TY - JOUR
T1 - Arecibo radar imagery of Mars
T2 - The major volcanic provinces
AU - Harmon, John K.
AU - Nolan, Michael C.
AU - Husmann, Diana I.
AU - Campbell, Bruce A.
N1 - Funding Information:
The National Astronomy and Ionosphere Center (Arecibo Observatory) was operated, under a cooperative agreement with the National Science Foundation (NSF), by Cornell University (for the 2005–2010 observations) and by a consortium comprising SRI International, Universities Space Research Association (USRA), and Universidad Metropolitana (for the 2012 observations). The S-band radar observations were also made possible with support from the National Aeronautics and Space Administration (NASA). Diana Husmann’s work at Arecibo was supported by a grant to Cornell University from the Research Experience for Undergraduates (REU) program of the NSF. We would like to thank the staff of Arecibo Observatory for their support, and in particular the following people: Victor Negrón, Alfredo Santoni, and Joe Greene for transmitter maintenance and operations; Bill Sisk for digital hardware support; and Phil Perillat for datataking software support. We also thank John Chandler and Jon Giorgini for ephemeris support. We are grateful to Chris Magri for kindly volunteering to do Mars observations for us on October 14 and 15, 2005. Spacecraft images used in this paper were from the online Mars Global Data Sets, Planetary Data System (PDS) Node, Arizona State University http://www.mars.asu.edu/data/ . The Mars Orbiter Laser Altimeter (MOLA) topographic data used in the delay-Doppler mapping were obtained from the PDS Geosciences Node, Washington University in St. Louis http://pds-geosciences.wustl.edu/missions/mgs/megdr.html . We wish to thank Lynn Carter and another, anonymous, reviewer for their constructive comments and suggestions.
PY - 2012/8
Y1 - 2012/8
N2 - We present Earth-based radar images of Mars obtained with the upgraded Arecibo S-band (λ=12.6 cm) radar during the 2005-2012 oppositions. The imaging was done using the same long-code delay-Doppler technique as for the earlier (pre-upgrade) imaging but at a much higher resolution (~3. km) and, for some regions, a more favorable sub-Earth latitude. This has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity (a proxy for small-scale surface roughness) over the major volcanic provinces of Tharsis, Elysium, and Amazonis. We find that vast portions of these regions are covered by radar-bright lava flows exhibiting circular polarization ratios close to unity, a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces. All of the major volcanoes have radar-bright features on their shields, although the brightness distribution on Olympus Mons is very patchy and the summit plateau of Pavonis Mons is entirely radar-dark. The older minor shields (paterae and tholi) are largely or entirely radar-dark, which is consistent with mantling by dust or pyroclastic material. Other prominent radar-dark features include: the " fan-shaped deposits" , possibly glacial, associated with the three major Tharsis Montes shields; various units of the Medusae Fossae Formation; a region south and west of Biblis Patera where " Stealth" deposits appear to obscure Tharsis flows; and a number of " dark-halo craters" with radar-absorbing ejecta blankets deposited atop surrounding bright flows. Several major bright features in Tharsis are associated with off-shield lava flows; these include the Olympus Mons basal plains, volcanic fields east and south of Pavonis Mons, the Daedalia Planum flows south of Arsia Mons, and a broad expanse of flows extending east from the Tharsis Montes to Echus Chasma. The radar-bright lava plains in Elysium are concentrated mainly in Cerberus and include the fluvio-volcanic channels of Athabasca Valles, Grjotá Valles, and Marte Valles, as well as an enigmatic region at the southern tip of the Cerberus basin. Some of the Cerberus bright features correspond to the distinctive " platy-ridged" flows identified in orbiter images. The radar-bright terrain in Amazonis Planitia comprises two distinct but contiguous sections: a northern section formed of lavas and sediments debouched from Marte Valles and a southern section whose volcanics may derive, in part, from local sources. This South Amazonis region shows perhaps the most complex radar-bright structure on Mars and includes features that correspond to platy-ridged flows similar to those in Cerberus.
AB - We present Earth-based radar images of Mars obtained with the upgraded Arecibo S-band (λ=12.6 cm) radar during the 2005-2012 oppositions. The imaging was done using the same long-code delay-Doppler technique as for the earlier (pre-upgrade) imaging but at a much higher resolution (~3. km) and, for some regions, a more favorable sub-Earth latitude. This has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity (a proxy for small-scale surface roughness) over the major volcanic provinces of Tharsis, Elysium, and Amazonis. We find that vast portions of these regions are covered by radar-bright lava flows exhibiting circular polarization ratios close to unity, a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces. All of the major volcanoes have radar-bright features on their shields, although the brightness distribution on Olympus Mons is very patchy and the summit plateau of Pavonis Mons is entirely radar-dark. The older minor shields (paterae and tholi) are largely or entirely radar-dark, which is consistent with mantling by dust or pyroclastic material. Other prominent radar-dark features include: the " fan-shaped deposits" , possibly glacial, associated with the three major Tharsis Montes shields; various units of the Medusae Fossae Formation; a region south and west of Biblis Patera where " Stealth" deposits appear to obscure Tharsis flows; and a number of " dark-halo craters" with radar-absorbing ejecta blankets deposited atop surrounding bright flows. Several major bright features in Tharsis are associated with off-shield lava flows; these include the Olympus Mons basal plains, volcanic fields east and south of Pavonis Mons, the Daedalia Planum flows south of Arsia Mons, and a broad expanse of flows extending east from the Tharsis Montes to Echus Chasma. The radar-bright lava plains in Elysium are concentrated mainly in Cerberus and include the fluvio-volcanic channels of Athabasca Valles, Grjotá Valles, and Marte Valles, as well as an enigmatic region at the southern tip of the Cerberus basin. Some of the Cerberus bright features correspond to the distinctive " platy-ridged" flows identified in orbiter images. The radar-bright terrain in Amazonis Planitia comprises two distinct but contiguous sections: a northern section formed of lavas and sediments debouched from Marte Valles and a southern section whose volcanics may derive, in part, from local sources. This South Amazonis region shows perhaps the most complex radar-bright structure on Mars and includes features that correspond to platy-ridged flows similar to those in Cerberus.
KW - Mars
KW - Mars, Surface
KW - Radar observations
UR - http://www.scopus.com/inward/record.url?scp=84864075335&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84864075335&partnerID=8YFLogxK
U2 - 10.1016/j.icarus.2012.06.030
DO - 10.1016/j.icarus.2012.06.030
M3 - Article
AN - SCOPUS:84864075335
SN - 0019-1035
VL - 220
SP - 990
EP - 1030
JO - Icarus
JF - Icarus
IS - 2
ER -