March 14, 2016 | David F. Coppedge

Solar System Is Weird Only if It Is Old

To someone who believes the solar system is billions of years old, no wonder its contents look weird.

Mercury is weird

David Rothery, planetary scientist at The Open University, remarks on The Conversation that “The more we learn about Mercury, the weirder it seems.” As we shall see, weirdness is not limited to Mercury.

For such a tiny planet, Mercury is a pretty big puzzle for researchers. NASA’s MESSENGER probe already has revealed that the planet is surprisingly rich in elements that easily evaporate from the surface, such as sulphur, chlorine, sodium and potassium. This is incredibly odd as these kind of substances most likely would disappear during a hot or violent birth – exactly the type of birth a planet so close to the sun, such as Mercury, would have had.

Scientists are also struggling to understand why Mercury is so dark and what its earliest planetary crust, created as the newly-formed planet cooled down, was made of. Research has now started to throw up answers – but these are raising a lot of new questions.

Perhaps their research is starting to “throw up answers” because all the proposed answers are making them nauseous. One thing is clear from this quote: the puzzles come from dating the planet as billions of years old. Elements that easily evaporate should not be there after that long. A BBC News article sounds more confident, explaining that the unexpected graphite found on the surface may have floated on top of Mercury’s original molten interior. It doesn’t however, address the puzzle of surface volatiles that should have disappeared during a hot or violent birth.

Mars is weird

A paper in Icarus examines a “young” crater named Zumba. It is 3 km in diameter with ejecta rays that extend outward for hundreds of kilometers. Remember when scientists thought that each crater was produced by a separate impact? (5/22/12). They say this one crater has 352,000 secondary craters, all from the same event. They think they can still date the Zumba impact to 570 million years, but earlier scientists thought they had a handle on crater count dating, too.

Mars is also weird because of its volcanoes and canyons. Space.com now claims that water carved its features, not a massive volcano. That’s right: rain and snow carved major valleys on Mars just as the giant Tharsis volcanoes were forming. This shows that the battle between the wet-Marsers and dry-Marsers is still going on. New Scientist has more on this theory that the crust tilted due to “true polar wander,” resulting in volcanoes and resultant flooding.

Mars suffered a major catastrophe to its weak magnetic field in October 2014 when a comet swept by, its coma reaching down to the surface. Several orbiters measured the effect. Astrobiology Magazine says the episode threw the magnetic field into chaos and accelerated the escape of some of its atmospheric molecules to space.

At first, the changes were subtle. As Mars’ magnetosphere, which is normally draped neatly over the planet, started to react to the comet’s approach, some regions began to realign to point in different directions. With the comet’s advance, these effects built in intensity, almost making the planet’s magnetic field flap like a curtain in the wind. By the time of closest approach — when the plasma from the comet was densest — Mars’ magnetic field was in complete chaos. Even hours after the comet’s departure, some disruption continued to be measured.

Espley and colleagues think the effects of the plasma tide were similar to those of a strong but short-lived solar storm. And like a solar storm, the comet’s close passage likely fueled a temporary surge in the amount of gas escaping from Mars’ upper atmosphere. Over time, those storms took their toll on the atmosphere.

This cannot be the first time such an event has happened. No one thinks the solar system scheduled it for us to observe while humans have the instruments to appreciate it. How many thousands, perhaps millions, of comets have swept near Mars in billions of years? Why is there any atmosphere left at all? The weakness of Mars’s magnetic field is a reminder that decay is in the future of Earth’s magnetic field as well—a physical phenomenon that cannot last for billions of years (5/17/12, 4/17/15, 5/08/15).

Ceres is weird

The Dawn spacecraft has been in orbit around asteroid Ceres for a year now. “A mountain emerges” in the images, says Astrobiology Magazine. Ahura Mons is 3 miles higher, taller than Mt. Rainier or Mt. Whitney on Earth. “No one expected a mountain on Ceres, especially one like Ahuna Mons,” the principal investigator said. “We still do not have a satisfactory model to explain how it formed.” Summing up the surprises, the deputy principal investigator remarked, “Ceres has defied our expectations and surprised us in many ways, thanks to a year’s worth of data from Dawn. We are hard at work on the mysteries the spacecraft has presented to us.”

Titan is weird

Saturn’s large moon Titan, large enough to be a planet in its own right, has lakes of liquid methane. Previously thought to be as calm as a mirror, evidence of ripples has come to light, reports New Scientist. Are winds picking up during the change from equinox to solstice? PhysOrg posted artwork of a deep global ocean on Titan, which is what scientists had expected to find in the 1990s. Cassini has only found scattered lakes, mostly in the northern hemisphere. While some are estimated to be over 600 feet deep, containing some 40 times the volume of all of Earth’s methane reserves, it is far less than estimates based on methane and ethane rain induced by the solar wind over billions of years. The ripples are surprising for a body that should have come to rest long ago. “Planetary scientists are taking note,” PhysOrg says, “…because these waves show that Titan has an active environment, rather than just being a moon frozen in time.Astrobiology Magazine posted comparison photos of a “mystery feature” in one of the lakes that seems to appear and disappear.

