ISRO's balloon experiment

Print edition : December 09, 2000

ONE way to test the theory of panspermia is to examine a sample of cometary material under the microscope and search for cometary micro-organisms. In fact, this is one of the chief objectives of the National Aeronautics and Space Administration's (NASA) Stardust Mission and also some other future space missions. There is already accumulated evidence to support the existence of prebiotic chemicals from remote-sensed data of the Comet Halley. The next step in settling the scientific question of panspermia involves the detection of viable micro-organisms from cometary material and inter-stellar space.

Stardust, a U.S. mission launched in February 2000 to collect comet samples.-NASA/ESA/GAMMA

The main aim of the Stardust Mission is to capture a sample of dust from the well-preserved Comet Wild-2 on January 2, 2004, and to return the material safely to the earth on January 15, 2006. The comet dust is to be captured in a tennis-racket-shaped "p article catcher" filled with aerogel, the material with lowest known density. The idea is that the aerogel would act as a soft landing cushion to slow the comet particles from an initial relative speed of 6.1 km a second to rest fairly gently, without si gnificantly altering the original chemical structures.

The Indian Space Research Organisation's (ISRO) ongoing balloon experiment aims to do essentially the same at a fraction of the cost of the Stardust Mission and may produce results well ahead of the NASA experiment.

It is known for some time now that cometary dust is present in the outer reaches of the earth's atmosphere. All that is required is to collect such dust non-destructively and without biological contamination. The ISRO experiment involves the collection o f such material by suction using a balloon-borne cryogenic pump comprising many sterilised chambers fitted with valves and cooled to liquid neon temperatures. When the valves are opened at pre-determined heights - between 15 km and 30 km - the ambient ai r, which will include cometary aerosols, is sucked in. These will be recovered on the ground and will be subjected to chemical and microbial examination under contaminant-free conditions. The flight will have two series of cryo-chambers to allow independ ent microbial analysis in India and the United Kingdom.

Sterilisation techniques that are to be used both in sample retrieval and experimental preparation are expected to achieve levels of microbial sterility that can essentially eliminate even the presence of a single contaminant micro-organism. At the same time, the use of extremely sensitive fluorescent dyes would enable the detection of single viable cells in the collected samples. The difference in the isotopic composition (of C, O and H) between terrestrial and extra-terrestrial bacterial material will be used to identify extra-terrestrial bacteria.

The key parameter that will be measured in the experiment is the microbial density profile with height. The stratosphere is expected to contain a mixture of terrestrial and extra-terrestrial organisms. However, if panspermia is a valid concept and there is a flux of such organisms from cometary material whose density increases with height, one expects the density profile to be U-shaped with a definitive minimum occurring at some altitude; that is, it will gradually drop up to a certain height and pick u p again with the increase of extra-terrestrial organisms higher up. In fact, a component of the experiment - which will include several balloon launches - is to determine this profile at different times, say, when there is a comet pass-by or there is an increase in solar wind which would increase the flux rate into the earth's atmosphere.

In April 1999, ISRO carried out a preliminary balloon flight with cryo-chambers riding piggyback on some other experimental flight. An initial analysis of the collected sample has indicated some surprises. The presence of some bacteria has been seen and analyses on that are in the process of being completed. The microbiological analysis was carried out at the Centre for Cellular and Molecular Biology (CCMB), Hyderabad. The results are expected to be published soon. Apparently, the finding involves known bacteria but its interaction with the environment seems to be somewhat different from what is known on the earth. However, this finding was to be confirmed by repeating it during the balloon experiment flight.

The institutes participating in the ISRO experiment are the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, the Tata Institute of Fundamental Research (TIFR), Mumbai, the Physical Research Laboratory (PRL), Ahmedabad, the CCMB, and the Centre for Astrobiology, University College, Cardiff, Wales. The experiment is coordinated by Jayant V. Narlikar, Director of IUCAA, and N. Chandra Wickramasinghe, director of the Cardiff Centre. The sterilisation and coordination of the microbial in vestigations are carried out by Pushpa M. Bhargava, former director of the CCMB, the other prime mover of the experiment besides Narlikar and Wickramasinghe. The experiment is expected to cost about Rs.1 crore, with the British sources contributing 15 to 20 per cent.

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