Mars is the fourth planet from the sun, and is easily visible in the night sky - even without a telescope! When looking at the sky, you may see the stars twinkling. You can look for the difference between a star and a planet by keeping an eye out for ‘stars’ that don’t twinkle, or ones that look like flat circular discs in the sky. Mars has a reddish colour that can be seen with the naked eye.
The time that it takes to get to Mars from Earth can be between 150 and 300 days, depending on where Mars is in relation to Earth, the speed of the launch, and the exact travel path that is taken. The distance between Earth and Mars is constantly changing, depending on their relative positions in their orbits. The closest that they have ever been (in recorded history) was in 2003, when they were 34.8 million miles (56 million km) apart.
NASA’s Mariner 4 spacecraft was the first to make the journey to Mars, in 1964. It took 228 days to reach Mars, and took a number of photographs when it arrived. Mariner 6 was next, in 1969. It took slightly less time: only 156 days. Mariner 7 took 131 days, and Mariner 9 took 167 days. Mariner 9 was the first spacecraft to orbit around Mars.
The spacecraft that was launched from Earth the fastest was NASA’s New Horizons, which left Earth in 2006 at a speed of 36,000 miles per hour (58,000 km per hour). If Mars was at its closest to Earth, it could have taken New Horizons as little as 39 days to reach Mars!
Mars is, on average, 55 million km away from Earth, but spacecraft can’t just fly straight there. Mars and Earth are both orbiting the sun, which means that when a spacecraft is launched from Earth it has to be aimed at where Mars is going to be, not where Mars currently is at the time of the launch.
The other factor that needs to be taken into account is fuel. More fuel can allow the spacecraft to travel faster - but more fuel is also heavier. The spacecraft needs to make sure it carries enough fuel to get to Mars and back, but not so much that it makes the spacecraft too heavy to fly.
NASA scientists use what is called a Hohmann Transfer Orbit - this is a method of travel that sends a spacecraft from Earth to Mars with the least amount of fuel. It works by putting the spacecraft into a slowly increasing orbit - it slowly gets further and further out, to the point where the spacecraft’s orbit intersects with the orbit of Mars. By calculating exactly where Mars will be at any given point in time, scientists can ensure that the spacecraft intersects with Mars’ orbit at the point where Mars will be.
In recent years, various organisations have proposed establishing a permanent colony on Mars. The “Mars One” organisation even proposes to establish a human settlement on Mars by 2025!
Mars Program Planning Group - NASA