Cryovolcanism on Titan? – Un volcanism cryogenic sur Titan?

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I attended the AGU Fall conference in San Francisco 2 weeks ago. I must admit that it is a delight to be able to attend such reputed conference without having to deal with airport, jet-lag and other inconveniences which comes when traveling. The AGU Fall conference is organized in the gigantic the Moscone Center, just 30 min away from my house. Additionally, because I organized a workshop about Io Volcanism just before the AGU (see the website on this link) which took me a lot of time, I did not present anything during this conference. I therefore had the pleasure to wander around at the poster sessions and listen to the talks of my colleagues without having any pressure.

There were a lot of interesting discussions about recent discoveries in the field of Planetary Science, even if AGU conference is essentially a geophysics conference. One of them, which got a lot of coverage by the main stream media, is the possible discovery of active cryovolcanism on Titan, satellite of Saturn.

This is an interesting and important discovery since it has been suspected for years that cryovolcanoes exist on Titan. Spectroscopic observations of Titan revealed the presence of methane clouds in its atmosphere. These clouds are quite localized and stable in time. Ground-based telescopes survey with adaptive optics  (link) showed that there are at mid latitude near 40 deg S, 350 deg W. This methane gas could come from volcanoes for instance. Cryovolcanism is a low temperature form of volcanism for which the erupted magma is a mixture of water and ammonia/methane (on Earth it is molten rocks or “basaltic” and the temperatures are higher ~1200 Deg C)

Did the JPL astronomers see an active cryovolcano? Not really. Based on what I saw at their talk and read in the LPI abstract (available here), they detected some anomalies on the surface of Titan, area which became brighter (most likely because they have been covered with fresh ices) between various flybys by the Cassini spacecraft. 

Could we explain these variations of surface brightness by another process? Yes and No, apparently another group claimed that these variations could be due to the presence of localized fog of ethane. Collecting more data with Cassini spacecraft is key to favor one of these two scenarios. Indeed, the center-to-limb variation and the temporal variation from both processes should be different. It is also useful to notice that these active features are located in the southern hemisphere  (26 S and 10S) like the clouds of methane.

Whether or not there is active cryo-volcanoes on Titan reminds me the long debate that astronomers had when they discovered that Io was bright in the near-infrared and that this brightness varies with time (in the 70s). Some astronomers developed complex model to explain these observations whereas the most obvious explanation was that Io surface was covered with active like Earth. It is only when Voyager spacecraft took a picture of an active volcano on Io that this debate ended. 

I should also mentioned that, as mentioned by my colleague R. Lopes during an AGU session about volcanism in our solar system, radar observations of Titan surface revealed the presence of volcanic features (lava field & domes). Finally, three years ago a european group  published a paper in Nature showing an image of a dome volcano imaged in the near infrared. No activity has been revealed but the analogy between Earth dome volcano and this feature is striking.

Where does this volcanism comes from? We don’t think that Titan is tidally heat like Io, so this volcanism must be a remnant of the formation of the satellite. Meaning that the core of the satellite is  still warm because it remains insulated protected by a thick and poorly conductive crust. Enceladus, another satellite of Saturn, also possesses active cryo-volcanism which seems to come from  warmer interior as well. Active geysers were imaged in 2006  by the Cassini spacecraft.

To conclude, and because the coffee shop from where I am typing this post is about to close, volcanism seems to be pretty common in our solar system. We have seen active volcanoes on Earth, Io, Enceladus, and Titan; dormant volcanoes on Mars and Venus; scars on the surface of solar system bodies due to volcanism (Moon, Callisto, Ganymede, Triton). Volcanism is another very common geophysical process  in addition to erosion, impact cratering and tectonics which plays an important role in shaping a planet interior and surface, but also its atmosphere and its evolution with time.

In a few months/years, Cassini spacecraft may record the activity of a volcano during one of its flybys of Titan. This will be the ultimate proof to confirm that volcanism also exists on this satellite.

Your comments are always welcome,

F.

 

Version Francaise

Il y a 2 semaines je participais a la conference annuelle de l’AGU (American Geophysical Union) qui est organisee tous les ans a San Francisco. Il est tres agreable de pouvoir assister a une conference de ce niveau sans avoir a s’embeter avec les problemes lies aux voyages par avion, comme par exemple les files d’attente stressantes dans les aeroports, les decalages d’horaire et les vols annules a la derniere minute. Cette conference est organisee dans le Moscone Center, un centre de conference gigantesque en pleins coeur de San Francisco, juste a 30 min de chez moi en metro. Cette annee, j’avais pris la decision d’organiser un atelier de travail sur le volcanisme de Io, quelques jours avant la conference (see le lien). J’etais loin d’avoir imagine qu’un workshop de ~30 personnes sur deux jours me prendrait autant de temps. C’est donc libre de toute presentation et tout poster que j’ai pu ecouter mes collegues et voir leur poster presentant leur derniers travaux. Il est agreable de pouvoir librement apprecier d’assister a cette conference internationale.

Je ne pourrais pas resumer sur ce blogs l’ensemble des resultats interessants developpes durant la conference, neanmoins un d’entre eux m’a particulierement interesse et il a d’ailleurs ete discute dans beaucoup de journaux non-specialises: il s’agit de la decouverte d’un volcanisme cryogenic sur Titan.

