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Huygens News Thread, News as and when we find it
rlorenz
post Oct 12 2012, 03:01 PM
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QUOTE (MarcF @ Oct 12 2012, 07:11 AM) *
"Since the dust was easily lifted, it was most likely dry, suggesting that there had not been any ‘rain’ of liquid ethane or methane for some time prior to the landing."
This seems to be in contradiction with earlier results showing the presence of liquid methane in the soil, close to the surface.


A refinement, not a contradiction (I am a co-author of the DISR work just published, led by Stefan Schroeder and Erich Karkoschka). Titan is (consistently) interesting enough to defy the simplest descriptions.

It rains sometimes, not often. The subsurface was damp, the top few mm were not. Go to a beach a couple of days after rain and you'll see the same sort of thing (except the evaporation timescale may be very different for Titan).

The dust kicked up and indicated in the DISR optical instruments for a couple of seconds seems consistent with the thin fluffy layer indicated by the penetrometer.
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JRehling
post Oct 15 2012, 05:22 PM
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The error bars are still quite large, and will remain so until we've surveyed Titan for a half-Titan-year (we're at about 1/4 so far, with gaps), but there are estimates of total volume of precipitation, and precipitation per storm, plus the constraints we have on the frequency of such storms (we've seen one very large one). When I was reading the literature, looking for a consistent model that fit those various constraints, it seemed to fit if the equatorial regions experience rare, but very large storms, which deposit hurricane-like quantities of rain. A given location in the equatorial regions might go a very long time between storms, on the order of perhaps 80 to 400 years, with each storm soaking about 1% of Titan's equatorial regions. Those numbers are poorly constrained, but should set the expectations that Titan precipitation timescales do not need to be earthlike, and are probably much longer, although the driest deserts on Earth may present similar timescales.

There is reason to suspect that at least one kind of fine particulate condensate is drifting downward, covering exposed surfaces very slowly, providing optical depth on a scale similar to that of the rainfall. A rainfall would wash the fluffy condensate downstream, although what the drying process entails is wide open to speculation.

There's no real constraint on how long the near subsurface could remain wet after a rainfall. The Huygens landing site, which was on some of the relatively rare VIMS-dark-blue terrain might even be near the liquifer table.
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B Bernatchez
post Jan 15 2013, 06:38 PM
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Another new animation of the last moments of Huygens' descent has been released. http://www.jpl.nasa.gov/news/news.php?release=2013-019. Enjoy.
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titanicrivers
post Jan 13 2015, 02:20 AM
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Wednesday January 14th is the 10th anniversary of the Huygens probe landing on Titan. For those of you relatively new to UMSF blogs you should definitely review the pages of the Huygens News Thread again or for the first time to relive the moment!
Some of my favorite posts are:
#57: concern over the possible loss of half the DISR images http://www.unmannedspaceflight.com/index.p...post&p=4073
#60: tedstryk posts the first incredible image!!! http://www.unmannedspaceflight.com/index.p...post&p=4078
#63: best spontaneous reaction to the image http://www.unmannedspaceflight.com/index.p...post&p=4081
#66 and #67 more great emotional comments on the initial image http://www.unmannedspaceflight.com/index.p...post&p=4084 http://www.unmannedspaceflight.com/index.p...post&p=4085
#78 most convincing interpretation of the initial image http://www.unmannedspaceflight.com/index.p...post&p=4096
#106 first durable post of the surface image by Pando http://www.unmannedspaceflight.com/index.p...post&p=4124
#175: Pando posts a great resource for amateur images! http://www.unmannedspaceflight.com/index.p...post&p=4198
Best video of the landing http://www.youtube.com/watch?v=yrtw7AQ8zMQ (Note the Photojournal article on this is located here http://photojournal.jpl.nasa.gov/catalog/PIA08117 but I can no longer get the Quicktime movie to work.)
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Explorer1
post Jan 14 2015, 09:46 PM
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New JPL retrospective(also the first time I've seen a movie that blends the surface image with the descent imagery so well):

https://www.youtube.com/watch?v=TMxL3ZhO8A8

Still remember that day.... time flies!
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monty python
post Jan 16 2015, 06:23 AM
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I haven't seen this before either. And it's a great compliment to the DISR descent movie referenced above - especially how it ties in the last few images taken during descent and post landing image to the landing video.
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Explorer1
post Apr 7 2016, 09:12 PM
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A decade later, and the surface science continues (an apparent fog bank is identified!):
http://www.planetary.org/blogs/guest-blogs...e-of-titan.html

