C/2015 ER₆₁ (PanSTARRS)

Comet PanSTARRS and thePleiades cluster photographed from Italy on 22 August 2017
Discovery
Discovered by	Pan-STARRS 1 (F51)
Discovery date	15 March 2015
Orbital characteristics
Epoch	7 May 2017 (JD 2457880.5)
Observation arc	1.96 yr
Aphelion	2456±62 AU 1425/854 AU[1]
Perihelion	1.0421 AU
Semi-major axis	1229±31 AU 715/428 AU[2]
Eccentricity	0.99730
Orbital period	7591 years[1] 9000 years (epoch 2050)
Inclination	6.3490°
Longitude of ascending node	235.21°
Argument of periapsis	68.197°
EarthMOID	0.1016 AU[2][3]
MarsMOID	<0.00005 AU[3]
JupiterMOID	0.0794 AU[2][3]
SaturnMOID	0.2869 AU[3]
Physical characteristics[4]
Dimensions	2.6–2.8 km (1.6–1.7 mi)
Mean diameter	2.75 km (1.71 mi)
Comet total magnitude (M1)	14.74

C/2015 ER₆₁ (PanSTARRS) is acomet and innerOort cloud object. When classified as a minor planet, it had the fourth-largestaphelion of any known minor planet in the Solar System, after2005 VX3,2012 DR30, and2013 BL76. It additionally had the most eccentric orbit of any known minor planet, with its distance from the Sun varying by about 99.9% during the course of its orbit, followed by2005 VX3 with an eccentricity of 0.9973. On 30 January 2016, it was classified as a comet when it was 5.7 AU from the Sun.^[5] It comes close toJupiter, and a close approach in the past threw it on the distant orbit it is on now.

Though the comet nucleus was probably mildly active, early asteroidal estimates gave anabsolute magnitude (H) of 12.3,^[6] which would suggest a nucleus as large as 8–20 km in diameter. But it could easily be half that size due to activity brightening the nucleus.

C/2015 ER₆₁ was discovered on 15 March 2015 when it was 8.44 AU from the Sun,^[7] and magnitude 21.5.^[5] By early February 2016, the object reached magnitude 20, and made a close approach to Jupiter on 28 March 2016 of 0.9245 AU.^[2] This changed its orbit, significantly decreasing its aphelion distance from 1430 AU to ~1200 AU, and as it passed through the inner Solar System its aphelion decreased to 770 AU, and by 2020 it had an aphelion of 854 AU.

The barycentric orbital period will decrease from 19000 years (epoch 1950) to 9000 years (epoch 2050).

As of January 2017, it was magnitude 13, and increasing in brightness. On 4 April 2017, it was detected outbursting to magnitude 6.5. On 19 April 2017, it reached its closest point to Earth of ~1.2 AU. At this point, it was aboutapparent magnitude 8,^[8] and, assuming a size of 20 km, have an apparent size of 19mas. It came to perihelion (closest approach to the Sun) on 10 May 2017.^[1] It will not be 50 AU from the Sun until 2045.

• List of Solar System objects by greatest aphelion

^^ Because2015 ER₆₁'s orbit takes it so far from the Sun, a more accurate value for its orbit is a barycentric solution. Additionally, a close approach to Jupiter in 2016, and a travel through the inner solar system in 2017 drastically changes its orbit. Therefore, orbits for 2000–2016 and 2018–2100 are provided, respectively.

Wikimedia Commons has media related toC/2015 ER61 (PanSTARRS).

• C/2015 ER61 at theJPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• Non-periodic comets
• Inner Oort cloud
• Astronomical objects discovered in 2015
• Discoveries by Pan-STARRS
• Comets in 2015
• Comets in 2017

• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from April 2020
• Commons category link from Wikidata
• JPL Small-Body Database ID same as Wikidata