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Getting Ready for Dragonfly: Titan’s Impact Craters

What accounts for the differences in Titan’s craters? It will be helpful from an operational standpoint to learn more, for in 2027 the Dragonfly mission will launch, with Selk Crater a target. An equatorial dune crater, Selk is completely covered in a dark organic material, unlike other higher-latitude craters on the Saturnian moon that are scoured and cleansed by rain. We have learned from data produced by Cassini’s Visible and Infrared Mapping Spectrometer (VIMS) that Titan’s craters come in two kinds. Equatorial craters like Selk occur in dune fields and consist mostly of organics. Mid-latitude craters show a mix of organics and water ice.

The organic material generated by processes in Titan’s thick atmosphere is sand-like, piling up in equatorial regions but being eroded at the higher, wetter latitudes. For Dragonfly’s purposes, we want to know more about how the methane rain and streams affect the surface as we fine-tune the data analysis and monitoring techniques to be used in the mission.

What’s happening in Titan’s craters reminds us just how active the surface here is, says Anezina Solomonidou, a research fellow at the European Space Agency and lead author of a paper that explores the issue:

“The most exciting part of our results is that we found evidence of Titan’s dynamic surface hidden in the craters, which has allowed us to infer one of the most complete stories of Titan’s surface evolution scenario to date. Our analysis offers more evidence that Titan remains a dynamic world in the present day.”

Image: This composite image shows an infrared view of Saturn’s moon Titan from NASA’s Cassini spacecraft, acquired during the mission’s “T-114” flyby on Nov. 13, 2015. The spacecraft’s visual and infrared mapping spectrometer (VIMS) instrument made these observations, in which blue represents wavelengths centered at 1.3 microns, green represents 2.0 microns, and red represents 5.0 microns. A view at visible wavelengths (centered around 0.5 microns) would show only Titan’s hazy atmosphere. The near-infrared wavelengths in this image allow Cassini’s vision to penetrate the haze and reveal the moon’s surface. Credit: NASA/JPL/University of Arizona/University of Idaho.

Look closely at the above image and you’ll see Titan’s largest confirmed impact crater, called Menrva, near the limb above center to the left. Cassini was at about 10,000 kilometers from the moon during this approach, a good deal higher than many flybys, but the altitude allowed the VIMS instrument to cover wide areas at moderate resolution. You can also see two dark bands, parallel regions filled with dunes at the center of the image, with some regions of finer resolution inset in the image; these were acquired near the spacecraft’s closest approach.

But back to the evolution of those craters, which is the subject of the paper in Astronomy & Astrophysics. The differences between craters are telling, for they point to different evolution depending on geography. When objects make it through Titan’s atmosphere to impact on the surface, the heat generated by the event mixes organic materials and water ice from below. The cleansing methane rain subsequently falls in the mid-latitude plains, whereas in the equatorial regions, the impact areas are covered by a layer of sandy organic sediment.

The two classes of impact crater are strikingly different. Processes after the impact account for the outcomes. From the paper:

These observations agree with the evolution scenario proposed by Werynski et al. (2019), wherein the impact cratering process produces a mixture of organic material and water ice, which is later “cleaned” through fluvial erosion in the mid-latitude plains. However, the cleaning process does not appear to operate in the equatorial dunes; rather, the dune craters are quickly covered by a thin layer of sand sediment. This scenario agrees with other works that suggest that atmospheric deposition is similar in the low-latitudes and midlatitudes on Titan, but with more rain falling onto the higher latitudes causing additional processing of materials in those regions… In either case, it appears that active processes are working to shape the surface of Titan, and it remains a dynamic world in the present day.

Image: These six infrared images of Saturn’s moon Titan represent some of the clearest, most seamless-looking global views of the icy moon’s surface produced so far. The views were created using 13 years of data acquired by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on board NASA’s Cassini spacecraft. Credit: NASA/JPL-Caltech/Stéphane Le Mouélic, University of Nantes, Virginia Pasek, University of Arizona.

With a sea of water and ammonia beneath the crust, Titan is a place where a large impact will move organic materials between the surface and the ocean below, highlighting the significance of Dragonfly’s future work at Selk Crater as a way to probe the moon’s composition. And while it seems likely that erosion has obscured most impact craters from Titan’s past, we do have 90 potential features, according to the paper, that may be craters to work with. These features offer a window into the atmosphere’s influence on the surface through weathering while exposing material from the interior which Cassini’s RADAR instrument was unable to probe.

