C/2004 Q2 (Machholz)

For other comets discovered by Donald E. Machholz, see Comet Machholz.

Comet Machholz, formally designated C/2004 Q2, is a non-periodic comet discovered by Donald Machholz on 27 August 2004. It reached naked eye brightness in January 2005. Unusual for such a relatively bright comet, its perihelion was farther from the Sun than the Earth's orbit.

C/2004 Q2 (Machholz)

Comet Machholz photographed by Ralf Weber from Andalusia, Spain in February 2005
Discovery
Discovered by	Donald Machholz
Discovery date	27 August 2004
Orbital characteristics[1][2]
Epoch	30 March 2005 (JD 2453459.52005)
Observation arc	2.03 years
Number of observations	3,612
Aphelion	~5,100 AU (inbound) ~1,100 AU (outbound)
Perihelion	1.205 AU
Semi-major axis	~2,400 AU
Eccentricity	0.99950
Orbital period	~130,000 years (inbound) ~12,400 years (outbound)
Inclination	38.589°
Longitude of ascending node	93.622°
Argument of periapsis	19.505°
Mean anomaly	0.001°
Last perihelion	24 January 2005
TJupiter	1.066
Earth MOID	0.249 AU
Jupiter MOID	1.973 AU
Physical characteristics[3][4]
Dimensions	4.2–7.8 km (2.6–4.8 mi)
Mean diameter	6.0 km (3.7 mi)
Synodic rotation period	9.1±0.2 hours
Comet total magnitude (M1)	11.2

Physical characteristics

During its closest approach to Earth in January 2005, ground observations from La Palma, Spain revealed that the comet may have a rotation period of 9.1±0.2 hours,^[3] although a 2012 study regarding the morphological structures in its coma suggested it may have an orbital period of 0.74 days instead.^[5]

Between December 2004 and January 2005, observations from Lulin and La Silla observatories spotted two jets of carbon and cyanogen (CN) compounds that form a spiral-like structure within the coma, which were caused by two active surface regions in its nucleus.^[6] In March 2005, the GALEX spacecraft observed the comet in far-ultraviolet (FUV) light, where it determined that ionized methane (CH
₄) molecules dominated its coma, which explained the shorter than expected lifetime of carbon molecules detected.^[7]

Near-infrared measurements of the comet has indicated that its surface material generate an outflow in the form of fragments that separated into gas and dust under sublimation on time scales of the order of days.^[8]

Its nucleus has a mean diameter of 6.0 km (3.7 mi).^[4]

Orbit

C/2004 Q2 appears to pass near the Pleiades cluster in 2005.

Given the orbital eccentricity of this object, different epochs can generate quite different heliocentric unperturbed two-body best-fit solutions to the aphelion distance (maximum distance) of this object. For objects at such high eccentricity, the Suns barycentric coordinates are more stable than heliocentric coordinates. Using JPL Horizons the barycentric orbital elements for epoch 2050 generate a semi-major axis of 537 AU (80.3 billion km) and a period of approximately 12,400 years.^[1]

See also

• 96P/Machholz
• 141P/Machholz
• C/1978 R3 (Machholz)
• C/2018 V1 (Machholz–Fujikawa–Iwamoto)