Left unmitigated, rising temperatures from climate change will increase inequality and mortality rates in the U.S. by the end of the 21st century, a team of economists and climate scientists warn in a study published today. It's the first to project the impacts of climate change on individual counties in the U.S. Many of those predicted to be hit hardest are in fast-growing Arizona, Texas, and Florida.

Local differences: If steps are not taken to lessen the rate of warming from climate change, counties in the South and lower Midwest — which on average are already poorer and warmer — may lose as much as 20% of their income and may experience higher mortality rates. However, areas of the Pacific Northwest, the Great Lakes region and New England — which tend to be wealthier and cooler — could benefit economically from the change and see lower mortality rates.

Dire warning: The researchers predict mortality will increase by 5.4 deaths per 100,000 people for every one degree Celsius rise in temperature. "We show there are going to be as many additional deaths from climate change as there are car crashes, and possibly more. Of the sectors we looked at, the greatest costs by far to society are going to come from those additional deaths," Rising told Axios. But it would vary by region: in cold northern counties, warming reduces mortality whereas in southern ones it could rise.

Read more here.

• The buzz: Two landmark studies find a common pesticide can hurt bees. A debate has raged around whether neonicotinoids are causing the collapse of bee populations around the world.
• Winning smile: Researchers have broken down the features of a smile that convey emotions. It could inform facial reconstruction surgeries, computer graphics, robotics, and psychology.
• We're weak: A new study says chimps aren't super strong, humans are just weak. Evolution may have selected the ability to chase prey over feats of strength.
• Caregivers need care: Dementia patients whose caregivers are mentally stressed may die sooner. More people are caring for aging friends and family members, raising concerns about the impact on their health.

• Firefly phenomenon: One of the few species of synchronous fireflies exists in Great Smoky Mountains National Park.
• Success story: IEEE profiles how a brain implant helped one Tourette's syndrome patient.
• Spidey brain: New research in spiders supports an old idea that cognition can happen outside the brain, per Quanta.

This week, scientists reported they'd figured out the features of smiles that convey different emotions. The muscles that produce these expressions were first studied in a series of startling experiments by French neurologist Guillaume-Benjamin-Amand Duchenne.

• The experiment: He used small probes to electrically stimulate muscles in the faces of six different people and reproduce various expressions.
• What he found: Duchenne described the muscle actions that produce more than 30 distinct emotions, ranging from doubt and stupefaction to joy and terror (with and without pain or torture). He found that a combination of the muscle that pulls the lips up at the corners and the involuntary action of the orbicularis oculi muscle around the eye produces genuine smiles of happiness.
• The legacy: Darwin wrote about him, a smile and several diseases bear his name, and his claim that a true smile can't be faked has persisted.
• Go deeper: The photos from Duchenne's experiments are wild.

Axios' Erin Ross writes: It's thought that up to 10 tons of extraterrestrial dust lands on Earth each day. Among the deliveries are these tiny, metallic micrometeorites. Scientists normally hunt for the mini space rocks (typically 0.2 to 0.3 mm in diameter) in polar regions and at the bottom of the ocean, where the samples won't be contaminated by industrial pollution. But Jon Larsen, a jazz musician-turned-researcher, found this micrometeorite and others on some rooftops in Europe. He describes the alien dust, and his quest to find it, in his book In Search of Stardust.