Planetary Wanderings

Here are news briefs that are out of this world:

• Death Star Sighted:  On August 2, the Cassini Spacecraft took the best-ever pictures of Mimas, the little moon of Saturn with a huge crater Herschel that makes it look like the Death Star from Star Wars.  Why this little moon should be one of the most heavily cratered objects in the solar system, when nearby Enceladus is not, is a mystery.
• Aurora at Saturn:  Saturn put on a light show for Cassini, reported press releases from Jet Propulsion Laboratory and University of Colorado.  The planet’s own version of aurora australis was viewed from a better angle at more wavelengths recently, and was portrayed in lovely aqua blue against the butterscotch planet’s south pole.
• Mars Too Deadly for Human Travel:  Damping ancient dreams of humans walking on Mars some day, National Geographic News reported that “space weather” (solar radiation) could be too dangerous to make a manned mission feasible.  A solar flare storm like those seen in recent years (see 11/06/2003 entry) could be like placing astronauts in the path of nuclear explosions millions of times more powerful than those made by man.  Unless some new method of shielding is devised, politicians and managers may consider it too risky to send humans into the cosmic shooting gallery for years at a time.  A powerful storm missed Apollo astronauts by just months in 1972.  Even if humans survived the 9-month flight to the red planet (10/01/2002), the Martian surface environment does not offer the same protection as Earth (see 08/07/2003 entry).  See also the press release from University of Warwick.
• Titan Is Dry as a Bone:  Contrary to earlier predictions (10/16/2003), R. A. West et al. wrote in Nature¹ that the lack of specular (mirror-like) reflections from Earth-based radar echoes indicates that Titan (Saturn’s largest moon) lacks global oceans.  The BBC News took this to mean that Titan is as dry as a bone.  Even the sighting reported near the south pole makes the lake interpretation seem unlikely.
• Enceladus Is Hot Topic:  Science² took note of the announcement of cryovolcanism on Enceladus (07/14/2005).  Richard Kerr wrote, “the close-up encounter has only deepened the mystery of how a body as small as Enceladus can come up with enough energy for such an active geologic life.”  Treating it as a special case is “uncomfortable” to planetary scientists.  Leaving the solution as a mystery, Kerr concluded, “Theoreticians will have to redouble their efforts to hammer out a moon they can live with.”
• Mars Soil Mystifies:  Science³ published a story by Amos Banin, “The Enigma of the Martian Soil,” that suggested we still know very little about the Martian surface, even since Viking, Pathfinder and Mars Exploration Rovers have studied it up close.  Though we have more data, we have new questions.
• Mars Traffic Jam:  Add a fourth spacecraft to the orbital speedway around Mars.  The new Mars Reconnaissance Orbiter (MRO) launched successfully Thursday morning, August 11, carrying the biggest camera ever launched to the red planet.  It should be able to see objects the size of a card table on the surface when it begins its primary science mission in November 2006, and can transmit 10 times as much information per minute as previous orbiters.  A flood of high-res photography is coming.  MRO will provide several times as much data about Mars as all previous missions combined, said project manager James Graf.

¹R. A. West et al., “No oceans on Titan from the absence of a near-infrared specular reflection,” Nature 436, 670-672 (4 August 2005) | doi: 10.1038/nature03824.
²Richard A. Kerr, “Cassini Catches Mysterious Hot Spot on Icy-Cold Enceladus,” Science, Vol 309, Issue 5736, 859-860, 5 August 2005,[DOI: 10.1126/science.309.5736.859a].
³Amos Banin, “The Enigma of the Martian Soil,” Science, Vol 309, Issue 5736, 888-890, 5 August 2005, [DOI: 10.1126/science.1112794].

The Enceladus-Mimas dichotomy may force scientists to re-examine assumptions about cratering rates.  If impactors flying around the solar system do not pummel nearby objects equally, then either some moons are able to cover the craters, or the impactors are not randomly distributed.  Cratering rates are commonly assumed in determining ages of surfaces.  If you cannot constrain the density and frequency of impactors, and if the weathering processes are not well known, then crater-count dating is an exercise in guesswork.
    Planetary scientists will have to redouble their efforts to hammer out not only a moon they can live with, but a solar system they can live with.  This has two connotations.  First, the solar system is a deadly place; this underscores the beauty and habitability of our privileged planet.  Second, evolutionary scientists accustomed to thinking in billions of years can’t live comfortably with young phenomena like Enceladus, and a Titan that should have accumulated deep oceans of methane or ethane by now.  If you are unconstrained by long-age assumptions, can you live with these findings?