Satellite 'Aura' launch delayed

By Richard Black
BBC science correspondent

Aura completes the land, water and air series

The US space agency has delayed its launch of Aura, a satellite designed to check the health of the Earth's atmosphere.

The launch due on Sunday has been delayed for two days for technical reasons, officials said.

The Aura will peer through the stratosphere and troposphere, down to the air we breathe on the ground.

It will test whether international treaties such as the Montreal Protocol to repair the ozone layer are working.

The three-tonne spacecraft will also help scientists understand how atmospheric composition affects and responds to Earth's changing climate.

It has been due to launch from the Vandenberg Air Force Base, California, on Sunday.

Nasa says Aura is one of the most sophisticated environmental monitoring satellites ever built.

It is the third in the agency's series of satellites aimed at providing definitive data on the global environment.

The spacecraft promises significant returns for climate studies

The first two, Terra and Aqua, are studying the ground and the oceans. Aura will concentrate on the atmosphere, looking at gases, pollutants, and chemical reactions.

"Aura's going to be very helpful in tracking whether the ozone layer is recovering, in establishing the relationship between particulates and atmospheric gases and climate change; and Aura will hopefully also be a very useful tool in developing better predictions of air quality," Rick Pickering, Aura Project Manager at the Goddard Space Flight Center, told BBC News Online.

Last year, scientists produced the first concrete evidence that the ozone layer is in the process of recovering (even if the hole is presently getting bigger) after decades of damage caused by substances like CFCs.

But a return to full health will take about 50 years by current estimates - and global warming could change that timescale.

On climate change itself, one outstanding issue is the role of tiny particles in the atmosphere.

These aerosols, typically containing sulphur or carbon, come from natural sources, such as volcanoes, and from human sources, such as the soot from fossil fuel burning.

The ozone "hole" is still growing - but not as fast as it once was

Aerosols are an important but uncertain agent of climate change. By absorbing or scattering radiation, they can either warm or cool the troposphere. They can also modify clouds and affect precipitation.

If Aura can help scientists understand precisely what these particles are doing, how they behave and what they mean for the future of the global climate, that would be a significant return on the satellite's billion-dollar cost.

Aura has four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS); the Microwave Limb Sounder (MLS); the Ozone Monitoring Instrument (OMI); and the Tropospheric Emission Spectrometer (TES).

HIRDLS was built with a substantial UK contribution.