Mars as Anomalous Runt
The Mars rover Spirit is now dead in its tracks (JPL) but the planet under it continues to rumble, in theoretical overhauls and anomalies. Mars has been much on the mind of news reporters this week after a new paper speculated that the red planet grew up fast and then stopped as a runt.
In Nature,1 Dauphas and Pourmand studied ratios of isotopes of hafnium (Hf) and tungsten (W) to envision a history of Mars much different than previously assumed. Their model makes Mars form in about one-fifth or less the time previously assumed to be required. In the same issue of Nature,1 Alan Brandon summed up the new idea: “It seems that Mars had grown to near its present size by 2 million to 4 million years after the Solar System began to form,” he said. “Such rapid growth explains why the planet is much smaller than Earth and Venus.”
Any explanatory gains, however, appear to be offset by puzzles, according to Bloch’s Law, “Every solution breeds new problems.” Brandon said, “The authors finding that rocky bodies the size of Mars accreted within 2 million to 4 million years has ramifications for models of early planetary history.” Some of these ramifications confirm earlier theories, while others contradict them:
With such an early time for Mars accretion, which probably led to the formation of a global magma ocean, how do we explain the times for magma-ocean solidification of around 100 million years after the Solar System began to form that are obtained from measurements of Lu (lutetium)-Hf and Sm-Nd chronometers in Martian meteorites? Magma oceans are not supposed to take that long to solidfy [sic]. This suggests that, although Dauphas and Pourmand have provided us with a key constraint on the early formation and evolution of our planets, we still have much to learn.
None of the three authors explained how primary accretion (the gathering of dust particles into bodies large enough to grow by gravitational attraction) might have occurred; they all began by assuming large bodies were already present. They also assumed the truth of the controversial theory that earth’s moon formed by collision of a Mars-sized body into our planet. Philosophically speaking, it is usually not a good idea to resort to ad hoc conditions to explain anomalies.
Live Science posted three videos of Mars, The Changing Face of Mars, Where’d All the Water Go? and What Went Wrong on Mars? which includes some dramatic flyovers of Martian terrain based on orbital photographs. The narrator divines unobserved Martian prehistory as if an eyewitness. PhysOrg and Science Daily presented the Dauphas-Pourmand theory uncritically, treating the isotope ratios as unproblematic chronometers that allow scientists to see the unobserved past in a kind of crystal ball.
Space.com recounted the history of failed spacecraft at Mars, the “spacecraft graveyard.” Keep an eye on JPL Mars Exploration for latest news on this fall’s planned launch of the next-generation red rover, Mars Science Laboratory, recovering from an incident that did not damage the backshell (see PhysOrg).
1. N. Dauphas and A. Pourmand, “Hf-W-Th evidence for rapid growth of Mars and its status as a planetary embryo,” Nature 473 (26 May 2011), pages 489-492, doi:10.1038/nature10077.
2. Alan Brandon, “Planetary science: Building a planet in record time,” Nature 473 (26 May 2011), pages 460-461, doi:10.1038/473460a.
The question is not whether Mars had a history, but whether scientists are qualified as divination experts to read that history using tea leaves in the present that provide no opportunity for testing or falsification. Since this solution breeds new problems just like prior ones did, is amply seasoned with perhapses and maybes, and will undoubtedly be overturned in another few years, astute readers had best avoid following the priests to the shrine of scientism, instead filtering out what observational clues are meaningful and judging the reasonableness of inferences that could be made from them, keeping an open mind that is willing to think outside the consensus box. This sentence is shorter.