For The Mother: Retrograde Orbits/Spin

The Mother asked: How is it that Venus spins backward? Shouldn't the momentum that created the solar system keep everything spinning the same direction?

In theory, I believe you're right. Of the planets in the solar system, all of them orbit in the same direction so it makes sense that they'd rotate in that direction, too. The fact that so many planets rotate in the same direction (i.e. the same direction they're orbiting in) argues it, too.

But Venus doesn't and Uranus is tilted so far on it's axis (~98 degrees) that, depending on own's perspective, it can also be said to rotates backward. But really it's more lopsided.

So, why Venus and Venus only. Well, Venus is not the only item with retrograde motion. Several moons around Jupiter, Saturn and Neptune orbit in a retrograde way. Several of these items are believed to be captured Kuiper belt items. Kuiper belt items are items like comets and some very far flung planetary-type bodies that are far beyond the edge of the planets. Some objects, like comets, we see every so often because they have highly elliptical orbits and they can crash into planets (as happened to Jupiter a few years ago) or be captured, in theory, by the gravitational pull of a planet. As these items have their own spin and orbit (and will be going very fast as they get closer to the Sun), they can readily get caught by a planet, but not necessarily be in plane or going in the same direction when caught (it depends on whether it's incoming or out going and from what direction they approach the planet that captures them).

That, of course, doesn't apply to Venus. Venus is very similar in composition and characteristics to Earth and has a very circular orbit (which would be unlikely in a captured high speed body), in fact the most circular orbit in the solar system. So, why would it spin backwards even at a very slow rate?

The easy answer is, we don't know. There are speculations, of course. One is that the current year/day represents an equilibrium state between gravitational tidal locking by the Sun that tends to slow the rotation rate, and an atmospheric tide created by the solar heating of Venus' thick atmosphere. Ironically, in addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known.

But there are other speculations. Alex Alemi and David Stevenson of the California Institute of Technology, using their models, believe that Venus once had a moon (it doesn't have one now) that had been formed from a cataclysmic impact event. Ironically, they believe the retrograde motion now is the result of another cataclysmic impact that changed the rotation and, ironically, pulled the moon back into the planet. This, they believe, happened billions of years ago. Since the surface of the moon is highly volcanic with a new surface, much like the Earth has, there's no indication of any such impacts on the planet's surface.

Just goes to show that there are many strange things going on in the big wide universe. And we've got a long ways to go before we get more than scratching the surface on figuring out how what we can see today happened. By then, of course, we'll likely have a whole new set of mysteries to figure out.

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For Patricia: The End of the World

Patricia asked: It’s hard for me to decipher “real physics” from the fiction (in Sawyer’s novel) to the often hysteria one finds in media stories (I mean, the Collider does actually exist and they do conduct experiments which could go awry?). Add to that, all the hype over the approaching pole shift or Planet X or Mayan Calendar catastrophe in 2012 and I wonder how much of what we hear of potential or forthcoming astronomical calamities are actually predicted (or predictable) by physicists?

I hear you, Patricia. It’s hard for a lot of people to tell the difference, and these challenges are amplified by the tendency of mass media to (a) focus on the most dramatic elements (even if they are a small part of the whole), (b) they often put their own interpretation on what they hear, even if it’s completely erroneous and (c) they have been knownto put their ownslant on things. It wouldn’t matter so much if scientists had their own direct outlets to the general public, but most scientists tend to write papers for other scientists, so they use language the general public doesn’t understand and concepts that are not common knowledge.

I try not to do that, but I depend on you, my readers, to let me know when I fail.

The side effect of that, though, is that people get what’s going on in the scientific world through mass media and, never forget, media isn’t nearly as concerned with truth as they are with sensation. If a twist in the truth makes a story inflammatory or exciting, most news agencies will pursue it. It’s their business.

This also includes many of our documentaries and shows on Discovery or the Science channel. Scientists might be involved, but the conclusions and dramatic overvoicing are there to make it more exciting, more appealing, more memorable. That means that scientists (such as archaelogists) who, in the real world, would never say something as an absolute (unless they were complete hacks) say things like: “From this picture painted on Pharoah’s tomb, we know the Pharoah was a devoted family man.” No, we know nothing of the kind. It’s certainly possible, but the closest thing we could say we know is that someone (perhaps not even the Pharoah) wanted him to be remembered that way. I could go on and on about the distortion of science, but you really asked about science and doomsday scenarios.

So, here’s what I know. Mayan end of the world, Christian apocalypse, ancient-religion/culture of your choice doomsday - I don’t know any respectable scientist who thinks the end is coming at a specific date. There are scholars and scientists who will say such and such ancient people believed or predicted such and such would be the end of the world, but no one I know of takes it as more than a historical curiousity.

Are there potential doomsday scenarios scientists are worried about? You bet, but none of them have a definitive date. And some are “end of the world” and some are “the world will get difficult for many people on earth.” The Large Hadron Collider is not one that I think reputable scientists worry about.

Of the “world will get difficult” variety, we include most of the self-induced pollution/damage variety: overfishing and oceanic pollution affecting fish populations such that many starve. Ozone depletion leads to increased exposure to UV rays and increases in cancer. Radiation leakage and nuclear disasters (like Chernobyl) have the potential to impact different populations. Ditto for other forms of serious pollution. Loss of wetlands and other buffer zones make human populations more at risk along coastal areas. And, of course, the big one: global climate change as a result of our anthropomorphic changes to the atmosphere that melt glaciers (threatening the water supply for billions of people), induce/increase drought and or storm system, change the coastlines at worst case. I believe most understand that this will not destroy the human race, but can seriously inconvenience it and put many parts of the populace at risk. Also in this category, we include natural disasters like tsunamis, earthquakes, volcanic devastation. These aren’t really sizeable risks for the whole populace, but it can certainly do tremendous damage to affected areas (like those hit with the tsunami in the Indian Ocean a few years back).

When we get to “end of the world as we know it” scenarios, the list is considerably shorter: global thermonuclear war (which I hope is much more unlikely at this juncture than it was 30-50 years ago) and impact from a large asteroid or comet. The latter is something we don’t currently have a way to prevent, has happened in the (far distant) past with huge impacts on the life at the time, and we have clear visual proof that such impacts are devastating. Just look at what’s been done to the moon. Jupiter was hit with a comet in 1994 as we watched. So, yes, it can happen, but there’s no reason to expect it any time soon.

And, if it does happen, there won’t be many (if any) of us left to worry about it.

1. # shakespeareon 29 Mar 2009 at 9:43 pm edit this

   Yup, so we might as well stop polluting and otherwise take care of the earth as much as we can, and not worry about what we cannot possibly prevent.

   Great answer. Intelligent as always.

2. # Patriciaon 05 Apr 2009 at 11:38 am edit this

   I guess I feel better. Thanks!

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