Comet 67P is weird

Rosetta’s comet has turned up some surprises, too. PhysOrg says that ESA scientists have inferred a relatively homogeneous interior, lacking caverns from escaped volatiles. This implies that Comet 67P is a fluffy aggregate with very low density. Crystalline ice suggests parts of the interior date from the early solar system, Science Daily says. The article doesn’t explain, though, that the age inference depends on theory about which isotopes of argon, nitrogen and carbon date are primordial and which are more recent. “If comets are made of crystalline ice, this means that they must have formed at the same time as the Solar System, rather than earlier in the interstellar medium,” the article states confidently. “The crystalline structure of comets also shows that the protosolar nebula was hot and dense enough to sublime the amorphous ice that came from the interstellar medium.” Crystalline ice was not directly observed; it was inferred from the isotopes of argon present.

Pluto is weird

If you want to ski Pluto’s mountains, you have to learn how to navigate methane moguls. Latest images from New Horizons show methane ice on the peaks, “but it’s more exotic than the frozen stuff we’re used to here on Earth,” Space.com says. The bombshell news that came earlier is still puzzling the team:

New Horizons’ July 14 flyby, which took the spacecraft within just 7,800 miles (12,550 km) of Pluto’s surface, revealed the dwarf planet to be a complex world with surprisingly diverse landscapes. For example, in addition to the towering mountains, Pluto hosts a vast nitrogen-ice plain known as Sputnik Planum, which lacks any detectable craters.

Sputnik Planum’s unblemished surface indicates that the region was resurfaced very recently, which in turn suggests that Pluto harbors an internal energy source (which drives the resurfacing). What that energy source may be remains a mystery.

Something is “eating on Pluto,” Science Daily says; a geological feature looks like something took a bite out of the crust. Was it caused by sublimation of methane from below? The article speaks of “remnants of methane that have not yet sublimated away entirely,” but fails to explain why there is any left after 4.6 billion years.

Meteors are weird

PNAS scientists have a theory for why certain groups of metal-rich chondrites (chips off the parent asteroid block) have their own signature of short-lived radionuclides, if one is prepared to accept their ad hoc initial conditions. “The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.” Another PNAS paper piles on the ad hoc conditions to explain millimeter-size chondrules. “Moreover, the isotopic complementarity of chondrules and matrix requires that chondrules formed in a narrow time interval and were rapidly accreted to a parent body, implying that chondrule formation was a critical step toward forming planetesimals.” This sounds like special pleading. The fact that theory “requires” special indications points to difficulty explaining these objects within a general theory.

Asteroids are weird

Are you worried about the asteroid deficit? It may not be as serious as the federal deficit, but it keeps some planetary scientists scratching their gray hairs off. Nature describes what they’re worried about:

Models predict that numerous asteroids should be found on orbits that closely approach the Sun, but few have been seen. In addition, even though the near-Earth-object population in general is an even mix of low-albedo (less than ten per cent of incident radiation is reflected) and high-albedo (more than ten per cent of incident radiation is reflected) asteroids, the characterized asteroids near the Sun typically have high albedos.

To explain this, the authors find a possible physical mechanism, but it’s catastrophic:

We conclude that the deficit of low-albedo objects near the Sun arises from the super-catastrophic breakup (that is, almost complete disintegration) of a substantial fraction of asteroids when they achieve perihelion distances of a few tens of solar radii. The distance at which destruction occurs is greater for smaller asteroids, and their temperatures during perihelion passages are too low for evaporation to explain their disappearance. Although both bright and dark (high- and low-albedo) asteroids eventually break up, we find that low-albedo asteroids are more likely to be destroyed farther from the Sun, which explains the apparent excess of high-albedo near-Earth objects and suggests that low-albedo asteroids break up more easily as a result of thermal effects.

Catastrophic disruption can be rapid. In fact, an asteroid too close can be completely obliterated in just 250 years. OK, so how long has this been going on? 4.6 billion years? Why are there any left? The theory accounts for the asymmetrical distribution of albedos, but not the absolute ages of the bodies.

Update 3/16/15: Uranus Is Weird, too. See Space.com‘s “Top 5 Weird Facts About Mysterious Uranus.” Why does Uranus have rings? “The circumstances behind their formation are poorly understood,” the article says (they should be gone long before billions of years). Why doesn’t Uranus give off internal heat like the other gas giants? If it is so cold, why does it have storms? Why is the planet tilted almost on its side, and why is its magnetic field way out of alignment with its spin axis? Why is its moon Miranda so odd, with a mosaic of features scientists are still “puzzling to explain” 30 years after Voyager 2 photographed it?

Are there any other bodies in the solar system that are weird? Yes; the skulls of moyboys. They have to come up with weird conditions to keep things billions of years old.

 

 

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