August 4, 2007 | David F. Coppedge

Four Evidences of Cosmic Youth

Astronomers and planetary scientists routinely talk in millions and billions of years.  Three recent science news reports raise questions about how to fit apparently young objects into a vast timeline. 

  1. Lunar burps:  The moon is passing gas, reported Science News).  This explains the long history of observations of lunar transients, or bright flashes observed from Earth on certain parts of the moon.  Arlin Crotts (Columbia U) believes the flashes come from the decay of uranium that escapes through cracks, but mentions the possibility that volcanism is still active.
  2. Flinging rings:  Saturn’s G-ring has been explained in an announcement from Jet Propulsion Lab (see also Science Daily).  A persistent ring arc in the outer bright rings, confined by the moon Mimas, gets swept by the magnetic field, flinging particles into the tenuous G-ring.  (The G-ring lies between the thin F-ring and the broad E-ring fed by the Enceladus geysers; see 07/11/2006).  The original paper in Science1 says, “The dust-sized particles that dominate this ring’s optical properties should erode quickly in Saturn’s magnetosphere, yet there was no direct evidence for larger source bodies that could replenish the dust and no clear explanation for the concentration of such bodies in this one region.”  The article and original paper do not mention how long this has been going on, but presumably the material would have long been depleted well before millions of years, because particles in the arc are steadily being ground to dust by collisions.
  3. Bursting moons:  Speaking of Enceladus, a recent paper in Icarus2 said that tidal flexing cannot explain the heat coming out of this small moon, either now or in the past:

    The heating in Enceladus in an equilibrium resonant configuration with other saturnian satellites can be estimated independently of the physical properties of Enceladus.  We find that equilibrium tidal heating cannot account for the heat that is observed to be coming from Enceladus.  Equilibrium heating in possible past resonances likewise cannot explain prior resurfacing events.

    Meyer and Wisdom said that the neighboring moon Mimas, about the same size but closer to Saturn, experiences 11 times as much tidal heating but shows no sign of activity.  In their conclusion, they wondered that both Io (at Jupiter) and Enceladus (at Saturn) are both so active:

    But it is curious that one has to appeal to nonequilibrium tidal oscillations or episodic activity to heat both Io and Enceladus (Ojakangas and Stevenson, 1986).  If the fraction of time spent in an active state is, say, of order 20%, for each satellite, then the probability that both are found in an active state today is only 4%.

    Cassini will fly by Enceladus at very close range on March 10 and even sample particles in the plume; see announcement in Space.com.

  4. Veil unveilings:  Portions of the wispy Veil Nebula in Cygnus have been photographed in detail by the Hubble Space Telescope.  This highly-distended nebula is the remnant of a supernova explosion long thought to be tens of thousands of years old (see 02/16/2001).  Now, a press release posted by Science Daily claims the explosion “could have been witnessed and recorded by ancient civilizations” as recently as 5,000 years ago.

1Matthew M. Hedman, Joseph A. Burns, Matthew S. Tiscareno, Carolyn C. Porco, Geraint H. Jones, Elias Roussos, Norbert Krupp, Chris Paranicas, and Sascha Kempf, “The Source of Saturn’s G Ring,” Science, 3 August 2007: Vol. 317. no. 5838, pp. 653-656, DOI: 10.1126/science.1143964.
2Jennifer Meyer and Jack Wisdom, “Tidal Heating in Enceladus,” Icarus, Volume 188, Issue 2, June 2007, Pages 535-539.

Every once in awhile, it bears repeating: it is more empirically justifiable to infer young ages than old ages, because the observation-to-assumption ratio is much higher.  You can take an observed phenomenon and extrapolate it backward from the present a bit – that is reasonable.  But to start with an assumption of billions of years and then try to fit a short-lived phenomenon into it lowers the observation-to-assumption ratio by many orders of magnitude.  Would it be reasonable to observe a sparkler for 5 seconds, and then claim it has been burning for 100 years?  We think science should tether itself to the observations rather than run amok like a stray dog.

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Categories: Astronomy, Solar System

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