Its Raining Methane on Titans Dunes
Imagine a world where it rains liquid natural gas. That world is Titan, the Mercury-sized moon of Saturn. In Science this week,1 Cassini scientists reported large equatorial clouds over Titan’s vast dune fields, and a darkening of the surface after an apparent cloudburst. Since only hydrocarbons can be liquid at the temperatures there, and methane is the most abundant, they have concluded that it has rained methane on the bizarre moon that has some atmospheric properties familiar to Earth: weather reports.
The story has been reported on Space.com, PhysOrg, and National Geographic, echoing the press release from JPL. In National Geographic’s article, lead author Elizabeth Turtle estimated that the local weather may have varied from a drizzle to a flood. Changes in surface brightness after the clouds were noted between October 2010 and January 2011. According to the paper, the clouds extended over 1000 km but did not leave evidence of standing liquid on the ground.
Tetsuya Tokano from the University of Zoln in Germany commented on this discovery in the same issue of Science.2 The tropics on Earth are lush and wet; “But why are there apparently long dry seasons at Titan’s equator, in contrast to Earth’s tropical rainforest climate?” he asked. The Cassini scientists reason that due to Titan’s seasons, clouds do not remain near the equator for long. The rain did not leave lakes or puddles, but probably just wet the surface, including the icy sand grains making up the dunes.
1. Turtle, Lunine et al, “Rapid and Extensive Surface Changes Near Titan�s Equator: Evidence of April Showers,” Science 18 March 2011: Vol. 331 no. 6023 pp. 1414-1417, DOI: 10.1126/science.1201063.
2. Tetsuya Tokano, “Planetary Science: Precipitation Climatology on Titan, ” Science, 18 March 2011: Vol. 331 no. 6023 pp. 1393-1394, DOI: 10.1126/science.1204092.
None of the reports discussed the age issue, but it seems seasonal rains like this would have left evidence of vast deposits of sedimentation if cloudbursts have been going on for billions of years. It appears that the drainage channels are being formed by currently active dynamic weather and are not relics of past epochs. Unlike Earth, Titan does not appear to have plate tectonics or volcanoes (at least in abundance), and its surface winds are primarily confined to equatorial latitudes. That means the surface is pretty static. Methane may cycle through the atmosphere, but not liquid ethane that should have formed a global ocean miles deep after 4.5 billion years of steady precipitation (07/31/2008).
So we have raining methane on Titan, and reigning dogma on Earth. In fact, it’s reigning cats and dogmas, speaking of the reigning cats in academia who sit on their A.S.S. (age of the solar system) and never budge. Some stand-up scientist should model what the conditions on Titan would be expected to look like after billions of years of erosion and ask whether the model fits the observations. It might shed some light where the sun never shines.