UKRAINE

A 360-foot-tall steel and concrete hangar now covers Chernobyl's reactor 4, site of the 1986 nuclear meltdown. The structure replaced a leaking shield that was installed immediately after the disaster—and should prevent more radioactive debris from escaping.

MEXICO

Archaeologists discovered that the famed Kukulcán pyramid at Chichén Itzá is made up of three pyramids nested within one another. They theorize the structure was built in three phases: the innermost pyramid during the years A.D. 550–800, the middle layer in 800–1000 and the outermost layer in 1050–1300.

SPAIN

Scientists in the Canary Islands had to halt research projects for two months while waiting for a shipment of 29 transgenic mice. Commercial airlines to the islands had decided to stop transporting laboratory animals, citing safety concerns. A military plane eventually delivered the goods.

CHINA

The first clinical trial to employ cells edited by the genetic tool CRISPR/Cas9 is now under way in China. Three more are scheduled to begin next month. In all four, humans are injected with modified immune cells that researchers hope will fight targeted cancers.

INDONESIA

Particulate pollution from a string of wildfires in 2015 may have led to as many as 17,270 premature deaths from respiratory illness across Southeast Asia, according to a new report. The fires were intentionally set to clear land but grew out of control and burned through at least 6.4 million acres. They most likely were exacerbated by drier than usual El Niño weather.