Examinando por Autor "Brown, Anthony"

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Acceso Abierto
All-sky visible and near infrared space astrometry
(Springer Link, 2021-03-11) Hobbs, D.; Brown, Anthony; Hog, E.; Jordi, C.; Kawata, D.; Tanga, P.; Klioner, S. A.; Sozzetti, A.; Wyrzykowski, L.; Walton, N.; Vallenari, A.; Makarov, V.; Rybizki, J.; Jiménez Esteban, F. M.; Caballero, J. A.; McMillan, P. J.; Secrest, N.; Mor, R.; Andrews, Jeff J.; Zwitter, T.; Chiappini, C.; Fynbo, J. P. U.; Ting, Y. S.; Hestroffer, D.; Lindegren, L.; McArthur, B.; Gouda, N.; Moore, A.; González, O. A.; Vaccari, M.; Hobbs, D. [0000-0002-2696-1366]; Brown, A. [0000-0002-7419-9679]; Sozzetti, A. [0000-0002-7504-365X]; Secrest, N. [0000-0002-4902-8077]
The era of all-sky space astrometry began with the Hipparcos mission in 1989 and provided the first very accurate catalogue of apparent magnitudes, positions, parallaxes and proper motions of 120 000 bright stars at the milliarcsec (or milliarcsec per year) accuracy level. Hipparcos has now been superseded by the results of the Gaia mission. The second Gaia data release contained astrometric data for almost 1.7 billion sources with tens of microarcsec (or microarcsec per year) accuracy in a vast volume of the Milky Way and future data releases will further improve on this. Gaia has just completed its nominal 5-year mission (July 2019), but is expected to continue in operations for an extended period of an additional 5 years through to mid 2024. Its final catalogue to be released ∼ 2027, will provide astrometry for ∼ 2 billion sources, with astrometric precisions reaching 10 microarcsec. Why is accurate astrometry so important? The answer is that it provides fundamental data which underpin much of modern observational astronomy as will be detailed in this White Paper. All-sky visible and Near-InfraRed (NIR) astrometry with a wavelength cutoff in the K-band is not just focused on a single or small number of key science cases. Instead, it is extremely broad, answering key science questions in nearly every branch of astronomy while also providing a dense and accurate visible-NIR reference frame needed for future astronomy facilities.
Acceso Abierto
Hexagonal Prisms Form in Water-Ice Clouds on Mars, Producing Halo Displays Seen by Perseverance Rover
(AGU Advancing Earth and Space Science, 2022-10-03) Lemmon, M. T.; Toledo, D.; Apéstigue, Víctor; Arruego, Ignacio; Wolff, Michael; Patel, P.; Guzewich, Scott; Colaprete, A.; Vicente Retortillo, Álvaro; Tamppari, L. K.; Montmessin, F.; De la Torre Juárez, M.; Maki, Justin N.; McConnochie, Tim H.; Brown, Adrian Jon; Bell, J. F.; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN); NASA Jet Propulsion Laboratory (JPL); Arizona State University (ASU); Ministerio de Economía y Competitividad (MINECO); Gobierno Vasco; European Research Council (ERC); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Observations by several cameras on the Perseverance rover showed a 22° scattering halo around the Sun over several hours during northern midsummer (solar longitude 142°). Such a halo has not previously been seen beyond 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. From a possible 40–50 km altitude, and over the 3.3 hr 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 northern midsummer.
Acceso Abierto
The dynamic atmospheric and aeolian environment of Jezero crater, Mars
(Science Publishin Group, 2022-05-25) Newman, C. E.; Hueso, R.; Lemmon, M. T.; Munguira, A.; Vicente Retortillo, Álvaro; Apéstigue, Víctor; Martínez, Germán M.; Toledo, D.; Sullivan, Robert; Herkenhoff, K. E.; De la Torre Juárez, M.; Richardson, M. I.; Stott, A.; Murdoch, N.; Sánchez Lavega, Agustín; Wolff, Michael; Arruego, I.; Sebastián, E.; Navarro López, Sara; Gómez Elvira, J.; Tamppari, L. K.; Smith, Michael D.; Lepinette Malvitte, A.; Viúdez Moreiras, Daniel; Harri, Ari-Matti; Genzer, María; Hieta, M.; Lorenz, R. D.; Conrad, Pamela G.; Gómez, Felipe; McConnochie, Tim H.; Mimoun, D.; Tate, C.; Bertrand, T.; Belli, J. F.; Maki, Justin N.; Rodríguez Manfredi, J. A.; Wiens, R. C.; Chide, B.; Maurice, S.; Zorzano, María-Paz; Mora Sotomayor, L.; Baker, M. M.; Banfield, D.; Pla García, J.; Beyssac, O.; Brown, Adrian Jon; Clark, B.; Montmessin, F.; Fischer, E.; Patel, P.; Del Río Gaztelurrutia, T.; Fouchet, T.; Francis, R.; Guzewich, Scott; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN); Ministerio de Economía y Competitividad (MINECO); Agencia Estatal de Investigación (AEI); Gobierno Vasco; National Aeronautics and Space Administration (NASA); Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Despite the importance of sand and dust to Mars geomorphology, weather, and exploration, the processes that move sand and that raise dust to maintain Mars’ ubiquitous dust haze and to produce dust storms have not been well quantified in situ, with missions lacking either the necessary sensors or a sufficiently active aeolian environment. Perseverance rover’s novel environmental sensors and Jezero crater’s dusty environment remedy this. In Perseverance’s first 216 sols, four convective vortices raised dust locally, while, on average, four passed the rover daily, over 25% of which were significantly dusty (“dust devils”). More rarely, dust lifting by nonvortex wind gusts was produced by daytime convection cells advected over the crater by strong regional daytime upslope winds, which also control aeolian surface features. One such event covered 10 times more area than the largest dust devil, suggesting that dust devils and wind gusts could raise equal amounts of dust under nonstorm conditions.