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Hexagonal Prisms Form in Water-ice Clouds on Mars, Producing Halo Displays Seen by Perseverance Rover
  • +13
  • Mark T Lemmon,
  • Daniel Toledo,
  • Víctor Apéstigue,
  • Ignacio Arruego,
  • Michael J. Wolff,
  • Priyaben Patel,
  • Scott D. Guzewich,
  • Tony Colaprete,
  • Alvaro Vicente-Retortillo,
  • Leslie Tamppari,
  • Franck Montmessin,
  • Manuel de la Torre Juarez,
  • Justin N. Maki,
  • Timothy McConnochie,
  • Adrian Jon Brown,
  • James F Bell
Mark T Lemmon
Space Science Institute

Corresponding Author:[email protected]

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Daniel Toledo
Instituto Nacional de Tecnica Aeroespacial (INTA)
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Víctor Apéstigue
National Institute of Aerospace Technology (INTA)
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Ignacio Arruego
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Michael J. Wolff
Space Science Institute
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Priyaben Patel
University College London
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Scott D. Guzewich
NASA Goddard Space Flight Center
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Tony Colaprete
NASA Ames Research Center
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Alvaro Vicente-Retortillo
Centro de Astrobiología (INTA-CSIC)
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Leslie Tamppari
Jet Propulsion Laboratory
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Franck Montmessin
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Manuel de la Torre Juarez
Jet Propulsion Laboratory/California Institute of Technology
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Justin N. Maki
Jet Propulsion Laboratory, California Institute of Technology
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Timothy McConnochie
Space Science Institute
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Adrian Jon Brown
Plancius Research
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James F Bell
Arizona State University
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Observations by several cameras on the Perseverance rover showed a 22° scattering halo around the Sun over several hours on the morning of sol 292 (15 December 2021). Such a halo has not previously been seen off Earth. The halo occurred during the aphelion cloud belt season and the cloudiest time yet observed from the Perseverance site. The halo required crystalline water-ice cloud particles in the form of hexagonal columns large enough for refraction to be significant, at least 11 µm in diameter and length. Near 44 km altitude, fall speeds would have been 0.3-1 m/s for the smallest allowed particles. Over the 3.3-hour duration of the halo, particles could have fallen 3-12 km, causing downward transport of water and dust. Halo-forming clouds are likely rare due to the high supersaturation of water that is required but may be more common in northern subtropical regions during mid-northern summer.