Why hasn't anyone landed on Neptune?

Answer 1

There are two reasons: Neptune is too far away and the environment on Neptune's surface wouldn't allow the astronauts that land there to survive.

Distance:

In astronomy a unit called Astronomical Units (AU) is sometimes used to measure distances; one AU is the average distance from Earth to the Sun. Neptune is 30 AU away from the Sun. To reach Neptune in a space craft traveling 11.2 km per second (which is how fast you must go to escape earth's orbit) you would need to travel for 12 years and there are also many other complications. How will the astronauts get food and water? Do we send them up with 12 years worth of food and water? They'll also need another 18 years worth of food to sustain them while they are actually at Neptune and on their way back. How much fuel will they need? Most likely more fuel that human beings have ever produced in history. How will they get oxygen? We have no idea how much oxygen they'll need, and still it will add more weight, which will require more fuel to move. How will the people on Earth communicate with them? Neptune is four light-hours aways, meaning that any communication between Neptune and Earth will take 4 hours one-way or 8 hours round-trip. Also, will the astronauts themselves survive? Over the course of 12 years the risk of the astronauts dying before they get to there destination goes up. We have no experience with sending people on a space mission that will take over 24 years.

Neptune's Surface:

The surface of Neptune is another impossible obstacle when it comes to landing on Neptune. Neptune's surface is covered in ice and glaciers; there also an atmosphere consisting of ammonia, methane, and helium. Neptune also has a thick atmosphere and there are constant violent storms on the surface. One such storm, known as the "Great Dark Spot" is the size of the Earth! Neptune's environment would completely prevent any space trips to Neptune within the foreseeable future.