4337 Arecibo

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4337 Arecibo
Discovery
Synodic rotation period
32.972823 h (Gaia DR3)[5]: 16 
32.85±0.38 h[6][5]
60°±[5]: 16 
261°±[5]: 16 
0.077±0.004[7][1]
0.06±0.02[8]
11.9±0.1[7] · 12.45[8]
12.52[1][2]

4337 Arecibo (

stellar occultation observations by David Gault and Peter Nosworthy in May 2021, distinguishing it as the first asteroid moon discovered and confirmed solely using the occultation method.[9]

History

Discovery

This asteroid was discovered by American astronomer

minor planet number of 4337 from the Minor Planet Center on 11 January 1990.[12]
: 90 

Naming

The asteroid was named after the Arecibo Observatory in Puerto Rico, home to the world's largest filled-aperature radio telescope in the 20th century. The name was proposed by radar astronomer Steven J. Ostro, in recognition of the observatory's indispensable contributions to the characterization of Solar System bodies including asteroids.[2] The official naming citation was published by the Minor Planet Center on 8 June 1990.[13]: 155 

Occultations and satellite discovery

On 19 May 2021, two

UTC, but then unexpectedly detected a secondary, shorter-duration occultation three seconds later.[9][4]: 3  The observed drop in the star's brightness for both events was much greater than would be expected for a double star with one component occulted, leading Gault and Nosworthy to the conclusion that the secondary occultation was more likely caused by a natural satellite orbiting Arecibo.[4]
: 3 

Several days after the discovery of Arecibo's satellite, other occultation astronomers were alerted to follow up in another occultation event by Arecibo over North America on 9 June 2021.[9] Richard Nolthenius and Kirk Bender, separated from each other by 8.2 km (5.1 mi) across and 8 km (5.0 mi) along Arecibo's shadow path, successfully observed the 9 June 2021 occultation from central California.[4]: 3  As Arecibo passed in front of a magnitude 12.0 star, they detected the primary two-second-long occultation starting at 10:58 UTC and then the satellite make a secondary occultation three seconds later, confirming the existence of Arecibo's satellite.[9][4]: 4  The satellite discovery and confirmation results from the May and June 2021 occultations were formally published by Central Bureau for Astronomical Telegrams on 20 June 2021.[14] Discoverers Gault and Nosworthy recognize Arecibo's satellite as the first asteroid moon discovered by amateur astronomers, and confirmed using the occultation method.[9][a]

On 30 June 2021, astronomers across the United States prepared for another occultation by Arecibo to further follow up on its satellite, but majority of them experienced technical difficulties and unfavorable weather conditions, resulting in only 5 out of 15 different sites making successful observations. Only 3 of the 5 successful sites reported positive detections (Nolthenius, Bender, and Christopher Kitting of CSU East Bay reported positives) with a single occultation; the other two had misses and did not detect the satellite. It is possible the satellite and main body were a blended image, given the close orbit later determined.[4]: 4 

Orbit and classification

Arecibo orbits the Sun in the

602), a very large family of carbonaceous asteroids that are believed to have originated as fragments from an impact event on Themis.[15]
: 320 

Because of its low orbital inclination, Arecibo is visible along the ecliptic at apparent magnitudes 16–18.[2] Arecibo is too faint to be seen with the naked eye, even when at its peak brightness of magnitude 16 at opposition—a telescope of at least 60 cm (24 in) in aperture size is required to see it.[16]

Physical characteristics

The spectral class of Arecibo is unknown, but it can be assumed to be a carbonaceous C-type,[3] similar to most members of the Themis family.[15]: 320  Like most members of the Themis family, Arecibo likely has a highly porous internal structure with a low density below 1.3 g/cm3, as indicated by its mass determined from the satellite's orbital motion.[5]: 17 

Diameter and albedo

Based on occultation observations from 9 June 2021, the primary body of the Arecibo system measures 24.4 ± 0.6 km (15.16 ± 0.37 mi) in diameter, assuming that it has a spherical shape.

