It occurs to me that there are two rather obvious mechanisms that could be limiting the obvious signs of cratering on Titan. The one that seems to get all the discussion is weathering/resurfacing -- it's common to date planetary surfaces by crater counts, after all.

But Titan has another mechanism going that we here on Earth are all too familiar with -- atmospheric destruction of impactors. Titan not only has an atmosphere, it's something like 1.5B at the surface, so it's even denser than our atmosphere. Result: a lot of the impactors that would leave visible craters on other planetary bodies burn up in Titan's atmosphere.

Also, while some reports are saying that the radar has discovered the only two craters found on Titan, I seem to see craters of varying sizes and levels of degradation in both the radar images and the ISS images. Circular features that remind me strongly of craters, at any rate. Not very many of them, but they're there, I think. So, there ought to be a way to use crater counting, even on Titan.

So, I guess my question is: Is there a correction algorithm of some kind that can account for the winnowing of impactors by Titan's atmosphere? If so, can it be applied to help us use crater counting to determine surface ages? And, I guess more basically, what's the current thinking on how important atmospheric winnowing is in the lack of numerous Titanian craters?

-the other Doug

The atmosphere will only stop the small comets. So, they didn't expect any small craters anyway. But there still should be large craters. If you look at other moons of saturn, you see they have much more large craters.

the craters could be absent due to uplifting and tectonic processes, be covered by deposits (tholins?) or eroded away. What the important mechanisms are is still not known.

More importantly, Titan & Earth share the mechanism with Venus, which has more craters to work with (although resurfacing's no slouch there either). So, based on studies of Venus and the differences between Titan & Venus, craters <20 km are not expected on Titan. There's a reference for that in the Porco Nature paper. There's also a reference indicating 100s of craters >20 km per billion years, based on the other Saturn satellites.

And yes, the Porco paper points out 5 possible craters, and suggest a 130-300 Myr old surface.

There is a comparatively recent presentation on cratering on Titan, which even includes some preliminary data from the T13 SAR radar swath (April 30, 2006).
http://www.rssd.esa.int/SYS/docs/ll_transf...Lorenz_pres.pdf

Additionally, here is a short article on cratering on Titan.
http://www.rssd.esa.int/SYS/docs/ll_transf...6379_lorenz.pdf
Most of it has already been discussed in the Nature article from June 8, 2006 (T3 SAR radar swath), however it might be appreciated by people without access to Nature Journal. Interestingly, Figure 3 of that article suggests that the whole south pole of Titan could potentially be one giant (1600 km diameter) impact crater!

That's not what they're implying. Note the word 'fictitious' used for the smaller 1000 and larger, 1500 km diameter crater depicted in the map projection, probably for illustration purposes only.

They in fact go even further in the text saying:


What they were trying to show in Figure 3 is that with each new SAR swath the area where you can stuff a huge crater into (without intersecting any area imaged so far) rapidly gets smaller. So at one point we'll be able to say for certain there are no craters larger than 1500 km on Titan.

Ooops! Memo to myself: "First read, then write!"