☄ Schwassmann-Wachmann 1 29P/Schwassmann-Wachmann 1

How to follow comet Schwassmann-Wachmann 1 live

The panel above recomputes the position of Schwassmann-Wachmann 1 every second in your browser: its distance from the Sun and from Earth, its position in the sky (right ascension and declination). It runs on the same kind of engine observatories use, a Kepler solver applied to the JPL osculating orbital elements, so the numbers are not a static snapshot, they keep ticking.

Just below, the top-down map of the Solar System shows exactly where Schwassmann-Wachmann 1 is right now among the planets. You can fast-forward time with the day slider, zoom and pan, compare its distance to another body with a click, and press "Next event" to jump straight to perihelion. It is the most direct way to grasp the orbit of Schwassmann-Wachmann 1 with no math at all.

Comet fact sheet

About Schwassmann-Wachmann 1

29P/Schwassmann-Wachmann 1 is one of the most peculiar objects in the Solar System. Discovered on 15 November 1927 by German astronomers Arnold Schwassmann and Arno Arthur Wachmann at Hamburg-Bergedorf Observatory, it occupies a nearly circular orbit between Jupiter and Saturn with a period of about 14.9 years.

What makes it unique among known comets is the frequency and violence of its brightness outbursts: dozens of times a year, without warning, the nucleus releases enormous amounts of gas and dust, pushing the magnitude from 16 to 17 (visible only in large telescopes) to 11 to 12 (accessible to amateurs) within hours to days. The mechanism is cryovolcanism, eruptions triggered by super-cooled volatiles accumulated beneath the crust. Observations with the James Webb Space Telescope (JWST), published in Nature Astronomy in 2024 by Sara Faggi's team, mapped CO and CO2 jets with heterogeneous compositions across distinct regions of the nucleus.

History and discovery

Arnold Schwassmann and Arno Wachmann were working at Hamburg-Bergedorf when they discovered the comet in November 1927 on photographic plates taken with the observatory's 1-metre refractor. The computed orbit was immediately unusual: no known comet had such a circular and distant path.

The initial classification was "atypical short-period comet." Over the following decades observers noted that the object never developed a normal tail near perihelion (which sits at 5.77 AU from the Sun, farther than Jupiter), but instead produced intense, unpredictable activity outbursts at any point along the orbit. That combination made it a priority target for studies of physical processes inside cometary nuclei and, later, of the Centaur population.

Orbit, classification and outbursts

29P's orbit is nearly circular, with an eccentricity of only 0.044 and an inclination of 9.4 degrees. Perihelion lies at 5.77 AU and aphelion at 6.25 AU, placing the comet entirely in the Jupiter-Saturn region. This orbital type is characteristic of the Centaurs, trans-Jovian objects that are neither classical comets nor main-belt asteroids, and 29P is considered the prototype of that group.

The outbursts are 29P's most studied phenomenon. Long-term light-curve analyses show that outbursts of different magnitudes occur at different frequencies: small outbursts (1 to 2 magnitudes) happen dozens of times per year, while large ones (4 to 6 magnitudes) are rarer but still recorded several times per decade. In November 2022, a major outburst raised magnitude by more than 4 points in a few hours. Cryovolcanism driven by eruptions of frozen CO and CO2 is the best-supported hypothesis.

Nucleus and the Centaur class

29P/Schwassmann-Wachmann 1 is the prototype of the Centaur class, objects occupying orbits between those of the giant planets and believed to have migrated inward from the Kuiper Belt. Centaurs are transient objects: their orbits are dynamically unstable and they will eventually be ejected from the Solar System or destroyed upon fragmentation after a close encounter with a giant planet.

The nucleus diameter is estimated at around 32 km by recent measurements, making it one of the largest known cometary nuclei. That large size, combined with a cold orbit beyond 5 AU from the Sun, allows CO and CO2 to be abundant enough to sustain intense activity even without water sublimation, which requires being much closer to the Sun.

How to observe

At rest, 29P has magnitude 16 to 17, requiring a telescope of at least 400 mm aperture. During major outbursts, however, magnitude drops to 11 or 12, bringing it within range of 150 to 200 mm amateur telescopes. Since outbursts are unpredictable, the best strategy is to follow alerts from cometary monitoring networks such as the COBS (Comet Observation Database) or the ALPO (Association of Lunar and Planetary Observers).

The comet has no perihelion close to Earth: its orbit lies entirely beyond Jupiter. This means sky position is always determined by the Earth-Sun-comet geometry along the nearly circular orbit. Check JPL Horizons for current position and expected magnitude.

• Quiescent magnitude: 16 to 17 (400 mm+ required)
• Major outburst magnitude: 11 to 12 (150 to 200 mm)
• Outburst alerts: COBS, ALPO, CARA (Italian network)
• Orbital period: 14.9 years (no close perihelion)

Science: JWST, cryovolcanism and Nature Astronomy 2024

NIRSpec observations with the James Webb Space Telescope, conducted on 20 February 2023 (one day before an observed optical outburst) as part of GO program 2416 (PI: McKay), produced the most detailed molecular maps ever obtained of 29P. Results published in Nature Astronomy in 2024 by Sara Faggi and collaborators revealed localised jets with heterogeneous compositions: distinct regions of the nucleus emit different mixtures of CO and CO2, suggesting compositional heterogeneity possibly linked to the bilobate nature of the nucleus.

Beyond JWST data, radio telescope observations with APEX (Atacama Pathfinder Experiment) during the large 2021 outburst measured CO and other volatile molecular production in real time. The combination of multi-wavelength data allowed, for the first time, characterisation of the outburst chemistry from eruption through coma dispersal. 29P serves as a natural laboratory for understanding how comets and Centaurs behave at large heliocentric distances where water does not sublimate but CO and CO2 dominate activity.

Facts worth knowing

• 29P/Schwassmann-Wachmann 1 is the prototype of the Centaur class, transient objects that migrated from the Kuiper Belt and will eventually be ejected or destroyed.
• JWST mapped CO and CO2 jets with heterogeneous compositions in February 2023; results were published in Nature Astronomy in 2024 by Sara Faggi's team.
• The nucleus diameter is estimated at around 32 km, one of the largest known cometary nuclei.
• The comet releases roughly 150 kg of CO per second in its normal active state, not counting outbursts.
• In November 2022 a major outburst raised magnitude by more than 4 points in a few hours, turning the comet from a large-observatory-only target to one reachable with a 150 mm amateur telescope.
• The nucleus rotation period is about 57 days, and outbursts tend to follow a rhythm modulated by that period, suggesting specific active regions are periodically exposed to sunlight.

Other comets

See the full comet catalogue.