Were Mercury and Mars separated at birth?

Line up Mercury, Venus, Earth and Mars according to their distance from the sun and you'll see their size distribution is close to symmetrical, with the two largest planets between the two smallest. That would be no coincidence -- if the pattern emerged from a debris ring around the sun.

Brad Hansen of the University of California, Los Angeles, built a numerical simulation to explore how a ring of rocky material in the early solar system could have evolved into the planets. He found that two larger planets typically form near the inner and outer edges of the ring, corresponding to Venus and Earth. A number of smaller bodies also form within the ring. These are typically scattered away by the larger two, but if they experience collisions on the way, they can end up in stable orbits similar to those of Mercury and Mars. Once beyond the ring, they cannot acquire mass and so remain pint-sized.

"This is nicely consistent with various properties of Mercury and Mars," says Hansen, who presented the work at the American Astronomical Society meeting in Long Beach, California. Both small planets have features that could have been caused by giant impacts. In one run of Hansen's simulation, Earth received a smash, too, much like the one thought to have created the Moon.

An alternative is that early in the history of the solar system there are vast amounts of gas, rock, etc. in orbit around the Sun.

All of this collapses into a number of gas giants with rocky cores.

The gas giants gradually spiral in toward the Sun. Some, of course, crash into the Sun and disappear. Others are eventually scoured of their gas as the Sun goes through more active phases on the way to its mainstream steady state.

It's at that point they stop spiraling in to the Sun.

What you end up with is a bunch of rocky planets near the Sun and a bunch of gas giants at vast distances from the Sun.

Recent discoveries of solar systems with large gas giants close to the central star suggest the "spiraling in" scenario may be more nearly correct.

Think of the planetary array between Jupiter and the Sun as consisting of a bunch of steel balls on a string.

The Sun and Jupiter so outweigh all the others (in terms of momentum if nothing else), the worst that can happen to them is to be alternately thrown out of the Jupiter/Sun system, or the Sun/Jupiter system while at the same time, easily kept captive by either one or both in quite circular orbits.

In the outer part of the ring you have a Uranus/Neptune/Saturn/Jupiter system. Here the intermediary planets retained their gas shells (I believe only one of 'em has a rocky core though ~ that'd be Jupiter). They have dramatically different mass though, and Neptune regularly gets tossed out of its orbit, whipped around, jerked this way and that, and ends up cockeyed.

Los Alamos Computers Probe How Giant Planets Formed
Science News
July 22, 2004
Working with a French colleague, Didier Saumon of Los Alamos' Applied Physics Division created models establishing that heavy elements are concentrated in Saturn's massive core, while those same elements are mixed throughout Jupiter, with very little or no central core at all. The study, published in this week's Astrophysical Journal, showed that refractory elements such as iron, silicon, carbon, nitrogen and oxygen are concentrated in Saturn's core, but are diffused in Jupiter, leading to a hypothesis that they were formed through different processes. Saumon collected data from several recent shock compression experiments that have showed how hydrogen behaves at pressures a million times greater than atmospheric pressure, approaching those present in the gas giants. These experiments - performed over the past several years at U.S. national labs and in Russia - have for the first time permitted accurate measurements of the so-called equation of state of simple fluids, such as hydrogen, within the high-pressure and high-density realm where ionization occurs for deuterium, the isotope made of a hydrogen atom with an additional neutron. Working with T. Guillot of the Observatoire de la Cote d'Azur, France, Saumon developed about 50,000 different models of the internal structures of the two giant gaseous planets that included every possible variation permitted by astrophysical observations and laboratory experiments.
Did Jupiter Bully Other Planets in Sibling Rivalry?
by Robert Roy Britt
8 December 1999
One possible explanation, discussed in Thursday's issue of the journal Nature, is that Uranus and Neptune formed much closer to the center of the action than their current positions might indicate. In this scheme, Jupiter and Saturn were bullies of a protoplanetary playground, shoving the other two future giants out of the way.
Jupiter gave birth to Uranus and Neptune
by Dr David Whitehouse
8 December, 1999
Not too long ago, scientists regarded the orbits that the planets circle our Sun as being the ones they were born in. Now they are realising that this is not the case. Uranus and Neptune may have migrated outwards and Jupiter may have come in from the outer cold. Scientists have always been slightly puzzled by the positions of Uranus and Neptune because in their present locations it would have taken longer than the age of the Solar System for them to form. Scientists from Queen's University suggest that the four giant planets started out as rocky cores in the Jupiter-Saturn region, and that the cores of Uranus and Neptune were tossed out by Jupiter's and Saturn's gravity.
Jupiter's Composition Throws Planet-formation Theories into Disarray
by Robert Roy Britt
Nov 17 1999
Examining four-year-old data, researchers have found significantly elevated levels of argon, krypton and xenon in Jupiter's atmosphere that may force a rethinking of theories about how the planet, and possibly the entire solar system, formed. Prevailing theories of planetary formation hold that the sun gathered itself together in the center of a pancake-shaped disk of gas and dust, then the planets begin to take shape by cleaning up the leftovers. In Jupiter's current orbit, 5 astronomical units from the sun, temperatures are too warm for the planetesimals to have trapped the noble gases. Only in the Kuiper belt -- a frigid region of the solar system more than 40 AU from the sun -- could planetesimals have trapped argon, krypton and xenon.

