C/2025 Y1 (ATLAS)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2025 Y1 (ATLAS) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2027-10-14T01:11:19.011840Z |
| Orbit solution date (soln_date, UTC) | 2026-09-08T09:12:18Z |
| Obs used | 1486 |
| NEO | - |
| M1 | 6.500 |
| K1 | 9.250 |
| PC | 0.030 |
| Discovery observation (MPC, UTC) | 2025-12-26T13:40:40.656000Z |
| Discovery magnitude (MPC) | 18.75 o |
| Discovery observatory (MPC) | T05 · ATLAS-HKO, Haleakala |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2026-04-04.0000000 |
| e | 0.99955225 |
| q (au) | 2.601924 |
| a (au) | 5811.155784 |
| i (deg) | 14.556983 |
| Ω (om, deg) | 166.551828 |
| ω (w, deg) | 124.297849 |
| M (ma, deg) | 359.998758 |
Magnitude
Scatter + Global Linear
$$ M_a = (1.374 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 1.374 |
| n | 6.000 |
| gf | 1.000 |
| gb | -0.895 |
| 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 |
|---|---|---|---|
| 2025-11-19 | 2026-04-06 | -0.8421 | +0.883 |
| 2026-04-06 | 2026-08-05 | +2.7612 | -2.141 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Finding Chart
Ephemeris
| Date/Time (UTC) | RA (J2000) | Dec (J2000) | Nearest HIP | Dist from HIP (arcmin) |
|---|---|---|---|---|
| 2026-09-20 00:00 | 13:30:33.66 | -00:55:34.9 | HIP 65987 | 25.90 |
| 2026-09-20 12:00 | 13:31:00.65 | -00:58:04.9 | HIP 65987 | 19.69 |
| 2026-09-21 00:00 | 13:31:27.73 | -01:00:35.0 | HIP 65987 | 14.43 |
| 2026-09-21 12:00 | 13:31:54.90 | -01:03:05.2 | HIP 65987 | 11.53 |
| 2026-09-22 00:00 | 13:32:22.14 | -01:05:35.5 | HIP 65987 | 12.76 |
| 2026-09-22 12:00 | 13:32:49.47 | -01:08:05.9 | HIP 65987 | 17.28 |
| 2026-09-23 00:00 | 13:33:16.89 | -01:10:36.4 | HIP 65987 | 23.26 |
| 2026-09-23 12:00 | 13:33:44.38 | -01:13:07.0 | HIP 65987 | 29.86 |
| 2026-09-24 00:00 | 13:34:11.96 | -01:15:37.7 | HIP 66367 | 36.52 |
| 2026-09-24 12:00 | 13:34:39.62 | -01:18:08.4 | HIP 66391 | 31.19 |
| 2026-09-25 00:00 | 13:35:07.36 | -01:20:39.3 | HIP 66391 | 24.67 |
| 2026-09-25 12:00 | 13:35:35.17 | -01:23:10.2 | HIP 66391 | 18.78 |
| 2026-09-26 00:00 | 13:36:03.07 | -01:25:41.2 | HIP 66391 | 14.34 |
| 2026-09-26 12:00 | 13:36:31.05 | -01:28:12.2 | HIP 66391 | 12.98 |
| 2026-09-27 00:00 | 13:36:59.11 | -01:30:43.3 | HIP 66391 | 15.55 |
| 2026-09-27 12:00 | 13:37:27.25 | -01:33:14.4 | HIP 66391 | 20.66 |
| 2026-09-28 00:00 | 13:37:55.47 | -01:35:45.6 | HIP 66643 | 25.57 |
| 2026-09-28 12:00 | 13:38:23.77 | -01:38:16.9 | HIP 66643 | 18.68 |
| 2026-09-29 00:00 | 13:38:52.14 | -01:40:48.2 | HIP 66643 | 12.50 |
| 2026-09-29 12:00 | 13:39:20.60 | -01:43:19.5 | HIP 66643 | 8.77 |
| 2026-09-30 00:00 | 13:39:49.13 | -01:45:50.8 | HIP 66643 | 10.55 |
| 2026-09-30 12:00 | 13:40:17.73 | -01:48:22.2 | HIP 66643 | 16.14 |
| 2026-10-01 00:00 | 13:40:46.42 | -01:50:53.6 | HIP 66643 | 22.92 |
| 2026-10-01 12:00 | 13:41:15.18 | -01:53:25.0 | HIP 66886 | 21.57 |
| 2026-10-02 00:00 | 13:41:44.02 | -01:55:56.4 | HIP 66886 | 18.16 |
| 2026-10-02 12:00 | 13:42:12.94 | -01:58:27.8 | HIP 66886 | 17.62 |
| 2026-10-03 00:00 | 13:42:41.93 | -02:00:59.2 | HIP 66886 | 20.22 |
| 2026-10-03 12:00 | 13:43:11.00 | -02:03:30.6 | HIP 66922 | 24.94 |
| 2026-10-04 00:00 | 13:43:40.14 | -02:06:02.0 | HIP 66922 | 24.86 |
| 2026-10-04 12:00 | 13:44:09.36 | -02:08:33.4 | HIP 66922 | 27.08 |
| 2026-10-05 00:00 | 13:44:38.65 | -02:11:04.8 | HIP 66922 | 31.13 |
| 2026-10-05 12:00 | 13:45:08.02 | -02:13:36.1 | HIP 67279 | 35.26 |
| 2026-10-06 00:00 | 13:45:37.46 | -02:16:07.4 | HIP 67279 | 27.49 |
| 2026-10-06 12:00 | 13:46:06.97 | -02:18:38.6 | HIP 67279 | 19.72 |
| 2026-10-07 00:00 | 13:46:36.56 | -02:21:09.8 | HIP 67279 | 11.96 |
| 2026-10-07 12:00 | 13:47:06.22 | -02:23:41.0 | HIP 67279 | 4.37 |
| 2026-10-08 00:00 | 13:47:35.95 | -02:26:12.1 | HIP 67279 | 4.20 |
| 2026-10-08 12:00 | 13:48:05.75 | -02:28:43.1 | HIP 67279 | 11.82 |
| 2026-10-09 00:00 | 13:48:35.62 | -02:31:14.0 | HIP 67385 | 19.21 |
| 2026-10-09 12:00 | 13:49:05.57 | -02:33:44.9 | HIP 67385 | 17.96 |
| 2026-10-10 00:00 | 13:49:35.58 | -02:36:15.7 | HIP 67385 | 20.03 |
| 2026-10-10 12:00 | 13:50:05.67 | -02:38:46.4 | HIP 67599 | 17.41 |
| 2026-10-11 00:00 | 13:50:35.82 | -02:41:17.0 | HIP 67599 | 9.83 |