Thirty Meter Telescope

Astronomy's next generation observatory.


Alternate Site Studies

The Thirty Meter Telescope International Observatory (TIO) selected Maunakea, in Hawaii, as the preferred site to build and operate TMT. However, in December 2015, the Hawaii Supreme Court ruled that the state’s permitting process was flawed, and the State Board of Land and Natural Resources was ordered to re-do the permit process. TMT is currently working to regain the required permit and start onsite construction in Hawaii. While Maunakea continues to be TIO’s preferred site, TMT has investigated alternative sites to ensure construction can begin in a timely fashion.

Alternate Site Studies Process and Report

From February 2016 through October 2016, four potential sites for the TMT were evaluated to provide an alternative location for the observatory. Although Maunakea remains the preferred setting for building TMT, an alternate site is needed for the case that access to Maunakea is not possible in a timely way. All of the alternative sites considered were excellent for carrying out the core science of the TMT and the interactions with potential host countries and organizations were uniformly very positive. On October 31st, 2016, the TIO Board of Directors selected the ‘Observatorio del Roque de Los Muchachos’ (ORM), in La Palma, on the Canary Islands (Spain) as the alternate site for TMT.


  • A report describes the selection studies and process.
  • A one-page document describing the Maunakea and Observatorio del Roque de Los Muchachos (ORM) site characteristics.
  • A one-page document describing the characteristics of the five sites studied for TMT.