29P/Schwassmann–Wachmann

29P/Schwassmann–Wachmann
29P/Schwassmann–Wachmann imaged by Gemini Observatory in 2021
Discovery
Discovered byArnold Schwassmann
Arno Arthur Wachmann
Discovery siteHamburg Observatory
Discovery dateNovember 15, 1927
Designations
P/1902 E1; P/1927 V1
1908 IV; 1927 II; 1941 VI;
1957 IV; 1974 II; 1989 XV
Orbital characteristics[1]
EpochJanuary 1, 2023 (JD 2459945.5)
Observation arc13.83 years
Earliest precovery date4 March 1902
Number of
observations		622
Aphelion6.318 AU
(30 September 2026)[2]
Perihelion5.777 AU
Semi-major axis6.047 AU
Eccentricity0.0447
Orbital period14.87 years
Max. orbital speed12.7 km/s
Inclination9.364°
312.39°
Argument of
periapsis		50.913°
Last perihelionMarch 7, 2019[3]
Next perihelionFebruary 18, 2035[4]
TJupiter2.986
Earth MOID4.781 AU
Jupiter MOID0.792 AU
Physical characteristics[5]
Dimensions60.4 ± 7.4 km (37.5 ± 4.6 mi)
58 days[6][7]
0.033
Comet total
magnitude (M1)		10.1
~14[8]

Comet 29P/Schwassmann–Wachmann, also known as Schwassmann–Wachmann 1, was discovered on November 15, 1927, by Arnold Schwassmann and Arno Arthur Wachmann at the Hamburg Observatory in Bergedorf, Germany.[9] It is a large comet 60 km in diameter and is known for being observable throughout the whole orbit and having frequent outbursts where it brightens by 2-3 magnitudes. The most recent outbursts were in February 2026, April 2026, and May 2026. The comet will come to solar conjunction on 26 September 2026,[10] and will come to aphelion on 30 September 2026.[2] It crossed the celestial equator in late 2025 and is headed further into southern skies until April 2029 when it will have a declination of −31.[11]

Discovery

It was discovered photographically, when the comet was in outburst and the magnitude was about 13.[9] Precovery images of the comet from March 4, 1902, were found in 1931 and showed the comet at 12th magnitude.[9]

Orbit and physical properties

The comet reached its most recent perihelion on March 7, 2019.[1] It spends its entire orbit just beyond Jupiter at 5.8–6.3 AU from the Sun where the comet remains active with a coma as it is close to the snow line. It will reach aphelion on 30 September 2026.[2]

The comet is a member of a class of objects called "centaurs", of which at least 1000 are known.[12] These are small icy bodies with orbits between those of Jupiter and Neptune. The centaurs have been recently perturbed inward from the Kuiper belt, a disk of trans-Neptunian objects occupying a region extending from the orbit of Neptune to approximately 50 AU from the Sun. Frequent perturbations by Jupiter[1] will likely accumulate and cause the comet to migrate either inward or outward by the year 4000.[13] A number of centaurs appear to be dynamically and perhaps even physically related to 29P; such objects may traverse the coma of 29P when in outburst.[14]

The comet nucleus is estimated to be 60.4±7.4 kilometers in diameter.[1][5] As of 2026, the comet has a rotation period of about 58 days.[6][7]

Outbursts

The comet is unusual in that while normally hovering at around 16th magnitude, it suddenly undergoes an outburst. This causes the comet to brighten by 1 to 5 magnitudes.[15] This happens with a frequency of 7.3 outbursts per year,[15] fading within a week or two. The magnitude of the comet has been known to vary from 18th magnitude to 10th magnitude, a more than thousand-fold increase in brightness, during its brightest outbursts. Between 2014 and 2026, there have been 120 outbursts observed or about 10 outbursts per year.[6] Outbursts are very sudden, rising to maximum in about 2 hours, which is indicative of their cryovolcanic origin; and with the times of outburst modulated by an underlying 58-day periodicity possibly suggesting that its large nucleus is an extremely slow rotator.[7]

Comet 29P after outburst, this is a stack of 20 images centered on the comet's movement, frames taken with a 0.40m telescope F10 + CCD at La Cañada Observatory (MPC-J87) 04-Oct-2008 02:24 UT the stacked images have been Larson–Sekanina filtered to enhance the details, on the left a radial process with delta = −1 px to better show the expanding shells of gas and dust, on the right a rotational gradient with alpha=15 degrees displaying various jets.[16][17]
Comet 29P photographed at Ka-Dar Observatory
Comet 29P photographed at Ka-Dar Observatory
The quasi-circular orbit of 29P/Schwassmann–Wachmann compared to Jupiter and Saturn
The quasi-circular orbit of 29P/Schwassmann–Wachmann compared to Jupiter and Saturn

