# Seeing through the haze: The Cassini/Huygens challenge of mapping Titan's surface

Benoît Seignovert, Stéphane Le Mouélic, Christophe Sotin

► To cite this version:

Benoît Seignovert, Stéphane Le Mouélic, Christophe Sotin. Seeing through the haze: The Cassini/Huygens challenge of mapping Titan's surface. 20 years celebration of the Huygens landing, Sep 2025, Paris, France. 10.57745/KCR2QM. hal-05305573

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https://hal.science/hal-05305573v1

Submitted on 9 Oct 2025

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<figure><img src="image_1.png" /></figure>
# Seeing through the haze

## The Cassini/Huygens challenge of mapping Titan's surface

Benoît Seignovert<fnref n="1" />, Stéphane Le Mouélic<fnref n="2" /> & Christophe Sotin<fnref n="2" />

<figure><img src="image_2.png" /></figure>

doi: 10.57745/KCR2QM

<footnote n="1">¹Observatoire des Sciences de l'Univers Nantes Altantique (Osuna), CNRS UAR 3281, Nantes Université</footnote>

<footnote n="2">²Laboratoire de Planétologie et Géosciences (LPG), CNRS UMR 6112, Nantes Université</footnote>
# Pioneer 11 (1979)

## First image of Titan from a spacecraft

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /><figcaption>Raw data</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Processed image?</figcaption></figure>
Voyager 1 & 2 (1980 - 1981)

<figure><img src="image_6.png" /><figcaption>Smith et al. 1982</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Smith et al. 1981</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Karkoschka et al. 1995</figcaption></figure>

No structure visible
on the surface
Voyager 1 & 2 (1980 - 1981)

<figure><img src="image_9.png" /></figure>
Sensing Titan surface (1991)

<figure><img src="image_10.png" /></figure>

"The optical depths that we derive for Titan's haze and clouds are small enough to allow us to **sense the surface of Titan** at 4900, 6250, and 7700 cm-1. The most plausible interpretation of the albedos determined at these wavenumbers suggests a surface dominated by "dirty" water ice. A global ethane ocean is not compatible with these albedos.

<figure><img src="image_11.png" /></figure>
# Hubble Space Telescope (1994)

## First orbital observations

<figure><img src="image_12.png" /></figure>

F673N

<figure><img src="image_13.png" /></figure>

F850LP

<figure><img src="image_14.png" /></figure>

F1024M

0.85 - 1.05 µm

<figure><img src="image_15.png" /></figure>

Smith et al. 1996

PIA01465
Adapted from
Richardson et al. 2004

<figure><img src="image_16.png" /></figure>

Voyager 1
Orange filter

<figure><img src="image_17.png" /></figure>

HST
F850LP
CFHT (1998)

Resolved ground based images

with adaptative optics

in the wings of the CH₄ bands

Coustenis et al. 2001

<figure><img src="image_18.png" /></figure>

H1 (1.60 µm) | H2 (1.64 µm) | J1 (1.29 µm) | J2 (1.18 µm)
# Gemini & Keck (2001)

## Resolved ground based images with adaptive optics

<figure><img src="image_19.png" /></figure>

18/12/2001

<figure><img src="image_20.png" /></figure>

20/12/2001

He I (2.06 µm)

<figure><img src="image_21.png" /></figure>

21/12/2001

Roe et al. 2002
VTL (2002-2004)

Hartung et al. 2004

<figure><img src="image_22.png" /></figure>

(1.575, 1.600, 1.625) µm

Best knowledge
**before Cassini-Huygens**

1.575 µm

Gendron et al. 2004

<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /></figure>
1477459118_1

<figure><img src="image_25.png" /></figure>

VIMS

<figure><img src="image_26.png" /><figcaption>TA Cassini first
observations (2004)</figcaption></figure>

ISS UV3 (0.338 µm)

N1477322123_4
1477459118_1

<figure><img src="image_27.png" /></figure>

VIMS

TA Cassini first
observations (2004)

<figure><img src="image_28.png" /></figure>

ISS CB3 (0.930 µm)

N1477322195_4
PIA08119

Aerial Views of Titan Around the Huygens Landing Site

Altitude

West

North

East

South

150 km

100 mi

30 km

20 mi

8 km

5 mi

1.5 km

1 mi

0.3 km

0.2 mi

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

Huygens landing (2005)

Seeing below the haze

*down to the ground*

PIA06440

<figure><img src="image_34.png" /></figure>
<figure><img src="image_35.png" /></figure>

Images Courtesy:
ESA, NASA, JPL, University of Arizona
Panorama by René Pascal, February 6, 2005

