Devangshu Datta: Icarus revisited

TECHNO BEAT

When the Genesis capsule crashed into the Utah Desert on September 8, science-fiction buffs recalled the Arthur C Clarke classic The Wind from the Sun.

The present crash sets back an epic project designed to analyse solar wind, as the stream of ions driven out by the sun's internal furnaces is known.

Clarke's story, published in distant 1963, centred on a race between yachts powered by solar wind. He speculated that extremely thin sails measuring thousands of square kilometres in terms of surface area could be deployed to capture solar wind. The acceleration would be minimal but continuous. Eventually, a "sunjammer" might become the fastest object in the universe.

In the near-vacuum of outer space, solar wind is found everywhere. Ions are electrically charged atoms stripped of free-wheeling electrons; these react to magnetic fields.

Solar wind mostly flows outside the magnetic field of the earth (and other planets). When it does interact with a magnetic field, the effects are spectacular. The Aurorae-coloured lights in the sky often visible at either pole "" are caused by interactions between ions and the earth's magnetic field.

Pure solar wind, uncontaminated by planetary magnetism, can provide vital clues about the sun's composition. The Genesis robot was launched in August 2001 to collect samples of solar wind.

Genesis was sent to a Lagrange Point (LP), an area in space where the gravitational pulls of earth and sun are balanced. An stationary object stays indefinitely at rest within an LP in accordance with Newton's First Law.

LPs are found far beyond the magnetic field of the third rock from the sun. Hence, pure solar wind samples can be collected and Genesis did just that for over two years.

The sun produces massive quantities of heat, light and other forms of energy and will do so for millions of years. The energy is released by nuclear fusion: elements are combined to produce heavier elements.

The commonest reaction is the fusion of hydrogen (the lightest and most common element in the universe) to produce helium (number two on the "light & common" list). But heavier elements are also combined in fusion.

An examination of solar wind should yield reasonably accurate guesses about the proportions of elements in the sun. In turn, that would allow more refined inferences about physical conditions there and about the nature of planet formation and composition.

The solar particles were carefully sealed for protection on the return journey. Samples were stored in a disc-shaped capsule some 1.6 metres in diameter.

This contained a few grains of solar wind embedded in protective wafers made of sapphire, silicon, diamond and gold. Each type of wafer was designed to protect samples that would be analysed for concentrations of different elements.

The spacecraft was designed to release the capsule some 30,000 metres above sea-level after making the return journey from the LP. The release was perfect in terms of navigation and distance.

The capsule was supposed to float slowly down on a multi-parachute system. Two helicopters were to try and grab the chutes with hooks while the capsule was still in flight above the Utah Desert.

Unfortunately the parachutes didn't open and the choppers didn't have a hope. The capsule crashed well within the target zone, but hit the ground at 300 km/ hr. Despite the robust design, samples were lost and contaminated, though enough may have survived to make Genesis a qualified success.

The main priority was to detect and measure isotopes of oxygen and nitrogen. These two gases are respectively present in a ratio of roughly 21 per cent to 78 per cent in the earth's atmosphere. All other gases together account for the remaining 1 per cent of atmosphere.

Enough oxygen and nitrogen samples appear to have survived, though experiments for other elements will be hindered by contamination. Many samples have survived but in varying condition.

The next few years will be spent trying to recover these. Perhaps somebody will also be paying attention to the task of designing a chute system that opens on schedule!