| 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) |
| 2026-05-12 00:00 |
03:43:52.77 |
-00:26:35.6 |
HIP 17451 |
16.94 |
| 2026-05-12 12:00 |
03:43:59.14 |
-00:26:14.5 |
HIP 17451 |
16.51 |
| 2026-05-13 00:00 |
03:44:05.52 |
-00:25:53.9 |
HIP 17506 |
15.09 |
| 2026-05-13 12:00 |
03:44:11.91 |
-00:25:33.8 |
HIP 17506 |
13.58 |
| 2026-05-14 00:00 |
03:44:18.30 |
-00:25:14.1 |
HIP 17506 |
12.09 |
| 2026-05-14 12:00 |
03:44:24.70 |
-00:24:54.9 |
HIP 17506 |
10.66 |
| 2026-05-15 00:00 |
03:44:31.11 |
-00:24:36.2 |
HIP 17506 |
9.30 |
| 2026-05-15 12:00 |
03:44:37.52 |
-00:24:17.9 |
HIP 17506 |
8.04 |
| 2026-05-16 00:00 |
03:44:43.94 |
-00:24:00.2 |
HIP 17506 |
6.95 |
| 2026-05-16 12:00 |
03:44:50.36 |
-00:23:42.9 |
HIP 17506 |
6.11 |
| 2026-05-17 00:00 |
03:44:56.79 |
-00:23:26.1 |
HIP 17506 |
5.63 |
| 2026-05-17 12:00 |
03:45:03.22 |
-00:23:09.8 |
HIP 17506 |
5.62 |
| 2026-05-18 00:00 |
03:45:09.65 |
-00:22:53.9 |
HIP 17506 |
6.07 |
| 2026-05-18 12:00 |
03:45:16.08 |
-00:22:38.6 |
HIP 17506 |
6.89 |
| 2026-05-19 00:00 |
03:45:22.51 |
-00:22:23.8 |
HIP 17506 |
7.97 |
| 2026-05-19 12:00 |
03:45:28.94 |
-00:22:09.4 |
HIP 17506 |
9.21 |
| 2026-05-20 00:00 |
03:45:35.37 |
-00:21:55.6 |
HIP 17506 |
10.56 |
| 2026-05-20 12:00 |
03:45:41.80 |
-00:21:42.3 |
HIP 17506 |
11.99 |
| 2026-05-21 00:00 |
03:45:48.22 |
-00:21:29.4 |
HIP 17506 |
13.46 |
| 2026-05-21 12:00 |
03:45:54.65 |
-00:21:17.1 |
HIP 17506 |
14.96 |
| 2026-05-22 00:00 |
03:46:01.07 |
-00:21:05.3 |
HIP 17506 |
16.48 |
| 2026-05-22 12:00 |
03:46:07.48 |
-00:20:53.9 |
HIP 17506 |
18.02 |
| 2026-05-23 00:00 |
03:46:13.89 |
-00:20:43.1 |
HIP 17701 |
18.78 |
| 2026-05-23 12:00 |
03:46:20.29 |
-00:20:32.8 |
HIP 17701 |
17.19 |
| 2026-05-24 00:00 |
03:46:26.69 |
-00:20:23.0 |
HIP 17701 |
15.60 |
| 2026-05-24 12:00 |
03:46:33.08 |
-00:20:13.8 |
HIP 17701 |
14.02 |
| 2026-05-25 00:00 |
03:46:39.46 |
-00:20:05.0 |
HIP 17701 |
12.44 |
| 2026-05-25 12:00 |
03:46:45.83 |
-00:19:56.7 |
HIP 17701 |
10.88 |
| 2026-05-26 00:00 |
03:46:52.20 |
-00:19:49.0 |
HIP 17701 |
9.32 |
| 2026-05-26 12:00 |
03:46:58.55 |
-00:19:41.8 |
HIP 17701 |
7.79 |
| 2026-05-27 00:00 |
03:47:04.90 |
-00:19:35.1 |
HIP 17701 |
6.28 |
| 2026-05-27 12:00 |
03:47:11.23 |
-00:19:28.9 |
HIP 17701 |
4.82 |
| 2026-05-28 00:00 |
03:47:17.55 |
-00:19:23.3 |
HIP 17701 |
3.48 |
| 2026-05-28 12:00 |
03:47:23.86 |
-00:19:18.1 |
HIP 17701 |
2.44 |
| 2026-05-29 00:00 |
03:47:30.16 |
-00:19:13.5 |
HIP 17701 |
2.18 |
| 2026-05-29 12:00 |
03:47:36.44 |
-00:19:09.5 |
HIP 17701 |
2.91 |
| 2026-05-30 00:00 |
03:47:42.71 |
-00:19:05.9 |
HIP 17701 |
4.13 |
| 2026-05-30 12:00 |
03:47:48.97 |
-00:19:02.9 |
HIP 17701 |
5.52 |
| 2026-05-31 00:00 |
03:47:55.21 |
-00:19:00.4 |
HIP 17701 |
6.98 |
| 2026-05-31 12:00 |
03:48:01.44 |
-00:18:58.4 |
HIP 17701 |
8.47 |
| 2026-06-01 00:00 |
03:48:07.64 |
-00:18:57.0 |
HIP 17701 |
9.97 |
| 2026-06-01 12:00 |
03:48:13.84 |
-00:18:56.1 |
HIP 17701 |
11.48 |
| 2026-06-02 00:00 |
03:48:20.01 |
-00:18:55.8 |
HIP 17701 |
13.00 |