40P/Väisälä
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 Comet Väisälä 1 imaged on 20 January, 2026, by ZTF | |
| Discovery[1] | |
|---|---|
| Discovered by | Yrjö Väisälä |
| Discovery site | University of Turku, Finland |
| Discovery date | February 8, 1939 |
| Designations | |
| P/1939 CB P/1949 Y1 | |
| |
| Orbital characteristics[2] | |
| Epoch | May 5, 2025 (JD 2460800.5) |
| Observation arc | 86.16 years |
| Earliest precovery date | January 18, 1939 |
| Number of observations | 1,243 |
| Aphelion | 8.079 AU |
| Perihelion | 1.824 AU |
| Semi-major axis | 4.951 AU |
| Eccentricity | 0.63169 |
| Orbital period | 11.018 years |
| Inclination | 11.639° |
| 128.90° | |
| Argument of periapsis | 52.029° |
| Mean anomaly | 342.92° |
| Last perihelion | November 12, 2025[3] November 15, 2014 |
| Next perihelion | 2036-Nov-22[4] |
| TJupiter | 2.535 |
| Earth MOID | 0.823 AU |
| Jupiter MOID | 0.077 AU |
| Physical characteristics[5] | |
Mean diameter | 4.2 km (2.6 mi) |
| Comet total magnitude (M1) | 11.6 |
| Comet nuclear magnitude (M2) | 14.8 |
40P/Väisälä is a periodic comet that was discovered on February 8, 1939. Its orbit was determined on April 26, 1939.[3] In 1994, the diameter of its nucleus was found to be 4.2 km (2.6 mi), similar in size to that of Comet Encke.[5] It came to perihelion on November 12, 2025.
Comet Väisälä was discovered accidentally on photographs exposed for minor planets. Originally, it was given the asteroid designation 1939 CB.[1][5] However, additional findings revealed that the object was of cometary nature. The visual magnitude of Väisälä at the time of its discovery was 15. The orbital characteristics of the new comet at the time of its discovery were "a period of about 10 years, a perihelion date of April 26, 1939, and a perihelion distance of 1.75 AU (262 million km)."[1]
Outburst
The comet was observed to brighten by 2.7 magnitudes between 19 January and 20 January 2026, from magnitude 17.1 to 14.4, when the comet was 1.95 AU from the Sun. The appearance of the comet also changed, featuring a compact source centered at the comet's nucleus instead of the coma and nucleus of the previous day. The ejecta on 21 January had expanded to 5 arcseconds.[6]
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