Cette decouverte est interessante et importante sur plusieurs points. Il y a quelques annees, avant l’arrivee de la sonde Cassini en orbite around Saturne, des etudes spectroscopiques avaient montre la presence de nuages de methane dans l’atmosphere de ce satellite. Un suivi par des observations prises par des telescopes au sol equipes de systeme d’optique adaptative a montre que ces nuages (link) sont stables et localises a mid-latitudes (40S, 350 W). On imagine que ces nuages de methane sont le resultat d’un volcanisme de glace qui emet un magma compose d’une mixture d’eau et de methane/ammonium. Sur notre planete, le volcanisme est de type “basaltique” et le magma  dont la temperature atteint 1200 deg Celsius est compose de roches fondues.

Est ce que les astronomes du JPL ont observe un volcan actif grace aux donnees Cassini? Pas exactement, d’apres leur presentation et un resume de leur travaux publie en fevrier 2009 lors de la conference LPSC (disponible ici), ils ont detecte en realite deux regions de Titan dont la brillance s’est modifie entre plusieurs survol de la sonde Cassini. Ces regions qui sont devenues plus brillantes auraient ete recouverte de glaces fraiches. 

Peut on expliquer ces variation de brillance par un autre phenomene? Oui et non. Comme toujours dans ce genre d’analyse, il y a plusieurs interpretations possibles. Un autre groupe pense que ces variations ne sont dues qu’a la presence de brouillard d’ethane tres localise (un peu comme le fog de San Francisco en ete). En collectant plus de donnees, la sonde Cassini donnera une reponse definitive sur cette question. En effet, l’evolution et les variations lumineuses centre-limbes (prises a differentes geometries d’illumination) dues a un brouillard sont differentes de celles dues a une surface glacee.  Il est aussi utile de noter que ces regions sont localisees dans l’hemisphere sud (26S and 10S) comme les nuages de methane que l’on observe. 

La presence ou non de cryovolcanisme sur Titan est debattu dans notre communaute. Et il est similaire a celui qu’avait les astronomes lorsqu’on observa des variations lumineuses dans l’infrarouge proche sur Io, satellite de Jupiter dans les annees 1970. En lisant la literrature de l’epoque, on s’apercoit que certains collegues avaent fait preuve d’une imagination debordante pour expliquer ce phenomene alors que la solution la plus evidente etait justement la presence d’un volcanisme sur ce satellite. C’est seulement en 1979 lorsque la sonde Galileo pris les cliches d’un volcan actif sur ce astre exotique que le debat pris fin et que l’on se focalisa a expliquer l’origine de ce volcanisme. 

Il y a plusieurs indications de l’existence d’un cryovalcanisme sur Titan qui montre que cette idee est loin d’etre farfelue. Ma collegue Rosaly Lopes du JPL a montre par exemple l’existence de structures a la surface de Titan visualisees par des donnees radars qui sont vraisemblablement d’origine volcanique, comme des  champs de lave ou des montagnes volcaniques. En mai 2005, des astronomes europeens ont montre sur des images infrarouges prises par la sonde Cassini une structure qui ressemble fortement a une montagne volcanique.

D’ou vient ce volcanisme? On ne pense pas que comme Io pour Jupiter, le volcanisme de Titan soit produit par des effets de maree car il n’y a pas de resonnances entre Titan et un autre satellite de Saturne. Il est possible que ce volcanisme de basse temperature (T~200 K) vienne de la chaleur primordiale capturee lors de la formation du satellite. L’interieur du satelllite serait reste plus chaud car toute l’energie n’a pas s’echapper en raison de la presence d’une croute a la surface faiblement conductrice et de large epaisseur. On a observe en 2006  un autre cryo-volcanisme localise sur le pole sud de Encelade (satellite de Saturne) qui pourra etre du au meme phenomene. 

Pour finir, (le coffee shop d’ou je vous ecris va fermer), le volcanisme est omnipresent dans notre systeme solaire. Il est actif sur la Terre, Io, Titan et Encelade, “endormi” sur Mars et Venus, et a marque l’histoire de la surface de la Lune, Triton et les satellites galileens. Le volcanisme est un autre phenome geologique  tout comme l’erosion, les crateres d’impact et la tectonique qui joue un role important pour expliquer la nature et structure de la surface, l’interieur, mais aussi l’atmosphere et l’evolution des astres du systeme solaire. 

Dans quelques mois/annees, la sonde Cassini enregistrera peut etre une activite volcanique en directe lors d’un de ses survols. La preuve ultime confirmant l’existence de ce volcanisme exotique.

N’hesitez pas a me faire part de vos commentaires,

F.

 

About Franck Marchis

Dr. Franck Marchis is a Researcher at the Carl Sagan Center of the SETI Institute since July 2007. Over the past 15 years, he has dedicated his research to the study of our solar system using mainly ground-based telescopes equipped with adaptive optics. More recently he has been also involved in the definition of new generation of AOs for 8 -10 m class telescopes and future Extremely Large Telescopes. He has developed algorithms to process and enhance the quality of images, both astronomical and biological, using fluorescence microscopy. His currently involved in the development of the Gemini Planet Imager, an extreme AO system for the Gemini South telescope which will be capable of imaging and record spectra of exoplanets orbiting around nearby stars.

3 Responses to Cryovolcanism on Titan? – Un volcanism cryogenic sur Titan?

  1. Yassin Abboud says:

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