T16 RADAR SAR Swath, Land o' lakes Options

[David]

If by "confirm" you mean a point at which everyone unequivocally accepts a "liquid lakes" explanation for these particular RADAR data, then probably not until a probe actually lands in one, if then. In other words, I'm sure that up until that point there will be holdouts who will offer, for example, heuristic plausibility arguments positing alternative explanations.

When they come into sunlight, could Cassini detect specular glints from them?

Also, have we seen features that could be dry lakes elsewhere on Titan?

[Guest_AlexBlackwell_*]

When they come into sunlight, could Cassini detect specular glints from them?

Possibly, but it would depend on the geometry. At any rate, there should be data on the diffuse and specular components in the RADAR scatterometry data, which do not depend on solar illumination.

[volcanopele]

Unfortunately, it is very difficult to search for specular glints in the polar regions. I think our farthest south data point is 53 S from Rev09 last June. We can search for specular glints using the altimeter, if we were to fly right over a lake, like during T38 (or T39, can never remember which) when we fly directly over Ontario Lacus.

BTW, there seems to be some confusion over the liquid state of Ontario Lacus. Ontario is a dark, footprint-shaped feature in the south polar region. The shape of the margin and its location in an area where clouds have been observed has led to the suggestion that it maybe a lacustrine feature. Based on data currently available, we can not tell if there are currently liquids in the lake or if it is a playa instead. Doesn't mean we know either way. It could be lake currently filled with liquids, it could be a mud flat. We don't know.

However, I think the picture is emerging that the lakes we see in RADAR were last filled with liquids last northern summer during the rainy season and that since the onset of winter in the region, these lakes are either evaporating or emptying into underground reservoirs. Some of these lakes reside in basins only partly filled with "liquid" (for the rest of this post, liquid stands in for RADAR-smooth material at high latitudes) with no apparent topography confining the location of the liquids into a subsection of the basin. Perhaps these lakes were filled in summer, and are now emptying thanks to the decade-long dry season. The antarctic lakes have now filled up from 5 years of monsoon rains, so it would be interesting to compare them to the arctic lakes when RADAR views them in T38 (or T39).

[volcanopele]

Note: South is up in both cutouts in the release, and radar illumination from above.

[JRehling]

I know Jason and some of the other Yahoo! planetary_sciences alumni will remember the following wager that someone made with a few of us just over two years ago:

"I have wagered $20 that Titan's surface lacks Cassini-resolvable bodies of liquid."

I was in on that. If you are like me, you've thought about that bet over a hundred times since then. The poor fellow on the other side became mighty scarce (prematurely) after one of the first flybys (even before Huygens).

The bet's not over, but it looks good.

[JRehling]

Hopefully Cassini lasts years beyond its primary mission, enabling it to observe seasonal changes (Titan and Saturn's blue northern hemisphere).

If attitude control propellent is truly the life-limiting factor for Cassini, then the variable in our control is the number of pointing operations (under current operational norms, the number of flyby observations) per unit time. Even if Titan were the only object under consideration, the choices would be, at the extremes, dozens of flybys at the current rate, obtaining more RADAR (especially) and VIMS coverage, but only lasting a couple of years (going just past equinox) or a more languid rate of coverage, making few observations (perhaps many "blind" flybys with few or no observations), but lasting well into the next Titanian seasons. Obviously, flybys of the other satellites would subtract from the Titan observations.

These lakes might relegate Iapetus, aside from its late-primary-mission closeup, to "see you next mission" status. Enceladus will still hold its own as an extended mission candidate, but the other icy moons are looking forgettable in comparison.

[qraal]

Hi All

Lacustrine wannabes at last!

These lakes might relegate Iapetus, aside from its late-primary-mission closeup, to "see you next mission" status. Enceladus will still hold its own as an extended mission candidate, but the other icy moons are looking forgettable in comparison.

Hate to say it, but there's nothing as interesting as Titan and Enceladus amongst the rest. Titan we're more likely to learn much, much more about by an extended mission.

Has anyone looked into aerobraking Cassini into a survey orbit around Titan?

Adam

[Bjorn Jonsson]

Has anyone looked into aerobraking Cassini into a survey orbit around Titan?

This has been discussed here before (I don't remember where) and it is not possible.

[JRehling]

Also, have we seen features that could be dry lakes elsewhere on Titan?

Quite a few, I'm sure. There are linear features in north of Tsegihi that I've always thought are (probably) dry versions of the Scottish lochs. In fact, they were among the very first features to show up in any Cassini images.

It's a reasonable conjecture that the entire darker equatorial region is a dry sea. In fact, it may be hard to explain unless it were at some point entirely submerged.

[David]

Quite a few, I'm sure. There are linear features in north of Tsegihi that I've always thought are (probably) dry versions of the Scottish lochs. In fact, they were among the very first features to show up in any Cassini images.

Hm. On earth, lochs are glacial features. So are the scattered Minnesota-style lakes to which the Titanian lakes are being compared. But glaciation isn't possible on Titan -- is it?

[The Messenger]

Hm. On earth, lochs are glacial features. So are the scattered Minnesota-style lakes to which the Titanian lakes are being compared. But glaciation isn't possible on Titan -- is it?

It's hard to figure how liquid methane would carve up a surface, especially since we are still very uncertain about what the surface is. Although it is unlikely, water-ice cannot be ruled out as the culprit.

[ljk4-1]

It's hard to figure how liquid methane would carve up a surface, especially since we are still very uncertain about what the surface is. Although it is unlikely, water-ice cannot be ruled out as the culprit.

Has sulfur in any significant amounts been detected on Titan?

Or anything particulary corrosive? Or perhaps a substance that is
harmless by itself but becomes corrosive when combined with other
elements on Titan under its particular climate conditions?

[JRehling]

Hm. On earth, lochs are glacial features. So are the scattered Minnesota-style lakes to which the Titanian lakes are being compared. But glaciation isn't possible on Titan -- is it?

Good point on the origin -- I was thinking of the structure alone. The features on Titan are probably tectonic, being parallel to the whole Fensal region.

[Olvegg]

And what about translucency of luiqud for radar beam? Note that coastal areas of even darkest lakes (for example, one in the left up corner) are brighter, rather grey than black. It could be interpreted as sandbank, but also as shallow water (shallow methane? ), which doesn't absorb radar signal completely. The change of brightness is gradual, without contrast boundaries. All this would mean these lakes are quite deep!

[Guest_AlexBlackwell_*]

This has been discussed here before (I don't remember where) and it is not possible.

This questions pops up so frequently on discussion boards that there should be an FAQ posted somewhere. I posted a brief note in another thread on this issue. And as you note, the short answer is no, Cassini is not designed to aerobrake.