Thomas Jones writes:
Last January, a pair of scientists at the California Institute of Technology, Konstantin Batygin and Michael Brown, announced that they had discovered compelling evidence of an as-yet-unseen giant planet – Planet X – orbiting the Sun, seven times further out than Neptune. This isn’t the first time that astronomers have believed there may be nine planets in the solar system. From its discovery in 1930 until 2006, Pluto – smaller than our moon, and nearly forty times as far from the Sun as the Earth is – was considered the ninth. And between 1859 and 1915 it was widely believed, for perfectly sound reasons, that a small planet known as Vulcan lurked invisibly close to the Sun, inside the orbit of Mercury. How that belief came about, and how Einstein came to demolish it, is the subject of Thomas Levenson’s eye-opening book.