Perihelion date: 4 March 2022
Perihelion distance (q): 1.5
Aphelion distance (Q) : 4.7
Period (years): 5.6
Eccentricity (e): 0.51
Inclination (i): 10.5
JPL orbit diagram
The comet, also known as Tempel 1, was discovered on April 3, 1867, by Wilhelm
Tempel, an astronomer working in Marseille. At the time of discovery, it approached
perihelion once every 5.68 years (designations 9P/1867 G1 and 1867 II).
It was subsequently observed in 1873 (9P/1873 G1, 1873 I, 1873a) and in 1879 (1879
III, 1879b). Photographic attempts during 1898 and 1905 failed to recover the comet,
and astronomers surmised that it had disintegrated. In fact, its orbit had changed.
Tempel 1's orbit occasionally brings it sufficiently close to Jupiter to be altered, with a
consequent change in the comet's orbital period. This occurred in 1881 (closest
approach to Jupiter of 0.55 AU), lengthening the orbital period to 6.5 years. Perihelion
also changed, increasing by 50 million kilometres, rendering the comet far less visible
Tempel 1 was rediscovered 13 orbits later in 1967 (as 9P/1967 L1, 1966 VII), after
British astronomer Brian G. Marsden performed precise calculations of the comet's
orbit that took into account Jupiter's perturbations. Marsden found that further close
approaches to Jupiter in 1941 (0.41 AU) and 1953 (0.77 AU) had decreased both the
perihelion distance and the orbital period to values smaller than when the comet was
initially discovered (5.84 and 5.55 years, respectively). These approaches moved
Tempel 1 into its present libration around the 1:2 resonance with Jupiter.
Despite an unfavorable 1967 return, Elizabeth Roemer of the Catalina Observatory
took several photographs. Initial inspection revealed nothing, but in late 1968 she
found a June 8, 1967 exposure (Tempel 1 had passed perihelion in January) that held
the image of an 18th magnitude diffuse object very close to where Marsden had
predicted the comet to be. A single image does not allow an orbit computation, so the
next return had to be awaited.
Roemer and L. M. Vaughn recovered the comet on January 11, 1972, from Steward
Observatory (9P/1972 A1, 1972 V, 1972a). The comet became widely observed,
reached a maximum brightness of magnitude 11 during May, and was last seen on
Since that time the comet has been seen at every apparition. Tempel 1 is not a bright
comet; its brightest apparent magnitude since discovery has been 11, far below
naked-eye visibility. Its nucleus measures 7.6 km × 4.9 km (4.7 mi × 3.0 mi).
Measurements taken by the Hubble Space Telescope in visible light and the Spitzer
Space Telescope in infrared light suggest a low albedo of only 4%. A two-day rotation
rate was also determined.
On 4 July 2005 at 05:52 UTC (01:52 EDT), Tempel 1 was deliberately struck by one
component of the NASA Deep Impact probe, one day before perihelion. The impact
was photographed by the other component of the probe, which recorded a bright
spray from the impact site. The impact was also observed by earthbound and space
telescopes, which recorded a brightening of several magnitudes. The crater that
formed was not visible to Deep Impact due to the cloud of dust raised by the impact,
but was estimated to be between 100 and 250 meters in diameter and 30 meters
deep. The probe's spectrometer instrument detected dust particles finer than human
hair, and discovered the presence of silicates, carbonates, smectite, metal sulfides
(like fool's gold), amorphous carbon and polycyclic aromatic hydrocarbons. Water ice
was detected in the ejecta.
The water ice came from 1 meter below the surface crust (the devolatized layer
around the nucleus). In part because the crater formed during the Deep Impact
collision could not be imaged during the initial flyby, on 3 July 2007, NASA approved
the New Exploration of Tempel 1 (or NExT) mission. The low-cost mission utilized the
already existing Stardust spacecraft, which had studied Comet Wild 2 in 2004.
Stardust was placed into a new orbit so that it approached Tempel 1. It passed at a
distance of approximately 181 km (112 mi) on February 15, 2011, 04:42 UTC.
This was the first time that a comet was visited twice. On February 15, NASA
scientists identified the crater formed by Deep Impact in images from Stardust. The
crater is estimated to be 150 m (490 ft) in diameter, and has a bright mound in the
center likely created when material from the impact fell back into the crater. The
geometry of the flyby allowed investigators to obtain considerably more three-
dimensional information about the nucleus from stereo pairs of images than during
Deep Impact's encounter. Scientists were able to quickly spot locations where an
elevated flow-like formation of icy material on the comet's surface receded due to
sublimation between encounters.
Observations (VEMag = visual equivalent magnitude)