Expert: Tom Whiting - 4/28/2010

Question
Hi Tom,

Venus perplexes me.  It's retrograde rotation, youthful surface, and extreme atmospheric pressure and temperature, seem to me as inconsistent with stable planetary conditions - especially for one which is 4.5 billion years old.  My intuition leads me to suppose that Venus has suffered some cataclysmic event in the not too distance past.

The current popular theory that Venus' crust, lacking plate tectonics, holds in the interior heat until it suddenly (and cyclically) erupts and resurfaces the entire planet, does not explain the rotational anomaly.

Assuming this theory, do we know what Venus' interval base atmospheric pressure should be?  Can this be calculated by using the known atmospheric loss rate, from the solar wind, and projecting forward with a minimal out-gassing factor?

I would appreciated your thoughts on this.  There is so much we don't know about our closest neighbor, and why it is such an inhospitable place.

Thank you,
Bob

Answer
Hi Bob,
Actually I consider Venus the most stable planet in the Solar System, with it's near-perfect,
almost circular orbit, and a rotation rate that's probably only a few million years from a helio-stationary (continuous sun facing) rotation.  (Like our own moon, you can't get much more stable
than that.) Plus Venus only varies 1 or 2 degrees off the ecliptic... I think any major asteroid impact in the past would have significantly changed one or more of those characteristics, like we see with Mercury; wild swings away from the ecliptic and highly elliptical orbit.
I actually don't consider the surface temperature and pressure "extreme" for it's location...
maybe (or perhaps) that's normal evolution for a rocky planet only 67 million miles from the sun.

So to me, that shows no violent impacts in the past history.  The surface is a different story with probably active volcanoes and lots of out-gassing. So whatever it is now after 4.6 billion years, that's the 'stable' surface condition... and the current surface temperature and pressure ARE the base numbers. No one knows what the past history was, but the past conditions probably would not represent the equilibrium conditions of today.

Too bad Venus was just a little too close to the sun, otherwise it may have ended up more Earth-like.  It just got too hot, being just inside the accepted habitable zone.
We (the Earth) hit the power ball life lottery, of perhaps odds of one trillion to one, and Venus didn't... that's all.
(otherwise we'd live there, and be debating today of why planet Earth is too cold and frozen over, being too far from the sun, like we currently do with Mars).
Just my opinion,
Clear Skies,
Tom Whiting
Erie, PA  USA