According to this cool answer the Huygens lander on Saturn's moon Titan had a flood light to aid in photography of the surface because of the very low ambient light levels due to the 9.5x farther distance than Earth from the Sun, and also absorption and scattering of the already low sunlight level from Titan's thick atmosphere.

Since images exist that show foreground together with background, I'm assuming the light was not always necessary.

Did it work? Was it ever used? Are there photos that are taken using this light?

below: unsourced image from this question.

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below: Huygens image of the surface of Titan, from here

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1 Answer 1


The plan was to switch the lamp on 4 minutes before landing and leave it on.

Descent Imager/Spectral Radiometer lamp turned on
Close to the surface, Huygens's camera instrument will turn on a light. The light is particularly important for the 'Spectral Radiometer' part of the instrument to determine the composition of Titan's surface accurately.

There are 2 lights?

  • Surface Science Lamp
  • Lamp for measurement of reflection spectrum of surface below 100 m altitude

But from 'The Descent Imager/Spectral Radiometer (DISR) experiment on the Huygens entry probe of Titan', these might be one and the same.

A 20 watt lamp and collimator are used to provide spectrally continuous illumination of the surface during the last 100 m of the descent for measurements of the reflection spectrum of the surface.

Surface Science Lamp The purpose of the surface science lamp (SSL) is to illuminate the surface of Titan in spectral regions where strong atmospheric absorption bands prevent sunlight from penetrating to Titan’s surface. The SSL permits continuous measurements of the spectral reflectivity of the surface to be made throughout the entire spectral range. The SSL is a 20 Watt lamp with a parabolic reflector which illuminates the surface and fills the narrow 3 × 9 degrees FOV of the IR spectrometer with enough light to give a S/N of 50 at 60 m altitude within the strong methane bands even if the surface reflectivity is as low as 0.05. The lamp system is activated when an altitude of 700 meters is reached (given by the radar altimeter) and is operated during the last several minutes of the descent where a continuous sampling of the reflection spectrum of the surface is obtained using both the DLVS and DLIS.

Approximately two minutes after impact, the surface science lamp is switched off. After that it is alternately switched on and off every two minutes.

So about half the photos taken by Huygens should be with the lamp on.

The study 'The reflectance spectrum of Titan’s surface at the Huygens landing site determined by the Descent Imager/Spectral Radiometer' indicates that the light was used as planned.

We reconstruct the reflectance spectrum of the landing site in the 500-1500 nm range from Downward Looking Visual and Infrared Spectrometer data that show evidence of lamp light.

  • $\begingroup$ Nice answer! Hopefully we can find at least one image that shows the light survived the voyage and impact. $\endgroup$
    – uhoh
    Commented Jan 4, 2018 at 10:13
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    $\begingroup$ HRI710 should show it, but I can't find it yet. $\endgroup$
    – Hobbes
    Commented Jan 4, 2018 at 10:29
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    $\begingroup$ saers.com/recorder/craig/titan/LiquidMethaneOnTitan.html has a low-res copy of HRI710, looking for the original. $\endgroup$
    – Hobbes
    Commented Jan 4, 2018 at 10:42
  • $\begingroup$ Can you help me figure out where it is in that link? $\endgroup$
    – uhoh
    Commented Jan 20, 2018 at 16:01
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    $\begingroup$ it's in the mosaic image about halfway down the page. saers.com/recorder/craig/titan/TitanLandingPointV2.jpg in the middle of this image, a section is marked '710', this section contains a bright spot. $\endgroup$
    – Hobbes
    Commented Jan 20, 2018 at 16:33

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