 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | Claudine Rinner |
| Discovery site | Oukaïmeden Obs. |
| Discovery date | 21 December 2017 |
| Designations | |
| 2017 YE5 | |
| tltv005[3][4] | |
| Apollo · PHA · NEO[5] | |
| Orbital characteristics[5] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 2 | |
| Observation arc | 0.74 yr (270 days) |
| Earliestprecovery date | 12 December 2017 |
| Aphelion | 4.818AU |
| Perihelion | 0.818 AU |
| 2.818 AU | |
| Eccentricity | 0.70964 |
| 4.73yr (1,728 days) | |
| 155.681° | |
| 0° 12m 29.952s / day | |
| Inclination | 6.218° |
| 103.927° | |
| 110.794° | |
| Knownsatellites | 1 |
| Earth MOID | 0.0209 AU |
| TJupiter | 2.877 |
| Physical characteristics | |
| 0.90±0.05 km or900±50 m (for each body)[6][7] | |
Meandensity | 0.6–1.2 g/cm3[8] |
| 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 abinary pair ofasteroids of approximately equal size and mass, each about 0.9 km (0.56 mi) in diameter. Classified as anear-Earth asteroid andpotentially hazardous object of theApollo group,2017 YE5 was discovered by amateur astronomerClaudine Rinner at theOukaïmeden Observatory on 21 December 2017. On 21 June 2018, the pair of asteroids passed within 15.5lunar distances or approximately 6 million km (3.7 million mi) from Earth. During the close encounter,2017 YE5 was resolved in high detail by concurrentradar observations by theArecibo andGreen Bank observatories, along with individual observations by theGoldstone Solar System Radar.2017 YE5 is likely anextinct or dormant comet due to its distant elliptical orbit and dark red surface.[8]
2017 YE5 was discovered on 21 December 2017, by French amateur astronomerClaudine Rinner at theOukaïmeden Observatory inMarrakesh,Morocco.[10] The discovery formed part of the Morocco Oukaïmeden Sky Survey (MOSS) directed by Zouhair Benkhaldoun at theCadi Ayyad University. The MOSS survey was designed for searching and characterizing the orbits ofsmall Solar System bodies such asnear-Earth asteroids andcomets.[11] As the sixth near-Earth asteroid discovered by the MOSS survey,[12]2017 YE5 was found in images taken by the Oukaïmeden Observatory's 0.5-meterreflecting telescope, which was remotely operated by Rinner.[1][11] At the time of discovery,2017 YE5 was about 1.1 AU (160 million km; 100 million mi) away from Earth, located in theconstellation ofGemini at anapparent magnitude of 19.8.[13][a]
The discovery of2017 YE5 was subsequently reported to theMinor Planet Center'sNear-Earth Object Confirmation Page (NEOCP), where a preliminary orbit was calculated from additional observations conducted at multiple observatories.[4] Follow-up observations of2017 YE5 spanned six days starting from its discovery, and the object was formally announced in aMinor Planet Electronic Circular issued by the Minor Planet Center on 27 December 2017.[1]
Precovery observations of2017 YE5 were first identified and reported to the Minor Planet Center in February 2018. These observations were from theMount Lemmon Survey, which had observed2017 YE5 on 14 December 2017, seven days prior to its discovery by the Oukaïmeden Observatory.[2][14] Earlier precovery observations by thePan-STARRS1 survey on 12 December 2017 were later identified in May 2018, and are now known to be the earliest reported observations of2017 YE5.[2][15]
Upon discovery, the asteroid was given the temporary internal designationtltv005.[3][4] After follow up observations confirming the object, it was then given theprovisional designation2017 YE5 by the Minor Planet Center on 27 December 2017.[1] The provisional designation signifies the object's discovery date and year, with the second letter and numbers indicating that it is the 130th object discovered during the second half of December 2017.[16][b]2017 YE5 has not yet been issued a permanentminor planet number by the Minor Planet Center due to its shortobservation 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]
2017 YE5 orbits theSun at an average distance of approximately 2.82astronomical units (0.422×10^9 km; 0.262×10^9 mi), taking 4.73 years to complete one orbit. The orbit of2017 YE5 is slightly inclined to theecliptic plane by 6.2 degrees, with its farthestapsis oriented below the ecliptic.2017 YE5 has a highly elongated orbit with anorbital eccentricity of 0.71. Over the course of its orbit,2017 YE5 approaches 0.82 AU from the Sun atperihelion and recedes 4.82 AU from the Sun ataphelion, beyond the outer extent of theasteroid belt.[17]
At aphelion,2017 YE5 approaches close toJupiter's orbit, with aminimum orbital intersection distance (MOID) of 0.42 AU.[5][2] At such close proximity to Jupiter's orbit,2017 YE5 has likely been gravitationallyperturbed by Jupiter, indicated by itsTisserand parameter of 2.877, which is considered to be characteristic ofcomets.[5][18] Because of its comet-like Tisserand parameter and relatively large orbit for a near-Earth object,2017 YE5 has been suspected to be anextinct or dormantJupiter-family comet.[18] Additional evidence for its cometary origin was found by optical and infraredspectroscopy in 2018, which revealed a reddish and low-albedo surface, consistent with theD-typespectral classification.
