Cosmic rays

The Crab Nebula in Taurus
The Crab Nebula in Taurus. It is the remnant of a supernova explosion at a distance of about 6,000 light-years, observed almost 1,000 years ago, and a source of cosmic rays. (Image: ESO)
A bank of cosmic ray detection equipment at Mawson station.

The sun's vast magnetic field and its solar wind plasma (outward-flowing ionised gas) are big influences on radiation intensity in near-Earth space. Solar flares can generate dramatic increases in radiation near the Earth and on rare occasions at the Earth's surface. Understanding such radiation is essential for our studies of space weather, which influences satellite communication systems, for high altitude air transport and space research generally.

Cosmic rays are made up of very high-energy charged particles which are affected by magnetised regions of the inner solar system that they pass through. They are normally harmless, but sometimes can create havoc with increasingly sophisticated electronic systems around the world, particularly satellite communications systems. Finding ways to forecast these bursts of cosmic energy is an immediate, practical, reason for cosmic ray research. A broader purpose is to improve our understanding of the radiation environment in near-Earth space. By examining how cosmic ray variations change with energy between the northern and southern hemispheres and over the whole range of latitudes in each hemisphere, information can be obtained about the nearby radiation environment that cannot be detected by optical, radio, x-ray or other astronomical techniques.

At Australia's Mawson research station, in Antarctica, the Bureau of Meteorology operates a combined surface and underground observatory providing data to an international research network. This observatory, which houses the world's only underground detectors at polar latitudes, is the largest such complex in the Southern Hemisphere. It provides for viewing of certain directions in the sky that are inaccessible from other latitudes and allows easier extraction of information than any other cosmic ray installation. Surface observations at Kingston, Tasmania, are also collected by the Bureau of Meteorology.

Besides affecting cosmic rays approaching Earth, the sun generates magnetic storms which reach Earth about four days later. These storms, known as space weather, can create havoc with satellite systems - and sometimes even ground based systems like electric power grids. On rare occasions, the sun can even blast the Earth with its own form of cosmic radiation. In space, these sudden radiation bursts can be many hundreds or even thousands of times higher than normal, and even at sea level can for short periods increase background radiation by up to four times (though this is not hazardous to people). The multi-year Mawson data record is being used to find ways to predict space radiation storms up to two days in advance, allowing time to minimise their effects.

The amount of cosmic radiation increases with altitude and is also higher near the magnetic poles. Australian Antarctic data is used in studies of long-term radiation risks that cosmic radiation (including the rare solar cosmic ray bursts) may pose for astronauts and high altitude aircraft crews, particularly those working on polar routes. As part of these studies the Mawson observatory has been included in a US-Russia-Australia collaboration known as Spaceship Earth, to collect and deliver real-time space radiation measurements to satellite and aircraft operators and other industries sensitive to space weather effects. The special characteristics of the chosen observatories will allow the radiation to be determined almost instantaneously over any point on Earth.