2017 YE5

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2017 YE5
Synodic rotation period
14.88±0.02 h[8]
0.02–0.04[8]
D[8]
26.8[9]
19.2 (combined)[5][2]
19.3[6]

2017 YE5 is a

lunar distances or approximately 6 million km (3.7 million mi) from Earth. During the close encounter, 2017 YE5 was resolved in high detail by concurrent radar observations by the Arecibo and Green Bank observatories, along with individual observations by the Goldstone Solar System Radar. 2017 YE5 is likely an extinct or dormant comet due to its distant elliptical orbit and dark red surface.[8]

Discovery

2017 YE5 was discovered on 21 December 2017, by French amateur astronomer

constellation of Gemini at an apparent magnitude of 19.8.[13][a]

2017 YE5 imaged by the Oukaïmeden Observatory on 30 December 2018

The discovery of 2017 YE5 was subsequently reported to the

Minor Planet Electronic Circular issued by the Minor Planet Center on 27 December 2017.[1]

Precovery observations of 2017 YE5 were first identified and reported to the Minor Planet Center in February 2018. These observations were from the Mount Lemmon Survey, which had observed 2017 YE5 on 14 December 2017, seven days prior to its discovery by the Oukaïmeden Observatory.[2][14] Earlier precovery observations by the Pan-STARRS1 survey on 12 December 2017 were later identified in May 2018, and are now known to be the earliest reported observations of 2017 YE5.[2][15]

Nomenclature

Upon discovery, the asteroid was given the temporary internal designation tltv005.

minor planet number by the Minor Planet Center due to its short observation arc of 270 days, which is insufficient for an orbit to be accurately determined.[5][2] 2017 YE5 is expected to receive a minor planet number once it has been observed for over at least four oppositions, which would take several years.[16] Once it receives a minor planet number, it will be eligible for naming.[16]

Orbit and classification

2017 YE5 orbits the

aphelion, beyond the outer extent of the asteroid belt.[17]

Animation of 2017 YE5's orbit during the 2018 close encounter with Earth, with the asteroid belt and orbits of the planets for scale

At aphelion, 2017 YE5 approaches close to

Jupiter-family comet.[18] Additional evidence for its cometary origin was found by optical and infrared spectroscopy in 2018, which revealed a reddish and low-albedo surface, consistent with the D-type spectral classification
.

As a

potentially hazardous asteroid (PHA) by the Minor Planet Center, under the definition that PHAs have Earth MOIDs less than 0.05 AU and absolute magnitudes brighter than 22.[2][19]

Despite being considered potentially hazardous, there is no risk of

Sentry Risk Table on 6 January 2018, after extensive observations and refinements of its orbit ruled out future possibilities of Earth impacts.[14][20]

2018 Earth approach

On 21 June 2018 at 20:53 

angular separation of 66 degrees from the Sun.[21][c] After the close encounter with Earth, 2017 YE5 continued its approach to aphelion, passing by Mars from a distance of 0.0441 AU (6.6 million km; 4.1 million mi) on 30 July 2018.[5][10]

Observations

Collage of Goldstone delay-Doppler images of 2017 YE5 during its close approach to Earth[18]

The June 2018 encounter with 2017 YE5 provided an opportunity for

monostatic Goldstone Solar System Radar (GSSR) in California, but failed to detect the asteroid due to uncertainties in the radar pointing position. 2017 YE5 was later successfully imaged and observed with the GSSR on 21 June 2018, revealing the asteroid's binary nature. Led by radar astronomer Marina Brozović, GSSR observations of 2017 YE5 spanned four days, lasting until 24 June 2018.[18] During these observations, the GSSR's preliminary findings were alerted to astronomers at the Arecibo Observatory in Puerto Rico for further study.[23][10]

Arecibo radar observations of 2017 YE5 began on 23 June 2018.

eclipses occurring between the components of the binary system.[7]

