Odds against Earth-like planets

http://news.bbc.co.uk/2/hi/science/nature/2701977.stm ^ | January 28, 2003 | Dr David Whitehouse

[RadioAstronomer]

The Earth's orbit does oscilate between a circle and an ellipse (OK, a lesser and greater elongated ellpise) about every 105,000 years.

Its prehelion precesses also.

[Physicist]

These two cases (particularly the former) are considerably easier to detect than the case of a Jovian in a distant circular orbit. Thus, the available data shows a strong selection bias.

Ding! Ding! Ding! We have a winner. They use wobbles to detect planets, they see only the wobbliest systems, and they conclude that planetary systems are too wobbly to support Earth-like worlds. Nicely done.

[Stavka2]

Does the sun still circle the Earth?

[RadioAstronomer]

prehelion = perihelion. Sigh. :-(

[HighWheeler]

Dammit I screwed up. You need the 18 inch globe with the BB, and stand 161 feet away. The actual scale size of the Earth would be .165 inches, and the BB is about .172, which is close enough at only 4% over the actual size.

[HighWheeler]

LOL! We use the playground or the hallway. The playground is preferred.

[RadioAstronomer]

Luna is constantly leaching energy from each rotation around the Earth, and is adding distance from us every day. There will be day in the far, far future that Luna finally escapes the Earth's gravity and ventures off on its own. It will be a tiny light by the time that happens.

I disagree. The Earth will continue to slow down as the moon recedes and eventually the Earth and the Moon will be locked together into a mutual orbit around a common center of mass. There will be perturbations by the Sun and Jupiter; however, they should not cause the Earth/Moon system to decouple.

[longshadow]

The Earth will continue to slow down as the moon recedes and eventually the Earth and the Moon will be locked together into a mutual orbit around a common center of mass.

What you are really saying is that the difference in angular momentum of the Earth's current rotation and it's rotation when it will be phase-locked with the moon is insufficient to raise the moon's velocity above the Earth's escape velocity, right?

OTOH, if the change in the Earth's angular momentum were in excess of what is required to make the moon exceed the Earth's escape velocity, then we would eventually wave "bye-bye" to the moon....

[Swordmaker]

...and pass out a BB to every kid in the class.

Whoa... better watch out... some school district interpret that little bronze ball to be a BULLET! You could get your entire class expelled!

[Swordmaker]

They use wobbles to detect planets, they see only the wobbliest systems, and they conclude that planetary systems are too wobbly to support Earth-like worlds.

Wouldn't that be a 'circular argument?'

Sorry... couldn't resist.

[HighWheeler]

Yeah, but these are private schools that have intelligent administrators, teachers, and students. No need for cookie cutter stupidity.

[anobjectivist]

I wouldn't be quick to call something with an eccentric orbit like Cruithne or pluto a planet or moon, it's really a captured object.

[stanz]

.... any real studies on the limited data that our technology affords at the moment should be taken as premature, incorrect guesses.

Exactly. At present we lack the kind of technological capabilities required to assess planetary genesis, evolution, orbit and life-support conditions.

[MHGinTN]

Regarding life in other solar systems, we gaven't exhausted the possibilities in our own solar system since it is possible for life to arise on a moon of Jupiter or Saturn where water is present in sufficient quantities and the tidal forces create internal heat sufficient to maintain conditions for life. Now, intelligent life, much higher order life than bacteria arising is another story.

[RadioAstronomer]

Regarding life in other solar systems, we gaven't exhausted the possibilities in our own solar system since it is possible for life to arise on a moon of Jupiter or Saturn where water is present in sufficient quantities and the tidal forces create internal heat sufficient to maintain conditions for life. Now, intelligent life, much higher order life than bacteria arising is another story.

I agree. As far as intelligent life? I truly do not know. I hear arguments from both sides on this issue. SETI is a VERY long shot at finding out. But IMHO, it is worth the effort.

[MHGinTN]

Absolutely worth it and we ought to be putting more funding into it, world wide.

[HighWheeler]

There are a helluva lot more people than me calling it a moon of Earth. Check google.

[RadioAstronomer]

What you are really saying is that the difference in angular momentum of the Earth's current rotation and it's rotation when it will be phase-locked with the moon is insufficient to raise the moon's velocity above the Earth's escape velocity, right?

The total angular momentum of the earth moon system, which is spin angular momentum plus the orbital angular momentum, is constant. (The Sun plays apart also) Friction of the oceans caused by the tides is causing the Earth to slow down a tiny bit each year. This is approximately two milliseconds per century causing the moon to recede by about 4 centimeters per year. As the Earth slows down, the Moon must recede to keep the total angular momentum a constant. In other words as the spin angular momentum of the earth decreases, the lunar orbital angular momentum must increase. Here is an interesting side note. The velocity of the moon will slow down as the orbit increases.

The escape velocity of the Earth is about 11Km/sec and the current orbital velocity of the moon is about 1.026km/sec.

[RadioAstronomer]

Absolutely worth it and we ought to be putting more funding into it, world wide.

Thanks :-)

[Doctor Stochastic]

And putting the ellipse oscillation with the wobble wobble and the perhelion permutation gives the Milankovitch cycles. (Which Milankovitch worked out without the aid of a computer.)