Planet found orbiting backward between two stars
While our Sun prefers to go solo, many other stars are parts of binary systems, with a pair of stars gravitationally bound to each other. In some cases, the stars are far enough apart that planets can form around each of them. But there are also plenty of tight binary systems, where the stars orbit each other at a radius that would place them both comfortably inside our Solar System. In these systems, exoplanets tend to be found at greater distances, in orbits that have them circling both stars.
On Wednesday, scientists described a system that seems to be neither of the above. It is a tight binary system, with a heavy central star that’s orbited by a white dwarf at a distance two to three times larger than Earth’s orbit. The lone planet confirmed to be in the system is squeezed in between the two, orbiting at a distance similar to Earth’s distance from the Sun. And, as an added bonus, the planet is orbiting backward relative to the white dwarf.
Orbiting ν Octantis
The exosolar system is termed ν Octantis (or Nu Octantis), and its primary star is just a bit heavier than our Sun (1.6 solar masses). It’s orbited by a far dimmer companion that’s roughly half of our Sun’s mass, but which hasn’t been characterized in detail until now. The companion’s orbit relative to the central star is a bit lopsided, ranging from about two astronomical units (AU, the typical Earth-Sun distance) at its closest approach to roughly three AU at its farthest. And, until yesterday, the exact nature of the companion star was not clear.
