60 CHROMATOGRAPHY
Top of the list of the mission objectives is to study the origin of comets, the relationship between cometary and interstellar material, and its implications with regard to the origin of the Solar System. In order to achieve this, the following measurements will be made:
n Global characterisation of the nucleus, determination of dynamic properties, surface morphology and composition;
n Determination of the chemical, mineralogical and isotopic compositions of volatiles and refractories in a cometary nucleus;
n Determination of the physical properties and interrelation of volatiles and refractories in a cometary nucleus;
n Study of the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma (dust/gas interaction);
n Global characterisation of asteroids, including determination of dynamic properties, surface morphology and composition1
.
In order to successfully undertake these measurements, the equipment and instrumentation available on Rosetta and the Philae lander had to be carefully considered.
GC and the Philae Lander Due to their formation from dust particles in the solar nebula, and thanks to the fact that their interiors remain cold, comets are thought to preserve the most unspoiled material in the solar system. When they do get closer to the sun, volatile components and dust particles are released which creates the cometary data. Billions of years ago, it is believed that material from comets was delivered to the Early Earth, and it is thought that by understanding the physico- chemical structure of comets,
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we will gain an insight into the development of Earth and, excitingly, the initial conditions that prompted the start of life on Earth.
To better understand this, the Rosetta mission spacecraft consists of two main elements: the Rosetta space probe orbiter, which features twelve instruments, and the Philae robotic lander, which consists of ten. Te lander’s instruments weigh 26.7 kilograms (59lb), making up nearly one third of its mass. Tese include:
n APXS (Alpha Proton X-ray Spectrometer), to analyse the chemical element composition of the surface below the lander;
n COSAC (Te Cometary Sampling and Composition) Te combined gas chromatograph and time of flight mass spectrometry will perform analysis of soil samples and determine the content of volatile components;
n PTOLEMY, gas chromatograph analyser;
n MUPUS (Multi-Purpose Sensors for Surface and Sub- Surface Science);
n ROMAP (Rosetta Lander Magnetometer and Plasma Monitor)2
.
Gas chromatography (GC) is a vital part of the Rosetta project as it enables the mission to characterise, identify, and quantify volatile cometary compounds, including larger organic molecules, through in situ measurements of surface and subsurface samples 3,4
.
As shown, the Philae lander counts two gas chromatographs (COSAC and PTOLEMY) among its equipment. COSAC consists of eight capillary GC columns while PTOLEMY is a GC/MS system with three columns.
As with every piece of equipment on the lander, these needed to be specifically chosen to meet with the unique task of carrying out GC in a completely foreign environment, away from the support of laboratory personnel.
Agilent Technologies supplied two capillary GC columns to COSAC– an Agilent J&W Carbobond (specially made for this mission) and an Agilent J&W CP-Chirasil-DEX CB, and additional three columns to PTOLEMY– an Agilent J&W CP-PoraPLOT Q, an Agilent J&WCP-Molsieve 5A and an Agilent J&W CP-Sil 8 CB – for use within the Philae lander.
Fig. 2. Rosetta is the first mission to engage with a comet, accompany it on its orbit, and deploy a lander.
Photo: ESA/ATG Medialab
Tere were some major obstacles to be considered when deciding on which instrumentation to take up to the comet – the lack of access after launch, the durability required for such a long mission, and the broad range of potential samples, to name a few.
Of key importance to the mission is using columns comprehensively tested for column bleed, inertness, efficiency and consistent reproducibility. Optimal peakshape symmetry with low-level response contributes greatly to the reliability and efficiency of the instrumentation to deliver accurate results back to the analysts on the ground. In this way, the ESA researchers are assured that the information they are receiving is dependable.
Te three types of Agilent J&W GC columns provided for use within the lander held a variety of features which made them particularly suited to meeting this challenge.
Initially, the Agilent J&W CP- PoraPLOT Q column is capable of analysing both polar and non-
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