Japan Aerospace Exploration Agency's Akari and NASA's Wide-field Infrared Survey Explorer (WISE) determined smaller diameters of 17.6 and 19.7 km (10.9 and 12.2 mi), respectively, with corresponding geometric albedos of 0.10 and 0.08.[3] The discrepancy between the occultation and infrared measurements may be caused by a highly flattened shape for both components of the Arecibo system; in this case the occultation-derived primary diameter would represent the maximum extent of its shape.[5]: 17  WISE's estimates for Arecibo's absolute magnitude range from 11.9 to 12.6, with an average of 12.4 assumed by the Collaborative Asteroid Lightcurve Link.[3] The Minor Planet Center and Jet Propulsion Laboratory's Small-Body Database both determine an absolute magnitude of 12.5 based on visible photometry only.[2][1]

Rotation

In July 2021, a preliminary rotational

synchronous rotation with the satellite's orbital period.[5]
: 16 

Based on Gaia photometry, Arecibo's north pole points in the direction of

ecliptic latitude 68°. Gaia astrometry for the satellite's orbit yields a pole orientation of ecliptic longitude 261°± and ecliptic latitude 60°±, in agreement with the photometry-derived pole orientation.[5]: 16  This suggests the axial tilt of Arecibo primary is aligned with the satellite's orbital inclination at 30° with respect to the ecliptic.[b]

Satellite

Discovery[14]
Discovered byD. Gault
P. Nosworthy
Discovery date19 May 2021
Orbital characteristics[5]: 16 
49.9±1.0 km
32.972823 h
Inclination30°± wrt ecliptic[b]
Satellite of4337 Arecibo
Physical characteristics
Mean diameter
13±1.5 km[4]: 4 
Mean density
<1.3 g/cm3[5]: 17 

Arecibo hosts a relatively large

occulting a star on 19 May 2021, and was confirmed in another occultation on 9 June 2021.[9][a]

Orbit

The observed

milliarcseconds, respectively.[14][4] In July 2021, Nolthenius presented a preliminary analysis suggesting that the satellite's orbital radius should lie in the range of 100–293 km (62–182 mi), based on an assumed system density of 1.9 g/cm3 and an outer orbital stability limit set by Jupiter's gravitational influence.[18]: 39  Because no photometric measurements of Arecibo's rotation period were available at that time, constraints on the satellite's orbital period were solely limited to the three occultations observed in 2021, which suggested periods of 20 days and its shorter-period aliases of 10 days, 5 days, and 2.5 days.[18]
: 39 

On 13 June 2022, a team of European astronomers led by Paolo Tanga, on behalf of the European Space Agency, published a proof-of-concept analysis of the Arecibo system using high-precision astrometry and photometry from the Gaia mission, as part of its third data release.[19][5]: 16  They found that Arecibo exhibits periodic oscillations in brightness and position that are both compatible with a period of 32.972823 hours (1.3738676 d), consistent with earlier ground-based photometry from July 2021 and establishing the satellite's orbital period.[6][5]: 16  They determined a smaller orbital radius of 49.9 ± 1.0 km (31.01 ± 0.62 mi) and an inclination of 30°± with respect to the ecliptic, precisely coinciding with the satellite's positions observed in the May and June 2021 occultations.[5]: 16 [b] Given the satellite's close proximity to the primary body and coincidence of brightness and position oscillation periods, the satellite is likely in synchronous orbit with the primary's rotation period.[5]: 16 

Physical characteristics

Periodic oscillation in Arecibo's position measured by the Gaia spacecraft, signifying the presence of a large orbiting satellite

The initial detection of the satellite in the 19 May 2021 occultation provided poor constraints on its size due to close spacing between the observers' sites.[14] The 9 June 2021 occultation proved to be more reliable with wider spacing between observer sites, providing a best-fit satellite diameter of 13 ± 1.5 km (8.08 ± 0.93 mi) for an assumed spherical shape for the satellite.[4]: 4  Given this diameter estimate, this makes the satellite about half the size of the primary body in the Arecibo system.[5]: 16 

The satellite is massive enough to induce measurable positional wobbling of the Arecibo primary, although with an unexpectedly low amplitude of up to 2.7 milliarcseconds from Gaia's view, or 8.5% of the maximum observed angular separation between the satellite and primary.[5]: 16  This small positional wobbling of the Arecibo primary implies a very low satellite-to-primary mass ratio relative to the satellite-to-primary diameter ratio, which could either be explained by a highly flattened shape or a very low density for the satellite.[5]: 17  Tanga and collaborators favor the high flattening scenario as it yields more realistic density values and can explain the infrared underestimation of the primary's diameter.[5]: 17  In this case, the occultation-derived satellite diameter would represent its maximum shape extent and its minimum possible density would be 1 g/cm3, which is expected for a highly porous asteroid of the Themis family.[5]: 17 

