| Parameter |
Value |
| Designation |
C/2021 P4 (ATLAS) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2022-07-30T09:00:29.151360Z |
| Orbit solution date (soln_date, UTC) |
2024-07-30T14:57:24Z |
| Obs used |
954 |
| NEO |
- |
| M1 |
10.800 |
| K1 |
8.000 |
| PC |
0.030 |
| Discovery observation (MPC, UTC) |
2021-08-10T12:53:31.315200Z |
| Discovery magnitude (MPC) |
19.44 o |
| Discovery observatory (MPC) |
T05 · ATLAS-HKO, Haleakala |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2022-01-11.0000000 |
| e |
0.99656560 |
| q (au) |
1.080462 |
| a (au) |
314.600427 |
| i (deg) |
56.310801 |
| Ω (om, deg) |
348.094879 |
| ω (w, deg) |
175.822404 |
| M (ma, deg) |
359.964608 |
Magnitude
Scatter + Global Linear
$$
M_a = (9.803 + 3.189\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
9.803 |
| n |
3.189 |
| gf |
0.800 |
| gb |
-0.502 |
| k |
1.000 |
| δ90 |
10.000 |
| 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 |
| 2021-08-10 |
2022-05-06 |
+2.3130 |
-1.380 |
| 2022-05-06 |
2022-06-13 |
-2.7466 |
+0.127 |
| 2022-06-13 |
2022-07-22 |
+21.5821 |
-2.646 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-07-29 00:00 |
22:54:49.65 |
-42:25:58.6 |
HIP 113248 |
23.35 |
| 2026-07-29 12:00 |
22:54:40.16 |
-42:27:06.0 |
HIP 113248 |
23.44 |
| 2026-07-30 00:00 |
22:54:30.60 |
-42:28:12.9 |
HIP 113248 |
23.71 |
| 2026-07-30 12:00 |
22:54:20.98 |
-42:29:19.5 |
HIP 113248 |
24.18 |
| 2026-07-31 00:00 |
22:54:11.30 |
-42:30:25.7 |
HIP 113248 |
24.83 |
| 2026-07-31 12:00 |
22:54:01.56 |
-42:31:31.4 |
HIP 113248 |
25.65 |
| 2026-08-01 00:00 |
22:53:51.75 |
-42:32:36.7 |
HIP 113248 |
26.61 |
| 2026-08-01 12:00 |
22:53:41.89 |
-42:33:41.6 |
HIP 113196 |
27.11 |
| 2026-08-02 00:00 |
22:53:31.97 |
-42:34:46.0 |
HIP 113103 |
27.17 |
| 2026-08-02 12:00 |
22:53:21.99 |
-42:35:50.0 |
HIP 113103 |
26.79 |
| 2026-08-03 00:00 |
22:53:11.95 |
-42:36:53.6 |
HIP 113103 |
26.59 |
| 2026-08-03 12:00 |
22:53:01.86 |
-42:37:56.6 |
HIP 113103 |
26.57 |
| 2026-08-04 00:00 |
22:52:51.70 |
-42:38:59.2 |
HIP 113103 |
26.74 |
| 2026-08-04 12:00 |
22:52:41.50 |
-42:40:01.3 |
HIP 113103 |
27.08 |
| 2026-08-05 00:00 |
22:52:31.24 |
-42:41:03.0 |
HIP 112874 |
26.70 |
| 2026-08-05 12:00 |
22:52:20.93 |
-42:42:04.1 |
HIP 112874 |
25.00 |
| 2026-08-06 00:00 |
22:52:10.56 |
-42:43:04.7 |
HIP 112874 |
23.37 |
| 2026-08-06 12:00 |
22:52:00.14 |
-42:44:04.9 |
HIP 112874 |
21.84 |
| 2026-08-07 00:00 |
22:51:49.67 |
-42:45:04.5 |
HIP 112874 |
20.43 |
| 2026-08-07 12:00 |
22:51:39.16 |
-42:46:03.6 |
HIP 112874 |
19.16 |
| 2026-08-08 00:00 |
22:51:28.59 |
-42:47:02.1 |
HIP 112874 |
18.08 |
| 2026-08-08 12:00 |
22:51:17.97 |
-42:48:00.2 |
HIP 112874 |
17.21 |
| 2026-08-09 00:00 |
22:51:07.31 |
-42:48:57.7 |
HIP 112874 |
16.59 |
| 2026-08-09 12:00 |
22:50:56.60 |
-42:49:54.6 |
HIP 112874 |
16.26 |
| 2026-08-10 00:00 |
22:50:45.85 |
-42:50:51.0 |
HIP 112874 |
16.22 |
| 2026-08-10 12:00 |
22:50:35.06 |
-42:51:46.8 |
HIP 112874 |
16.49 |
| 2026-08-11 00:00 |
22:50:24.22 |
-42:52:42.0 |
HIP 112874 |
17.04 |
| 2026-08-11 12:00 |
22:50:13.34 |
-42:53:36.6 |
HIP 112874 |
17.86 |
| 2026-08-12 00:00 |
22:50:02.41 |
-42:54:30.7 |
HIP 112874 |
18.91 |
| 2026-08-12 12:00 |
22:49:51.45 |
-42:55:24.1 |
HIP 112874 |
20.16 |
| 2026-08-13 00:00 |
22:49:40.45 |
-42:56:17.0 |
HIP 112874 |
21.56 |
| 2026-08-13 12:00 |
22:49:29.41 |
-42:57:09.2 |
HIP 112541 |
20.12 |
| 2026-08-14 00:00 |
22:49:18.34 |
-42:58:00.9 |
HIP 112541 |
18.35 |
| 2026-08-14 12:00 |
22:49:07.23 |
-42:58:51.9 |
HIP 112541 |
16.66 |
| 2026-08-15 00:00 |
22:48:56.09 |
-42:59:42.2 |
HIP 112541 |
15.10 |
| 2026-08-15 12:00 |
22:48:44.91 |
-43:00:32.0 |
HIP 112541 |
13.71 |
| 2026-08-16 00:00 |
22:48:33.71 |
-43:01:21.1 |
HIP 112541 |
12.54 |
| 2026-08-16 12:00 |
22:48:22.47 |
-43:02:09.5 |
HIP 112541 |
11.67 |
| 2026-08-17 00:00 |
22:48:11.20 |
-43:02:57.3 |
HIP 112541 |
11.16 |
| 2026-08-17 12:00 |
22:47:59.90 |
-43:03:44.5 |
HIP 112541 |
11.06 |
| 2026-08-18 00:00 |
22:47:48.58 |
-43:04:31.0 |
HIP 112541 |
11.39 |
| 2026-08-18 12:00 |
22:47:37.23 |
-43:05:16.8 |
HIP 112541 |
12.11 |
| 2026-08-19 00:00 |
22:47:25.86 |
-43:06:01.9 |
HIP 112541 |
13.16 |