C/2010 X1 (Elenin)

Brightness

In April 2011, the comet was around magnitude 15 (roughly the brightness of Pluto), with a coma (expanding tenuous dust atmosphere) estimated to be about 80,000 km in diameter.{{cite web |access-date=2011-04-13 |archive-date=2012-08-10 |archive-url=https://web.archive.org/web/20120810132947/http://spaceobs.org/en/2011/04/10/comet-elenin-continues-to-increase-in-size-and-another-close-approach-with-a-large-main-belt-asteroid/ |url-status=dead |access-date=2011-05-25 |archive-date=2011-06-03 |archive-url=https://web.archive.org/web/20110603191336/http://spaceobs.org/en/2011/05/25/perhaps-the-closest-approach-of-comet-elenin-to-a-main-belt-asteroid/ |url-status=dead |access-date=2011-08-04 |archive-date=2011-11-01 |archive-url=https://web.archive.org/web/20111101052500/http://spaceobs.org/en/2011/08/04/diameter-of-coma-of-comet-elenin-exceeded-200000-km/ |url-status=dead |access-date = 2011-06-06 |archive-url = https://web.archive.org/web/20120429114606/http://www.comet-observation.com/ |archive-date = 2012-04-29 |access-date=2011-08-30 |archive-date=2011-10-11 |archive-url=https://web.archive.org/web/20111011232331/http://spaceobs.org/en/2011/08/24/interaction-between-comet-elenin-and-coronal-mass-ejection-from-the-sun/ |url-status=dead |archive-url=https://web.archive.org/web/20110915045909/http://astrobob.areavoices.com/2011/08/28/comet-elenin-tired-of-too-much-pr/ |archive-date=2011-09-15 |access-date=2011-08-28}} As of mid-September 2011 the comet had become dimmer than magnitude 10.5, and appeared around magnitude 12 as seen by STEREO-A.{{cite web |access-date=2011-09-17}} (STEREO-A image) the comet is projected to be about magnitude 14 and fading.{{cite web |access-date = 2011-09-25 |archive-url = https://web.archive.org/web/20111015112053/http://severastro.narod.ru/sla/com/lc/current/c2010x1.gif |archive-date = 2011-10-15 |access-date=2011-10-11 |access-date=2011-10-23}}{{cite web |access-date = 2011-10-23 |archive-url = https://archive.today/20130124051700/http://www.global-rent-a-scope.com/gras-news/2011/10/24/a-dust-cloud-once-called-comet-elenin.html |archive-date = 2013-01-24 |access-date=2011-10-26}}

Between 1 August and 12 August 2011,{{cite web |access-date=2011-07-28}} NASA repeatedly rolled the STEREO-B spacecraft to view the forward scattering of light as the spacecraft, comet, and Sun aligned.{{cite web |access-date=2011-08-02}} (Aug 6th to Aug 12th animation) , Comet Elenin was visible in STEREO-B without rolling the craft.{{cite web |access-date=2011-08-17}} Because it disintegrated, SOHO failed to detect the forward scattering of light in late September.{{cite web |access-date=2011-07-28 |archive-date=2012-03-22 |archive-url=https://web.archive.org/web/20120322135800/http://spaceobs.org/en/2011/07/28/the-test-roll-was-succesful-lets-wait-for-august-1/ |url-status=dead |access-date=2011-08-24}} Had the comet not disintegrated, it would have allowed the dust scattering function to be studied simultaneously from two different locations.

C/2010 X1 made its closest approach to the Sun (perihelion) on 10 September 2011 at a distance of 0.4824 AU. The remnant of Elenin made its closest approach to Earth on 16 October 2011, at a distance of 0.2338 AU{{cite web |access-date=2023-09-03}} or slightly closer than the planet Venus, at a relative velocity of 86,000 km/h. Before the August fading of the comet, the Minor Planet Center ephemeris projected that the originally bright comet Elenin would reach about 6th magnitude in September and October 2011,{{cite web |archive-url = https://web.archive.org/web/20121024231954/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=c&o=CK10X010 |archive-date = 2012-10-24 |access-date = 2011-03-20

Original and future orbit

Given the orbital eccentricity of this object, its orbital period is not a fixed value, because it is frequently perturbed by the gravity of the planets. Near perihelion, using an August 2011 epoch, Kazuo Kinoshita shows C/2010 X1 to have a heliocentric orbital period of 600,000 years, though more perturbations will occur. For objects at such high eccentricity, the Sun's barycentric coordinates are more stable than heliocentric coordinates. The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. Using JPL Horizons with an observed orbital arc of 271 days, the barycentric orbital elements for epoch 2200 generate a hyperbolic orbit with an eccentricity of 1.0004.{{cite web |access-date = 2023-09-03

Before entering the planetary region (epoch 1800), Elenin had a calculated barycentric orbital period of tens of millions of years with an apoapsis (aphelion) distance of about 97000 AU. Elenin was probably in the outer Oort cloud with a loosely bound chaotic orbit that was easily perturbed by passing stars.

References

References

1. "CoLiTec - Collection Light Technology, software for automated asteroids and comets discoveries.".
2. [[Apparent magnitude#Calculations. Math]]: (\sqrt[5]{100})^{19.5-6.5}\approx 158489
3. Elenin, Leonid. "Comet Elenin FAQ | SpaceObs".
4. (October 25, 2011). "NASA Says Comet Elenin Gone and Should Be Forgotten". NASA/JPL.
5. Math: [[Apparent magnitude#Calculations
6. Atkinson, Nancy. (August 29, 2011). "Comet Elenin Could Be Disintegrating". Universe Today.
7. Mike Wall. (14 October 2011). "Debris of 'Doomsday' Comet Elenin to Pass By Earth on Sunday". Space.com.
8. (2011-03-31). "Comet C/2010 X1 (Elenin)". Remanzacco Observatory in Italy – Comets & Neo.
9. Kazuo Kinoshita. (2011-02-26). "C/2010 X1 (Elenin)". Comet Orbit Home Page.
10. Elenin, Leonid. (7 March 2011). "Influence of giant planets on the orbit of comet C/2010 X1".
11. Kaib, Nathan A.. (2009). "2006 SQ372: A Likely Long-Period Comet from the Inner Oort Cloud". [[The Astrophysical Journal]].