As anear-Earth object, the orbit of2017 YE5 crosses that of Earth's, which leads to occasional close approaches to the planet. It has asemi-major axis (orbital distance) greater than 1 AU and a perihelion distance within that of Earth's, therefore it is formally classified under theApollo group of near-Earth asteroids.[5][2]2017 YE5's Earth MOID is approximately 0.021 AU (3.1 million km; 2.0 million mi), or about 8lunar distances.[5] Given a small Earth MOID,2017 YE5 is considered apotentially hazardous asteroid (PHA) by the Minor Planet Center, under the definition that PHAs have Earth MOIDs less than 0.05 AU andabsolute magnitudes brighter than 22.[2][19]
Despite being considered potentially hazardous, there is no risk ofimpact by2017 YE5, as it will not make any close Earth encounters within 12 lunar distances or 0.03 AU (4.5 million km; 2.8 million mi) over the next 200 years.[5]2017 YE5 was removed from the JPLSentry Risk Table on 6 January 2018, after extensive observations and refinements of its orbit ruled out future possibilities of Earth impacts.[14][20]
On 21 June 2018 at 20:53 UTC,2017 YE5 made its closest approach to Earth from a distance of 0.03986 AU (5.96 million km; 3.71 million mi), or 15.52 lunar distances.[5] During the encounter,2017 YE5 approached Earth at a rate of 15.5 km/s (35,000 mph) and its apparent visual brightness peaked aroundmagnitude 15, too faint to be seen with the naked eye.[5][18] At closest approach,2017 YE5's apparent motion in the sky was 0.51 degrees per hour and was in the constellation ofAndromeda, with an apparent magnitude of 16.6 and anangular 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]
The June 2018 encounter with2017 YE5 provided an opportunity forradar observatories to study the asteroid's characteristics in detail.[18][22] On 17 June 2018, the first radar observations of2017 YE5 were attempted by themonostaticGoldstone Solar System Radar (GSSR) inCalifornia, 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 astronomerMarina Brozović, GSSR observations of2017 YE5 spanned four days, lasting until 24 June 2018.[18] During these observations, the GSSR's preliminary findings were alerted to astronomers at theArecibo Observatory inPuerto Rico for further study.[23][10]
Arecibo radar observations of2017 YE5 began on 23 June 2018.[18] The2017 YE5binary system was observed using abistatic radar system where the Arecibo Observatory transmitted a radar signal to the pair of asteroids while theGreen Bank Observatory inWest Virginia received the signal reflected from the asteroids.[23][10] Led by Arecibo radar astronomersAnne Virkki, Flaviane Venditti, Sean Marshal, along with Patrick Taylor at the Green Bank Observatory, bistatic radar observations resolved2017 YE5 at a resolution of 7.5 meters per pixel.[24] Radar observations of2017 YE5 ended on 26 June 2018 after it had moved out of Arecibo's view.[18] Concurrently, optical observations were also carried out by various observatories in order to compile alight curve of the binary system.[10][25] Optical observations of2017 YE5 continued after the June 2018 encounter and detected possible mutual events oreclipses occurring between the components of the binary system.[7]
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 by2017 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]
 Animation of bistatic radar images of2017 YE5 from Arecibo and Green Bank Observatory | |
| Discovery[18] | |
|---|---|
| Discovered by | Marina Brozović(first observer) |
| Discovery site | Goldstone Obs. |
| Discovery date | 21 June 2018(first observed) |
| Orbital characteristics[6] | |
| 1.8 km(separation from primary) | |
| 23.7±0.1 h[8] | |
| Satellite of | 2017 YE5 |
| Physical characteristics[6] | |
| 0.90±0.05 km or900±50 m | |
| Albedo | 0.02–0.04[8] |
The secondary component of2017 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 becontact binary lobes as the components were viewed in front of each other. Additional radar observations by the Arecibo and Green Bank observatories resolved the2017 YE5 system in high resolution, confirming that the two components were indeed separate objects.[7]
2017 YE5 is an equal-massbinary 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 are1994 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 than1 g/cm3, indicating a significantmacroporosity of their internal structures. Given their measured diameters and absolute magnitudes, the opticalalbedos of their surfaces are calculated to be as dark ascharcoal, reflecting less than 3% of incident light.[7][10] Unlike other binary asteroid systems observed by radar, the components of2017 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, andsurface roughnesses.[23]
The pair of asteroids orbit each other around a common center of mass (barycenter) between them. Their mutual orbital period is 22 hours (0.92 days), with an orbital separation of 1.8 km (1.1 mi) or 4 times the component radii.[6] It is uncertain whether both components rotatesynchronously with their mutual orbital period, as there is evidence ofnon-principal-axis rotation (or rotationalprecession) and axial misalignment of both components. Light curve measurements of2017 YE5 taken between June and August 2018 show a secondary period of 14.88 hours and radar images suggest that theobliquities of the components are misaligned by a few degrees.[7][8]
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