Largest Moon of Neptune Separated and Captured
Triton, Neptune's largest companion, was once a mini-planet in its own right before the gas giant's gravity demoted it to the moon. Before that, however, Triton may have been a twin object accompanied by a celestial body of about the same size, report astronomers Craig Agnor and Douglas Hamilton. The researchers conclude this from their calculations of Triton's unusual orbit around Neptune and simulations of the capture process.
Only a meeting of Neptune and a twin planetesimal easily explains Triton's observed orbit today, according to scientists from the University of California at Santa Cruz and the Observatory of the Cote d'Azur. The early triton twin was catapulted into the far reaches of the solar system by gravity. Previous models had only been able to simulate the formation of the eccentric triton orbit with the help of various complicated assumptions.
At around 1.4 Pluto masses, Triton is the largest moon in the solar system with an irregular orbit around its mother planet. The companion follows an ellipse in its orbit and also runs retrograde - i.e. in the opposite direction to the usual direction - around the planet. Its resemblance to Pluto had already given rise to various theories about the co-formation of today's Neptune and the still binary Pluto-Charon system.
