There Goes the Solar System


My Very Excellent Mother Just Served us Nine Pizzas.
My Very Easy Method Just Speeds Up Naming Planets.
My Very Early Morning Jam Sandwiches Usually Nauseate People.
Mon Vieux Tu M'as Jeté Sur Une Nouvelle Planète!

-- Various mnemonic devices for remembering the order of the nine planets

I just found out that Mercury is shrinking.

The planet, already our most diminutive neighbor, has lost around 3 miles of its 3,000 mile diameter in its life, or one tenth of one percent.This may not sound like much, but in geological terms, three miles is immensely significant.

This boggling fact was discovered -- well, rather, confirmed -- by the ongoing MESSENGER mission, which is the first long-term survey of Mercury since the Mariner 10 spacecraft became the planet's first terrestrial visitor in 1974. After an exorbitantly complex journey, in 2008, MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) revealed hitherto-unseen views of Mercury: cliffs and faults criss-crossing the planet's ragged surface, vast lava plains, and a particular geological feature, a kind of curved cliff, called a lobate scarp.


A lobate scarp of note, Discovery Rupes.

These lobate scarps are witness to Mercury's shrinkage. See, Mercury is a tiny planet mostly made up of a giant iron core, which was presumably once entirely molten. This core, as it's cooled and solidified over the eons, has contracted the entire planet in on itself and literally buckled its surface into craggy faults -- causing the aforementioned lobate scarps. This process, ostensibly, is still going on. Sure, these geological features aren't particularly exotic-looking. But they're the indicators of some serious change, and it's something we should reckon with.

OK. Space is something with which we, as a technological species, must inevitably relate. And yet, its inconceivable vastness and lack of warmth -- the fact that we, with our wet eyes and spongy lungs, die instantly beyond the comfort of our atmosphere -- make it difficult to work with. Certainly, we're interested. Our scientists send probes to the planets to map, find lobate scarps, and name them; as people, we endeavor to understand our surroundings, and delight in new discoveries like these.

And yet, how many among us look up at the starry night sky and think, "all this is home"? The Universe, to most, is an uncaring colossus, impersonal and frightening. The very idea of floating in space conjures up horrific images of Frank Poole drifting out to his tenebrous death in 2001: A Space Odyssey (I often nightmare upon this subject). Few of us think of space, or the Universe for that matter, as being a direct part of our experience; we are, for all intents and purposes, ideologically separate from it, our planet a warm little island in a sea of otherness, nothingness.

The only aspect of outer space that strikes us with any sense of familiarity is our cosmic family unit, the solar system. "Our" solar system. We learn the order of the planets in grammar school, through various absurd mnemonics, and all know bits and pieces of scientific lore about each: Mercury oppressively small, Mars close, dusty and red, Saturn with its elegant rings, and Jupiter a giant of swirling red clouds. Some of us have affinities and distastes -- I, for example, find Venus horrible. We know "our" planets, see them as our fellows, as odd-coupled roommates in the neighborhood. We feel, au fond, territorial.

Which is why, perhaps, any changes in the established order can irk us fantastically. Take Pluto, for example. Long a beloved member of the solar system, its 2006 demotion from planet to dwarf planet ignited ire among thousands, who saw the move as needlessly draconian, as well as an affront to the harmony of our solar system. 54 members of the California state assembly proposed a resolution condemning the International Astronomical Union for "scientific heresy," and for inciting "psychological harm to some Californians who question their place in the universe." Of course, Pluto continued to exist, unconcerned.

Will Mercury's gradual shrinkage stir up our collective possessiveness of the solar system in the same way? Mercury, like Pluto, remains the same planet, and, perhaps, a few miles of lost girth won't have the same effect on the populace. Still, I find its contraction stupidly, personally upsetting. I am, in short, like the supposed Californian, for whom incremental, nominal, or perceived changes in the solar system causes them to question their place in the universe.

As Pluto shrank in status, so now Mercury shrinks in stature. Is nothing sacred?

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I gather we have no idea whether it will continue to shrink, and how rapidly? Theoretically, if it continues, it'll eventually lose orbit and crash into the sun, right? That would be a bummer - with the loss of Pluto, we appear to be running out of planets, which I'm sure is in some way the fault of Republicans - but let's face it, it would also be sortof awesome.

I will make it my quest for the month of April to discover how much more, if any, shrinkage is to come!

Theoretically, if it continues, it'll eventually lose orbit and crash into the sun, right?

No, it may get smaller but it will still retain the same mass. Not an expert but I don't think the orbit will change at all.

Mercury's orbit may not be changing, if it's not losing mass, but it's rotation will be changing. This has consequences further for it's geology due to changing tidal stretching.

The question of if it loses mass as a result of volcanism related to the faults s how much volatile material is let out.

Very interesting. Learn something new every day.

I think Mercury will be okay. Well at least until our beloved sun starts running out of helium and gets 30 times larger. Then we shall join Mercury, Venus and perhaps Mars inside the walls of a big puffy star. You also have to count all the material that falls on Mercury, and there is loads of it.

By Denis Stritar (not verified) on 02 Jun 2010 #permalink

Mercury is AN AWSOME planet!

thank god! i thought i was the only in the world that actully knew something about space! god bless you all!!!!!

I got a better mnemonic: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (maybe Pluto)