Future approaches

Over the course of its orbit in the next 200 years, 2017 YE5 will continue to pass by Earth, though it will not make any approaches as close as the June 2018 encounter. The next Earth encounter by 2017 YE5 will be on 15 April 2037, when it will pass by Earth from a nominal distance of approximately 0.238 AU (35.6 million km; 22.1 million mi).[5][10] In the next 100 years, 2017 YE5 will make three Earth encounters within 0.2 AU (approximately 80 lunar distances), which will occur in February 2051, July 2088, and May 2107. The expected nominal approach distances for these dates are 0.123 AU, 0.179 AU, and 0.145 AU, respectively.[5]

Binary system

S/2018 (2017 YE5) 1
Goldstone Obs.
Discovery date21 June 2018 (first observed)
Orbital characteristics[6]
1.8 km (separation from primary)
23.7±0.1 h[8]
Satellite of2017 YE5
Physical characteristics[6]
Mean diameter
0.90±0.05 km or 900±50 m
Albedo0.02–0.04[8]

The secondary component of 2017 YE5 was discovered in Goldstone radar observations conducted by Marina Brozović on 21 June 2018.[18] From the first Goldstone radar images, the two components appeared to be contact binary lobes as the components were viewed in front of each other. Additional radar observations by the Arecibo and Green Bank observatories resolved the 2017 YE5 system in high resolution, confirming that the two components were indeed separate objects.[7] Under satellite naming conventions by the International Astronomical Union, the satellite would be provisionally designated S/2018 (2017 YE5) 1.[26]

Physical characteristics

Artist's rendering of the 2017 YE5 binary system, with the contrasting surface brightnesses and shapes of each component

2017 YE5 is an equal-mass binary asteroid consisting of two components approximately 0.9 km (0.56 mi) in diameter. Equal-mass binary systems are relatively rare among the population of binary near-Earth asteroids as they constitute less than 1% of radar-observed near-Earth asteroids larger than 200 m (660 ft) in diameter.[7] 2017 YE5 is one of only four systems of that kind known; the other three are 1994 CJ1, 69230 Hermes, and (190166) 2005 UP156.[7]

From their mutual orbit and measured diameters, both components are calculated to have low bulk densities less than 1 g/cm3, indicating a significant macroporosity of their internal structures. Given their measured diameters and absolute magnitudes, the optical albedos of their surfaces are calculated to be as dark as charcoal, reflecting less than 3% of incident light.[7][10] Unlike other binary asteroid systems observed by radar, the components of 2017 YE5 appear to display a distinct difference in their shape, surface brightness and radar reflectivity. These differences imply that the two components may also have different densities, compositions, and surface roughnesses.[23]

Orbit and rotation

Animation of Goldstone radar images of 2017 YE5 on 23 June 2018. The separation between the two components becomes more apparent as they move away from each other.

The pair of asteroids orbit each other around a common center of mass (

obliquities of the components are misaligned by a few degrees.[7][8]

Notes

  1. celestial coordinates of 2017 YE5 at the time of discovery were 07h 06m 15.35s −21° 17′ 11.9″.[1] See Gemini
    for constellation coordinates.
  2. ^ In the convention for minor planet provisional designations, the first letter represents the half-month of the year of discovery while the second letter and numbers indicate the order of discovery within that half-month. In the case for 2017 YE5, the first letter 'Y' corresponds to the second half-month of December 2017 while the succeeding letter 'E' indicates that it is the 5th object discovered on the 6th cycle of discoveries (with 5 cycles completed). Each completed cycle consists of 25 letters representing discoveries, hence 5 + (5 completed cycles × 25 letters) = 130.[16]
  3. ^ The celestial coordinates of 2017 YE5 at 20:53 UTC are 00h 39m 07.692s +45° 13′ 22.92″. The solar elongation at the time was 66.3 degrees.[21] See Andromeda for constellation coordinates.

