Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet.
It's not considered as a destination for human exploration or aerospace activities, however, it's been studied by several spacecrafts and is of interest for scientists and researchers to understand more about our solar system, its formation and its physical characteristics.
Examples of missions that have studied Neptune include:
- Voyager 2: A NASA spacecraft that flew by Neptune in 1989 and provided the first close-up images of the planet and its moons.
- Hubble Space Telescope: The telescope has been used to study Neptune's atmosphere and to search for new moons and rings around the planet.
- New Horizons: A NASA spacecraft that flew by Pluto in 2015 and will continue to study the Kuiper Belt and other objects in the outer solar system.
As for future missions, NASA has not yet announced any specific mission to study Neptune. However, NASA's proposed "Dragonfly" mission, a proposed drone-like rotorcraft lander, would explore the atmosphere and surface of Saturn's largest moon, Titan, which has a thick atmosphere and many similarities to Neptune's largest moon, Triton.
It's worth noting that observing and studying objects in the outer solar system, such as Neptune, is challenging due to the distance, and the weak sunlight. Therefore, these missions are generally focused on remote sensing and rely on sophisticated instruments to study the planet and its moons from a distance.