Canary Islands Announced as TMT 2nd Site

[TomK]

I suspect there were only two real possibilities for an alternative site, La Palma or San Pedro Martir in Mexico. The Mexican site is higher, but not by a huge amount (roughly 1500 feet higher). That would have benefited infrared observations, but it's still quite low for decent mid-infrared astronomy. Although both are regarded as "dark" sites, I think La Palma has slightly worse light pollution. Overall, though, my guess is the decision was influenced by La Palma's existing infrastructure, meaning the TMT would likely become operational more quickly there.

Chile has great sites, but to have all three of the world's giant optical telescopes in the southern hemisphere doesn't make a lot of sense.