The paper is Solomonidou et al., “The chemical composition of impact craters on Titan,” Astronomy & Astrophysics Vol. 641, A16 (September 2020). Abstract.


Comments on this entry are closed.

  • Robert October 30, 2020, 14:49

    Why will Dragonfly only fly 108 miles on Titan? The baseline mission is 2.7 years and battery charging is done by an RTG. Is that just the extent of the planned mission with possible extensions later or is there a hard technological limit? Thanks.



    • Andrei November 1, 2020, 6:29

      It most likely a figure arrived at from the distance they think they will do each fly session multiplied by mission days.
      John Hopkins state several hundred kilometers only, no exact number.
      While NASA state ‘more than’ 175 km.
      The RTG will not be at full power even at the start of the mission, the long flight time from Earth means it will have lost a bit during transit.
      I find the mission time and distance stated very optimistic, it’s first type of mission in a new environment. When it rain and show on the craft, the lighter elements will boil off, but the heavier compounds will remain. The mission is somewhat to the south so it will try to avoid the risk of having the propellers and instruments covered in tar. But there is many unknowns still.

      • charlie November 2, 2020, 13:37

        So several of your comments immediately brings up questions into my mind. How do you personally know that the heavier compounds will remain on the craft? Why do you suppose that there is going to be heavier molecular organic compounds to begin with ? Does anyone have any belief that there’s going to be complex organic compounds and especially some kind of heavier tar like residues ?

        With regards to the RTGs, I’ve always wondered why to begin with there is not a mixture of slower and faster decaying radioactive elements such that as the fast ones decay away and provide power the slower ones kick in and permit the continuation of power at basically the same level. Does anyone know why this is never been done ? Is this Dragonfly expected to maintain contact with the original landing craft or is it going to be autonomous and make direct contact with Earth ?

        • Andrei November 4, 2020, 12:23

          The Titan atmosphere got a chemistry that combined with UV light and cosmic radiation will create various compounds. Many of these PAH are already known CH3C≡CH etc.
          But what I wrote about are the heavier tholins.
          Scroll down to appendix A on this paper to see an image.
          Drogonfly will be warm or even hot compared to Titan conditions, this means the more volatile compounds will bake out, leaving a tar like substance behind.
          The question is how much rains down in a given time period, and that is why I said ‘there is many unknowns’.
          Dragonfly will get a film of such materials that risk clogging instruments and make camera images dim long before that hopeful 2,7 year mission time, if the flightworthniess will be in danger from too much on propellers and moving parts is not known.
          I am very interested in studies of Titan, and happy that this mission will be funded. But it is also my job to point out potential risks, and that was what my post was about.

          Communication with Earth will be direct, there is no orbiter planned for this mission. So the Dragonfly need to be sent to a region where there is line of sight with Earth. During Titan night the Dragonfly will sit on the ground taking measurements.
          To avoid damage and drag the antenna is stored during flight. Direct commands while in flight will not be done, the transmission time is to long. So the Dragonfly will navigate autonomously and avoid any obstacles on it’s own. I have not seen any information if Dragonfly will be able to avoid bad weather with precipitation.

  • Alex Tolley October 31, 2020, 6:59

    If tholins produced in the upper atmosphere of Titan slowly collect in these craters, I wonder if these might be good locations for resource extraction for colonies requiring a rich source of readily transportable organics. These deposits of tholins and sand might be rather like the Canadian tar sands and require similar steam extraction. It will be interesting to see what Dragonfly can discover about these tholins
    when it lands on Titan.

    • Andrei November 1, 2020, 6:34

      I have always been unhappy on some who have talked about ‘desert’ and ‘sand’ on Titan. It is a cold desert only in the sense there is little precipitation of methane / ethane. The ‘sand’ is actually granular snow of hydrocarbons. And ‘sand dunes’ is should be named snowdrift. So no such extraction needed, the snow is easily melted in the temperature range humans work in and the compounds released.

      • Alex Tolley November 1, 2020, 11:45

        Thank you for the correction. This makes the resource even more attractive – just dig it up, “box” it, and ship it. No separation from non-organic inert material required. If Ceres becomes the water supply for the inner system, Titan becomes the supplier of organics and nitrogen. Various metal asteroids, possibly primarily Psyche, become the metal supply. Metals, water, and organics, almost everything needed for a space-based civilization.

