| Parameter |
Value |
| Designation |
261P/Larson |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2019-06-17T05:55:39.953280Z |
| Orbit solution date (soln_date, UTC) |
2026-03-31T09:42:39Z |
| Obs used |
1333 |
| NEO |
- |
| M1 |
5.800 |
| K1 |
32.250 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2016-09-27.0000000 |
| e |
0.41834775 |
| q (au) |
2.050551 |
| a (au) |
3.525389 |
| i (deg) |
6.053412 |
| Ω (om, deg) |
294.373787 |
| ω (w, deg) |
62.549411 |
| M (ma, deg) |
212.105953 |
Magnitude
Scatter + Global Linear
$$
M_a = (10.843 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
10.843 |
| n |
6.000 |
| gf |
1.000 |
| gb |
-0.500 |
| 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 |
| 2025-05-25 |
2026-01-05 |
+24.5971 |
-8.320 |
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 |
01:24:32.10 |
+13:21:15.1 |
HIP 6694 |
21.69 |
| 2026-03-26 12:00 |
01:25:37.41 |
+13:27:17.7 |
HIP 6694 |
13.31 |
| 2026-03-27 00:00 |
01:26:42.72 |
+13:33:19.4 |
HIP 6705 |
17.18 |
| 2026-03-27 12:00 |
01:27:48.05 |
+13:39:20.1 |
HIP 6900 |
18.53 |
| 2026-03-28 00:00 |
01:28:53.37 |
+13:45:19.8 |
HIP 6900 |
4.97 |
| 2026-03-28 12:00 |
01:29:58.70 |
+13:51:18.4 |
HIP 6900 |
16.76 |
| 2026-03-29 00:00 |
01:31:04.04 |
+13:57:16.1 |
HIP 6983 |
22.96 |
| 2026-03-29 12:00 |
01:32:09.38 |
+14:03:12.8 |
HIP 7172 |
14.69 |
| 2026-03-30 00:00 |
01:33:14.73 |
+14:09:08.4 |
HIP 7172 |
13.75 |
| 2026-03-30 12:00 |
01:34:20.08 |
+14:15:03.0 |
HIP 7369 |
11.67 |
| 2026-03-31 00:00 |
01:35:25.44 |
+14:20:56.6 |
HIP 7369 |
7.71 |
| 2026-03-31 12:00 |
01:36:30.80 |
+14:26:49.1 |
HIP 7436 |
16.76 |
| 2026-04-01 00:00 |
01:37:36.17 |
+14:32:40.5 |
HIP 7436 |
27.46 |
| 2026-04-01 12:00 |
01:38:41.54 |
+14:38:30.9 |
HIP 7710 |
22.89 |
| 2026-04-02 00:00 |
01:39:46.92 |
+14:44:20.2 |
HIP 7784 |
17.12 |
| 2026-04-02 12:00 |
01:40:52.31 |
+14:50:08.4 |
HIP 7784 |
23.84 |
| 2026-04-03 00:00 |
01:41:57.69 |
+14:55:55.5 |
HIP 8073 |
26.32 |
| 2026-04-03 12:00 |
01:43:03.09 |
+15:01:41.5 |
HIP 8073 |
9.74 |
| 2026-04-04 00:00 |
01:44:08.48 |
+15:07:26.5 |
HIP 8073 |
7.88 |
| 2026-04-04 12:00 |
01:45:13.89 |
+15:13:10.3 |
HIP 8073 |
24.36 |
| 2026-04-05 00:00 |
01:46:19.30 |
+15:18:52.9 |
HIP 8262 |
23.96 |
| 2026-04-05 12:00 |
01:47:24.71 |
+15:24:34.5 |
HIP 8262 |
23.12 |
| 2026-04-06 00:00 |
01:48:30.13 |
+15:30:14.9 |
HIP 8262 |
32.51 |
| 2026-04-06 12:00 |
01:49:35.55 |
+15:35:54.2 |
HIP 8568 |
27.20 |
| 2026-04-07 00:00 |
01:50:40.98 |
+15:41:32.3 |
HIP 8568 |
29.56 |
| 2026-04-07 12:00 |
01:51:46.41 |
+15:47:09.3 |
HIP 8782 |
20.51 |
| 2026-04-08 00:00 |
01:52:51.85 |
+15:52:45.1 |
HIP 8782 |
16.98 |
| 2026-04-08 12:00 |
01:53:57.30 |
+15:58:19.7 |
HIP 8782 |
26.71 |
| 2026-04-09 00:00 |
01:55:02.74 |
+16:03:53.1 |
HIP 9076 |
25.99 |
| 2026-04-09 12:00 |
01:56:08.20 |
+16:09:25.4 |
HIP 9076 |
12.67 |
| 2026-04-10 00:00 |
01:57:13.65 |
+16:14:56.4 |
HIP 9076 |
14.17 |
| 2026-04-10 12:00 |
01:58:19.11 |
+16:20:26.2 |
HIP 9228 |
12.51 |
| 2026-04-11 00:00 |
01:59:24.58 |
+16:25:54.9 |
HIP 9228 |
13.26 |
| 2026-04-11 12:00 |
02:00:30.05 |
+16:31:22.3 |
HIP 9434 |
9.85 |
| 2026-04-12 00:00 |
02:01:35.52 |
+16:36:48.4 |
HIP 9434 |
6.81 |
| 2026-04-12 12:00 |
02:02:41.00 |
+16:42:13.4 |
HIP 9434 |
23.38 |
| 2026-04-13 00:00 |
02:03:46.48 |
+16:47:37.1 |
HIP 9613 |
24.76 |
| 2026-04-13 12:00 |
02:04:51.96 |
+16:52:59.5 |
HIP 9820 |
21.58 |
| 2026-04-14 00:00 |
02:05:57.44 |
+16:58:20.7 |
HIP 9820 |
8.36 |
| 2026-04-14 12:00 |
02:07:02.93 |
+17:03:40.6 |
HIP 9839 |
6.64 |
| 2026-04-15 00:00 |
02:08:08.42 |
+17:08:59.2 |
HIP 10050 |
18.38 |
| 2026-04-15 12:00 |
02:09:13.91 |
+17:14:16.6 |
HIP 10050 |
2.32 |
| 2026-04-16 00:00 |
02:10:19.41 |
+17:19:32.6 |
HIP 10050 |
14.76 |