C/2013 A1 (Siding Spring) is an Oort cloud comet discovered on 3 January 2013 by Robert H. McNaught at Siding Spring Observatory using the 0.5-meter (20 in) Uppsala Southern Schmidt Telescope.

At the time of discovery it was 7.2 AU from the Sun and located in the constellation Lepus. Comet C/2013 A1 probably took millions of years to come from the Oort cloud. After leaving the planetary region of the Solar System, the post-perihelion orbital period (epoch 2050) is estimated to be roughly 1 million years.

C/2013 A1 passed the planet Mars very closely on 19 October 2014, at a distance of 140,496.6 ± 4.0 km (87,300.5 ± 2.5 mi; 0.000939162 ± 2.7×10⁻⁸ au) . After its discovery, there was thought to be a chance of a collision with Mars, but this possibility was excluded when its orbit was determined more accurately.