Titan Methane Age Still a Problem
“Our new map provides more coverage of Titan’s poles, but even if all of the features we see there were filled with liquid methane, there’s still not enough to sustain the atmosphere for more than 10 million years.” So said Elizabeth Turtle, lead author of a paper in Geophysical Research Letters,1 in an article on the Cassini Imaging Team [ISS] website. She added, “How long Titan’s atmosphere has existed or can continue to exist is still an open question.” The press release was written up by Space.com and National Geographic.
A comparison of older and newer images suggests that cloudbursts of liquid methane may occur. Some of the polar lakes may dry up and others refill as the seasons change. Cassini is exploring Titan at its equinox. One goal of another extended mission would be to study seasonal changes until the next solstice in 2017.
Cassini instruments have difficulty characterizing the lakes. They could be very shallow. The Huygens probe landed in 2005 on a flat playa that appeared to have ice boulders that had tumbled out of canyons possibly carved by flash floods. Scientists in the 1990s had predicted that Titan’s surface might be submerged in a global ocean of liquid ethane and methane; that did not pan out. Instead, most of the equatorial region of the planet-size moon is blanketed with dunes. All the low-albedo features, assumed to be lakes, discovered to date have been in the polar regions.
How is the absence of methane explained? The press release said, “the new observations suggest that underground methane reservoirs must exist.” To what extent that conclusion was inferred from the need to keep Titan billions of years old was not stated. The original paper’s introduction referred to the quandary about methane destruction rates in the atmosphere, but then hid the solution underground:
Photochemical processes acting in the atmosphere convert methane into more complex hydrocarbons, substantial quantities of which may have precipitated from the atmosphere over Titan’s history [Yung et al., 1984; Lorenz and Lunine, 2005]. These processes create Titan’s atmospheric hazes and destroy methane over relatively short timescales, ~107-108 yr [Yung et al., 1984]. Therefore, Titan is hypothesized to have reservoirs of liquid methane to resupply the atmosphere [e.g., Lunine, 1993]. Knowledge of the distribution of liquids on Titan’s surface and clouds in its atmosphere, as well as any changes in either, provides constraints that are essential to furthering our understanding of Titan’s methane cycle, its atmospheric dynamics, its total methane inventory and, thus, the sustainability of its current atmosphere.
The constraints so far make it difficult to extrapolate Titan’s methane lifetime over another 1-2 orders of magnitude. After stating the problem, the paper focused on observations of changes in the lakes, but revisited the age problem in paragraph 10:
The low-albedo features observed by ISS at both poles cover over 600,000 km2, almost 1% of Titan’s total surface area; however, even if all of these features are currently liquid-filled, they do not appear to provide enough methane to keep Titan’s atmosphere resupplied for a substantial amount of time [Lorenz et al., 2008]. Thus, although Mitri et al.  have demonstrated that evaporation from lakes covering 0.002�0.02 of the surface could maintain the current methane relative humidity over short timescales, only a relatively small fraction of the liquid reservoirs required to replenish atmospheric methane over geologic timescales currently appears to exist on the surface.
No evidence for subsurface reservoirs was provided. Atmospheric methane is not a closed system. The solar wind depletes the methane and converts the remainder to ethane and complex hydrocarbons that should have been accumulating on the surface to extreme depths, if the process has been ongoing for billions of years. (This is a problem at Mars, too: see 01/16/2009). Instead, Titan appears to be mostly a dry world with very few craters and low relief, blanketed with icy sand dunes.
The popular write-ups either did not mention the problem or suggested the answer is underground. They focused instead on the fascinating idea of methane cloudbursts on a strange world. National Geographic not only avoided the subject, but ended with a tie-in to global warming: “It may be that global warming on Earth will take us slightly in a Titan-like direction, with heavier downpours separated by longer droughts.” The original paper said nothing about global warming.
1. Turtle et al, “Cassini imaging of Titan’s high-latitude lakes, clouds, and south-polar surface changes,” Geophysical Research Letters, VOL. 36, L02204, Jan 29, 2009, doi:10.1029/2008GL036186.
We’ve been bringing up this problem for years. This latest paper shows that no solution has been forthcoming for over two decades; in fact, the problem has only gotten worse. The consensus Age of the Solar System (A.S.S.) is 4.6 billion years. 10 million years is 1/450th of that value, and that is the maximum that the empirical evidence permits. If planetary scientists truly followed the evidence where it leads, as scientists are supposed to do, they would have to conclude Titan is young. Evidence from Enceladus, Iapetus, Mercury, comets, Mars, the moon and many other bodies that showcase evidence of youth could be adduced for support. The ramifications of that conclusion would be so far-reaching and unpalatable to the old-age, evolution-inebriated materialistic community, they have to resort to distraction to keep people from thinking about it. CEH thinks the sidestep is the most interesting part of the dance.
The comeback argument is that scientists “know” the solar system is old from other lines of evidence, e.g., radiometric dating of meteorites and rock units on Earth, and so forth. But they don’t “know” these things without making assumptions. Planetologists used to “know” that planets required billions of years to form from a solar nebula. That was before the revolution in thinking caused by the discovery of extrasolar planets. Their properties suggest – some say require – rapid formation to prevent destruction by migration. Indeed, a whole new “heretical” disk-instability hypothesis proposes that giant planets can form much more rapidly than thought. When you find a number of bodies in the solar system today with upper-limit ages converging at the recent end of the evolutionary timescale, it becomes increasingly implausible to believe we live at a special epoch when all these phenomena are observable. It should call into question the timescale itself.
For reasons philosophical rather than empirical, many in the old paradigm don’t wish to think along those lines. Others, from years of indoctrination in the paradigm, cannot even begin to think outside the box. They just chalk up the mysteries as anomalies. Anomalies are the stuff of which scientific revolutions are made.