“Faster, mommy, faster!” Allison’s toddler squealed as she ran down the hill by her house with her jogging stroller. As a longtime runner and running biomechanics researcher, she found herself in the same situation as many parents of young children: squeezing in runs between work meetings, meal prep and nap schedules.

A running stroller...

Mars, one of our closest planetary neighbors, has fascinated people for hundreds of years, partly because it is so similar to Earth^[1]. It is about the same size, contains similar rocks and minerals, and is not too much farther out from the Sun.

Because Mars and Earth share so many features, scientists have long wondered whether Mars...

Curious Kids^[1] is a series for children of all ages. If you have a question you’d like an expert to answer, send it to This email address is being protected from spambots. You need JavaScript enabled to view it.^[2]. How was the Earth built? – Noah, age 5, Florida It isn’t easy to figure out how the Earth was built, because it happened 4½ billion years ago, and no one was there to