Mercury (planet) at a steep angle. Mercury is 10° above the horizon when the planet appears directly above the Sun (i.e. its orbit appears vertical) and is at maximum elongation from the Sun (28°) and also when the Sun is 18° below the horizon, so the sky is just completely dark. This angle is the maximum altitude at which Mercury is visible in a completely dark sky. At middle latitudes, Mercury is more often and easily visible from the Southern Hemisphere than from the Northern. This is because Mercury's maximum western elongation occurs only during early autumn in the Southern Hemisphere, whereas
Planet Nine distant orbits around another star, or rogue planet, leaving one in a stable orbit around the Sun via a process similar to the capture of irregular satellites around the giant planets. If the planet originated in a system with a number of Neptune-massed planets, and without Jupiter-massed planets, it could be scattered into a more long-lasting distant eccentric orbit, increasing its chances of capture. Although the odds of the Sun capturing another planet from another star can be higher, a wider variety of orbits are possible, reducing the probability of a planet being captured on an orbit like that proposed