Monday, February 5, 2007

Beneath Titan's Veil

Two years ago, on the 12th of January, eyes across the world watched, with true excitement and a unique spirit of adventure, the landing of a probe on an alien world never seen before.
That probe was Huygens and catched an eight year ride with the Cassini spacecraft untill it plunged deeply into the unknown behind Titan’s veil.
Breath was hold untill the first data delivered revealed to human eyes a whole surprising new world, an astonishing primal landscape, closer to Earth than imagined, with river-like structures and small Titanian pebbles seeded on the soil surrounding Huygens’ landing site. Now, two years passed, Cassini is still on duty and the data retrieved from Huygens preciously helps scientists to gather and convert Titan’s intriguing details on a strong building of knowledge.

As a way to celebrate the mission’s anniversary, but also the discoveries currently being achieved, fruit of the work and dedication of a whole team, spacEurope had the previlege to have some of it’s questions answered by Jean-Pierre Lebreton, the mission’s Manager and Project Scientist.

Know more about Cassini-Huygens.



The first paragraph of ESA's press release on the anniversary’s occasion ends with a question:
"What lies beneath the haze?"
Now, with Huygens data and the impressive Cassini fly-bys, can we, in part respond to this question?
What sort of landscape and environment would surround a human if standing on, let's say, the Great Lakes region?
In order to permit a human brain to imagine such a different world, an Earth-like comparison turns things easier. On Titan, dramatic scenaries like the one caused by the Exxon Valdez spill, are expected to be not a sad exception but revealers of the moon’s (not ours...) healthy environment:

"The surface must be covered with thick layer of organic goo.
Something that may resemble a polluted area (an icy coast) on Earth after a black-wave.”

Personally, before the landing I had imagined Titan as a geographically harsh world, with strange, huge, crystal-like features.
When I had the first glimpse of the images sent by Huygens my immediate thought was (beside the "wow!" factor...) "Shores!"
Reading to Athéna Coustenis words, the team expected a, somehow, different scenario:
"The Descent Imager/Spectral Radiometer (DISR) pictures were an enormous surprise. We had expected a much smoother landscape."
What was the reason for this previous impression?

“Every observation by Cassini's radar shows that Titan surface is harsh. We see mountainous areas with short spatial scale sharp relief, flows, rivers. I am not sure why Athena expected a smoother landscape. She may have been "biased" by the tremendous work she did prior to Cassini-Huygens with ground based observations which showed that Titan was smooth but with limited spatial resolution (a few 100 km's). Now with cm-resolution by Huygens and 100's m resolution by the Cassini Orbiter impression have changed considerably.”

For those, like me, who get it hard to understand some chemistry results, I’ve asked Mr. Lebreton how do two specific isotopes, Ar40 and Ar36 give us answers about current activity in Titan’s subsurface domains and about the moon formation after Saturn.

“Ar40 comes for the decay of Potassium, indicating some geophysical activity in Titan's interior that releases this isotope." Just as curiosity, on Earth Potassium has several applications such as on chemical fertilizers, glass, lenses, matches, gun-powder or dietetic salt.
"Ar36 is primordial Argon" (used on lamp gas, fluorescent bulbs, Geiger counters, lasers or as an inerte welding gas) "indicated that trapped Ar36 is outgassing from the interior."

Another surprise was the near zero wind under 60 kms.
Can we talk about Titan as a still world most of it's time? With some sort of atmospheric dome protecting from upper atmospheric turbulence?

“No.” (OK, that was a clear answer, I’ll leave my theories and learn something from the specialists...)
“Titan does not appear to be meteorologically still, on the contrary.
The zero wind layer is surrounded by turbulent layers (above and below. We also knew (from stellar occultation observations that jet stream like features were present in the stratosphere above 200km.
Latest interpretation of the 2003 stellar occulation confirms this. The presence of dune fields of sand-like material on the surface also indicate surface wind.
Titan is anything but a still place.”

Huygens also measured, if I got this correctly, the temperature values from 1600 kms to the ground during its descent.
How accentuated was the curve?

“If I do understand the question here is the answer. The temperature profile was indirectly derived from accelerometry measurements during entry (from 1400 km high, may be up to 1600 kms, down to 155 kms). We see lots of structure/layers. Some were know from ground-based stellar occulations (temperature inversion just above 500 km altitude); detections of many haze layers by Cassini Camera is also indicative of a layered stratosphere which may suggest the presence of (gravity) waves propagating upwards.”

The three main elements composing the atmosphere, methane, ethane and nitrogen, how do they interact?
According to the results the first two provide humidity, what is the role of nitrogen?

“Nitrogen participates to the chemistry at high altitude; nitrogen is the main constituent of the atmosphere. The thermodynamic of the atmosphere and of the rain is also controlled by nitrogen.”

But there are still many questions to be answered...

“It's contribution to chemistry in the troposphere and on the surface is to be understood.”


How will it be, according to Christophe Sotin
suggestion, the approach of Cassini to study the lakes on an extended mission?

“Cassini will plan to flyover the lake region and make more observations, with the radar, to look for variation of the lakes and also for measuring the composition with the visual Infrared Mapping Spectrometer.”

Speaking of Titan's future exploration, what would be, in your oppinion, the best design for reaching the best results?
A ballon? A rover? A different concept underway?

“We are studying both in Europe and in the US, mission concepts for future missions to Titan.”

If you had nightmares about a rover getting it's wheels stucked on Titan’s goo just forget it...
“Despite what I said in a press conference 6 days after the landing, rovers would most likely not be the best way to explore Titan in the future. Mobility in the atmosphere (vertical and horizontal) will be best provided by hot air balloons (montgolfiere). Dropping long-lived probes on the surface would also be exciting (composition of surface material and seismic-like activity which would require probe survival for 1 or 2 Titan days).
A Titan orbiter would also be a good thing to have. As it seems, the complex organic chemistry is really initiated above 1000 km altitude.”

Is it being equationed a similar in concept mission, taking in account the success of the Cassini-Huygens one, to two of the most fascinating moons of our solar system, Europa and Io? Do you participate or are you aware if there is any advance study on how to penetrate Europa's icy secrets?

“A proposal for a Europa/Jupiter mission is expected in response to ESA's
Cosmic Vision AO to be released soon.”
I just can’t wait to hear more about that...

“One of the big questions that such a mission will have to answer is how thick is the icy layer above Europa's ocean (although the presence of an ocean is still to be confirmed). Hopefully such a misison will take shape through an international collaboration scenario. Europe, US and Japan are interested in such a mission, which could be conducted the way Cassini-Huygens is so successfully conducted (US-led), but a Europa/Jupiter mission could be either led by Europe or by the US, with Japan as the third major partner.”

You can understand, by Huygens Mission Manager words, that, undoubtfuly, in spite of the time needed to have a GO on a mission of this nature, Europa is on his mind...

“A properly designed Europa Orbiter should be able to answer many questions, and prepare the ground for surface penetrators, and then surface landers in subsequent missions. Europa's future exploration will take decades.
Cryorobots that would eventually melt through the ice layer are still far from being feasible.”

Having still the data under study and Cassini marvelling us, where can our knowledge about Titan arrive untill one future mission?

“Titan, once thought to be a frozen early Earth, appears to be as complex as any of the terrestrial planets in the solar system that have an atmosphere; Titan is probably more like the Earth than either Mars or Venus.”

We will be here, looking closer than ever to Titan, “definitively a World worth to explore further”.

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