C/2004 Q2 (Machholz)
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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.
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 Template:Val hours,Template:R although a 2012 study regarding the morphological structures in its coma suggested it may have an orbital period of 0.74 days instead.Template:R
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.Template:R In March 2005, the GALEX spacecraft observed the comet in far-ultraviolet (FUV) light, where it determined that ionized methane (Template:Chem) molecules dominated its coma, which explained the shorter than expected lifetime of carbon molecules detected.Template:R
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.Template:R
Its nucleus has a mean diameter of Template:Cvt.Template:R
Orbit
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 Template:Convert and a period of approximately 12,400 years.Template:R