Why do planets go out of orbit when increasing time step?

[Smolik]

In the solar system simulation: If I increase the time step rapidly to about 30 days (starting in 2008), mercury and earth goes out of orbit before the year 2020 Why is this happening?

[Bla]

Every time step, the program calculates the positions of all the objects in the simulation. So if you set it to 30 days, the positions are calculated every 30 days.
Mercury has an orbital period of just below 90 days, so this means its position would only be calculated three times every time it orbits the Sun. This makes it very inaccurate, so it flies off.
Earth takes about 365 days to orbit, so it maintains a very unstable orbit with about 12 points for some time before it flies off as well.

So generally, the lower the time step is, the more accurate the simulation is.

Also it should be fixed in the future:

In short, if the rings are "breathing" then the time step is too high. This issue will be mostly resolved in the new version we release later this year.

[Smolik]

Ok, that explains it nicely. Thanks for the answer.