Cash offer: a €1bn package has been turned down by the Thirty Meter Telescope International Organization. (Courtesy: TIO)

Members of the Thirty Meter Telescope (TMT) International Organization have turned down Spain’s €1bn offer to build the instrument at the Roque de los Muchachos Observatory in La Palma. The package was put forward in July with funding also provided from the European Investment Bank and Spain’s Official Credit Institute. The decision makes Hawaii’s Mauna Kea as the only possible option for the telescope.

The TMT, if built, would use a segmented primary mirror consisting of 492 elements of zero-expansion glass for a 30 m-diameter primary mirror that will allow astronomers to resolve the faintest and oldest galaxies.

The TMT’s members include the University of California, the California Institute of Technology, Canada, India, and Japan.

Officials at the TMT have not released a final construction cost for the telescope, but it is expected to be at least $3bn, of which $2bn has been…