Notes

  1. ^
    2258 Viipuri may also have a putative satellite that was solely detected in two single-chord occultations from 3 August 2013 and 19 September 2018, but the timespan between these detections is too sparse to determine the satellite's orbital motion.[18]
    : 40 
  2. ^
    ecliptic coordinates, where λ is ecliptic longitude and β is ecliptic latitude.[5]: 16  β is the angular offset from the ecliptic plane and inclination i with respect to the ecliptic is the angular offset from the ecliptic north pole at β = +90°; i with respect to the ecliptic would be the complement of β.[17]
    Therefore, given β = 60°, i = 90° – 60° = 30° from the ecliptic.

References

  1. ^ a b c d e f g "4337 Arecibo (1985 GB)" (2021-09-24 last obs.). Jet Propulsion Laboratory. Archived from the original on 7 February 2022. Retrieved 16 June 2022.
  2. ^ a b c d e f g "(4337) Arecibo = 1933 HE = 1979 FR3 = 1979 HG2 = 1985 GB". Minor Planet Center. Archived from the original on 4 October 2016. Retrieved 16 June 2022.
  3. ^ a b c d e f "LCDB Data for (4337) Arecibo". Asteroid Lightcurve Database (LCDB). Collaborative Asteroid Lightcurve Link. Archived from the original on 29 June 2022. Retrieved 16 June 2022.
  4. ^ from the original on 29 June 2022. Retrieved 16 June 2022.
  5. ^ (PDF) from the original on 13 June 2022. Retrieved 16 June 2022.
  6. ^ a b c Behrend, Raoul. "Asteroids and comets rotation curves, CdR & Regular variable stars light curves, CdL". Observatoire de Genève. Archived from the original on 3 August 2003. Retrieved 16 June 2022.
  7. ^ from the original on 16 June 2022. Retrieved 16 June 2022.
  8. ^ . 63.
  9. ^ a b c d e f g Nosworthy, Peter; Gault, Dave. "Arecibo Moon Discovery". Hazelbrook Observatory. Archived from the original on 28 January 2022. Retrieved 16 June 2022.
  10. ^ a b "M. P. C. 9671" (PDF). Minor Planet Circulars (9671). Minor Planet Center: 71. 4 May 1985. Archived (PDF) from the original on 10 August 2017. Retrieved 17 June 2022.
  11. ^ "M. P. C. 10039" (PDF). Minor Planet Circulars (10039). Minor Planet Center: 59. 29 September 1985. Archived (PDF) from the original on 10 August 2017. Retrieved 16 June 2022.
  12. ^ "M. P. C. 15690" (PDF). Minor Planet Circulars (15690). Minor Planet Center: 90. 11 January 1990. Archived (PDF) from the original on 24 February 2013. Retrieved 16 June 2022.
  13. ^ "M. P. C. 16445" (PDF). Minor Planet Circulars. Minor Planet Center. 8 June 1990. p. 155. Archived (PDF) from the original on 23 June 2021. Retrieved 16 June 2022.
  14. ^ a b c d "CBET 4981 : (4337) ARECIBO". Central Bureau Electronic Telegrams (4981). Central Bureau for Astronomical Telegrams. 20 June 2021. Archived from the original on 28 January 2022. Retrieved 16 June 2022.
  15. ^
    S2CID 119280014
    .
  16. ^ Houdart, Robert. "Telescope Limiting Magnitude Calculator". Cruxis. Archived from the original on 26 May 2021. Retrieved 17 June 2022.
  17. ^ "Coordinate transformations". Astronomy and Astrophysics. European Southern Observatory. January 1998. Archived from the original on 17 June 2021. Retrieved 17 June 2022.
  18. ^ a b c Nugent, Richard (January 2022). "The International Occultation Timing Association's 39th Annual Meeting, 2021 July 17-18 via Zoom Online" (PDF). Journal for Occultation Astronomy. 12 (1): 38–40. Archived (PDF) from the original on 3 April 2022. Retrieved 16 June 2022.
  19. ^ Roegiers, Tineke; Tanga, Paolo; Galluccio, Laurent (13 June 2022). "Is it a Solar System object?". European Space Agency. Archived from the original on 14 June 2022. Retrieved 16 June 2022.

External links