| Parameter |
Value |
| Designation |
C/2017 K4 (ATLAS) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2018-01-08T01:00:52.058880Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:33:33Z |
| Obs used |
556 |
| NEO |
- |
| M1 |
4.700 |
| K1 |
19.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2018-03-28.0000000 |
| e |
0.90585450 |
| q (au) |
2.648085 |
| a (au) |
28.127579 |
| i (deg) |
16.678706 |
| Ω (om, deg) |
298.897270 |
| ω (w, deg) |
15.111911 |
| M (ma, deg) |
0.521675 |
Magnitude
Scatter + Global Linear
$$
M_a = (6.069 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
6.069 |
| n |
6.000 |
| gf |
1.000 |
| gb |
-1.000 |
| 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 |
| 2016-05-06 |
2017-11-12 |
+3.1769 |
-1.847 |
| 2018-04-27 |
2019-01-27 |
-4.4170 |
+2.873 |
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 |
06:55:47.24 |
+28:29:33.1 |
HIP 33364 |
8.44 |
| 2026-09-20 12:00 |
06:55:49.68 |
+28:29:35.8 |
HIP 33364 |
8.00 |
| 2026-09-21 00:00 |
06:55:52.05 |
+28:29:38.5 |
HIP 33364 |
7.59 |
| 2026-09-21 12:00 |
06:55:54.37 |
+28:29:41.4 |
HIP 33364 |
7.20 |
| 2026-09-22 00:00 |
06:55:56.64 |
+28:29:44.3 |
HIP 33364 |
6.84 |
| 2026-09-22 12:00 |
06:55:58.85 |
+28:29:47.3 |
HIP 33364 |
6.51 |
| 2026-09-23 00:00 |
06:56:01.01 |
+28:29:50.5 |
HIP 33364 |
6.21 |
| 2026-09-23 12:00 |
06:56:03.11 |
+28:29:53.7 |
HIP 33364 |
5.94 |
| 2026-09-24 00:00 |
06:56:05.15 |
+28:29:57.0 |
HIP 33364 |
5.70 |
| 2026-09-24 12:00 |
06:56:07.14 |
+28:30:00.3 |
HIP 33364 |
5.50 |
| 2026-09-25 00:00 |
06:56:09.08 |
+28:30:03.8 |
HIP 33364 |
5.34 |
| 2026-09-25 12:00 |
06:56:10.95 |
+28:30:07.4 |
HIP 33364 |
5.21 |
| 2026-09-26 00:00 |
06:56:12.78 |
+28:30:11.0 |
HIP 33364 |
5.12 |
| 2026-09-26 12:00 |
06:56:14.54 |
+28:30:14.8 |
HIP 33364 |
5.06 |
| 2026-09-27 00:00 |
06:56:16.25 |
+28:30:18.6 |
HIP 33364 |
5.04 |
| 2026-09-27 12:00 |
06:56:17.90 |
+28:30:22.5 |
HIP 33364 |
5.05 |
| 2026-09-28 00:00 |
06:56:19.49 |
+28:30:26.5 |
HIP 33364 |
5.09 |
| 2026-09-28 12:00 |
06:56:21.03 |
+28:30:30.6 |
HIP 33364 |
5.15 |
| 2026-09-29 00:00 |
06:56:22.51 |
+28:30:34.8 |
HIP 33364 |
5.24 |
| 2026-09-29 12:00 |
06:56:23.94 |
+28:30:39.0 |
HIP 33364 |
5.34 |
| 2026-09-30 00:00 |
06:56:25.30 |
+28:30:43.4 |
HIP 33364 |
5.46 |
| 2026-09-30 12:00 |
06:56:26.61 |
+28:30:47.8 |
HIP 33364 |
5.60 |
| 2026-10-01 00:00 |
06:56:27.86 |
+28:30:52.3 |
HIP 33364 |
5.74 |
| 2026-10-01 12:00 |
06:56:29.05 |
+28:30:56.9 |
HIP 33364 |
5.89 |
| 2026-10-02 00:00 |
06:56:30.19 |
+28:31:01.6 |
HIP 33364 |
6.05 |
| 2026-10-02 12:00 |
06:56:31.26 |
+28:31:06.4 |
HIP 33364 |
6.21 |
| 2026-10-03 00:00 |
06:56:32.28 |
+28:31:11.2 |
HIP 33364 |
6.37 |
| 2026-10-03 12:00 |
06:56:33.24 |
+28:31:16.2 |
HIP 33364 |
6.53 |
| 2026-10-04 00:00 |
06:56:34.14 |
+28:31:21.2 |
HIP 33364 |
6.70 |
| 2026-10-04 12:00 |
06:56:34.98 |
+28:31:26.3 |
HIP 33364 |
6.86 |
| 2026-10-05 00:00 |
06:56:35.77 |
+28:31:31.5 |
HIP 33364 |
7.01 |
| 2026-10-05 12:00 |
06:56:36.49 |
+28:31:36.7 |
HIP 33364 |
7.17 |
| 2026-10-06 00:00 |
06:56:37.16 |
+28:31:42.1 |
HIP 33364 |
7.32 |
| 2026-10-06 12:00 |
06:56:37.76 |
+28:31:47.5 |
HIP 33364 |
7.46 |
| 2026-10-07 00:00 |
06:56:38.31 |
+28:31:53.0 |
HIP 33364 |
7.60 |
| 2026-10-07 12:00 |
06:56:38.79 |
+28:31:58.6 |
HIP 33364 |
7.74 |
| 2026-10-08 00:00 |
06:56:39.22 |
+28:32:04.3 |
HIP 33364 |
7.87 |
| 2026-10-08 12:00 |
06:56:39.59 |
+28:32:10.0 |
HIP 33364 |
7.99 |
| 2026-10-09 00:00 |
06:56:39.89 |
+28:32:15.9 |
HIP 33364 |
8.11 |
| 2026-10-09 12:00 |
06:56:40.14 |
+28:32:21.8 |
HIP 33364 |
8.22 |
| 2026-10-10 00:00 |
06:56:40.33 |
+28:32:27.7 |
HIP 33364 |
8.33 |
| 2026-10-10 12:00 |
06:56:40.46 |
+28:32:33.8 |
HIP 33364 |
8.43 |
| 2026-10-11 00:00 |
06:56:40.52 |
+28:32:39.9 |
HIP 33364 |
8.52 |