Solar analog (–0.21) for solar twin. 16 Cygni B is sometimes noted as twin, but is part of a triple star system and is very old for a solar twin at over 9 Gyr. Another way of defining solar twin is as a "habstar" — a star with qualities believed to be particularly hospitable to an Earth-like planet. Qualities considered include variability, mass, age, metallicity, and close companions. The requirement that the star remain on the main sequence for at least 3 Ga sets an upper limit of approximately 1.5 solar masses, corresponding to a hottest spectral type of F5 V. Such
Pioneer Terra Pioneer Terra Pioneer Terra is a region on the dwarf planet Pluto, north of Tombaugh Regio and east of Voyager Terra. It was discovered by the "New Horizons" spacecraft on 14 July 2015. It is named for the "Pioneer" program, which included "Pioneer 10" and "Pioneer 11", the first spacecraft to cross the asteroid belt and explore Jupiter and Saturn, as well as the first to explore the outer solar system; "Pioneer 6, 7, 8, and 9", which formed an "interplanetary weather network"; "Pioneer 1" through "5", which explored the Moon in various ways; and the Pioneer Venus project, consisting