C/2015 ER61 (PANSTARRS)
|Discovered by||Pan-STARRS 1 (F51)|
|Discovery date||15 March 2015|
|Comet, Amor, NEO, damocloid, scattered disc object, centaur|
|Epoch 2017-May-07 (JD 2457880.5)|
|Observation arc||1.96 yr|
|Aphelion||2456 ± 62 AU|
|1229 ± 31 AU|
9000 years (epoch 2050)
|Earth MOID||0.1018 AU|
|Mars MOID||~0.0002 AU|
|Jupiter MOID||0.0794 AU|
|Saturn MOID||0.2875 AU|
|20.5 (Jan 2016)|
14.74 (peak 1 May 2017)
C/2015 ER61 (PANSTARRS) is a comet, inner Oort cloud object, Amor near-Earth asteroid, and possibly a damocloid. When classified as a minor planet, it had the fourth-largest aphelion of any known minor planet in the Solar System, after 2005 VX3, 2012 DR30, and 2013 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 by 2005 VX3 with an eccentricity of 0.9973. On January 30, 2016, it was classified as a comet when it was 5.7 AU from the Sun. It comes close to Jupiter, 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 an absolute magnitude (H) of 12.3, 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.
2015 ER61 was discovered on March 15, 2015 when it was 8.44 AU from the Sun, and magnitude 21.5. By early February 2016, the object reached magnitude 20, and made a close approach to Jupiter on March 28, 2016 of 0.9245 AU. This changed its orbit, significantly decreasing its aphelion distance from 1430 AU to ~1200 AU, and as it passes through the inner Solar System its aphelion decreases to 770 AU, and by 2020 will have 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 April 4, 2017, it was detected outbursting to magnitude 6.5. On April 19, 2017, it will reach its closest point to Earth of ~1.2 AU. At this point, it will be about apparent magnitude 8, and, assuming a size of 20 km, have an apparent size of 19 mas. It will come to perihelion (closest approach to the Sun) on May 10, 2017. It will not be 50 AU from the Sun until 2045.
Orbital elements table
|Longitude ascending node
|Argument of perihelion|
|5.204 AU||Jupiter approach||2016/03/28||1291.9||1.04030||646.5||0.99839||16,420||6.24250||236.73||359.976||66.64|
|1.079 AU||Earth approach||2017/04/04||164.3||1.03830||82.7||0.98744||750||6.34595||235.27||359.953||68.30|
^ assuming an inactive nucleus and a comet-like albedo of 0.05
^ ^ Because 2015 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.
- Archive of JPL 13 (2015-Jun-04) as Amor near-Earth object
- "C/2015 ER61 (PANSTARRS) Orbit". Minor Planet Center. Archived from the original on 2017-03-02. Retrieved 2017-03-02.
- "JPL Small-Body Database Browser: (2015 ER61)" (last observation: 2016-01-23; arc: 1 yr). Jet Propulsion Laboratory. Archived from the original on 2015-06-24.
- Gray, Bill. "Find_Orb Orbit Determination Software". Project PLuto. Retrieved 22 April 2019.
- "Glossary: Absolute Magnitude (H)". JPL. NASA. Retrieved 14 September 2015.
- "MPEC 2016-C01 : COMET C/2015 ER61 (PANSTARRS)". IAU Minor Planet Center. 2016-02-01. Retrieved 2016-02-01. (CK15E61R)
- "Watching a Long Period Comet Turn On - C/2015 ER61 (PANSTARRS)". Bibcode:2016DPS....4830806M. Cite journal requires
- Seiichi Yoshida (2007-02-27). "C/2015 ER61 ( PanSTARRS )". Seiichi Yoshida's Comet Catalog. Retrieved 2017-03-02.