Titan Is Old-Age Problem, Despite News Media Coverage
A paper in Geophysical Research Letters1 about Saturn’s largest moon, Titan, reads like a good-news, bad-news joke. The good news is that Titan appears to have more hydrocarbons than Earth. The bad news is that it is not enough to save the assumption that Titan is 4.5 billion years old.
Several science news outlets picked up on the good news part after a press release from Jet Propulsion Lab announced, “Saturn‘s orange moon Titan has hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth, according to new data from NASA’s Cassini spacecraft.” Live Science interpreted this to mean, “Titan Has More Oil Than Earth” but only hinted at the age problem. It’s not really oil as we know it, anyway: it is primarily methane (liquid natural gas, the simplest hydrocarbon CH4) and ethane, the next simplest, plus an assortment of heavier hydrocarbons and nitriles that are solids under Titan conditions. The large dunes that decorate Titan’s equatorial regions may be partly composed of these solid products of solar photolysis.
What the science news reporters underplayed was the frustration that planetary scientists are feeling about Titan’s age. They all believe Titan is as old as Saturn and the rest of the solar system, presumably 4.5 billion years, but Titan’s unusual atmosphere sets severe constraints. Methane is being eroded at a rapid rate compared to such a timescale. Scientists estimate that known reserves of methane on Titan would be gone in 100 million years – maybe even 10 million. So why is there any left? 100 million years sounds like a long time, but is 1/45 the assumed age. 10 million is 1/450th.
The problem can best be illustrated by quoting what Tobias Owen said in 1999 before Cassini arrived. (Toby Owen was leader of the team that took the pictures of Titan during the Huygens Probe descent in January, 2005). In the reputable planetary science textbook The New Solar System (4th ed. Cambridge Press, 1999), written by the world’s leading planetary scientists, he said (p. 280):
Here we have another puzzle: Titan’s methane and hydrogen are constantly being broken apart, with some fragments escaping into space while others form new constituents that condense in the cold atmosphere and precipitate to the surface. At the present rate of destruction, all of the methane now in the atmosphere will be gone in just a few million years. This is a tiny period of time compared to the 4.5-billion-year lifetime of the solar system, so there must be a source of methane that replenishes the atmosphere. Could it be comets? Volcanoes? Underground springs? We simply don’t know.
There’s another problem. Owen also described what scientists expected to find on the surface under the haze:
One can calculate how much ethane has been produced on Titan over the entire history of the solar system (it is the most abundant byproduct in the photochemical destruction of methane). The result is that this remarkable moon could be covered by a global ocean of ethane with an average depth of up to several kilometers!
(Ibid., p. 282). Scientists already knew from earth-based radar observations that this ocean probably did not exist, but were not sure till Cassini began its reconnaissance in 2004 (10/16/2003, 10/28/2004, 12/05/2005). The Huygens Probe gave them “ground truth” that the surface was dry (01/15/2005, 01/21/2005). The Cassini Orbiter has now performed 40 flybys of Titan and has mapped about 20% of its surface with radar (next flyby, #41, happens on Feb. 22). The new paper by Lorenz et al provides the latest reliable status report: is there a source for the methane? What happened to the ethane ocean?
The problem is just as severe now as it was in 1999. To be sure, Cassini did spot some sizable lakes. A number of dark, flat regions were detected by Cassini radar that are most likely lakes filled with hydrocarbons (water, of course, would be frozen hard as rock at Titan temperatures). The lakes, however, are restricted to north polar regions (07/24/2006), above 70 degrees latitude; and surprisingly, only a couple of lakes have been found near the south pole so far. Some of the lakes, several bigger than the Great Lakes or the Caspian Sea, could be 100 meters deep. Collectively, these lakes could store vast quantities of hydrocarbons (assumed to be primarily liquid methane and ethane), amounting to hundreds of times more than all the natural gas and oil on Earth (assumed to be about 130 billion tonnes). The scientists gave estimates ranging from 8,000 to 300,000 cubic kilometers of liquid in Titan’s lakes. Unfortunately, this falls embarrassingly short of Owen’s prediction the whole globe would be submerged in an ocean with an average depth of several kilometers.
The dunes (03/01/2007, bullet 3), covering 40% of Titan’s equatorial regions, may store some of the hydrocarbons, but it is not clear what they are made of. The grains might be made primarily of water ice. Ethane, which should be liquid under surface conditions, is probably not a principal constituent (cf. 10/18/2006). Assuming they are half ice and half tholins (hydrocarbon-nitrile derivatives), there could be at least 400 times more material than the proven coal reserves on earth. As astonishing as these numbers are, they still fall short of expectations. A steady rain of liquid ethane and methane from the atmosphere should have precipitated into deep oceans over 4.5 billion years. Clearly, it has not.