References

  1. ^ a b c d e Rinner, C.; et al. (27 December 2017). "MPEC 2017-Y116: 2017 YE5". Minor Planet Electronic Circular. Minor Planet Center. Retrieved 16 February 2020.
  2. ^ a b c d e f g h "2017 YE5". Minor Planet Center. International Astronomical Union. Retrieved 18 February 2020.
  3. ^ a b "MPC official report for MOSS station". Société jurassienne d'astronomie. 30 May 2018. Retrieved 22 February 2020.
  4. ^ a b c "2017 YE5". NEO Exchange. Las Cumbres Observatory. 21 December 2017. Retrieved 16 February 2020.
  5. ^ a b c d e f g h i j k l m n "JPL Small-Body Database Browser: 2017 YE5" (2018-09-08 last obs.). Jet Propulsion Laboratory. 27 July 2019. Retrieved 16 February 2020.
  6. ^ a b c d e Johnston, Wm. Robert (27 May 2019). "2017 YE5". Johnston's Archive. Retrieved 16 February 2020.
  7. ^
    Bibcode:2019LPI....50.2945T
    . 2945. Retrieved 18 February 2020.
  8. ^
    doi:10.1093/mnras/stab2408
    .
  9. ^ "2017YE5". Near Earth Objects – Dynamic Site. Department of Mathematics, University of Pisa, Italy. Retrieved 16 February 2020.
  10. ^ a b c d e f g Davis, Jason (24 July 2018). "Planetary Society asteroid hunters help find rare type of double asteroid". The Planetary Society. Retrieved 24 July 2018.
  11. ^ a b Davis, Jason (3 July 2018). "Planetary Defense in the Moroccan Mountains". The Planetary Society. Retrieved 28 July 2018.
  12. ^ "MOSS-Observatory [Morocco Oukaïmeden Sky Survey]". Société jurassienne d'astronomie. 9 August 2018. Retrieved 18 February 2020.
  13. ^ "2017YE5 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery). Department of Mathematics, University of Pisa, Italy. Retrieved 22 February 2020.
  14. ^ a b "M.P.S. 867675" (PDF). Minor Planet Circular. Minor Planet Center. 18 February 2018. Retrieved 21 February 2020.
  15. ^ "M.P.S. 889315" (PDF). Minor Planet Circular. Minor Planet Center. 13 May 2018. Retrieved 1 March 2020.
  16. ^ a b c d "How Are Minor Planets Named?". Minor Planet Center. International Astronomical Union. Retrieved 18 February 2020.
  17. ^ Plait, Phil (3 September 2018). "2017 YE5: A rare binary asteroid caught on radar". Bad Astronomy. Syfy Wire. Retrieved 18 February 2020.
  18. ^ a b c d e f g h i j Benner, Lance A. M. (June 2018). "Goldstone Radar Observations Planning: Asteroids 2017 YE5, 1996 AW1, 2010 NY65, and 2018 LK". Asteroid Radar Research. Jet Propulsion Laboratory. Retrieved 18 July 2018.
  19. ^ "PHA (Potentially Hazardous Asteroid)". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 18 February 2020.
  20. ^ "Sentry: Earth Impact Monitoring – Removed Objects". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 18 February 2020.
  21. ^ a b "2017YE5 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at 21 June 2018 approach). Department of Mathematics, University of Pisa, Italy. Retrieved 1 March 2020.
  22. ^ Bartels, Meghan (12 July 2018). "Cosmic Double Take: Rare Binary Asteroid Discovered Near Earth". Space.com. Retrieved 18 February 2020.
  23. ^ a b c Cofield, Calla; Wendel, JoAnna (11 July 2018). "Observatories Team Up to Reveal Rare Double Asteroid". Jet Propulsion Laboratory. NASA. Retrieved 12 July 2018.
  24. ^ Virkki, A. K. (12 July 2018). "Observatories Team Up to Reveal Rare Double Asteroid". Planetary Radar Science Group. NAIC-Arecibo Observatory. Retrieved 18 February 2020.
  25. ^ "M.P.S. 900357" (PDF). Minor Planet Circular. Minor Planet Center. 1 July 2018. Retrieved 2 March 2020.
  26. ^ "Satellites and Companions of Minor Planets". Central Bureau for Astronomical Telegrams. International Astronomical Union. Retrieved 18 February 2020.

External links

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