☄ Tempel 2 10P/Tempel 2

How to follow comet Tempel 2 live

The panel above recomputes the position of Tempel 2 every second in your browser: its distance from the Sun and from Earth, its position in the sky (right ascension and declination), and a live countdown to the next perihelion. 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 Tempel 2 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 Tempel 2 with no math at all.

Comet fact sheet

About Tempel 2

Wilhelm Tempel had a sharp eye for fuzzy objects. On the night of July 4, 1873, in Milan, he logged a smudge in the sky that would become the tenth numbered periodic comet in history: 10P/Tempel 2. Tempel had discovered other comets before, but this one gained special importance for its exceptionally large nucleus within the Jupiter family and for a stable orbit that has allowed more than twenty-five documented perihelia to date, making it one of the most consistently observed targets in comet astronomy.

10P/Tempel 2 is not a visual spectacle. But for scientists studying the evolution of cometary nuclei, it is a unique laboratory: the observational record stretching back to 1873 allows tracking how the nucleus ages, loses mass, and slows its rotation over decades, an unmatched dataset among known periodic comets.

History and discovery

Ernst Wilhelm Leberecht Tempel was a German lithographer who became a self-taught astronomer and discovered 13 comets over his career, along with several asteroids. 10P was found on July 4, 1873 during one of his routine sky sweeps from the Brera Observatory in Milan. The "2" after his name distinguishes this comet from 9P/Tempel 1, the target of NASA's Deep Impact mission in 2005.

Since its discovery, 10P/Tempel 2 has been tracked with rare continuity: with more than twenty-five apparitions recorded over 150 years, it holds one of the longest observational histories of any periodic comet in modern astronomy. That extensive dataset allows scientists to study how the nucleus ages and loses mass with each perihelion passage, something impossible to do with comets observed only a few times.

Orbit and returns

10P/Tempel 2 has an orbital period of 5.36 years and belongs to the Jupiter belt, the group of comets whose aphelion lies near the giant planet's orbit (roughly 5.2 AU). Perihelion sits at 1.38 AU from the Sun, in the region between Earth and Mars. The next favorable perihelion occurs in 2027, when the comet should be well placed for northern-hemisphere observers in the second half of the year.

The orbit of 10P is notably stable for a Jovian comet, which has contributed to the continuity of observations. Jovian perturbations exist but are modest compared to comets whose perihelion passes closer to Jupiter. This stability allowed Lowell Observatory to accumulate systematic measurements for more than 25 years, an exceptional time series in the history of cometology.

Nucleus and family

The nucleus of 10P/Tempel 2 is exceptionally large for a Jupiter-family member: estimates from photometry and infrared thermometry point to a diameter of about 10.6 km, with a very low albedo of 0.022, meaning it reflects just 2.2 percent of sunlight and is effectively black. The nucleus is large enough to be detected in thermal images even when the comet is near aphelion at Jovian distance, something unusual among periodic comets.

Despite its size, 10P is not very active relative to its volume. Part of the surface is likely covered by a refractory crust that blocks sublimation of volatiles from the interior, a phenomenon known as "mantling." This crust forms from the deposition of non-volatile material (silicates, organic compounds) left behind when the ices sublimate in the surface layers. The result is a nucleus that appears dormant except where specific regions still have exposed ices.

• Nucleus diameter: ~10.6 km
• Albedo: 0.022 (reflects only 2.2% of sunlight)
• Rotation period (1988): 8.932 hours
• Rotation period (1999): 8.941 hours
• Rotation period (2010-11): 8.950 hours (documented slowdown)
• Group: Jupiter family (JFC)
• Detectable in thermal infrared out to aphelion (Jovian distance)

How to observe

10P/Tempel 2 can reach magnitude 8 to 9 at good oppositions, making it accessible to amateur telescopes of 4 inches. The next favorable perihelion will occur in 2027, when it should be well placed for northern-hemisphere observers in the second half of the year. Photographically, even modest telescopes reveal the coma and occasional tail structure, especially close to perihelion.

10P has no confirmed associated meteor shower. Observing the comet itself is the main interest, both for amateurs and professional astronomers who continue monitoring the nucleus spin-down. For planning observations, JPL Horizons provides daily ephemerides; Cometwatch (cometwatch.co.uk) also offers regularly updated brightness forecasts and position maps.

• Minimum instrument: 4-inch telescope
• Typical perihelion magnitude: 8 to 9 (favorable years)
• Next favorable perihelion: 2027 (northern hemisphere, second half of year)
• No associated meteor shower
• Ephemeris sources: JPL Horizons, Cometwatch

Science and historical observations

The scientific value of 10P/Tempel 2 lies in the spin-down documented over 25 years of systematic observations at Lowell Observatory, Arizona. Data published in The Astronomical Journal in 2012 (Knight, Mueller, Farnham, and collaborators) show that the rotation period increased from 8.932 hours in 1988 to 8.941 hours in 1999 and 8.950 hours in 2010-2011, a change of 18 milliseconds per year attributed to the torque generated by gas jets emerging from the surface during cometary activity.

This phenomenon, analogous to the YORP effect in asteroids, has implications for the long-term stability of cometary nuclei. If the slowdown continues at the same rate, 10P will eventually rotate so slowly that its morphology could change. Follow-up studies with the Discovery Channel Telescope (DCT) in 2013 confirmed the trend and refined the model of active region distribution on the nucleus surface. Observations with the Herschel Space Observatory detected ammonia and other parent molecules in 10P/Tempel 2, helping map the distribution of volatiles in Jovian-family nuclei.

Facts

• Wilhelm Tempel discovered 13 comets, but none is more continuously studied than 10P/Tempel 2, ironically the least visually spectacular of them.
• The 10.6-km nucleus is large enough to be detected in thermal images even near aphelion at Jovian distance, unusual among periodic comets.
• The nucleus spin-down rate is ~18 milliseconds per year, documented over 25 years of Lowell Observatory observations, one of the longest rotation-rate records in the history of cometology.
• Herschel Space Observatory observations detected ammonia and other parent molecules in 10P/Tempel 2, contributing to mapping volatile distributions in Jovian-family nuclei.
• NASA's Deep Impact mission in 2005 targeted 9P/Tempel 1, not 10P, but that mission's success increased scientific interest in the entire Tempel comet family.
• The albedo of 0.022 is among the lowest recorded for any Solar System body, making 10P's nucleus darker than bituminous coal.

Other comets

See the full comet catalogue.