MAYBE IT’S TIME TO ADJUST EXPECTATIONS: A tiny world beyond Neptune has an atmosphere that shouldn’t exist. “In the cold reaches of the outer solar system lie thousands of small objects known as trans-Neptunian objects (TNOs) because they lie outside the orbit of Neptune. A thin atmosphere has been observed around Pluto, the most famous TNO, but studies of other TNOs have yielded negative results. Most TNOs are so cold, and their surface gravity so weak, that they are not expected to retain atmospheres.”