ARECIBO, PUERTO RICO — For 57 years, until 2016, the Arecibo Observatory was the largest telescope on Earth.
But that legacy came crashing down last week, just when a regional earthquake's wave train passed through the site.
The collapse occurred when the tops of all three support towers snapped off, dropping the huge detector platform and its support cables onto the giant reflector dish below.
This collapse had been expected since a second support cable broke on 6 November, following the previous failure of a support cable in August.
Initial studies of the debris field indicate that the failure sequence started when a highly stressed cable in the weakened cable strand finally snapped, causing the central detector platform to detach and fall straight down.
That platform's support structure fell sideways into the side of the crater, suggesting that it stayed attached to the remaining two cables and swung sideways.
Engineers assume the tops of all three support towers snapped off when one of the three cable strands finally failed completely, causing enormous lateral stresses in directions that the towers were not designed to support.