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(left to right): DARPA; DAVID DOUBILET/NATIONAL GEOGRAPHIC IMAGE COLLECTION; NASA/JPL-CALTECH/UCLA

Top stories: Hypersonic weapons, acid waters, and interstellar comets

‘National pride is at stake.’ Russia, China, United States race to build hypersonic weapons

The U.S. military—and its adversaries—has long coveted hypersonic missiles, which travel at roughly five times the speed of sound. But until recently, the technical challenges of creating them have proved “a bridge too far.” Now, with advances in maneuverability, materials, and engine design, the United States, China, Russia, and other countries are pouring money into a new arms race.

Analysis challenges slew of studies claiming ocean acidification alters fish behavior

For more than 10 years, marine scientists have warned that seawater acidified by rising carbon dioxide—which threatens creatures with carbonate shells and skeletons—could also cause profound changes in the behavior of fish on tropical reefs. A paper published in Nature this week challenges a number of those findings, and suggests acidification might not lead to disoriented or hyperactive fish, after all.

How many of our comets come from alien solar systems?

Comets were long thought to come from our Solar System, made from the leftover gas and rocks pitched out as planets formed. But the recent arrival of two interstellar objects—a rock named ‘Oumuamua and a flashy comet called Borisov—has brought that assumption into question.

Russian journals retract more than 800 papers after ‘bombshell’ investigation

Academic journals in Russia are retracting more than 800 papers following a probe by a commission appointed by the Russian Academy of Sciences into unethical publication practices. The moves come in the wake of several other inquiries, suggesting the vast Russian scientific literature is riddled with plagiarism, self-plagiarism, and so-called gift authorship, in which academics receive co-authorship without having contributed any work.

How a chunk of human brain survived intact for 2600 years

Nearly 2600 years ago, a man was beheaded near modern-day York, U.K.—for what reasons, we still don’t know—and his head was quickly buried in the area’s clay-rich mud. When researchers found his skull in 2008, they were startled to find that his brain tissue, which normally rots rapidly, had survived for millennia—even maintaining features such as folds and grooves. At long last, researchers think they know why.