While lead researcher Tobias Owen does not put much stock in the idea that Jupiter might have migrated inward to its present position, other scientists on the team say the idea merits consideration. Owen expects the probes will find similarly high levels of noble gases in Saturn, Uranus and Neptune. Hints of these gases have even been found in the thick atmosphere of Venus, another planet now begging more study.

Even given the suggested scenario, what’s curious is the strange fluctuation in rotational speeds.

Earth and Mars are almost identical in daily rotation, while Venus is retrograde, having a longer day than its year.

Mercury has a very slow rotation also. It is about two thirds tidally locked.

Now what suggests itself is that those planets inbound from the center of gravity of all four planets were affected by the accumulation of differential masses having orbital speed faster than the main mass, giving them “reverse english” in billiards parlance.

Possibly that could also explain Earth and Mars, but it would take some computational time on a super-computer. Or perhaps Earth lost quite a bit of rotational speed to its parking brake partner, the moon.

Now the next question: How do we form them into a Klemperer Rosette?

Ooh, interesting:

Klemperer Rosettes

Tidal transfer of momentum (from the planet to the Sun, and vice versa) would be greater for Mercury than for Venus, so its slow rotation should be slower than Venus, but we see it's the other way. They have similar densities (in order, Earth, Mercury, Venus, Mars), with Mercury a much smaller mass, which suggests that Venus didn't originate in its current orbit, or that Mercury didn't, or both; could also mean (as an online friend pointed out to me) that Venus was walloped but good some while ago, and got turned over from that impact encounter. Mars and Earth have a similar length of day, but Mars' (24 hrs 37 minutes) might be expected to be a great deal slower at formation because of overall lower mass. All this assumes that the model of formation from an accretion disk around the Sun is pretty much correct.

Here’s a visual for ya.

Take an 11”x17” sheet of paper and draw the following:

At the left side of the page with a #2 pencil, draw the smallest circle you can. This is the Sun, the circle you draw will be way too big at this scale but what the heck it’ll work for the visual.

Next, about 1/3rd the distance from the left side of the page make a dot, that’s Mercury and as you might have guessed the dot is thousands of times way to big on this scale but now we’re just making a mark for reference. But try to make the dot as small as you can. :)

Next, about 2/3rds from the left of the page make another dot, That’s Venus and yes its also a couple thousand times to big but you have to be able to see it don’t ya?

Finally all the way to the right make your last dot and that’s Earth. As with the last two dots (planets) the smallest dot you can make (with a #2 pencil) is still thousands of times way too big at this scale but again this is just for reference.

Now hold the page out in front of you and even though the planets look like dust particles they are planets. Amazingly this looks nothing like the drawings of the solar system we’ve all grown up looking at but this one is to scale sorta, distance wise yes, planet sizes no. Also note that as big as the Sun really is, its nothing compared to the vast distances between the planets is it?

Anyway, now try and imagine dust particles floating around in all this empty space, touching and clinging to each other and wow, creating planets.

Nope, it ain’t gonna happen.
JB

I tend to reject the notion that Venus had anything other than a perfectly boring origin. It has so nearly perfectly circular an orbit that it simply must have accreted in position.

Earth’s early rotational speed, (after the moon-forming collision), was nearly Jovian in speed. It transferred a lot of momentum to the moon, pushing it higher in its orbit. (That particular form of anti-gravity is intriguing, but it seems to only work for large bodies.)

I think this accretion disk hypothesis for the inner planets is promising. The outer planets, like the original Olympian gods, seem to have done things that should not be discussed around women and children.

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