Thread by @markmccaughrean

#OTD in 2005, @esa's Huygens probe descended to the surface of Titan as part of the @CassiniSaturn mission.

I wasn't working for ESA at the time, but happily took part in an inadvertent experiment in public engagement that took place that day.

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@esa @CassiniSaturn IIRC, as imaging data arrived back from Saturn, they were transferred from @esaoperations to the DISR camera team at @uarizona via ftp.

The ftp account was public & unpassworded, & details of its existence leaked on to the internet.

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@esa @CassiniSaturn @esaoperations @uarizona Like many, I went on to the ftp account & downloaded images as they arrived. They were raw & uncalibrated as below, & Huygens was spinning, so it wasn't clear (at least to my untrained eye) that they were showing valleys, channels, & flood plains.

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planetary.org/blogs/guest-bl…

@esa @CassiniSaturn @esaoperations @uarizona But it was hugely exciting, as was seeing the first official processed & mosaiced images come out soon after.

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planetary.org/multimedia/spa…

@esa @CassiniSaturn @esaoperations @uarizona The same was true of the images Huygens took on the surface, showing pebble-like objects stretching across what turned out to be a dry riverbed, albeit that flows with liquid hydrocarbons, not water.

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planetary.org/multimedia/spa…

@esa @CassiniSaturn @esaoperations @uarizona Of course, since then, much better calibrated, processed, & mosaiced versions have been made from the Huygens data, many of them colourised to give a realistic impression of what it'd look like under Titan's very hazy upper atmosphere.

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planetary.org/multimedia/spa…

And some spectacular movies have been made by Erich Karkoschka at @UArizonaLPL showing the reconstructed descent of Huygens from space down to Titan's surface, with mosaiced images & with all the technical annotation you could possibly want.

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lpl.arizona.edu/sites/default/…

This one shows the wider context of the descent, along with oblique views of the descent to the surface, nicely narrated by David Harrington.

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And of course, there were many other instruments on Huygens to make an in situ analysis of Titan's atmosphere during the descent & of the surface after landing, the latter Huygens Surface Science Package led by John Zarnecki at @OpenUniversity.

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sci.esa.int/documents/3364…

A great summary of some of the key scientific findings from Huygens, its 2 hours 27 minute descent, & its minutes of activity on the surface after landing, have been collated here.

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sci.esa.int/web/cassini-hu…

Titan has an atmosphere 50% denser than the Earth's, &
one of the very neat things done was to record the sound of Huygen's descent & of Titan's winds using the probe's microphones.

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esamultimedia.esa.int/images/huygens…

There's also a funky sonification of the probe's radar data, which at the end, as Huygen's reached the surface, sounds very much like the chirp of gravitational waves emitted from a black hole merger 😎

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esamultimedia.esa.int/images/huygens…

Those audio recordings are available via @esa's website here.

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esa.int/Science_Explor…

There's much, much more that could be said about the @esa Huygens descent to Titan 15 years ago today, still the furthest out in the solar system that a landing has been attempted to date.

But let me end by returning to the story of the public ftp archive & the DISR images.

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@esa When I joined @esa in June 2009, I was head of the then Research & Scientific Support Department, home to the Project Scientists for our astrophysics, solar system, & fundamental physics missions.

That included Jean-Pierre Lebreton, @esa #CassiniHuygens Project Scientist.

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I had one-on-one meetings with all of the Project Scientists, to get to know them, their missions, & where the issues lay. It was very exciting to hear about all the science being done with @esa's missions, much of it outside my direct experience as an astronomer.

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During the meeting with Jean-Pierre, I told him that I'd downloaded the Huygens images from the open ftp site in Arizona on 14 Jan 2005, & how exciting it was.

He blanched, looked at me sternly, & said "You were one of *those* people!?"

Yup, guilty, your honour 🤷‍♂️

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That inadvertently open ftp site had caused a lot of kerfuffle that day, & I understand why. But it also posed some interesting questions about open data, proprietary periods, & public engagement, things that came back into full focus when #Rosetta arrived at #67P in 2014.

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I don't want to re-open that debate today though, which I believe is a complex issue that needs to be responsive to the legitimate concerns of various stakeholders, including the instrument teams, the wider scientific community, keen amateurs, & the general public.

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But in that moment 15 years ago today, sitting in my @UoE_Astro office in Exeter, watching images stream back across more than a billion kilometres from a human-made probe descending onto Titan, this astronomer knew how just how thrilling planetary exploration could be 😎

END