How long wil it take to reach nuptune from earth?

Answer 1

Every "How long..." question can be answered with the question "how fast...". It will be another hundred years or more before humans will ever be able to go to Neptune, and we will probably NEVER be able to land there. To send a robotic space probe, like the Cassini probe to Saturn, would probably take about 8 years from launch to arrival AT OUR CURRENT LEVEL OF TECHNOLOGY.

Wait another 10 years before launching, and there is every chance that the probe would arrive in five years or less. That's because rocket propulsion technology is advancing nicely. In fact, there is every possibility that within 25 years we would be able to launch a probe to Neptune or beyond that would travel ten or one hundred times faster than the Cassini probe did. This is because the probe would be assembled and launched from Earth orbit rather than having to launch directly from the Earth itself. A rocket to Neptune uses up most of its fuel just getting out of the Earth's gravity well, to say nothing of actually going anyplace else.