| 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
$$
M_a = (1.765 + 5.637\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
1.765 |
| n |
5.637 |
| gf |
0.909 |
| gb |
-0.972 |
| 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 |
+3.8976 |
-3.837 |
| 2023-12-04 |
2025-11-23 |
+11.9616 |
-10.547 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-03-26 00:00 |
03:36:09.56 |
-01:27:46.4 |
HIP 16809 |
7.02 |
| 2026-03-26 12:00 |
03:36:12.07 |
-01:26:54.4 |
HIP 16809 |
7.59 |
| 2026-03-27 00:00 |
03:36:14.66 |
-01:26:02.5 |
HIP 16809 |
8.26 |
| 2026-03-27 12:00 |
03:36:17.31 |
-01:25:10.8 |
HIP 16809 |
9.00 |
| 2026-03-28 00:00 |
03:36:20.04 |
-01:24:19.3 |
HIP 16809 |
9.80 |
| 2026-03-28 12:00 |
03:36:22.84 |
-01:23:27.9 |
HIP 16809 |
10.65 |
| 2026-03-29 00:00 |
03:36:25.71 |
-01:22:36.8 |
HIP 16809 |
11.54 |
| 2026-03-29 12:00 |
03:36:28.65 |
-01:21:45.8 |
HIP 16809 |
12.47 |
| 2026-03-30 00:00 |
03:36:31.66 |
-01:20:55.0 |
HIP 16809 |
13.43 |
| 2026-03-30 12:00 |
03:36:34.74 |
-01:20:04.5 |
HIP 16809 |
14.41 |
| 2026-03-31 00:00 |
03:36:37.88 |
-01:19:14.1 |
HIP 16809 |
15.42 |
| 2026-03-31 12:00 |
03:36:41.09 |
-01:18:23.9 |
HIP 16809 |
16.44 |
| 2026-04-01 00:00 |
03:36:44.37 |
-01:17:33.9 |
HIP 16809 |
17.49 |
| 2026-04-01 12:00 |
03:36:47.71 |
-01:16:44.2 |
HIP 16809 |
18.55 |
| 2026-04-02 00:00 |
03:36:51.12 |
-01:15:54.6 |
HIP 16809 |
19.63 |
| 2026-04-02 12:00 |
03:36:54.59 |
-01:15:05.3 |
HIP 16809 |
20.72 |
| 2026-04-03 00:00 |
03:36:58.13 |
-01:14:16.2 |
HIP 16809 |
21.83 |
| 2026-04-03 12:00 |
03:37:01.73 |
-01:13:27.3 |
HIP 16809 |
22.95 |
| 2026-04-04 00:00 |
03:37:05.38 |
-01:12:38.7 |
HIP 16809 |
24.08 |
| 2026-04-04 12:00 |
03:37:09.11 |
-01:11:50.3 |
HIP 16809 |
25.23 |
| 2026-04-05 00:00 |
03:37:12.89 |
-01:11:02.1 |
HIP 16809 |
26.39 |
| 2026-04-05 12:00 |
03:37:16.73 |
-01:10:14.1 |
HIP 16809 |
27.55 |
| 2026-04-06 00:00 |
03:37:20.63 |
-01:09:26.4 |
HIP 16809 |
28.73 |
| 2026-04-06 12:00 |
03:37:24.59 |
-01:08:39.0 |
HIP 16809 |
29.92 |
| 2026-04-07 00:00 |
03:37:28.61 |
-01:07:51.8 |
HIP 16809 |
31.12 |
| 2026-04-07 12:00 |
03:37:32.69 |
-01:07:04.9 |
HIP 17017 |
31.87 |
| 2026-04-08 00:00 |
03:37:36.82 |
-01:06:18.2 |
HIP 17017 |
31.83 |
| 2026-04-08 12:00 |
03:37:41.01 |
-01:05:31.7 |
HIP 17017 |
31.83 |
| 2026-04-09 00:00 |
03:37:45.25 |
-01:04:45.6 |
HIP 17017 |
31.88 |
| 2026-04-09 12:00 |
03:37:49.55 |
-01:03:59.7 |
HIP 17017 |
31.96 |
| 2026-04-10 00:00 |
03:37:53.90 |
-01:03:14.1 |
HIP 17120 |
31.66 |
| 2026-04-10 12:00 |
03:37:58.31 |
-01:02:28.7 |
HIP 17120 |
30.68 |
| 2026-04-11 00:00 |
03:38:02.77 |
-01:01:43.7 |
HIP 17120 |
29.71 |
| 2026-04-11 12:00 |
03:38:07.28 |
-01:00:58.9 |
HIP 17120 |
28.76 |
| 2026-04-12 00:00 |
03:38:11.85 |
-01:00:14.4 |
HIP 17120 |
27.82 |
| 2026-04-12 12:00 |
03:38:16.46 |
-00:59:30.2 |
HIP 17120 |
26.91 |
| 2026-04-13 00:00 |
03:38:21.12 |
-00:58:46.3 |
HIP 17120 |
26.03 |
| 2026-04-13 12:00 |
03:38:25.84 |
-00:58:02.7 |
HIP 17120 |
25.18 |
| 2026-04-14 00:00 |
03:38:30.60 |
-00:57:19.3 |
HIP 17120 |
24.36 |
| 2026-04-14 12:00 |
03:38:35.41 |
-00:56:36.3 |
HIP 17120 |
23.58 |
| 2026-04-15 00:00 |
03:38:40.27 |
-00:55:53.7 |
HIP 17120 |
22.85 |
| 2026-04-15 12:00 |
03:38:45.17 |
-00:55:11.3 |
HIP 17120 |
22.17 |
| 2026-04-16 00:00 |
03:38:50.12 |
-00:54:29.2 |
HIP 17120 |
21.56 |