The comet was discovered on 3 January 2013 by comet-hunter Robert McNaught at the Siding Spring Observatory in New South Wales Australia. After the initial discovery was made, astronomers at the Catalina Sky Survey in Arizona looked back through previous observations and found prior images of the comet dating back to 8 December 2012. Using these earlier findings and the newer data gathered since the early January discovery, scientists are able to plot the trajectory of the comet through its flyby of Mara on 19 October 2014.
Estimating the closest approach is a challenge, and each new piece of data will allow further refinement of the calculations. Just to show how variable this can be, yesterday’s best estimate was that the comet would pass approximately 109,200 km from Mars. Today, new astrometric data from the ISON-NM observatory indicates that the comet will pass less than 37,000 km from the planet’s surface! That should virtually guarantee that Mars will pass through the coma (the gaseous envelope surrounding the comet) as C/2013 A1 whizzes by the planet.
At the time of closest approach, the comet will be moving along at 56 km/s relative to Mars. Based on the current estimate of the absolute magnitude of the nucleus, the comet could have a diameter of of up to 50 kilometers. If those estimates hold true, and if the comet were to impact the surface, it could leave a crater 500 km in diameter and 2 km deep.
Observations will continue, and measurements will be refined further as more data comes in. One thing is for sure: there should be some great images to look forward to in October 2014.
Image caption: artists conception of a comet streaking through Martian skies.
Image credit: Chris Smith / NASA