Cassini-Huygens to Saturn and Titan

Talk given by Dr. Andrew Coates at the Society meeting on Wednesday 15th June 2005

      Dr. Andrew Coates began his talk by projecting a highly detailed picture of Saturn's rings taken during the Cassini-Huygens mission as the spacecraft approached the planet and showing the moon Mimas against the background of rings.

      He described the work done by the University of London (UCL) and the Mullard Space Sciences Laboratory covering Solar, Stellar, Planetary, Detection Physics, Climate Physics, Astrophysics and his own subject on Magnetospheres.  About 120 people worked on these various sciences and had contributed to the Mars Express mission and were also involved with instruments on board Rosseta, Deep Impact and Venus Express to be launched on 26th October 2005.  UCL were also looking at X-rays and the composition of the moon with ESA's Smart-1.

      Andrew also talked about Genesis that collected solar wind samples and then had a hard landing, although he did go on to say that there were a number of samples found to be intact and were still to be analysed.

      We then turned to the Cassini-Huygens mission by mentioning the astronomer Huygens (1629-1695) who was known for his work on the rings of Saturn, and also Cassini (1625-1712) whose work showed that the ring system was not solid and that there were well defined divisions in them, notably the large division towards the outer edge which became known as the Cassini Division.

      The Cassini-Huygens mission was an international project where various countries were invited by NASA to contribute experiments to be housed on the spacecraft.

      Andrew explained that he was the team leader responsible for the electron-spectrometer, which detected and measured the magnetosphere in the neighbourhood of Saturn and looked at the influence Titan had upon the findings.

      It had always been intended to return to Saturn but Titan had also been chosen for closer inspection because it was the largest moon and was also shrouded in haze.  The surface was known to be -180 degrees Celsius close to the triple point of methane where the gas becomes a solid at 93 degrees Kelvin.

      A number of questions remained about Saturn such as why did it radiate 80% more energy than it received; what was its internal structure and why do the equatorial winds move at 2/3 the speed of sound.  More information was needed to answer how the rings were formed and when.

      During the mission metallic hydrogen was detected beneath the surface of the planet and it was also discovered that the winds moved in one direction, suggesting that there was perhaps a seasonal effect.

      With respect to the rings it was found that they were restricted by the Roche Limit beyond which their volume cannot expand without losing material to orbiting bodies.  It was further established that the material composition of the rings was mainly water-ice and dust.

      During flybys of Titan, a search was made for the possible existence of hydrocarbon lakes and further observations of the moon's weather were also achieved.

      Andrew turned to the results from the electron spectrometer, which consists essentially of two concentric plates through which the energy level and incoming direction of encountered electrons could be measured as the spacecraft approached and orbited Saturn.  He showed some resulting diagrams of the plasma changes exhibiting the complex structure of the magnetosphere, which is twenty times that of the Earth's.  Also some startling effects produced by the presence of Titan were observed.

      Titan has no magnetic field of its own, but the upper atmosphere is ionised by energy from the Sun and this interaction with the solar wind creates a marked effect on Saturn's magnetosphere and the result could be clearly seen in Andrew's slide of the chart.

      The talk now turned to what was discovered about Titan during the various orbits of the moon.  The methane clouds had light and dark features when imaged in infrared and ultraviolet.  The atmosphere was found to be composed of methane, nitrogen, propane, diacetylene (unsaturated hydrocarbon) and benzene.  Ions were also detected of carbon 2,3,4,5,6 and unexpectedly carbon 7 and 8.

      Radar maps of 25% of Titan's surface were achieved in an attempt to find the most suitable landing/impact site for the Huygens probe that would prove most valuable source of data such as the "beach" on the edge of one of the methane "lakes".  Something else that surprised the mission scientists was the possible discovery of a 30 Km diameter volcano, which could go some way to explaining where the methane came from.

      Andrew then described in detail the events of the 14th of January 2005 when the Huygens completed its planned orbits of Titan and the descent through the atmosphere to the surface was initiated.  It had to land fairly quickly to make the best use of the remaining power in the on-board batteries.

      Signals were received at Green Bank in Virginia and a microphone on the craft detected the sound of the passing atmosphere during entry and descent, also Andrew played a sound version of the radar signals as it approached the surface.  The landing took place at 1025 GMT and the craft survived for three hours, collecting data and photographs.  One rock close by showed a crack in it, and it wasn't certain whether this had been caused by the impact or not.  The temperature of Huygens at the moment of landing was 25 degrees Celsius and this was taken into account when analysing the data, although the temperature would have fallen extremely quickly.

      Pressure gauges suggested that the surface was rather like the surface of a Crème Brûlée and had an orange colour. Andrew finished by saying that the data they had collected was going to keep them and subsequent scientists busy for tens of years.


