311P/PanSTARRS

For other comets of the same name, see List of Pan-STARRS discoveries.

311P/PanSTARRS, also known as P/2013 P5 (PanSTARRS), is an active asteroid and Encke-type comet discovered by Bryce T. Bolin using the Pan-STARRS telescope on 27 August 2013.^[1][6] Observations made by the Hubble Space Telescope revealed that it had six comet-like tails.^[7] The tails are suspected to be streams of material ejected by the asteroid as a result of a rubble pile asteroid spinning fast enough to remove material from it.^[3] This is similar to 331P/Gibbs, which was found to be a quickly-spinning rubble pile as well.

311P/PanSTARRS

Comet 311P/PanSTARRS imaged by the Hubble Space Telescope on 10–23 September 2013
Discovery[1]
Discovered by	Bryce T. Bolin
Discovery site	Haleakala Observatory (Pan-STARRS)
Discovery date	27 August 2013
Designations
MPC designation	P/2013 P5
Orbital characteristics[2]
Epoch	29 April 2017 (JD 2457872.5)
Observation arc	20.29 years
Earliest precovery date	17 January 2005
Number of observations	272
Aphelion	2.442 AU
Perihelion	1.936 AU
Semi-major axis	2.189 AU
Eccentricity	0.11567
Orbital period	3.238 years
Avg. orbital speed	0.304°/d
Inclination	4.966°
Longitude of ascending node	279.26°
Argument of periapsis	143.99°
Mean anomaly	337.88°
Last perihelion	1 January 2024
Next perihelion	30 March 2027
TJupiter	3.661
Earth MOID	0.949 AU
Jupiter MOID	2.818 AU
Physical characteristics
Mean diameter	~0.48 km (0.30 mi)[3]
Mean density	3.3±0.2 g/cm3[3]
Escape velocity	~0.240 m/s[3]
Synodic rotation period	≥ 5.4 hours[4]
Geometric albedo	0.29±0.09[5]
Comet total magnitude (M1)	18.98±0.10[5]

Three-dimensional models constructed by Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany, showed that the tails could have formed by a series of periodic impulsive dust-ejection events,^[a] radiation pressure from the Sun then stretched the dust into streams.^[7]

Precovery images from the Sloan Digital Sky Survey from 2005 were found, showing negligible cometary activity in 2005.^{[citation needed]}

Physical characteristics

The asteroid has a radius of about 240 m (790 ft).^[3] The first images taken by Pan-STARRS revealed that the object had an unusual appearance: asteroids generally appear as small points of light, but P/2013 P5 was identified as a fuzzy-looking object by astronomers.^[6] The multiple tails were observed by the Hubble Space Telescope on 10 September 2013, Hubble later returned to the asteroid on 23 September, its appearance had totally changed. It looked as if the entire structure had swung around.^[6] The Hubble Space Telescope continued to track the object through 11 February 2014.^[8] The comet-like appearance has resulted in the asteroid being named as a comet. The object has a low orbital inclination and always stays outside the orbit of Mars.^[2]

Possible satellite

On 19 April 2018, observations based on light curvature suggested a possible satellite around 311P/PANSTARRS approaching 200 meters.^[9] If true this would be one of the few minor planets designated as a comet known to harbor a satellite.

Exploration

Main article: Tianwen-2

The Tianwen-2 spacecraft is planned to get in orbit around 311P/PanSTARRS in the mid-2030s. It was launched on 28 May 2025 and it will first visit and take samples from asteroid 469219 Kamoʻoalewa from late 2026 to early 2027.^[10] After returning them to Earth, it will use its close encounter with Earth for a gravity assist towards 311P/PanSTARRS. When it arrives there, it will get into orbit and conduct a remote sensing study.^[11]

See also

• 354P/LINEAR, formerly known as P/2010 A2 (LINEAR)
• Yarkovsky–O'Keefe–Radzievskii–Paddack effect (YORP effect)

Notes

1. "She calculated that dust-ejection events occurred on April 15, July 18, July 24, Aug. 8, Aug. 26 and Sept. 4"