By Paul Rincon
Science reporter, BBC News, Cerro Paranal, Chile
European astronomers are planning to build an optical telescope that is four times as big as any in existence.
Astromoners hope the ELT will reveal celestial secrets
With a main mirror around 42m-wide, the Extremely Large Telescope (ELT) will allow remote objects to be studied in greater detail than ever before.
The powerful observatory will allow astronomers to see some of the first galaxies to form in the Universe.
It could also look for the signatures of life on distant planets circling other stars.
The European Southern Observatory (Eso) operates the 8.2m Very Large Telescope (VLT) at Cerro Paranal in Chile, which has been described as a "discovery machine".
An average of 1.5 scientific papers published each day is based on observations carried out at the VLT.
Eso is now scoping out a new facility that it hopes will instigate a new era in astronomy.
"We have a working area which is 42m, which is the average area between 30m and 60m," said Dr Andreas Kaufer.
"We want to present a full concept by the end of the year. It may be a bit ambitious, but we believe it is feasible."
Dr Kaufer admitted plans for the ELT had been partly driven by competition with the US, which is planning its own 30m telescope.
"We want to do something a bit bigger," he said.
Eso had previously looked at the feasibility of building a telescope 100m in size - around the size of all the telescope mirrors in the world put together.
The review board set up to evaluate the idea agreed it was feasible, but expressed concern over the cost of the project, which was projected to reach around 1.5bn euros (£1bn).
Instead, the project was scaled down to a 30-60m telescope.
The telescope would allow astronomers to see further into the Universe than has ever been possible before. This will allow them to see distant - and therefore very old - galaxies.
These would include some of the first ever galaxies to form in the Universe and also where the first stars formed.
"We want to see how the first galaxies developed. In astronomy, looking faint, looking far, also means looking far back in time," said Dr Kaufer.
"That is one of the big questions in astronomy - how did the Universe develop."
Back to the beginning
With a 100m telescope, astronomers may have been able to produce images of planets about the same size as Earth circling other stars. But this may be beyond the capabilities of a 42m telescope.
However, it could allow scientists to study the atmospheres of so-called extrasolar planets, looking for the spectral signatures of life such as methane gas and chlorophyll, the pigment used for photosynthesis by plants and cyanobacteria.
Eso officials say construction could begin as early as 2010-11.
Vista will view the skies through infrared wavelengths
But there is still no agreement over where to site the project. Large observatories like the VLT need to be located in remote, dry places with cloud-free skies for best observing conditions.
Sites under discussion include South Africa, Tibet, Morocco, Greenland and Antarctica.
Near to Eso's VLT site in Chile's Atacama desert, a UK-funded large observatory is nearing completion. Vista (Visible and Infrared Survey Telescope for Astronomy) will use infrared wavelengths to detect objects that are too distant or too cool to be seen using the visible spectrum.
The steel structure that will hold Vista's primary mirror in place has now been shipped to Chile and installed inside the telescope enclosure.
Project scientist Jim Emerson said he hoped the first pictures from the telescope will come as early as next summer.