      The next meeting of the Society is on Wednesday 20th July 2005.  We are delighted to welcome back Konrad Malin-Smith who will be guiding us around "Pulsars".

      The meeting takes place as usual in the Drama Studio of Uplands College, Wadhurst and begins at 7.30 pm.


      There will be no Society meeting during August BUT Michael Harte and his wife have again very kindly offered to host a "bring your own food" barbecue on Saturday 27th August at Greenman Farm, Wadhurst - on the south side of the B2099 immediately to the west of the railway bridge.  All Society members and friends are very welcome.  Bring your own food; - cutlery and plates will be provided.  Bring telescopes if possible.

      Michael suggests arriving around 1900.


  Wednesday 21st September 2005.  Alan Drummond will be giving a talk called "Perception in Astronomy"

  Wednesday 19th October 2005.  Peter Parish introduces us to "Planets and Small Telescopes"


      A Committee Meeting has been arranged for 2000 on Monday 11th July 2005 at the Abergavenny Arms, Frant.  Any members of the Society can come along and will be made very welcome.  




NASA has approached the Society with an offer to provide a short monthly news item.  This is the first we have received.

Moving a Mountain of a Dish by Patrick L. Barry

      Your first reaction: "That's impossible!"  How on earth could someone simply pick up one of NASA's giant Deep Space Network (DSN) antennas - a colossal steel dish 12 stories high and 112 feet across that weighs more than 800,000 pounds-move it about 80 yards, and delicately set it down again?

      Yet that's exactly what NASA engineers recently did.  One of the DSN dishes near Madrid, Spain, needed to be moved to a new pad. And it had to be done gingerly; the dish is a sensitive scientific instrument full of delicate electronics. Banging it around would not do.

      "It was a heck of a challenge," says Benjamin Saldua, the structural engineer at JPL who was in charge of the move. "But thanks to some very careful planning, we pulled it off without a problem!"

      The Deep Space Network enables NASA to communicate with probes exploring the solar system. Because Earth is constantly rotating, a single antenna on the ground can communicate with a probe for only part of the day, when the probe is overhead. By placing large dishes at three locations around the planet-Madrid, California, and Australia-NASA can maintain contact with spacecraft around the clock.

      To move the Madrid dish, NASA called in a company from the Netherlands named Mammoet, which specializes in moving massive objects. (Mammoet is the Dutch word for "mammoth.")

      On a clear day (bad weather might blow the dish over!), they began to slowly lift the dish. Hydraulic jacks at all four corners gradually raised the entire dish to a height of about 4.5 feet. Then Mammoet engineers positioned specialized crawlers under each corner. Each crawler looks like a mix between a flatbed trailer and a centipede: a flat, load-bearing surface supported by 24 wheels on 12 independently rotating axes, giving each crawler a maximum load of 194 tons!

      One engineer took the master joystick and steered the whole package in its slow crawl to the new pad, never exceeding the glacial speed of 3 feet per minute. The four crawlers automatically stayed aligned with each other, and their independently suspended wheels compensated for unevenness in the ground. 

      Placement on the new pad had to be perfect, and the alignment was tested with a laser. To position the dish, believe it or not, Mammoet engineers simply followed a length of string tied to the pad's centre pivot where the dish was gently lowered.

      It worked.  So much for "impossible."

      Find out more about the DSN at http://deepspace.jpl.nasa.gov/dsn/


      It isn't dark until almost midnight now but there are still a few events worth noting.  Mercury reaches greatest elongation on July 9th.  Venus is less than two degrees away at this time and shows about 90% of its illuminated surface and can be used as a guide just after the sun has set.  The moon is also very close on July 8th but shouldn't present too much of a problem being a new-ish moon.  As always, be exceptionally careful when observing anywhere near the Sun!

      Mars is becoming more easily visible in the early morning sky and it shouldn't be long before those with more powerful telescopes will be able to make out surface details, particularly as we get into August.

      On 4th July, NASA's "Deep Impact" mission sends a projectile into the core of Comet Temple 1 at 0600 UTC. It is hoped that data from this event will not only give clues as to what at least one comet is made of, but also may give signs as to the origins of the solar system.  It probably contains material from over 4 billion years ago.

      One of the main events in August is the Perseids meteor shower which has a maximum on about 12th August.  



Chairman          Tim Bance                   01732 832745                                  timbance@hotmail.com

Secretary         Ian Reeves                        01892 784255

Treasurer         Mike Wyles                   01892 542863                                 mikewyles@globalnet.co.uk

Publicity         Michael Harte                       01892 783292

& Web site                                                                                                    michael@greenman.demon.co.uk

Editor            Geoff Rathbone                01959 524727                                 Geoff@rathbone007.fsnet.co.uk

Any material for inclusion in the June Newsletter should be with the Editor by August 30th  2005