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SHARAD

SHARAD (Mars SHAllow RADar sounder) is a subsurface sounding radar embarked on the Mars Reconnaissance Orbiter (MRO) probe. It complements the MARSIS radar on Mars Express orbiter,[1] providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space).[citation needed]

File:MRO-SHARAD-top-view.jpg
Schematic view of SHARAD operation on Mars Reconnaissance Orbiter

SHARAD was developed under the responsibility of the Italian Space Agency (ASI, Agenzia Spaziale Italiana), and provided to JPL for use on board NASA's Mars Reconnaissance Orbiter spacecraft in the frame of a NASA/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Sapienza University of Rome is responsible for the instrument operations, while Thales Alenia Space Italia (formerly Alenia Spazio) designed and built the instruments. SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within the Alcatel Alenia Space facilities in the suburbs of Rome.

Science objectives

 
Radargram of north pole layered deposits from SHARAD shallow ground-penetrating radar on Mars Reconnaissance Orbiter

SHARAD is intended to map the first kilometer below the Mars surface,[citation needed] providing images of subsurface scattering layers with high vertical resolution (15 m), with the intent to locate water/ice/ deposits and to map the vertical structure of the upper subsurface layers.

Characteristics

SHARAD operates on a carrier frequency of 20 MHz, transmitting a "chirped" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μs and the nominal Pulse Repetition Frequency is 700.28 Hz. Transmitted power is 10 W peak. The antenna is a 10 m dipole. A synthetic aperture is generated on-ground to reduce the unwanted surface returns from off-nadir scatterers at the same range of the subsurface echoes.

SHARAD is physically divided into two elements:

  • the SEB (SHARAD electronic box), which contains all the electronics (instrument controller, transmitter, receiver and antenna impedance matching network), within a metal frame which acts as thermal radiator for the electronic modules inside (Mars Reconnaissance Orbiter is an open frame spacecraft, and SHARAD has an autonomous thermal control)
  • the antenna, made by two fiber tubes, folded and stowed in a cradle (covered by thermal insulator to protect it from the heating induced by the aerobraking). Once released, the antenna extends into position thanks only to the elastic property of the material. A metal wire running inside the non-conductive tubes represents the real radiating element of the antenna. The antenna was designed and manufactured by Northrop Grumman Astro Aerospace in Carpinteria, CA.

The instrument operates at fixed PRF (700.28 Hz) and the echo is received in rank 1 (i.e., after the second transmitted pulse). Two alternate (higher and lower) PRF are available to deal with the extended mission orbit range. An open-loop tracking system, based on a priori knowledge of the surface topography, is the nominal means to position the 135 μs receive window on the expected echo position (a closed-loop tracker is available as backup).

The instrument on-board signal processing is minimal, and consists in a coherent presuming of the received echoes (programmable between 1 and 32 in power of 2 steps) to reduce the generated data rate, with programmable number of bits (8, 6, 4).

The chirp signal is generated directly on the 20 MHz carrier by a digital chirp generator, and fed to the power amplifier, followed by a Transmit/Receive switch and the matching network. The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using an undersampling technique at a rate of 26.6 MHz. A single digital signal processor provides both the control and processing function.

The instrument industrial team is composed as follows:

  • Instrument design, integration and test: Alcatel Alenia Space Italia (Rome plant)
  • DES (Digital electronics subsystem): Alcatel Alenia Space Italia (Milan plant - formerly Laben)
  • Chirp Generator, Receiver: Alcatel Alenia Space Italia (Rome/L'Aquila plants)
  • Transmitter, matching network: Galileo Avionica (Milan, Italy)
  • Antenna: Astro Aerospace (Carpinteria, CA, USA)

History

While the initial studies date back to 2001, full-scale development was released only in February 2003. The Engineering Model (EM) of the instrument was delivered to Lockheed Martin Space Systems in Denver (responsible for the spacecraft) in March 2004, and integrated into the Orbiter Test Bed. The ProtoFlight Model (PFM) was delivered and integrated on the Mars Reconnaissance Orbiter in Denver in September 2004. Mars Reconnaissance Orbiter was launched from Cape Canaveral Air Force Station on August 12, 2005, with an Atlas V-Centaur launch vehicle, and reached Mars orbit on March 10, 2006. The aerobraking phase, needed to reach the operational orbit, lasted until August 30, 2006. On September 17, 2006, the SHARAD antenna was deployed, and the first in-flight test of the radar was successfully carried out on September 19. SHARAD has been operational since November 2006.

