How long will it take to get to each of the planets by various means?

It depends a lot on the particular trajectory that you take. Usually, the trajectories are in the form of a 'great arc' that gracefully connects a launch time at Earth with a destination point. These arcs are usually many times longer that the straight-line distance between the two planets at a particular moment in time. For reduced-cost travel, astrodynamicists often rely on gravity assists 'Slingshot Orbits' from the inner planets to reach Jupiter, and by Jupiter to reach more distant worlds. These loop-de-loops add years of extra travel time to a mission. Let's assume for our calculations that we just take the simplest direct approach and use the minimum 'opposition' distance between Earth and a planet.

The table below gives you some sense for how long it takes to get to each planet at different speeds.

The Space Shuttle, of course, can't leave Earth orbit but its speed is typical of manned spacecraft. The Galileo spacecraft which recently explored Jupiter traveled twice as fast. Ion rocket motors get their speed by being constantly accelerated 24-hours a day for many months, and two versions of this technology are given for a low-power and high-power ion engine. Finally, solar sails can reach speeds of nearly that of the solar wind, and engineers are hopeful that this technology will be tested in space very soon. As you can see, we are currently stuck in the mode of travel where it takes nearly 10 years to get to Pluto. Perhaps in another hundred years, this travel time will be reduced to a year or less...assuming Humanity feels a compelling economic need to continue this kind of exploration.
Method= Shuttle Galileo Ion A Ion B Solar Sail
Speed = 28,000mph 54,000mph 65,000mph 650,000mph 200,000mph
Mercury 52d 27d 22d 2.2d 7.3d
Venus 100d 52d 43d 4.3d 14d
Mars 210d 109d 90d 9d 29d
Jupiter 1.9yr 1yr 303d 31d 100d
Saturn 3.6yr 1.8yr 1.5yr 55d 179d
Uranus 7.3yr 3.8yr 3.1yr 113d 1yr
Neptune 11.4yr 5.9yr 4.9yr 179d 1.6yr
Pluto 15.1yr 7.8yr 6.5yr 238d 2.1yr

Note: Ion Drive using a constant thrust of  A) 0.1 pounds  B) 1 pound with 
turnaround deceleration added. Two years acceleration to reach top speed. 
Solar Sail - Interstellar Probe estimated speed. (Solar wind = 450 km/sec  
or one million mph)

This answer was updated in 2011. See my books: The Astronomy Cafe (1998) and Back to the Astronomy Cafe (2003) for more FAQs in printed form. Author: Dr. Sten Odenwald, Copyright 2011

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