NEPTUNE

The isolated azure ice giant remains a relative mystery

Neptune was the first planet to have its existence predicted by mathematical calculations before it was actually seen through a telescope on 23 September 1846. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest that the gravitational pull from another celestial body was responsible. German astronomer Johann Galle then relied on subsequent calculations to help spot Neptune. Astronomer Galileo Galilei had sketched the planet, but he mistook it for a star due to its slow motion.

Only one mission has flown by Neptune – Voyager 2 in August 1989 – meaning that astronomers have done most studies using ground-based telescopes. There are still many mysteries about the cool blue planet, such as why its winds are so speedy and why its magnetic field is offset. While Neptune is of interest because it’s in our Solar System, astronomers are also interested in learning more about the planet to assist with exoplanet studies. Specifically, some astronomers are interested in learning about the habitability of worlds that are somewhat bigger than Earth.

Those closer to Earth’s size are called ‘super-Earths’, while those that are closer to Neptune’s are ‘mini-Neptunes’. However, there’s some debate about those terms, given that today’s telescope technology doesn’t make it possible to view how much atmosphere is on those planet types, making it difficult to make a distinction.