$^{3}$Some of the images are available at http://mars.nasa.gov/comets/sidingspring/images 18 By including the 2014 October 7 HiRISE astrometry as well as some ad- ditional ground-based astrometry through 2014 October 13, which was the deadline for the final ephemeris delivery, we computed JPL solution 101. Ta- ble 3 shows the corresponding osculating orbital elements, nongravitational parameters, and close approach distance and time. Figure 1 shows the cor- responding b -plane prediction. Solution 101 was used to successfully observe C/2013 A1 during the close approach to Mars. The data analysis of the acquired images 3 is still ongoing, though some preliminary results were reported by Delamere et al. (2014). 2.4. Ephemerides Table 3: JPL solution 101. The orbital elements are ecliptic heliocentric and error bars correspond to 1 σ formal uncertainties. Epoch TDB 2014 Feb 3.0 Eccentricity 1 . 0007424 ± 0 . 0000029 Perihelion distance 1 . 3986359 ± 0 . 0000024 au Time of perihelion TDB 2014 Oct 25 . 32823 ± 0 . 00019 d Longitude of node 300 . 976279 ◦ ± 0 . 000048 ◦ Argument of perihelion 2 . 44097 ◦ ± 0 . 00015 ◦ Inclination 129 . 027341 ± 0 . 000020 ◦ A$_{1}$ (20 . 8 ± 2 . 6) × 10 − 9 au/d 2 A$_{2}$ ( − 13 . 2 ± 2 . 2) × 10 − 9 au/d 2 A$_{3}$ ( − 7 . 4 ± 1 . 3) × 10 − 9 au/d 2 Mars encounter distance 140751 ± 175 km Epoch of closest approach to Mars TDB 2014 Oct 19 18:28:38.5 ± 1 . 2 s