<figure><img src="image_36.png" /></figure>

Karkoschka et al. 2016

<figure><img src="image_37.png" /></figure>

Huygens
from **landscape**
to **map**
# Building a global VIMS map

Le Sotin et al. 2005

2004

<figure><img src="image_38.png" /></figure>

1.4 km/px
# Building a global VIMS map

Barnes et al. 2007

2005

<figure><img src="image_39.png" /></figure>

1.4 km/px
# Building a global VIMS map

<figure><img src="image_40.png" /></figure>
# Building a global VIMS map

<figure><img src="image_41.png" /></figure>
# Building a global VIMS map

2018

Le Mouélic et al. 2019

<figure><img src="image_42.png" /></figure>

1.4 km/px
# Building a global VIMS map

<figure><img src="image_43.png" /></figure>
# Building a global ISS map

2004

<figure><img src="image_44.png" /></figure>

PIA06086

730 m/px
# Building a global ISS map

PIA06201

2005

<figure><img src="image_45.png" /></figure>

730 m/px
# Building a global ISS map

PIA08346

2006

<figure><img src="image_46.png" /></figure>

730 m/px
# Building a global ISS map

PIA08399

2007

<figure><img src="image_47.png" /></figure>

730 m/px
# Building a global ISS map

PIA11149

2009

<figure><img src="image_48.png" /></figure>

730 m/px
# Building a global ISS map

2011

PIA14908

<figure><img src="image_49.png" /></figure>

730 m/px
# Building a global ISS map

PIA19658

2015

<figure><img src="image_50.png" /></figure>

730 m/px
# Building a global ISS map

2018

PIA22770

<figure><img src="image_51.png" /></figure>

730 m/px
# Building a global ISS map

2025

Weller et al. 2025

<figure><img src="image_52.png" /></figure>

730 m/px
# Building a global RADAR map

PIA08100

2005

<figure><img src="image_53.png" /></figure>

350 m/px
# Building a global RADAR map

2011

PIA20024

<figure><img src="image_54.png" /></figure>

350 m/px
# Building a global RADAR map

<figure><img src="image_55.png" /></figure>
<figure><img src="image_56.png" /><figcaption>Geological global map</figcaption></figure>
Merging the datasets VIMS + ISS

<figure><img src="image_57.png" /></figure>

VIMS

<figure><img src="image_58.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_59.png" /></figure>

VIMS (L*)

<figure><img src="image_60.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_61.png" /></figure>

VIMS (a*)

<figure><img src="image_62.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_63.png" /></figure>

VIMS (b*)

<figure><img src="image_64.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_65.png" /></figure>

ISS

<figure><img src="image_66.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_67.png" /></figure>

<figure><img src="image_68.png" /></figure>
# Merging the datasets VIMS + ISS

<figure><img src="image_69.png" /></figure>

VIMS + ISS

<figure><img src="image_70.png" /></figure>
Merging the datasets VIMS + ISS

<figure><img src="image_71.png" /></figure>

VIMS

North
pole

<figure><img src="image_72.png" /></figure>

ISS

<figure><img src="image_73.png" /></figure>

VIMS-ISS

<figure><img src="image_74.png" /></figure>

South
pole

<figure><img src="image_75.png" /></figure>

<figure><img src="image_76.png" /></figure>
<figure><img src="image_77.png" /></figure>

# landing site

<figure><img src="image_78.png" /></figure>

10.573°S 192.335°W

Karkoschka et al. 2016

Le Mouélic et al. 2019

DISR

(0.85 + 0.754) µm / 2

0.823 µm

0.935 µm

<figure><img src="image_79.png" /></figure>

<figure><img src="image_80.png" /></figure>

<figure><img src="image_81.png" /></figure>

ISS (0.930 µm)

<figure><img src="image_82.png" /></figure>

VIMS

(1.59 / 1.27 µm, 2.03 / 1.27 µm, 1.27 / 1.08 µm)

<figure><img src="image_83.png" /></figure>

RADAR (2.2 cm)
# Selk crater

<figure><img src="image_84.png" /></figure>

<figure><img src="image_85.png" /></figure>

DRAGONFLY

landing site (2034)

<figure><img src="image_86.png" /></figure>

Barnes et al. 2021

<figure><img src="image_87.png" /><figcaption>ISS (0.930 µm)</figcaption></figure>

<figure><img src="image_88.png" /><figcaption>VIMS (1.58 µm)</figcaption></figure>

<figure><img src="image_89.png" /><figcaption>RADAR (2.2 cm)</figcaption></figure>
Post Cassini

JWST observations (艹 C. Nixon's talk)

<figure><img src="image_90.png" /></figure>

4 Nov 2022

Webb NIRCam

<figure><img src="image_91.png" /></figure>

6 Nov 2022

Keck NIRC-2
<figure><img src="image_92.png" /></figure>

Adapted from Seignovert et al. 2021

doi: 10.5281/zenodo.17152190
Conclusions

Titan's atmosphere is unique in the solar system

Seeing through Titan's haze is hard!

It's surface is only visible in limited IR windows

It took 13+ years to build global maps

Most of its surface is known at km-scale

<figure><img src="image_93.png" /></figure>
(OF, J49) At: 545,000 km

<figure><img src="image_94.png" /></figure>

<figure><img src="image_95.png" /></figure>

NASA Caltech-JPL/Univ. of Arizona/LPG Number