September 29, 2014 | David F. Coppedge

Of Planets and People

Here’s a quick tour of the planets to see what’s newsworthy.

Mercury:  Planets with oddball orbits like Mercury, so close to the sun, seem unlikely locations for life, but Astrobiology Magazinebegs to differ.  Mercury (and exoplanets with similar “oddball” orbits) could get into a resonant state that might allow sunlight to support photosynthesis, the article says.  Conclusion: there could be thousands of other locations for life in the universe.  Closer reading shows admissions that it would be “challenging” for life to exist under those conditions.  For example, “the threat of prolonged periods of darkness and cold on these planets would present significant challenges to life, and could even potentially freeze their atmospheres,” yet a thick atmosphere would be needed to protect the planet from radiation, since slow spin would likely mean a weak magnetic field.  A photo caption adds another difficulty: “It is difficult to form Mercury in solar system simulations, suggesting that some of our assumptions about the small planet’s formation might be wrong, a new study suggests.”

Venus:  Astronomers at San Francisco State think they have learned how to detect a “Venus zone” about any given exoplanet.  This can help them distinguish between habitable planets around other stars from those “likely to exhibit the unlivable conditions found on the planet Venus.”  In current thinking, Earth and Venus had similar starting conditions.  “Knowing how common Venus-like planets are elsewhere will also help astronomers understand why Earth’s atmosphere evolved in ways vastly different from its neighbor.”

Earth:  Geomagnetic storm?  Not to worry:  A couple of weeks ago, a major geomagnetic storm from the sun hit the Earth.  Nothing happened.  Life went on, most people oblivious to the danger.  In advance of the arrival, Science Magazine explained in “A geomagnetic storm is coming—should I worry?” that the only effect people might notice is some especially beautiful displays of auroras.   An idea posted on PhysOrg suggests that Mars became barren and lifeless when its atmosphere was stripped from coronal mass ejections (CMEs) from the sun; Earth, by contrast, has always been protected because of its strong, global magnetic field.  Why Venus retains a thick atmosphere without a strong magnetic field was not explained.  For more about Earth, see today’s other entry, “Earth as a Habitable Planet.”

Mars:  The big news at Mars has been the arrival of NASA’s new MAVEN spacecraft (PhysOrg) and India’s first venture into Martian exploration, the Mars Orbital Mission, or MOM (PhysOrg).  Aside from that, the rovers continue roving and the previous orbiters continue orbiting.   Astrobiology Magazine shows that hope for life on Mars seen in meteorites has not disappeared: “A tiny fragment of Martian meteorite 1.3 billion years old is helping to make the case for the possibility of life on Mars, say scientists.”  A similar announcement launched the new “science” of astrobiology in 1996.  This new article’s perhapsimaybecouldness index is high: “Life as we know it, in the form of bacteria, for example, could be there, although we haven’t found it yet. It’s about piecing together the case for life on Mars – it may have existed and in some form could exist still.”

Jupiter:  Since the story about possible plate tectonics on Europa (see 9/08/14), Jupiter has been a relatively silent planet in the news.

Saturn, however, is a newsy place.  NASA awarded the Cassini Team high honors as an “excellent” mission, handily beating out the Mars Curiosity Rover, whose team has lacked focus (PhysOrg).  What’s new in Saturn science?

  • Rings:  Cassini scientists are baffled over the reduction in bright clumps in the rings since Voyager flew by in 1981, a JPL press release says.  “Compared to the age of the solar system — about four-and-a-half billion years — a couple of decades are next to nothing.” Yet “Saturn’s F ring looks fundamentally different from the time of Voyager to the Cassini era,” one scientist said.  Astrobiology Magazine also discussed this mystery.  Despite the puzzle, the article presented a positive spin, saying that the observed processes are helping astronomers understand the origin of our solar system.

“In addition to the drama of moons that come and go over less than a human lifetime, studies of the ring system give insight into how solar systems in general are built.
“The sort of processes going on around Saturn are very similar to those that took place here 4.6 billion years ago, when the Earth and the other large planets were formed,” notes [Robert] French [SETI Institute]. “It’s an important process to understand.

