Space Time

The Case for Visiting the Outer Planets

Scientists are begging NASA to go back to Uranus and Neptune

Shannon Stirone
Published in
5 min readMar 7, 2019


Credit: SCIEPRO/Getty Images

UUntil NASA’s Voyager 2 spacecraft reached Uranus and Neptune in the 1980s, the outer planets were simply fuzzy blobs that could only be viewed through ground-based telescopes. We had no idea what they actually looked like.

But when Voyager 2 made its closest approach to Uranus in 1986, the space probe revealed a light teal planet with rings. Three years after the Uranus flyby, Voyager 2 introduced us to Neptune, a vibrant ultramarine blue planet with a dark oval storm that penetrated deep into the atmosphere. Suddenly these two ambiguous blobs became real worlds — as real as our own. They had clouds and storms as well as bands of winds and weather all their own. After hundreds of years of wondering, we finally glimpsed these distant worlds comparatively up close. So, why haven’t we been back for 30 years?

Funding is a perennial issue for NASA, and there simply isn’t enough money to reach every planet scientists want to visit. There’s also the sheer distance of Uranus and Neptune: Uranus is about two billion miles away from Earth, and Neptune is roughly another billion miles farther. Reaching these planets with the technology we have now can easily take a decade.

As it happens, the next ideal time to launch a mission to the outer planets is fast approaching. A spacecraft could use Jupiter as a gravity assist — a method of stealing some of Jupiter’s massive gravitational force to slingshot a spacecraft away even faster and therefore shaving years off the travel time. But to do that, a mission would need to be ready by the 2030s; otherwise our alignment with Jupiter will change, making a gravity assist impossible. NASA’s New Horizons spacecraft used Jupiter to gain speed, and while it became the fastest spacecraft headed to the outer solar system, it still took nine years to reach Pluto.

Scientists are urging NASA to take advantage of the timing and start planning a mission to Uranus and Neptune. Amy Simon, a senior scientist for planetary atmospheres research at NASA’s Goddard Space Flight Center, recently published a paper with her colleagues outlining an epic outer planets voyage. While both planets are…