Two travelers from far beyond Neptune return home

TUCSON, Ariz. — Two visitors from the edge of the solar system appear to be returning to their birthplace. One is made of rock, the other slathered in organic compounds; neither looks like other bodies from the Oort cloud, the icy debris field that envelops the solar system. The objects may be relics from the solar system’s formative years, thrown to the Oort cloud while the planets were still forming over 4 billion years ago.

One body, designated C/2013 P2 Pan-STARRS, is making a rare appearance as it loops around the sun once every 51 million years. Karen Meech, a planetary scientist at the University of Hawaii in Honolulu, and colleagues discovered the object in August 2013, when it was about three times as far from the sun as Earth is.