| Parameter |
Value |
| Designation |
C/2021 A9 (PANSTARRS) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2023-12-01T09:07:05.606400Z |
| Orbit solution date (soln_date, UTC) |
2026-03-07T11:42:49Z |
| Obs used |
449 |
| NEO |
- |
| M1 |
6.600 |
| K1 |
9.250 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-01-12T15:24:10.569600Z |
| Discovery magnitude (MPC) |
21.44 w |
| Discovery observatory (MPC) |
F51 · Pan-STARRS 1, Haleakala |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2022-09-29.0000000 |
| e |
1.00315922 |
| q (au) |
7.760340 |
| a (au) |
-2456.412915 |
| i (deg) |
158.022662 |
| Ω (om, deg) |
314.842967 |
| ω (w, deg) |
211.451996 |
| M (ma, deg) |
-0.003468 |
Magnitude
Scatter + Global Linear
$$
M_a = (1.616 + 5.710\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
1.616 |
| n |
5.710 |
| gf |
0.906 |
| gb |
-0.970 |
| k |
1.000 |
| δ90 |
1.000 |
| Parameter |
Symbol |
Range |
Description |
| Absolute magnitude at 1 AU from Sun and Earth |
H0 |
-5 to 20 |
Intrinsic brightness of the comet |
| Photometric slope parameter |
n |
2 to 6 |
Rate of brightness change with heliocentric distance |
| Forward scattering asymmetry factor |
gf |
0.8 to 1 |
Degree of forward scattering |
| Backward scattering asymmetry factor |
gb |
-1 to -0.5 |
Degree of backward scattering |
| Partitioning coefficient |
k |
0.8 to 1 |
Ratio between forward/backward scattering contributions |
| Dust-to-gas brightness ratio |
δ90 |
1 to 10 |
Relative contribution of dust scattering to gas emission |
Reference: EPSC-DPS2025-160
Residuals (Piecewise)
$$\epsilon = a \log_{10} r_{\mathrm{au}} + b$$
| Start (UTC) |
End (UTC) |
a |
b |
| 2020-12-12 |
2023-11-25 |
+3.7459 |
-3.703 |
| 2023-12-04 |
2026-01-19 |
+13.1211 |
-11.601 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
03:46:09.72 |
-04:02:25.8 |
HIP 17674 |
31.91 |
| 2026-09-20 12:00 |
03:45:58.70 |
-04:04:13.1 |
HIP 17416 |
33.37 |
| 2026-09-21 00:00 |
03:45:47.57 |
-04:06:00.4 |
HIP 17416 |
30.13 |
| 2026-09-21 12:00 |
03:45:36.34 |
-04:07:47.8 |
HIP 17416 |
26.89 |
| 2026-09-22 00:00 |
03:45:25.00 |
-04:09:35.3 |
HIP 17416 |
23.63 |
| 2026-09-22 12:00 |
03:45:13.56 |
-04:11:22.9 |
HIP 17416 |
20.39 |
| 2026-09-23 00:00 |
03:45:02.02 |
-04:13:10.4 |
HIP 17416 |
17.17 |
| 2026-09-23 12:00 |
03:44:50.37 |
-04:14:58.0 |
HIP 17416 |
14.00 |
| 2026-09-24 00:00 |
03:44:38.63 |
-04:16:45.7 |
HIP 17416 |
10.95 |
| 2026-09-24 12:00 |
03:44:26.78 |
-04:18:33.3 |
HIP 17416 |
8.20 |
| 2026-09-25 00:00 |
03:44:14.83 |
-04:20:21.0 |
HIP 17416 |
6.16 |
| 2026-09-25 12:00 |
03:44:02.78 |
-04:22:08.7 |
HIP 17416 |
5.74 |
| 2026-09-26 00:00 |
03:43:50.63 |
-04:23:56.3 |
HIP 17416 |
7.24 |
| 2026-09-26 12:00 |
03:43:38.38 |
-04:25:44.0 |
HIP 17416 |
9.84 |
| 2026-09-27 00:00 |
03:43:26.03 |
-04:27:31.6 |
HIP 17416 |
12.91 |
| 2026-09-27 12:00 |
03:43:13.58 |
-04:29:19.2 |
HIP 17344 |
10.25 |
| 2026-09-28 00:00 |
03:43:01.03 |
-04:31:06.7 |
HIP 17344 |
6.80 |
| 2026-09-28 12:00 |
03:42:48.39 |
-04:32:54.3 |
HIP 17344 |
3.63 |
| 2026-09-29 00:00 |
03:42:35.65 |
-04:34:41.7 |
HIP 17344 |
2.57 |
| 2026-09-29 12:00 |
03:42:22.81 |
-04:36:29.1 |
HIP 17344 |
5.18 |
| 2026-09-30 00:00 |
03:42:09.88 |
-04:38:16.4 |
HIP 17344 |
8.62 |
| 2026-09-30 12:00 |
03:41:56.85 |
-04:40:03.7 |
HIP 17344 |
12.23 |
| 2026-10-01 00:00 |
03:41:43.72 |
-04:41:50.9 |
HIP 17344 |
15.90 |
| 2026-10-01 12:00 |
03:41:30.51 |
-04:43:37.9 |
HIP 17344 |
19.61 |
| 2026-10-02 00:00 |
03:41:17.19 |
-04:45:24.9 |
HIP 17344 |
23.36 |
| 2026-10-02 12:00 |
03:41:03.79 |
-04:47:11.7 |
HIP 17167 |
26.22 |
| 2026-10-03 00:00 |
03:40:50.29 |
-04:48:58.5 |
HIP 17167 |
23.85 |
| 2026-10-03 12:00 |
03:40:36.70 |
-04:50:45.1 |
HIP 17167 |
21.89 |
| 2026-10-04 00:00 |
03:40:23.02 |
-04:52:31.5 |
HIP 17167 |
20.47 |
| 2026-10-04 12:00 |
03:40:09.25 |
-04:54:17.9 |
HIP 17167 |
19.72 |
| 2026-10-05 00:00 |
03:39:55.39 |
-04:56:04.0 |
HIP 17167 |
19.73 |
| 2026-10-05 12:00 |
03:39:41.44 |
-04:57:50.0 |
HIP 17167 |
20.49 |
| 2026-10-06 00:00 |
03:39:27.40 |
-04:59:35.8 |
HIP 17167 |
21.96 |
| 2026-10-06 12:00 |
03:39:13.28 |
-05:01:21.5 |
HIP 17167 |
24.00 |
| 2026-10-07 00:00 |
03:38:59.06 |
-05:03:06.9 |
HIP 17167 |
26.49 |
| 2026-10-07 12:00 |
03:38:44.77 |
-05:04:52.1 |
HIP 17167 |
29.33 |
| 2026-10-08 00:00 |
03:38:30.38 |
-05:06:37.1 |
HIP 17027 |
31.86 |
| 2026-10-08 12:00 |
03:38:15.91 |
-05:08:21.9 |
HIP 17027 |
31.27 |
| 2026-10-09 00:00 |
03:38:01.36 |
-05:10:06.5 |
HIP 16779 |
31.01 |
| 2026-10-09 12:00 |
03:37:46.73 |
-05:11:50.8 |
HIP 16779 |
27.60 |
| 2026-10-10 00:00 |
03:37:32.02 |
-05:13:34.8 |
HIP 16779 |
24.37 |
| 2026-10-10 12:00 |
03:37:17.22 |
-05:15:18.6 |
HIP 16779 |
21.39 |
| 2026-10-11 00:00 |
03:37:02.35 |
-05:17:02.1 |
HIP 16779 |
18.81 |