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alan
post Feb 4 2017, 04:22 PM
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Bouncing on Titan: Motion of the Huygens Probe in the Seconds After Landing

https://arxiv.org/abs/1702.00667
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Stefan
post Feb 4 2017, 07:41 PM
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QUOTE (alan @ Feb 4 2017, 05:22 PM) *
Bouncing on Titan: Motion of the Huygens Probe in the Seconds After Landing

https://arxiv.org/abs/1702.00667

Please know that this is an older paper. I decided to put it on arXiv to make the work available for free. I consider it a poor man's open access.
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JRehling
post Feb 5 2017, 05:40 PM
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Thanks for posting this. I hadn't heard of the notion that the lander may have tilted during the surface lifetime. It seems like, if so, the imaging should show a very clear signal to this effect even if the tilt was very subtle.
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scalbers
post Apr 21 2017, 06:38 PM
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I've been looking at this recently (2015) narrated and improved video of the Huygens descent and landing. They pay good attention to detail with rendering of atmospheric colors, and haze/visibility. The view from the surface shows how the sun would look, a small pale red disk in the middle of a fairly uniformly lit sky.

https://www.youtube.com/watch?v=9L471ct7YDo

Inferring from this (and some published papers), it seems Saturn would be a little challenging to see from the surface with the naked eye. Perhaps a ghostly reddish image at night superimposed on the uniform scattered light background, if Saturn isn't too close to the horizon. Titan aerosol tau values are about 6.5, 8, and 11 in red, green, and blue wavelengths. Rayleigh scattering has some effect as well, more than on Earth.


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rlorenz
post Apr 22 2017, 03:50 PM
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QUOTE (scalbers @ Apr 21 2017, 01:38 PM) *
Inferring from this (and some published papers), it seems Saturn would be a little challenging to see from the surface with the naked eye. Perhaps a ghostly reddish image at night superimposed on the uniform scattered light background, if Saturn isn't too close to the horizon. Titan aerosol tau values are about 6.5, 8, and 11 in red, green, and blue wavelengths. Rayleigh scattering has some effect as well, more than on Earth.


I think I talked about this a bit in 'Lifting Titan's Veil'.... maybe with red-tinted sunglasses, and better yet, perhaps polarizing ones, you might see well enough to pick out a limb (remember Saturn will show phases, but only from the subsaturn hemisphere of Titan!)
I recall reading somewhere that the optical sensitivity of women typically extends to longer wavelengths than men (meaning the red/infrared distinction may be dependent on the individual!)

At 940nm - the near-infrared methane window most often used by Cassini's camera to observe Titan's surface, and the wavelength used by TV remotes, and accessibly by 'Nightshot' video cameras etc. the optical depth is only one or two. Since you probably don't want your eyeballs to freeze anyway, it would be easy to implement some near-IR goggles or a visor to go with the oxygen mask you'd need to enjoy the view
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scalbers
post Apr 22 2017, 04:11 PM
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Glad this is talked about in your book. I was taking "naked eye" rather literally, though I agree red glasses would help a bit. I'm unsure how polarized the skylight would be with the multiple scattering going on. For daytime sightings I would pin some hope on when Saturn is near the sun (<6 degrees or so) and forward scattering in Saturn's atmosphere brightens the high phase angle crescent (with surface brightness >10 times the low phase value). It should also be located near the zenith. An artistic example I can find online that gets the general idea is here. The disk of Saturn subtends about 6 degrees.


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rlorenz
post Apr 22 2017, 05:01 PM
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QUOTE (scalbers @ Apr 22 2017, 11:11 AM) *
I'm unsure how polarized the skylight would be with the multiple scattering going on.


Agreed. I'm also unsure about whether a Saturn crescent with high surface brightness (seen in the daytime sky) would be easier or not to see than a dimmer (per steradian) full-phase Saturn in Titan's night sky...

I've been waiting/hoping someone will set up a decent spherical-geometry Monte-Carlo scattering code to really understand the astronomy-on-Titan possibilities (which bear on navigation, btw)
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scalbers
post Apr 22 2017, 05:14 PM
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I think the nighttime scenario would usually be quite a bit easier. The possible exception is if Saturn is within a couple of degrees of the sun and there isn't too much of a solar aureole. The sun's glare itself could be then be an issue - holding out your thumb would be in order.

It would indeed be nice to use the Monte Carlo method - I'm in the very early stages of assembling some code. I'm also seeing if my more approximate scattering model developed for Earth can be applied to Titan.


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