June 11, 2009 | David F. Coppedge

This Place Really Has Atmosphere

Of all the bodies in the solar system, only eight have a substantial atmosphere.  If you add in those with tenuous atmospheres, you can add in Triton and Mercury, and maybe a few others, till it becomes pedantic to call it an atmosphere if there are only a few short-lived molecules hovering over a moon.  Atmospheres are interesting because they circulate, creating winds and clouds and a host of interesting effects that some scientists spend their entire careers studying (to say nothing of weathermen).  They also can dissipate into space over time.  What does the ambience of gas around a sphere have to do with life, evolution, and dating methods?  Here are some recent reports.

  1. Mercury:  One doesn’t envision the planet Mercury with an atmosphere, but it has a very slight one.  Why it has any is a puzzle.  So close to the sun, any volatiles should have heated up and escaped from its weak gravity.  Science Daily reported, though, that the solar wind supplies a tenuous atmosphere that hangs around a little while.  Charged particles from the sun liberate molecules from the surface in a process called sputtering (a kind of erosion on an atomic scale).  But then, Mercury’s slight magnetic field should keep the solar wind at bay.  The report says that magnetic “tornados” allow solar wind to reach the surface at certain points and times.  The MESSENGER spacecraft found that these “flux transfer events” allow solar wind particles to replenish the thin atmosphere.  Space.com also discussed this story, saying, “For some reason, there are more tornadoes than scientists had anticipated.”
        The sun may not be the only source of gas surrounding this small planet.  Nature this week (June 11) called attention to a recent discovery by MESSENGER of a bright patch on the surface:1 

    Baked by the Sun and blasted by impacts, Mercury is thought to have lost much of its volatile content – such as water vapour and carbon dioxide – early in its history.  But its interior may have been bubblier than thought, according to Laura Kerber of Brown University in Providence, Rhode Island, and her colleagues.  Using observations from the MESSENGER spacecraft, the researchers spotted the remnants of a volcano that they say was driven by explosive magma with high volatile concentrations.

    If the volatiles on Mercury resemble those on Earth, as alleged, this complicates theories on the origin of the planets.  It means “Mercury formed from volatile-rich planetesimals from the outer Solar System that migrated inwards.”

  2. Earth:  The solar wind batters Earth’s atmosphere, too.  Fortunately, our strong magnetic field keeps most of our gas intact.  National Geographic News said, though, that the sun does steal some of our atmosphere.  The same magnetic energy that protects us also funnels some of the solar wind inside, where it gets heated and escapes.  In fact, we’re losing more oxygen and hydrogen than Venus and Mars.  Not to panic, though: estimates show it would last several more billion years.  The article noted that most of Mars’ original atmosphere was probably lost due to the lack of a global magnetic field.
        A planet’s atmosphere is linked to its geology.  Astrobiologists considering conditions for life on other planets need to consider this.  Science Daily reported that without plate tectonics, an atmosphere cannot be sustained.  “If you have plate tectonics, then you can have long-term climate stability, which we think is a prerequisite for life,” said Rory Barnes (University of Washington).  But tectonics can be too severe as well (think Jupiter’s volcanic moon Io).  The close-in habitable zone around red dwarfs has a side effect of generating strong tides and more volcanic activity.  “The planet must be at a distance where tugging from the star’s gravitational field generates tectonics without setting off extreme volcanic activity that resurfaces the planet in too short a time for life to prosper,” the article said.  So now there is a “Tidal Habitable Zone” to worry about.  Barnes said, “Overall, the effect of this work is to reduce the number of habitable environments in the universe, or at least what we have thought of as habitable environments.”
  3. Mars:  A report on Science Daily claims that meteor bombardment might have helped Earth and Mars become more habitable.  How?  by modifying their atmospheres.  Researchers at Imperial College London calculated that impacts during the so-called Late Heavy Bombardment could have delivered 10 billion tonnes of water vapor and carbon dioxide to both Earth and Mars.  Why, then, are the planets so different today?  They claim Mars’ lack of global magnetic field exposed it to erosion by the solar wind.  Also, a decline in volcanic activity cooled the atmosphere so that the remaining water molecules froze out.
        The article from Science Daily mentioned above also speculated about how Mars might become more friendly to life.  “If Mars were to move closer to the sun, the sun’s tidal tugs could possibly restart the tectonics, releasing gases from the core to provide more atmosphere.  If Mars harbors liquid water, at that point it could be habitable for life as we know it.”
        Meanwhile, don’t worry that germs carried by our rovers might be seeding Mars with Earth life.  A story on Astrobiology Magazine says the ultraviolet radiation is intense enough to sterilize everything on the surface.  There’s no escape, even inside salt crystals.  And that’s not the only hazard to life.  Andrew Schuerger, a NASA scientist listed “at least 13 separate factors on Mars that can kill Earth microbes, not counting perchlorate salts uncovered by NASA’s Phoenix Mars Lander in the polar region of Mars.”  Earth life would be in even more danger from ionizing radiation if it were not for our atmosphere – with its tenuous ozone layer absorbing most of the sun’s ultraviolet rays.
  4. Titan:  The atmosphere of Saturn’s giant moon Titan has been in the news a couple of times this month.  For one thing, summer is refusing to leave its south pole.  A press release from JPL’s Cassini Mission summarizes a paper in Nature about this.2  New Scientist said that Titan’s atmosphere is turning out to be “much more complicated than we ever imagined,” according to Henry Roe of Lowell Observatory.  That, he said, is the “real story” that “we’re only just beginning to acknowledge within the field” of atmospheric science.  Science Daily also reported on the latest findings about Titan’s sluggish seasons.  So did Space.com.

That last article on Space.com tossed in the L-word where the others didn’t: “It [Titan] has a thick atmosphere and the right chemistry to support some forms of life,” the article said.  “It actually resembles a frozen version of Earth, several billion years before organisms here began pumping oxygen into our atmosphere.”

1.  Research Highlights, “Planetary Science: Mercurial Mercury,” Nature 459, 755 (11 June 2009) | doi:10.1038/459755c.
2.  Rodriguez et al, “Global circulation as the main source of cloud activity on Titan,” Nature 459, 678-682 (4 June 2009) | doi:10.1038/nature08014.

The atmosphere in the Creation Restaurant is nicer.  There’s no hot air.  The well-mannered customers do not emit foul-smelling gas (04/08/2002).  They don’t moan over their gastric pains (05/02/2003 and 08/22/2005 commentary).  You won’t inhale any stale, foul-smelling smoke about life emerging from dust.  There are no rude customers puffing on Charlie brand cigars (02/05/2002) while making up stories about things they never saw.  It’s one big non-smoking section.  Ahhhhh.  Take a deep breath and savor the aroma of a healthy science atmosphere.

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