Comet 161p Hartley-IRAS

 

Comet 161p Hartley-IRAS. Seestar S30 EQ mode. 30x60 sec exposures. Credit: Pip Stakkert at the JPO.

Single 60 second exposure showing the Cometary Nucleus 'unsmeared by relative motion (very noisy) Credit: Kurt Thrust.

" The Seestar S30 struggled with this small and faint comet, currently between mag +11 and +14, which is also cruising fairly low in the sky in the Constellation Pegasus. It is a periodic comet and is due to return in 21 years time. The image appears to show a tail but this is a visual effect due to relative motion and the length of exposure over 30 minutes" - Joel Cairo CEO of the Jodrell Plank Observatory.

Report by Gary Gemini Coms Officer at the JPO

Comet 161P/Hartley-IRAS

Captured: October 11, 2026

Overview & Physical Characteristics

• Nucleus Size: Comet 161P/Hartley-IRAS possesses a remarkably compact solid core, with an estimated nuclear diameter of approximately 0.4 km (assuming a standard low albedo of 0.04).

• Coma and Morphology: Surrounding the nucleus is an active, diffuse dust coma spanning roughly 1 to 3 arcminutes in apparent diameter. Depending on thermal outgassing activity, it displays a condensed central region typical of periodic comets undergoing solar heating.

• Spectral Profile: The spectrum of 161P is characterized by a combined solar reflection continuum blended with distinct emission bands from volatile gas species and fine silicate dust particles released as sub-surface ices sublimate.

Current Trajectory & Distance

• Distance from Earth: As of mid-October 2026, the comet is positioned at a geocentric distance of approximately 0.57 AU (~85.5 million kilometers), following its recent closest approach to Earth on October 2, 2026, at 0.50 AU (~75.3 million kilometers).

Orbital Mechanics

• Orbital Period: 161P follows an elongated periodic orbit with a period of 21.46 years.

• Perihelion and Aphelion: Its perihelion distance ($q$) is 1.27 AU (bringing it just outside Earth's orbit and inside Mars), while its aphelion distance ($Q$) stretches outward to roughly 14.19 AU, carrying it far beyond the orbit of Saturn.

• Eccentricity and Inclination: The orbit features a high eccentricity of 0.836 and a retrogradely inclined plane of 95.8° relative to the ecliptic, giving it a unique dynamical path through the inner Solar System.

" We have recently downloaded a copy of the freeware AffiityPhoto3 and James Ritson's Astro V20 macros that run within it. The above image is the first we have processed using some of the many features offered by this excellent software. First impressions are very good indeed!" - Kurt Thrust current Director of the Jodrell Plank Observatory.