrestrial mass planets? I'd now have
to say, not much.

R Odd, when I made that claim it was considered an attack on SETI.

Agreed. You still haven't answered my other question, though. Given
the lack of observational evidence for terrestrial planets, is it
worth searching for them?

If I were a gambling man, though, I'd be willing to bet that
terrestrial planets are numerous, for the following reasons.
First, if Jupiter mass planets can form, it seems like forming
something only 0.3% of their mass should be much easier.

R Should be? Seems to me that they require different materials. As to
R the dynamics of planetary formation, some of the planets exist
R where our current models say they cannot exist. I don't think we
R have any solid basis for making predictions.

Actually, current models involving planetary migration seem to do
reasonably well in explaining the locations of "hot Jupiters."
Indeed, models of planetary migration are helping to explain some
long-standing puzzles about Uranus and Neptune.

Indeed, at a party last night, somebody pointed out that we
actually know of three extrasolar *cometary* systems. Second, we
know of three terrestrial mass planets orbiting PSR B1257+12,

R Lower bounds again, they may well be of the 0.1 jupiter mass class.

I don't think so. I'd have to check Wolszczan's papers, but I think
the detection of the mutual gravitational interactions between the
planets pretty well nails their masses to be terrestrial.

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