Did Venus Have A Moon? Options

[nprev]

...or two?

http://skytonight.com/news/home/4353026.html

[nprev]

Argh...my apologies for misunderstanding you, RN.

Well, the central point I was trying to make was that Mars' rotation period does not seem to be an artifact of primordial major impacts, although I'm sure that some such events certainly had an influence. Venus' case is entirely different...and just to throw a bit more churn into the mix, what in blazes must've happened to Uranus???

I am willing to accept chaotic early System events like major collisions as likely explanations for some current dynamic oddities like the Venusian rotation period & direction. However, Sagan's Law must still apply: extraordinary theories require extraordinary evidence. Using this heuristic, the "two-moon Venus" (or even one-moon) scenario seems difficult to defend.

(Did someone just mutter "Hyperion"??? Quiet, you! )

[JRehling]

what in blazes must've happened to Uranus???

This is solidly off-Venus-topic, but I was wondering recently: What if Uranus once orbited in the plane of its rotation and the tugs of other giant planets pulled it towards the ecliptic while the axis remained gyroscopically (near) fixed?

[ugordan]

What if Uranus once orbited in the plane of its rotation

That would be one very inclined orbit. Which brings up another question: why Uranus? why not Neptune too? What made Uranus form in such a weird orbit?

[helvick]

That was my thinking too.

To nudge this slightly back on topic. There are plenty of theories out there (Martian polar wander, the long term stability of the earth's inclination resulting from the moon etc) that seem to imply that the obliquity of the planets should be fairly widely distrubuted. In that case no really odd mechanics is required to explain the Uranian tilt. However if it really is that "simple" then how come it's the only really extreme one?

edited: replaced inclination with obliquity. Doh!

[JRehling]

That was my thinking too.

To nudge this slightly back on topic. There are plenty of theories out there (Martian polar wander, the long term stability of the earth's inclination resulting from the moon etc) that seem to imply that the inclination of the planets should be fairly widely distrubuted. In that case no really odd mechanics is required to explain the Uranian tilt. However if it really is that "simple" then how come it's the only really extreme one?

We can probably exclude Mercury and Venus as being solar-locked, and we can perhaps exclude Earth on the anthropic principle (would we be here as an advanced species to discuss the issue if Earth had Uranus's inclination?).

That leaves us with Mars and four giants, plus choose-as-you-like for other worthy bodies to include in the discussion. Pluto is tidally locked to its satellite, which probably excludes that one from consideration (Mars and the giants are NOT locked to their satellites, to say the least). Eris is unknown.

Jupiter and Ceres are very low inclination. Earth, Mars, Saturn, and Neptune are eerily similar in their modest inclinations; Vesta is also in that general vicinity. Then Uranus is the big outlier. Mars, at least, is prone to swings over geological time. Earth and probably Saturn seem to be stabilized and I'm quite sure that the other three giants are too big/too far from anything to get tossed around.

It's important to note that this is a very small n. You can't call any trends you spot statistically significant. I wonder if the "expected" distribution is flat or clustered in Gaussian fashion around 0. The data leads me to the wild guess that it is the latter, and it's a fluke that the "midrange" instances are clustered around 25 degrees with nothing between 6 and 21 or between 30 and 90. If one standard deviation is 30 degrees, we would expect about 2/9 to be in each of these bins: 0-10, 11-20, 21-30. The first bin got its quota and it just happened that the third bin ended up with "both" of the planets that "should have" been in the second bin, and one that "should" have been in a higher-number bin. Three little flukes. A friend of mine had a phone number with "666" in it -- things like this happen.