Norbert Reuter and Gary Lee explore the way in which gas chromatography columns are making a difference to analysis being carried out thousands of miles from home.
In 1999, the European Space Agency (ESA) started the Rosetta Mission. This ground breaking venture would be the first ever landing of a man-made spacecraft on a comet, providing an unprecedented insight into what goes on beyond our atmosphere. With the analysis taking place outside the confines of a laboratory, it was essential that the equipment on board Rosetta was completely reliable and capable of sending back accurate, valuable information to researchers on the ground.
Launched in March 2004 on an Ariane 5 rocket and controlled from the European Space Operations Centre (ESOC), in Darmstadt, Germany, Rosetta is the first mission in history to engage with a comet, accompany it on its orbit of the Sun, and deploy a lander onto its surface. During its journey towards comet 67P/Churyumov-Gerasimenko which took place over a decade, the spacecraft has already been passed by two asteroids: 2867 Steins in 2008 and 21 Lutetia in 2010.
The probe is named after the well-known Egyptian Rosetta stone, which features a decree in three individual languages. Meanwhile, the lander is named after the Nile island Philae – it was here that an obelisk was discovered with inscriptions that, when compared with the Rosetta stone, provided a greater understanding of the Egyptian writing system. Similarly, it is hoped that these spacecraft will further our knowledge of comets and the early Solar System.
Following its launch, Rosetta needed several acceleration bypasses by Earth and Mars to finally follow the path of 67P/Churyumov-Gerasimenko‘s and will arrive at the comet in August 2014 with the lander deployed in November. The mission will orbit the comet for 17 months and undertake the most detailed study of a comet ever attempted.
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:
* Global characterisation of the nucleus, determination of dynamic properties, surface morphology and composition;
* Determination of the chemical, mineralogical and isotopic compositions of volatiles and refractories in a cometary nucleus;
* Determination of the physical properties and interrelation of volatiles and refractories in a cometary nucleus;
* Study of the development of cometary activity and the processes in the surface layer of the nucleus and the inner coma (dust/gas interaction);
* 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, 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. The lander’s instruments weigh 26.7 kilograms (59lb), making up nearly one third of its mass. These include:
* APXS (Alpha Proton X-ray Spectrometer), to analyse the chemical element composition of the surface below the lander;
* COSAC (The Cometary Sampling and Composition) The combined gas chromatograph and time of flight mass spectrometry will perform analysis of soil samples and determine the content of volatile components;
* PTOLEMY, gas chromatograph analyser;
* MUPUS (Multi-Purpose Sensors for Surface and Sub-Surface Science);
* 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.
There 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.
The 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-polar volatile compounds, giving it a broad applicability – a great advantage when trying to limit the amount of instrumentation on the lander, while still ensuring all needed measurements could be carried out. Q type porous polymer columns with repeatable retention times for long term stability are especially important for ensuring efficiency and reliability throughout the mission.
This focus on efficiency is mirrored in the other GC columns installed in the Philae robotic lander. The Agilent J&W CP-Molsieve 5Å was selected for separation of permanent gasses such as helium, hydrogen, xenon, and argon. With its high efficiency and symmetrical peakshape performance, this PLOT column plays an important role to accurately monitor the composition of these noble gases on the comet surface and in the atmosphere.
The third GC column – an Agilent J&W CP-Sil 8 CB – has a general purpose ‘5% phenyl-‘ stationary phase which provides selectivity and temperature limit that has been classically used for a broad range gas phase separations including environmental semivolatile compounds.
The fourth GC column, the Agilent J&W Carbobond which was specially designed for this mission is Agilent’s unique Ultimetal treated stainless steel column design which is able to separate the typical permanent gases we find in our atmosphere with the addition of some light hydrocarbons as well as carbon monoxide and carbon dioxide.
The fifth and final GC column, the Agilent J&W CP-Chirasil-DEX CB, is a uniquely bonded chiral phase to separate and identify compounds in racemic mixtures (like mirrored images or the left hand to the right hand) – which often occur in nature.
All the columns provided to the Rosetta mission are produced with the sole aim of delivering accurate data quickly while requiring little to no maintenance. This range of column chemistries and selectivites combined with the level of quality and reliability is an essential element mirrored throughout the design of Rosetta and Philae programmes. They are capable of undertaking delicate, sensitive readings in foreign environments, and deliver precisely the data required to draw some real conclusions.
Summary
The Rosetta mission is a milestone project, and could shortly be providing researchers with valuable information that will assist our understanding of the early stages of the Earths, and our own, development. This would not be possible without accurate, efficient equipment which the ESA could confidently send to meet the comet 67P/Churyumov-Gerasimenko.
Agilent J&W GC columns have long set a standard for the highest level of performance and reliability, thanks to constant improvement, years of experience and industry-leading testing to ensure column to column consistency. It is these standards which make them suited for this unique project and, come November 2014 (at the time of going to press), will play a role in generating the first set of highly anticipated data.
Norbert Reuter is Channels Support Organisation manager and Gary Lee is GC Columns product manager, with Agilent Technologies.
References:
1 ESA Rosetta Mission. Accessed online 01 July 2014. http://sci.esa.int/rosetta;
2 Rosetta (spacecraft). Accessed online 01 July 2014. http://en.wikipedia.org/wiki/Rosetta_%28spacecraft%29;
3 COSAC, THE COMETARY SAMPLING AND COMPOSITION EXPERIMENT ON PHILAE. FRED GOESMANN et al. 2006. http://ipag-3.obs.ujf-grenoble.fr/homepages/IMG/pdf/cosac.pdf;
4 PTOLEMY – AN INSTRUMENT TO MEASURE STABLE ISOTOPIC RATIOS OF KEY VOLATILES ON A COMETARY NUCLEUS. I.P. WRIGHT et al. 2006. http://ipag-3.obs.ujf-grenoble.fr/homepages/IMG/pdf/ptolemy.pdf