Findings

Further information: Scalloped topography

The SHARAD radar penetrated the north polar layered ice deposits of Mars and revealed a relatively small (about 100 meter) maximum deflection of the underlying rock, which suggests a strong lithosphere greater than 300 kilometers thick.[2] Radar results consistent with massive deposits of water ice in middle latitudes support a debris-covered glacier hypothesis.[3]

On November 22, 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars using SHARAD. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior.[4][5][6]

Mars - Utopia Planitia
Scalloped terrain led to the discovery of a large amount of underground ice
enough water to fill Lake Superior (November 22, 2016)[4][5][6]
 
Martian terrain
 
Map of terrain

The calculations for the volume of water ice in the region were based on measurements from SHARAD, the ground-penetrating radar instrument on the Mars Reconnaissance Orbiter (MRO).

 
SHARAD finds ice by measuring its radar returns from the surface and from a deeper lower surface. The depth to the lower surface was found from HiRISE images of gaps in the surface.

SHARAD radar data when combined to form a 3D model reveal buried craters in the north polar cap. These may be used to date certain layers.[7]

Research, published in April 2011, described a large deposit of frozen carbon dioxide near the south pole. Most of this deposit probably enters Mars' atmosphere when the planet's tilt increases. When this occurs, the atmosphere thickens, winds get stronger, and larger areas on the surface can support liquid water. [8] After more analysis, it was discovered that if these deposits were all changed into gas, the atmospheric pressure on Mars doubles.[9] There are three layers of these deposits; each are capped with a 30-meter layer of water ice that prevents the CO2 from sublimating into the atmosphere. In sublimation a solid material goes directly into a gas phase. These three layers are linked to periods when the atmosphere collapsed when the climate changed.[10]

Interactive Mars map

<imagemap>

Image:Mars Map.JPG|thumb|center|620px|alt=Map of Mars| Interactive image map of the global topography of Mars. Hover over the image to see the names of over 60 prominent geographic features, and click to link to them. Coloring of the base map indicates relative elevations, based on data from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor. Whites and browns indicate the highest elevations (+12 to +8 km); followed by pinks and reds (+8 to +3 km); yellow is 0 km; greens and blues are lower elevations (down to −8 km). Axes are latitude and longitude; Polar regions are noted.

