A few weeks ago I wrote a piece on this blog asking the question what is our solar system made of? I explained our need to know the composition of the starting material from which our solar system formed. The solar photosphere is believed to be relatively unchanged from the average composition of the solar nebular, and hence represents the average initial composition of the solar system. The sun itself is much too hot to be sampled directly, but we can access it through the solar wind.
NASA’s Genesis mission collected samples of the solar wind and returned them to Earth for chemical analysis. The aim is to measure the elemental and isotopic composition for most elements. The data will then enable us to improve our understanding the processes by which our solar system formed and evolved.
The Genesis spacecraft launched on the 8th August 2001, onboard a Delta rocket from Cape Canaveral. After a 1,500,000 km (930,000 miles), 3 month journey through space, it reached its destination – a point known as Lagrangian Point L1, where the gravity of the Earth and Sun cancel each other out. The spacecraft spent 2 and a half years orbiting around L1, facing the sun. During this time, solar wind ions were implanted into collector arrays.
The collector arrays were about the size of a bicycle tyre, made up of about 55 individual 10cm hexagon wafers. These hexagons were made from 15 different types of high-purity materials including aluminium, sapphire, silicon, gold and diamond-like carbon. The materials were chosen for their durability, purity, cleanliness, ability to retain solar wind and ease of analysis.
The bulk collector arrays continually sampled the solar wind for 884 days, while separate arrays sampled the different “types” or regimes of the solar wind.
The sample capsule returned to Earth on the 8th September 2004. It was important to make sure the capsule did not hit the ground, as this could damage the delicate collector targets. The plan was that parachutes would open, slowing the capsule’s descent, and then crazy stuntmen hanging out of a helicopter would use something akin to a long fishing rod to catch it midair.
Unfortunately this part of the mission did not go to plan. The parachutes failed to open, and the sample capsule hit the ground at 193 miles per hour. The impact caused severe damage to the capsule and the collector targets inside.
The capsule was taken to the Johnson Space Center in Houston, where a team set about assessing the damage and trying to determine whether anything could be recovered. Check back again soon to find out how they got on…