Mars Returns

A follow up post to yesterday's, but with a bit more detail about what's happening with Mars and why - for those of you looking to expand your science literacy (and your minds).

The biannual date between Mars and Earth happens because both planets take a different amount of time to orbit the Sun. Earth takes 365+ days and Mars takes approximately 687 days. Therefore, Earth moves faster in it's orbit and gradually "laps" Mars in the race around the Sun. The approach and subsequent passing of Mars is what occurs every two years. However, not every meeting generates such great views of the Red Planet.

As mentioned in the previous post, both planets have elliptical orbits and as such, this complicates the occurrence of these close encounters. The diagram below best illustrates what's going on here. It show how two elliptical orbits have a point where their paths come closest together and where they are farthest apart. Also shown in the diagram, to an exaggerated effect, is that Mars' orbit is more eccentric than Earth's, i.e. it's orbit is more elliptical and in fact over five times more so. If you combine this with the different speeds of each planet in their orbit, they won't always be nearest to each other at the same point in space each time Earth is about to lap Mars.


You may or may not recall a huge fuss about Mars from 2003. This was because Earth lapped Mars that year very close to the point where their orbits are the closest they ever get, approximately 34.6 million miles. This happens roughly every 15-17 years as the lapping point precesses around the Sun over time; it takes 15-17 years to occur back at the same point in space. Each biannual meeting of the planets since a closest encounter like in 2003 will produce less and less spectacular viewing opportunities of the Red Planet until the lapping point comes around again. However, while the planets are still within a certain range of each other, the viewing can still be quite exciting. After this we will have to wait another nine years before the fun begins anew. Compared to 2003, Mars will be 20 million miles farther away this year, at a distance of 55 million miles as Earth overtakes it. But surprisingly, 20 million miles makes less of a difference than you might think. There is still a good show to be had.

(photo credit: Our Dark Skies, http://www.ourdarkskies.com)