Pipes have now been put in place in Lake Nyos and nearby Lake Monoun to siphon water from the lower layers up to the surface and allow the CO2 at the bottom of the lake to slowly bubble out, preventing a repeat of 1986 tragedy.

BBC: 1986: Hundreds gassed in Cameroon lake disaster

Observations from orbit have identified clay and sulfate minerals in the lower layers, indicating a wet history.

ENGADGET: NASA's Curiosity rover receives long-distance OTA update, 'brain transplant' on Mars

Though Texas increasingly looked like a broad, bragging California, full of high-tech clusters and with the white Anglo culture besieged by Latinos and Asians, Mrs Richards was well aware of the unchanging lower layers.

ECONOMIST: Ann Richards

But those lower-energy X-rays can be further distorted by layers of gas between the black hole and the Earth, and previous spin observations have been contentious.

BBC: First glimpse of a black hole's spin