  • Titan:  January will mark the 10th anniversary of the Huygens Probe landing on Titan (see PhysOrg for Cassini firsts).  A paper in Icarus wrestles with the brightness of parts of Saturn’s giant moon.  Some areas look like fresh bedrock of water ice, while others seem consistent with solid organic compounds precipitated out of the atmosphere.  There appears to be more water ice than earlier thought.  For instance, the vast equatorial dune fields seem enriched in water ice, and so must not be primarily piles of precipitated atmospheric hydrocarbons.  Another paper on Icarus wrestles with the nature and fate of evaporite deposits.  Space.com attempts to find whether missing Titan rains might be stored in underground reservoirs.

Uranus and Neptune: the “water giants” don’t get much press because the last flyby missions took place in 1986 and 1989 (see 8/25/14 story about Neptune’s active moon Triton).  Planetary scientists, however, continue to model them on computers.  A French team now claims success explaining Uranus and Neptune in their models, according to PhysOrg.  Speaking of problems with accretion, location and deuterium-to-hydrogen ratios, the new French model “solves all of these problems at once.”  PhysOrg puts a question mark at the end of “The origin of Uranus and Neptune elucidated?”  If history is any guide, the success will be short-lived, until the next team addresses the mysteries of these two planets (cf 5/30/02).  Meanwhile, a paper in Nature thinks that water absorption lines in Neptune are in “good agreement with the core-accretion theory of planet formation”—a bit of a stretch for a spectral line.

  • Miranda, a small moon of Uranus, made news recently, even though the one-and-only encounter was by Voyager 2 back in 1986.  And a famous encounter it was, showing one of the most bizarre moon surfaces in the solar system, decked out with dramatic “coronae” or raised regions completely different from the cratered surroundings.  Leading theories at the time invoked multiple impact scenarios to account for the strange surface, claiming the moon must have disrupted and re-accreted several times.  Now, a new team publishing in Geology claims it can account for the coronae with a variation on plate tectonics driven by tidal heating.  The new theory was summarized on Astrobiology Magazine and PhysOrg.  To work, it had to occur when the small moon was in an eccentric orbit some time in the unobservable past, the scientists say.  The summaries do not explain why the coronae are less cratered than the surrounding terrain, nor why they have sharp boundaries and high cliffs.

Pluto:  The outermost “planet” or “dwarf planet” (most people still want to call Pluto a “planet,” according to Space.com and National Geographic) is awaiting its first NASA visit next July.  The New Horizons spacecraft is getting close enough for distant pictures; it has imaged Pluto’s small moon Hydra, PhysOrg reported.  Meantime, Icarus reported evidence for “longitudinal variability of ethane ice on the surface of Pluto” from Earth-based telescopes.  “Ethane ice is seen to vary with longitude in an unexpected way,” the team says.  “Volatile transport is responsible for the observed distribution.” Any observations should be considered tentative till the spacecraft arrives for a closer look.

Comets:  The Philae lander on the Rosetta spacecraft is getting ready for its historic landing on 7P/Churyumov-Gerasimenko in November.  PhysOrg printed an interview with Claudia Alexander, one of the planetary scientists working on the Rosetta mission, about what the year-long orbiting mission and three-day landing mission hopes to find.

Exoplanets:  A paper in Nature and an article on PhysOrg deal with planet formation.  Both struggle with the problem of dust and small pebbles accreting into bodies large enough to attract more material by gravity before they migrate into a death spiral into the star.  PhysOrg takes some comfort from the fact that exoplanets are common, and from a recent discovery of possible pebble-sized objects in the Orion Nebula, but advises caution, because astronomers are not sure if the pebbles (if that’s what are observed) are growing by accretion, or “if they are debris remnants from another process.”  Nature says that “models of migration have not successfully predicted any populations of planets before they were observed.”  In another surprise, Astrobiology Magazine reported an exoplanet that makes its parent star look “deceptively old.”  According to one astronomer, “We think the planet is aging the star by wreaking havoc on its innards.”

Is it the planets (Gr. planetai, wanderers) who wander, or the scientists who wander as they wonder about the universe, without a God to plan it?

 

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