WASHINGTON (Reuters) - The oldest planet ever detected is nearly 13 billion years old and more than twice the size of Jupiter, locked in orbit around a whirling pulsar and a white dwarf, astronomers said on Thursday. Compared with the relative youth and stability of our own celestial neighborhood, where Earth and the other planets orbit a single 5-billion-year-old star in a quiet neighborhood of the Milky Way, the ancient group that holds the oldest planet has had a boisterous past, scientists said at a NASA (news - web sites) briefing. The old planet is located near the heart of...