December 19, 2017 | David F. Coppedge

Planetary Youth Continues After Cassini

The data gathering phase is over, but the data mining phase will continue for years. This entry also shares some news about other solar system objects showing youthfulness.

Cassini lived long past its expiration date, gathering unprecedented data at Saturn for 13 years, and some Jupiter science en route. Spacecraft die, but data can live indefinitely. We can expect more surprises from the Saturn system as researchers mine the 635 gb of science data. Already, some 4,000 papers have been published. Here are some recent tidbits:

Iapetus from Cassini (JPL PIA06166, 12/31/04)

Formation of the bulge of Iapetus through long-wavelength folding of the lithosphere (Icarus). The closeups of an equatorial mountain range 12 miles high circling Iapetus continue to baffle physicists. Was it a collapsed ring? Did the moon rotate real fast long ago? Kay and Dombard have a new theory in this paper: a tectonic process rather than a rotational process. “A lithosphere with latitudinally variable thickness folds during an epoch of global contraction,” they propose. Their model requires a 30-degree temperature difference between the poles and the equator driven by decay of short-lived radioisotopes. Any unique structure, though, prompts philosophical questions about why it happened here and nowhere else.

Close-up of equatorial ridge from Cassini (JPL, PIA08372, 9/10/07)

Testing models for the formation of the equatorial ridge on Iapetus via crater counting (Icarus). In this paper, Dombard and two other colleagues try to establish a date for the formation of the equatorial ridge on Iapetus. After measuring 7,748 craters, they decided the ridge is young! This will ‘impact’ theories of formation of the mountain range. Guess which theory seems favored now? Spike Psarris would chuckle: another lucky impact brought in to rescue billions of years.

Comparison of the crater size-frequency distributions show that the crater distribution on the ridge appears to be depleted in craters larger than 16 km with an abruptly enhanced crater population less than 16 km in diameter up to saturation. One possible interpretation is that the ridge is a relatively younger surface with an enhanced small impactor population. Finally, the compiled results are used to examine each ridge formation hypothesis. Based on these results, a model of ridge formation via a tidally disrupted sub-satellite appears most consistent with our interpretation of a younger ridge with an enhanced small impactor population.

Electrical and chemical coupling between Saturn and its rings (Swedish Institute of Space Physics). Electric rings? That’s cool. Using data from the Langmuir probe (part of the Radio and Plasma Wave Spectrometer instrument), Swedish scientists called the first results “surprising.” They have found that “there is a strong coupling, both chemically and electrically, between the atmosphere of Saturn and its rings.” Jan-Erik Wahlund said, “It is as though the small ice particles in the D-ring suck up electrons from the ionosphere.” Could that interaction continue for billions of years?

Enceladus’s crust as a non-uniform thin shell: I. tidal deformations (Icarus). Mikael Beyeuthe is starting a series of papers trying to explain the geyser activity on Enceladus. “The geologic activity at Enceladus’s south pole remains unexplained, though tidal deformations are probably the ultimate cause,” he begins. What other force is there? He constructs a model of thin crustal shells to try to keep the geysers going. “The combination of crustal thinning and convection below the poles can amplify south polar stresses by a factor of 10, but it cannot explain the apparent time lag between the maximum plume brightness and the opening of tiger stripes.” Next he plans to explore the effect of non-uniform crust on tidal dissipation. He will probably find some way to keep the heat on, because as every planetary scientists knows in advance, this moon has to be 4.5 billion years old.

Other Planetary News

Bright Areas on Ceres Suggest Geologic Activity (JPL News). For those who expected this old asteroid to be cold and dead, “Ceres is surprisingly active.” In fact, Carol Raymond, deputy principal investigator of the Dawn mission, thinks it could still be active. “Geological processes created these bright areas and may still be changing the face of Ceres today,” she says. When cryovolcanoes can’t suffice, impacts can come in to rescue theories.

Global radar map of Venus (JPL)

Lava-filled blocks on Venus may indicate geological activity (Phys.org). The presence of grooves and grabens on Venus is causing a re-think about geological activity on Venus:

For planetary scientists, Venus’s geologic heartbeat flat-lined around 700 million years ago.

Now, a global view of some well-known deformation features on Venus’s surface may indicate it’s capable of crustal motion, and that motion might even be happening today, scientists reported Monday at the 2017 American Geophysical Union Fall Meeting in New Orleans.

Formation, stratification, and mixing of the cores of Earth and Venus (Icarus). This is the paper that makes habitable planets far more rare, as we reported 12/13/17. Venus differs profoundly from Earth, not having a magnetic field, because it was not hit by a large impact that supposedly hit Earth to form the moon. The five scientists “hypothesize that the accretion of Venus is characterized by the absence of such energetic giant impacts and the preservation of its primordial stratifications.” How does that idea fit the other anomaly at Venus of global volcanism that has apparently erased 90% of its earlier history?

Explosive volcanism on Mercury: Analysis of vent and deposit morphology and modes of eruption (Icarus). Another volcanic anomaly is Mercury. This planet should long ago have solidified, but it has large volcanic provinces. This trio of scientists, including veteran planetologist James Head, finds another case of surprising youth. “We find evidence for formation into relatively recent mercurian history,” they say.

Evidence for youth among the planets and moons in our solar system is everywhere. For planetary scientists who cannot give up their belief in old things, we’ll help them with a new word. For something that looks young but must be old to keep secular materialism alive, call it yold.

 

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