Planned new telescopes, including the Thirty Meter Telescope, have attracted controversy due to their potential cultural and ecological impact. The multi-telescope outrigger extension to the Keck telescopes, which required new sites, was eventually canceled. Three or four of the mountain's 13 existing telescopes must be dismantled over the next decade with the TMT proposal to be the last area on Mauna Kea on which any telescope would ever be built.