      • Michael million November 2, 2020, 16:14

        More like tardrift, other than venus, earth and maybe mars nitrogen is scarce in the inner system. Export may be a problem due to the gravity of Saturn though. I would think a tether system would work here to eject nitrogen products though.

        • Andrei November 4, 2020, 18:54

          Tardrift is a good word also, for us who understand that tar would be hard as rock at that temperature. I drool over the possibilities of those amino acids, the chance of actual life is very small there’s a couple of aminoacids missing for life as we know it, but it’s not nonexistent. If so some part should be set aside as a reservation. A tether is a good idea, a sky hook would also work to pick up packages lifted by balloon, the low gravity permits a space elevator. For the inner solar system Titan could become a powerhouse for space colony populations, and in the very long term also if and when we got the tools and economy to transform entire planets – creating entire biospheres will requite a lot of organics. Dreams of a distant future….

          • Alex Tolley November 5, 2020, 12:04

            Skyhook yes. Space elevator not really, as Titan has a slow rotation as it is totally locked to Saturn. It would have the same problem of an extremely long tether as our Moon, but with the added problem of the dense Titan atmosphere at the anchor point. The skyhook looks like a better solution to me, although hooking payloads off a balloon/airship strikes me as a very difficult exercise.

            • Andrei November 5, 2020, 17:38

              @Alex Tolley
              Yes you are entirely correct on the space elevator I was aware of the slow rotation and even hesitant when writing it, and wished we could edit after posting.
              I imagined that balloons would be expendable and cheap hydrogen and plastics made from easily obtained hydrocarbons. For an airship yes possible with packages on top, add a GPS with centimeter precision for positioning, and steer it in place in the calm atmosphere with only slow winds. And the packages having a large loop on top, carbonfiber perhaps for the hook to be picked up and lifted.

  • andy November 1, 2020, 8:35

    Sounds like an interesting mission concept. I am somewhat disappointed that this is going to the equatorial deserts rather than the lakes though.

  • Geoffrey Hillend November 1, 2020, 16:05

    Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) instrument scans Titan’s surface in the near and mid infra red, a light that is invisible to the naked eye. It can penetrate the hydrocarbon haze of Titan because infra red radiation has a longer wavelength than the visible spectrum since it’s shorter wavelengths are closer to the size of the haze particles, the visible spectrum gets scattered by the haze aerosols, but the longer infra red waves bend around the aerosols, and pass through the atmosphere. A similar effect happens with protoplanetary dust clouds where we can detect the thermal infra red radiation of the star, but not see the star in the visible light.

  • Geoffrey Hillend November 1, 2020, 16:51

    To be precise Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) does not scan anything. It has a camera which is sensitive to infra red light.

  • Mike Serfas November 2, 2020, 14:22

    What do we know now about cryovolcanoes on Titan? I’ve seen reports of candidates and even eruptions, but has a detailed catalog of most of them been assembled? Will Dragonfly be in a position to observe any of these?

    Like the Selk crater, cryovolcanoes bring liquid water to the surface, where it is mixed with hydrocarbons and in all likelihood there is some source of energy for chemoautotrophy. But if they’re still active the signs of life may be more obvious, or they might make be a potential tourist destination. True, the water may be chilly for a swim, potentially containing enough ammonia to make it liquid at nearly 100 degrees C below freezing – but do we know that’s the case?

  • James Franklin November 3, 2020, 8:51

    I am dissapointed, I would have thought NASA would be looking at Titan with a more holistic view than Dragonfly will give. I am not knocking the mission, but wish that someone had the vision to build and launch a mission than consisted of a Hi-Res orbitor, a Derigable craft to fly in the Titanian atmosphere that carried a number of small landers that could be parachuted down to locations that were found to be of special interest.

    A derigable in the Titan atmosphere would allow the sampling and imaging over a massive area, potentially globally over several years. Temperature inversions and an RTG could be used to generate electrical power for sensors, controls and propulsion.

    It is time to be bold.

  • ljk January 24, 2021, 20:22

    There may be seas on Titan that are over 1,000 feet deep, or 300 meters for the rest of humanity outside America, Liberia, and Burma:


    Of course the global ocean of liquid water on Europa may be up to 60 miles deep. With the fact that the moon is less massive than Earth, that means the deepest parts have no more pressure from the surrounding water than what is experienced in the Marianas Trench. Heavy, but not undoable.