Did Cassini find new sources for methane? Radar images do show some apparent cryovolcanos (06/09/2005). This means that something appears to erupt from underneath and flow out over the surface in places. The paucity of impact craters (03/28/2007, bullet 4) also suggests geological activity. Huygens produced clear images of runoff channels presumed to be drainage from occasional methane cloudbursts. None of these sources, however, seems adequate to balance the budget and allow withdrawals for billions of years. If they were, the authors would not have said this:
The total inventory we measure is substantially smaller than the reservoir estimated to be produced throughout the age of the solar system if methane photoloysis were to have occurred continuously at its present rate. The apparent dearth of material (compared to these model predictions – a summary is given by Lorenz and Lunine [1996], of several hundred meters thickness, or ~107�108 km3) may indicate one or more of four things. First, other undetected organic materials are present, but not morphologically distinct. It is commonly assumed on the basis of bulk cosmological abundance that Titan’s bedrock is dominated by water ice, but the near-surface may in fact be dominated by organic material. Furthermore, even at the low latitudes dominated by arid landforms like dunes, the Huygens probe indicated that at least some surface materials are moistened by liquid methane [Lorenz et al., 2006b; Niemann et al., 2005] so some amount of liquid is present (perhaps in very large amounts) beyond the obvious lakeforms. Second, the photochemical models may not correctly predict the ultimate yields of surface deposits (c.f. the relative yields of solids and liquids – see next paragraph). Thirdly, photochemical production may have been interrupted for long periods in Titan’s past if the delivery of methane to the surface was episodic and led to occasional methane depletion. The identification of cryovolcanic features on the surface [Sotin et al., 2005; Lopes et al., 2007] supports such a picture. A final more speculative possibility is that some process has destroyed or subducted the deposits, such that they no longer exist at the surface.
Each of the proposed solutions seems ad hoc, invoked only to save the billions-of-years age. The present is supposed to be the key to the past in typical geological parlance. Proposing episodes where the observed processes stopped for long periods seems contrived. Besides, the photochemical destruction of methane is supposed to be irreversible (03/11/2005). Once ethane rains down, it should stay put and remain liquid. Cassini found otherwise. They reiterate the problem:
Finally, the liquid inventory, while extending over a large enough area to permit evaporative fluxes to match photochemical depletion on short timescales [Mitri et al., 2007], is not enough in volume terms to sustain the concentration of this greenhouse gas in the atmosphere on geological timescales. Put another way, there is an order of magnitude less liquid in the lakes than there is methane in the atmosphere, and photochemical models predict that inventory to be depleted in ~10 Myr [million years]. This makes the present climatic situation somewhat precarious – the observed surface reservoir, even if mostly methane, is unable to buffer the atmospheric methane for long, and unless volcanic resupply matches methane loss at just the right rate, significant climate change is likely in the future and by implication in the past….
In other words, if methane could not have been sustained in the atmosphere for 4.5 billion years, it should have been long gone. One consequence would be that its greenhouse warming of Titan would also have stopped – leading to a catastrophic condensation of most of the nitrogen to the surface! (01/17/2002).
If Cassini continues working for several more years, scientists hope to find out if the north polar lakes will migrate to the south as the seasons change and the south pole becomes warmer. It seems unlikely at this point, though, that vast quantities of the missing liquids will turn up (09/14/2006, 01/09/2007, 11/14/2004). A positive footnote was sounded by World Net Daily: if oil doesn’t come from dead dinosaurs, maybe Earth has more than we think.
1. Lorenz et al, “Titan’s inventory of organic surface materials,” Geophysical Research Letters, Vol. 35, L02206, January 29, 2008, doi:10.1029/2007GL032118.
Why do the science reporters ignore the bad news for evolution and long ages? Here was a falsification of a clear prediction, calculated from the laws of chemistry and physics. The only rational solution is that Titan is not as old as claimed. The ethane budget is monstrously short of predictions. Only trace amounts were found in the atmosphere or on the surface. The leading planetary scientists who wrote this paper, some of whom have been studying Titan for more than 20 years, are completely baffled and can only offer weird-science explanations that cannot be observed to salvage their long age belief.
Is this what you hear from the popular science press? Of course not. They only mention the fun stuff: “Look at all the gas on Titan – hundreds of times more than earth!” as if we should go fill up our cars there. And the angle they love most is the L-word Life combined with the E-word Evolution. Lorenz said, “We are carbon-based life, and understanding how far along the chain of complexity towards life that chemistry can go in an environment like Titan will be important in understanding the origins of life throughout the universe.” Happy, happy, happy. Isn’t Fantasyland fun. Where are you going to get the straight scoop unless you read Creation-Evolution Headlines? Spread the word: our shortcut address is http://crev.info .