Asteroid 2015 XY261Discovery[1][2][3] Discovered by| Pan-STARRS 1 (first observered) Discovery site| Haleakala Obs. Discovery date| 6 December 2015 Designations MPC designation | 2015 XY261 Minor planet category | Apollo * NEO[1][2] Orbital characteristics[1] Epoch 23 March 2018 (JD 2458200.5) Uncertainty parameter 5 Observation arc| 0.025 yr (9 days) Aphelion| 2.1890 AU Perihelion| 0.8003177 AU Semi-major axis | 1.4945093 AU Eccentricity| 0.4644947 Orbital period (sidereal) | 1.83 yr (667 days) Mean anomaly | 62.24896° Mean motion | 0° 32m 22.041s / day Inclination| 1.59013° Longitude of ascending node | 86.91527° Argument of perihelion | 61.94406° Earth MOID| 0.00184 AU (0.72 LD) Physical characteristics Dimensions| 9.7–22 meters[4] Absolute magnitude (H) | 27.2[1] 2015 XY261 (also written 2015 XY261) is an Apollo near-Earth asteroid[2] that is also a Mars crosser. It is roughly 10–22 meters in diameter and passed less than 1 lunar distance, 0.0025696 AU (384,410 km; 238,860 mi) from Earth on 15 December 2015.[5] ## 2015 flyby[edit] This small dim asteroid approached Earth in opposition, having an elongation from the Sun of over 160 degrees from mid November 2015. However, due to its absolute magnitude even though it had a very low phase angle during the approach it was too dim for contemporary telescopes to spot it so early, as it was significantly fainter than apparent magnitude 23.[6] However it got brighter as it approached and a few weeks later, on 6 December 2015 it was spotted by Pan-STARRS at an apparent magnitude of 21.5 using a 1.8-meter (71 in) Ritchey–Chrétien telescope.[3] On 15 December 2015 at 13:52 UT, the asteroid passed 0.0019277 AU (288,380 km; 179,190 mi) from the Earth and three and a half hours later at 17:17 UT passed 0.00354 AU (530,000 km; 329,000 mi) from the Moon.[5] This flyby is notable because the discovery was 9 days prior to closest approach. This is one of the earliest discoveries of an asteroid during approach. Discounting cataloged objects which were discovered during previous orbits, most asteroids are discovered with little or no warning. 2015 XY261 was the only asteroid to pass within 1 LD of Earth in 2015 that was discovered more than a week before closest approach. See List of asteroid close approaches to Earth in 2015. 1 LD, the distance between the Earth and Moon - sizes and distance to scale. ## References[edit] 1. ^ a b c d "JPL Small-Body Database Browser: (2015 XY261)" (2015-01-29 last obs.). Jet Propulsion Laboratory. Retrieved 28 July 2018. 2. ^ a b c "2015 XY261". Minor Planet Center. Retrieved 28 July 2018. 3. ^ a b "MPEC 2015-X153: 2015 XY261". IAU Minor Planet Center. 30 January 2015. Retrieved 28 July 2018. (K15Bp3P) 4. ^ "Absolute Magnitude (H)". NASA/JPL. Archived from the original on 2 March 2001. Retrieved 28 July 2018. 5. ^ a b "JPL Close-Approach Data: (2015 XY261)" (last observation: 2015-01-29; arc: 10 days). Retrieved 28 July 2018. 6. ^ "2015XY261 Ephemerides for 15 January 2015 through 1 February 2015". NEODyS (Near Earth Objects - Dynamic Site). Retrieved 28 July 2018. ## External links[edit] * 2015 XY261 at NeoDyS-2, Near Earth Objects—Dynamic Site * Ephemerides * Observation prediction * Orbital info * MOID * Proper elements * Observational info * Close approaches * Physical info * Orbit animation * 2015 XY261 at ESA–space situational awareness * Ephemerides * Observations * Orbit * Physical properties * Summary * 2015 XY261 at the JPL Small-Body Database * Close approach * Discovery * Ephemeris * Orbit diagram * Orbital elements * Physical parameters * v * t * e 2015 in space * « 2014 2016 » Space probe launches | | Space probes| * SMAP (weather satellite; Jan 2015) * LISA Pathfinder (technology demonstration; Dec 2015) | Space observatories| * DSCOVR (weather satellite; Feb 2015) * Astrosat (space telescope; Sep 2015) Impact events| * 2015 Kerala meteoroid * 2015 Thailand bolide * WT1190F impact Selected NEOs| * Asteroid close approaches * 2015 BP513 * (357439) 2004 BL86 * 2015 AZ43 * (523775) 2014 YB35 * 1566 Icarus * 2015 HM10 * 2015 TC25 * 2015 TB145 * 2007 VE191 * (33342) 1998 WT24 * (85989) 1999 JD6 * 2015 SO2 Exoplanets | * Aldebaran b * evaporation of Gliese 436 b * Gliese 1132 b * HD 155233 b * HD 164595 b * HD 219134 (b * c * d * f * g? * h?) * HIP 11915 b * K2-3d * K2-18b * K2-22b * K2-24b * K2-24c * KELT-4Ab * Kepler-438b * Kepler-440b * Kepler-442b * Kepler-444 (b * c * d * e * f) * Kepler-451b * Kepler-452b * Kepler-453b * KOI-4878.01 * LkCa 15 b * spectrum of 51 Pegasi b * WASP-121b * Wolf 1061c Discoveries| * 2015 BP519 * US 708 * EGS-zs8-1 (announced) * WISE J224607.57−052635.0 * 1SWASP J093010.78+533859.5 * ASASSN-15lh * EGSY8p7 * Tabby's Star * 541132 Leleākūhonua * VFTS 352 contact binary * GW150914 (first observation of gravitational waves) * GW151226 Comets | * 15P/Finlay * C/2014 Q2 (Lovejoy) * 88P/Howell * C/2014 Q1 (PanSTARRS) * C/2015 G2 (MASTER) * C/2013 US10 (Catalina) * 67P/Churyumov–Gerasimenko * 10P/Tempel Space exploration| * Rosetta (orbiting comet 67P; Nov 2014 / Mar 2015) * Dawn (Ceres orbit insertion; Mar 2015) * MESSENGER (end of mission; Apr 2015) * New Horizons (flyby of Pluto; Jul 2015) * Akatsuki (Venus orbit insertion; Dec 2015) * Outer space portal * Category:2014 in space — Category:2015 in space — Category:2016 in space * v * t * e Small Solar System bodies Minor planets| * Designation * Groups * List * Moon * Meanings of names Asteroid| * Active * Aten asteroid * Asteroid belt * Family * Jupiter trojan * Near-Earth * Spectral types Distant minor planet| * Cis-Neptunian object * Centaur * Neptune trojan * Damocloid * Trans-Neptunian object * Detached * Kuiper belt * Oort cloud * Scattered disc Comets| * Extinct * Great * Halley-type * Hyperbolic * Long-period * Lost * Near-parabolic * Periodic * Sungrazing Other| * Cosmic dust * Meteoroids * Space debris *[v]: View this template *[t]: Discuss this template *[e]: Edit this template