Question: @chris how long does it take to get to mars from earth

Susan Cartwright answered on 19 Jun 2015:

It depends on when you go, and on exactly how you do it.

Both Mars and Earth are orbiting the Sun, at different speeds; in addition, Mars’ orbit is distinctly elliptical, so its distance from the Sun varies over a Martian year. To send a probe to Mars, you have to aim it for Mars’ orbit and time it so that Mars will be at that point when the probe gets there. In the meantime, your probe is itself in orbit around the Sun, in a much more elongated orbit which crosses both the Earth’s orbit and Mars’.

The simplest case is when the probe’s orbit touches Earth’s at its closest to the Sun, and touches Mars’ at its furthest point (this is called a Hohmann transfer orbit, after the guy who did the first calculations). A Hohmann transfer to Mars should take about 8.5 months on average, although it does depend on where you start, because Mars’ orbit is not a circle. If you expend a bit more fuel, and have a transfer path that is not a simple elliptical orbit, you can get there a bit more quickly: the Mars Express probe, which had a favourable orbital geometry, only took 7 months, being launched on 2 June 2003 and arriving on Christmas Day 2003. In contrast, the Indian Mars Orbiter was launched on 5 November 2013 and didn’t enter Martian orbit till 24 September 2014, nearly 11 months, and Mars Global Surveyor, launched 7 November 1996 and entering Mars orbit 12 September 1997, took 10 months. This is not because ESA built a faster spacecraft: it’s the variation in the relative geometry of Earth in its nearly circular orbit and Mars in its elliptical one.