US: Particles from the solar wind could tell us about the materials that formed our galaxy, writes Dick Ahlstrom
Scientists will get a remarkable new view of the sun later this afternoon when the first extraterrestrial samples recovered since 1972 parachute into the Earth's atmosphere.
A metal canister jettisoned from a passing spacecraft will ferry solar particles captured in space back to Earth for analysis.
The canister's precious cargo, space dust from the sun, returns after a 36-month effort to recover particles from the solar wind, the blast of material continually ejected from the sun's surface. Scientists hope the dust will give them samples of the very stuff from which the solar system was built billions of years ago.
The canister's recovery over the Utah desert in the US represents the end of the Genesis mission organised by NASA. Genesis launched on August 8th, 2001, and arrived in deep space well beyond the moon, where for 850 days through to April 1st, 2004, it collected particles carried on the solar wind.
The canister is expected to bear no more than 10 to 20 micrograms - equivalent to a few grains of sand - of solar wind particles but this will be plenty to allow a first-time look at material coming directly from the sun.
Scientists believe the matter making up the solar wind resembles the dust, gas and ice from which the various bodies of our solar system evolved. Most of the solar wind is made up of hydrogen and helium, but studies suggest it also carries small amounts of more than 60 other elements.
Its recovery should give important new insights into the composition of the sun, but also information about the raw materials that went into the formation of the solar system.
The $264 million (€220 million) mission concludes today at about 5.30 p.m. Irish time with a dramatic helicopter recovery of the canister, expected to be carried live over the web by NASA television.
In true Hollywood style, two stunt pilots will attempt to snag the parafoil chute bearing the canister using 4 m-long hooks deployed underneath two chasing helicopters.
While the effort looks more like theatre than real science, NASA claims it has a good reason for the mid-air capture. The Genesis spacecraft carries delicate collector arrays that hold the solar wind particles and its designers fear that even a soft parachute landing could damage the collectors.
The bicycle-wheel-sized collector carries arrays that are suitably exotic for such a mission. Spacecraft designers chose precious materials including gold, sapphire, diamond and silicon to entrap solar wind particles.
The collector was able to record the speed, density, temperature and approximate composition of the solar wind particles and an electron monitor kept track of the numbers of these particles arriving from the sun.
"The science canister on the spacecraft contains the precious solar wind particles in their original state, protected from breakage and contamination with terrestrial material during launch and recovery," according to Dr Donald Burnett, Genesis principal investigator at the California Institute of Technology in Pasadena.
The trick now is to prevent the canister from crashing on the desert's surface over the Utah Testing and Training Range of the US Air Force. On May 2nd, Genesis conducted an Earth fly-by, positioning itself for today's daylight recovery.
The canister will be ejected into the atmosphere at 3.55 p.m. Irish time and at about 33 km (108,000 feet), a parachute will open to slow the capsule. Six minutes later, the parafoil opens at 6.1 km (20,000 feet), beginning a slow descent to the surface.
The two helicopters will be waiting to snag the chute as the canister descends, after which the cargo will be shipped to NASA's Johnson Space Centre, Houston, Texas, for analysis. Genesis handlers have a fallback position should any targeting problems arise, with the spacecraft diverted into a holding pattern in orbit and a second entry attempt in 24 days' time.
"The mission will deliver good science," improving the quality of information available to us on the composition of the sun, stated Prof Luke Drury of the Dublin Institute for Advanced Studies.