C/2021 D2 (ZTF)
| Parameter |
Value |
| Designation |
C/2021 D2 (ZTF) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2022-02-03T23:30:34.882560Z |
| Orbit solution date (soln_date, UTC) |
2026-01-13T08:12:19Z |
| Obs used |
654 |
| NEO |
- |
| M1 |
13.300 |
| K1 |
4.500 |
| PC |
- |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-11-09.0000000 |
| e |
1.00133730 |
| q (au) |
2.946303 |
| a (au) |
-2203.174195 |
| i (deg) |
83.831242 |
| Ω (om, deg) |
305.677385 |
| ω (w, deg) |
125.029250 |
| M (ma, deg) |
-0.000829 |
Magnitude
Scatter + Global Linear
$$
M_a = (15.459 + 2.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
15.459 |
| n |
2.000 |
| gf |
1.000 |
| gb |
-0.786 |
| k |
0.800 |
| 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 |
| 2021-02-19 |
2021-05-22 |
+15.5304 |
-9.660 |
| 2021-05-22 |
2021-08-10 |
-4.5062 |
+2.220 |
| 2021-08-10 |
2022-02-03 |
+4.5771 |
-2.449 |
| 2022-02-21 |
2022-12-25 |
+12.4249 |
-5.266 |
| 2022-12-25 |
2023-04-22 |
+30.3439 |
-17.115 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-02-03 00:00 |
07:41:09.38 |
-49:55:43.1 |
HIP 37416 |
14.11 |
| 2026-02-03 12:00 |
07:40:53.89 |
-49:55:10.9 |
HIP 37416 |
13.32 |
| 2026-02-04 00:00 |
07:40:38.47 |
-49:54:37.3 |
HIP 37416 |
12.97 |
| 2026-02-04 12:00 |
07:40:23.11 |
-49:54:02.5 |
HIP 37416 |
13.10 |
| 2026-02-05 00:00 |
07:40:07.82 |
-49:53:26.4 |
HIP 37416 |
13.68 |
| 2026-02-05 12:00 |
07:39:52.59 |
-49:52:49.1 |
HIP 37416 |
14.66 |
| 2026-02-06 00:00 |
07:39:37.44 |
-49:52:10.5 |
HIP 37416 |
15.97 |
| 2026-02-06 12:00 |
07:39:22.35 |
-49:51:30.6 |
HIP 37416 |
17.52 |
| 2026-02-07 00:00 |
07:39:07.33 |
-49:50:49.5 |
HIP 37416 |
19.27 |
| 2026-02-07 12:00 |
07:38:52.39 |
-49:50:07.2 |
HIP 37416 |
21.15 |
| 2026-02-08 00:00 |
07:38:37.52 |
-49:49:23.6 |
HIP 37416 |
23.14 |
| 2026-02-08 12:00 |
07:38:22.72 |
-49:48:38.8 |
HIP 37416 |
25.20 |
| 2026-02-09 00:00 |
07:38:08.00 |
-49:47:52.9 |
HIP 36928 |
25.94 |
| 2026-02-09 12:00 |
07:37:53.37 |
-49:47:05.7 |
HIP 36928 |
23.66 |
| 2026-02-10 00:00 |
07:37:38.81 |
-49:46:17.3 |
HIP 36928 |
21.46 |
| 2026-02-10 12:00 |
07:37:24.33 |
-49:45:27.7 |
HIP 36928 |
19.33 |
| 2026-02-11 00:00 |
07:37:09.93 |
-49:44:37.0 |
HIP 36928 |
17.32 |
| 2026-02-11 12:00 |
07:36:55.62 |
-49:43:45.1 |
HIP 36928 |
15.46 |
| 2026-02-12 00:00 |
07:36:41.39 |
-49:42:52.0 |
HIP 36928 |
13.81 |
| 2026-02-12 12:00 |
07:36:27.25 |
-49:41:57.8 |
HIP 36928 |
12.45 |
| 2026-02-13 00:00 |
07:36:13.20 |
-49:41:02.4 |
HIP 36928 |
11.49 |
| 2026-02-13 12:00 |
07:35:59.24 |
-49:40:05.9 |
HIP 36928 |
11.02 |
| 2026-02-14 00:00 |
07:35:45.36 |
-49:39:08.3 |
HIP 36928 |
11.10 |
| 2026-02-14 12:00 |
07:35:31.58 |
-49:38:09.6 |
HIP 36928 |
11.73 |
| 2026-02-15 00:00 |
07:35:17.89 |
-49:37:09.8 |
HIP 36928 |
12.81 |
| 2026-02-15 12:00 |
07:35:04.30 |
-49:36:08.9 |
HIP 36928 |
14.23 |
| 2026-02-16 00:00 |
07:34:50.80 |
-49:35:06.9 |
HIP 36777 |
13.92 |
| 2026-02-16 12:00 |
07:34:37.40 |
-49:34:03.8 |
HIP 36777 |
13.35 |
| 2026-02-17 00:00 |
07:34:24.09 |
-49:32:59.7 |
HIP 36777 |
13.22 |
| 2026-02-17 12:00 |
07:34:10.89 |
-49:31:54.6 |
HIP 36777 |
13.54 |
| 2026-02-18 00:00 |
07:33:57.78 |
-49:30:48.4 |
HIP 36777 |
14.29 |
| 2026-02-18 12:00 |
07:33:44.78 |
-49:29:41.2 |
HIP 36777 |
15.39 |
| 2026-02-19 00:00 |
07:33:31.87 |
-49:28:32.9 |
HIP 36777 |
16.77 |
| 2026-02-19 12:00 |
07:33:19.08 |
-49:27:23.7 |
HIP 36681 |
15.64 |
| 2026-02-20 00:00 |
07:33:06.38 |
-49:26:13.5 |
HIP 36681 |
13.91 |
| 2026-02-20 12:00 |
07:32:53.79 |
-49:25:02.3 |
HIP 36681 |
12.39 |
| 2026-02-21 00:00 |
07:32:41.31 |
-49:23:50.1 |
HIP 36681 |
11.14 |
| 2026-02-21 12:00 |
07:32:28.94 |
-49:22:37.0 |
HIP 36681 |
10.27 |
| 2026-02-22 00:00 |
07:32:16.67 |
-49:21:23.0 |
HIP 36681 |
9.88 |
| 2026-02-22 12:00 |
07:32:04.51 |
-49:20:08.0 |
HIP 36681 |
10.02 |
| 2026-02-23 00:00 |
07:31:52.47 |
-49:18:52.1 |
HIP 36681 |
10.66 |
| 2026-02-23 12:00 |
07:31:40.53 |
-49:17:35.3 |
HIP 36678 |
11.69 |
| 2026-02-24 00:00 |
07:31:28.71 |
-49:16:17.7 |
HIP 36678 |
13.02 |