During 2025, there were 8 notable outbursts occurring as four pairs of twin events: January 2/6, February 1/2, May 13/25, and December 4/11. The December outburst reached about magnitude 13.[18]

In 2026, there was an outburst on February 9/15 to magnitude 12.6V.[19] On April 15 there was outburst from magnitude 16 to 13.[20] Another outburst occurred on May 29.[6]

References

  1. 1 2 3 4 "29P/Schwassmann–Wachmann 1 – JPL Small-Body Database Lookup". ssd.jpl.nasa.gov. Jet Propulsion Laboratory. Retrieved May 5, 2009.
  2. 1 2 3 "Horizons Batch for 29P/Schwassmann–Wachmann 1 (90000395) on 2026-Sep-30" (Aphelion occurs when rdot flips from positive to negative). JPL Horizons. Retrieved September 29, 2025.
  3. ↑ 29P past, present and future orbital elements
  4. ↑ "Horizons Batch for 29P/Schwassmann–Wachmann 1 (90000395) on 2035-Feb-18" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on June 17, 2022. Retrieved October 1, 2021.
  5. 1 2 C. A. Schambeau; Y. R. Fernández; C. M. Lisse; N. Samarasinha; L. M. Woodney (2015). "A new analysis of Spitzer observations of Comet 29P/Schwassmann–Wachmann 1". Icarus. 260: 60–72. arXiv:1506.07037. Bibcode:2015Icar..260...60S. doi:10.1016/j.icarus.2015.06.038. S2CID 119298410.
  6. 1 2 3 4 Richard Miles (May 31, 2026). "New outburst and confirmation of ~58-day rotation period". Retrieved June 1, 2026.
  7. 1 2 3 Miles, Richard (July 1, 2016). "Discrete sources of cryovolcanism on the nucleus of Comet 29P/Schwassmann–Wachmann and their origin". Icarus. 272: 387–413. Bibcode:2016Icar..272..387M. doi:10.1016/j.icarus.2015.11.011.
  8. ↑ Yoshida: 29P (2012–2026)
  9. 1 2 3 Kronk, Gary W. (2001–2005). "29P/Schwassmann–Wachmann 1". Archived from the original on October 22, 2008. Retrieved October 13, 2008. (Cometography Home Page)
  10. ↑ "Solar conjunction for 29P (90000395) in September 2026". JPL Horizons. Retrieved June 12, 2026.
  11. ↑ "Maximum Southern Declination in April 2029". JPL Horizons. Retrieved February 14, 2026.
  12. ↑ "JPL Small-Body Database Search: orbital class (CEN)". Jet Propulsion Laboratory. Archived from the original on September 17, 2020. Retrieved June 1, 2026.
  13. ↑ "Twelve clones of 29P/Schwassmann–Wachmann diverging by the year 4000". Archived from the original on June 23, 2015. Retrieved April 30, 2009. (Solex 10) Archived December 20, 2008, at the Wayback Machine
  14. ↑ de la Fuente Marcos, C.; de la Fuente Marcos, R.; Licandro, J.; Serra-Ricart, M.; Martino, S.; de Leon, J.; Chaudry, F.; Alarcón, M. R. (May 13, 2021). "The active centaur 2020 MK4". Astronomy & Astrophysics. 649 (1): A85 (15 pages). arXiv:2104.01668. Bibcode:2021A&A...649A..85D. doi:10.1051/0004-6361/202039117. S2CID 233024896.
  15. 1 2 Trigo-Rodríguez; Melendo; García-Hernández; Davidsson; Sánchez (2008). "A continuous follow-up of Centaurs, and dormant comets: looking for cometary activity" (PDF). European Planetary Science Congress. Retrieved October 13, 2008.
  16. ↑ Trigo-Rodriguez et al., Outburst activity in comets, I. Continuous monitoring of comet 29P/Schwassmann–Wachmann 1
  17. ↑ Trigo-Rodriguez et al., Outburst activity in comets, II. A multi-band photometric monitoring of comet 29P/Schwassmann–Wachmann 1 arXiv:1009.2381
  18. ↑ 29P: Twin strong outbursts (11 Dec 2025)
  19. ↑ Amongst the 5 brightest eruptions (10 February 2026)
  20. ↑ Latest event appears to be timed at 2026 04 15.35 (15 Apr 2026)
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