[Mr. K]

I think it is a miracle in itself that planets sustain (nearly) circular orbits- do you have any cluse how little it would take to knock them out of the precise balance of mass/speed that puts it into orbit? (circular OR otherwise)

[Doctor Stochastic]

The Earth's orbit does oscilate between a circle and an ellipse (OK, a lesser and greater elongated ellpise) about every 105,000 years.

[Junior]

Planets weren't put into orbit, they formed there from the disk of debris surrounding the nascent star. The disk is already spinning nearly circular, hence the planetary orbits would be nearly circular.

[Magnum44]

I think it is a miracle in itself that planets sustain (nearly) circular orbits- do you have any cluse how little it would take to knock them out of the precise balance of mass/speed that puts it into orbit? (circular OR otherwise)

Considering the mass of even a small planet, LOTS of energy would be required. We couldn't do it with our own Earth if we tried.