The orbital oddball

HR 5183 b – a ‘super-Jupiter’ three times the mass of the Solar System’s largest planet – is unique as its orbit is highly eccentric. While most planets trace out an almost-circular orbit, this gas giant traces out an egg-shaped orbit around its parent star HR 5183.

Astronomers discovered the exoplanet from the tiny wobble its gravity causes upon its parent star, which in turn causes a dip in brightness. The process took a staggering 20 years of observations with three telescopes, including Hawaii’s W. M. Keck Observatory. Despite this long period of observation, we are yet to see the world complete a full orbit, with researchers estimating that this could take between 45 and 100 Earth years – probably 74 years.

If HR 5183 b was to follow its orbit in the Solar System, it would pass closer to the Sun than Jupiter, then move to the outer edges of our planetary system, swinging past Neptune. Highly eccentric orbits such as this have been observed before, but normally by planets and other objects that are much closer to their host stars.

If HR 5183 b’s loose association with its parent star is something of a surprise, some worlds have gone to even further extremes, disassociating with their parent stars entirely to wander the universe alone.