NASA has been told to prioritise a mission to Uranus.
An influential panel of scientists has called on the US space agency to conduct further exploration on the “ice giant”.
Uranus orbits the Sun 19 times further out than Earth and has only been visited once in a brief flyby by the Voyager-2 probe in 1986.
Experts think that an in-depth study of Uranus can help them understand the many similar-sized objects being discovered around other stars.
The recommendation to explore Uranus has been made in a document published by the US National Academies of Sciences, Engineering, and Medicine (NAS). NASA has broadly followed the recommendations made in previous reports.
Professor Leigh Fletcher, a scientist at the University of Leicester, told BBC News: “We think we understand how something gets to be the size of Earth and Venus.
“But in the middle, in that kind of sweet spot between those end-members – we don’t fully understand how a world can start to grow and grow and not just carry on to become Jupiter-mass in size. A mission to Uranus could help us answer that.”