poly 377 357 423 380 407 405 369 389 Acheron Fossae poly 1316 75 1305 231 992 408 677 224 651 71 1069 169 Acidalia Planitia poly 564 320 555 402 464 416 449 348 489 317 Alba Mons poly 160 408 355 401 311 594 156 594 Amazonis Planitia poly 832 741 903 744 897 793 749 880 776 950 831 1052 829 1121 510 1126 653 854 Aonia Planitia poly 1186 320 1477 394 1040 732 960 635 952 525 Arabia Terra poly 155 70 578 72 580 258 156 429 377 238 284 224 308 283 158 408 Arcadia Planitia poly 875 1108 872 1128 956 1131 957 1041 906 1047 904 1084 Argentea Planum poly 871 871 935 887 926 942 884 967 837 918 Argyre Planitia poly 880 356 962 441 889 505 824 412 Chryse Planitia poly 515 777 575 751 671 792 684 835 580 854 Claritas Fossae poly 981 456 992 493 1076 412 1044 386 Cydonia Mensae poly 346 685 514 740 526 838 363 797 Daedalia Planum poly 1858 405 1968 412 1954 514 1860 505 Elysium Mons poly 1692 500 1945 509 2009 342 2092 588 2085 671 2007 689 Elysium Planitia poly 1848 617 1870 616 1882 638 1878 637 1848 639 Gale crater poly 1645 865 1675 858 1645 782 1600 789 Hadriaca Patera poly 1378 766 1418 783 1392 882 1356 874 Hellas Montes poly 1410 772 1515 769 1618 869 1493 943 1387 894 Hellas Planitia poly 1599 731 1610 599 1711 593 1750 717 Hesperia Planum poly 928 703 919 746 960 761 959 726 Holden crater poly 524 827 588 867 564 900 511 881 Icaria Planum poly 1587 447 1672 520 1619 575 1555 568 1538 500 Isidis Planitia poly 1531 475 1518 514 1547 516 1552 484 Jezero crater poly 1032 72 1030 87 1112 94 1124 166 1032 170 Lomonosov crater poly 153 569 280 579 293 650 156 651 Lucus Planum poly 356 411 400 451 357 486 329 465 Lycus Sulci poly 1243 254 1311 258 1309 310 1244 304 Lyot crater poly 738 489 823 493 792 597 704 573 Lunae Planum poly 1367 964 1552 989 1531 1099 1361 1078 Malea Planum poly 832 1047 920 1048 916 1124 839 1125 Maraldi crater poly 572 326 612 356 676 303 658 276 Mareotis Fossae poly 664 301 752 369 700 454 628 400 Mareotis Tempe poly 872 491 976 477 1054 609 953 635 Margaritifer Terra poly 1853 283 1857 333 1903 330 1899 281 Mie crater poly 309 233 346 235 344 265 303 267 Milankovič crater poly 1694 508 1665 562 1767 637 1798 575 Nepenthes Mensae poly 801 855 931 819 941 861 871 857 848 883 Nereidum Montes poly 1529 438 1446 412 1462 371 1525 404 Nilosyrtis Mensae poly 1197 672 994 834 978 1072 1276 1086 1365 785 Noachis Terra poly 471 410 547 418 532 488 479 470 Olympica Fossae poly 390 417 481 505 373 547 353 483 Olympus Mons poly 137 1061 139 1144 2102 1143 2103 1063 Planum Australe poly 1804 1124 1844 649 1663 650 1592 1129 Promethei Terra poly 1276 219 1262 253 1373 329 1383 302 Protonilus Mensae poly 151 729 314 737 323 852 156 885 Sirenum poly 1370 899 1432 952 1373 972 1339 933 Sisyphi Planum poly 585 631 784 692 697 823 574 807 Solis Planum poly 570 638 608 673 574 707 531 670 Syria Planum poly 602 232 645 243 595 314 561 306 Tantalus Fossae poly 727 306 790 260 840 392 731 497 693 567 Tempe Terra poly 1850 652 2080 675 2086 1128 1799 1125 Terra Cimmeria poly 1403 483 1547 596 1476 690 1350 749 1242 696 1214 642 Terra Sabaea poly 158 816 589 900 655 1124 171 1123 Terra Sirenum poly 547 484 611 530 488 714 413 656 Tharsis Montes poly 576 385 604 401 585 445 564 428 Tractus Catena poly 1583 607 1782 679 1762 800 1604 771 1531 738 Tyrrhena Terra poly 452 529 505 568 475 583 445 570 Ulysses Patera poly 608 432 641 439 633 467 605 456 Uranius Patera poly 1413 79 1421 296 1627 447 1820 471 1853 364 1832 277 1894 254 1918 311 1829 476 2079 214 2078 80 Utopia Planitia poly 589 582 907 651 865 716 572 655 Valles Marineris poly 139 51 142 132 2103 133 2104 53 Vastitas Borealis poly 824 475 915 593 889 632 789 604 Xanthe Terra

desc bottom-left</imagemap>


See also

  • LRS, Lunar radar sounder (LRS) is a orbiting low frequency radar sounder and altimeter over Earth's Moon
  • MARSIS, Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a orbiting low frequency radar sounder and altimeter over Mars
  • RIME, Radar for Icy Moons Exploration (RIME) is a orbiting low frequency radar sounder and altimeter for Jupiter's Icy moons
  • Tianwen-1, The Tianwen-1 mission plans an Orbiter Subsurface Radar (OSR) and rover based Ground-Penetrating Radar (GPR) for Mars
  • WISDOM (radar), Water Ice and Subsurface Deposit Observation on Mars (WISDOM) is a ground-penetrating radar on the ExoMars rover

References

  1. ^ R. Orosei et al., "Science results from the MARSIS and SHARAD subsurface sounding radars on Mars and their relevance to radar sounding of icy moons in the Jovian system", EPSC2010-726, European Planetary Science Congress 2010, Vol. 5 (accessed Nov. 17 2014)
  2. ^ Phillips, R. J.; Zuber, M. T.; Smrekar, S. E.; Mellon, M. T.; Head, J. W.; Tanaka, K. L.; Putzig, N. E.; Milkovich, S. M.; Campbell, B. A.; Plaut, J. J.; Safaeinili, A.; Seu, R.; Biccari, D.; Carter, L. M.; Picardi, G.; Orosei, R.; Mohit, P. S.; Heggy, E.; Zurek, R. W.; Egan, A. F.; Giacomoni, E.; Russo, F.; Cutigni, M.; Pettinelli, E.; Holt, J. W.; Leuschen, C. J.; Marinangeli, L. (2008). "Mars north polar deposits: stratigraphy, age, and geodynamical response". Science. 320 (5880): 1182–1185. Bibcode:2008Sci...320.1182P. doi:10.1126/science.1157546. hdl:11573/69689. PMID 18483402. S2CID 6670376.
  3. ^ Holt, J. W.; Safaeinili, A.; Plaut, J. J.; Head, J. W.; Phillips, R. J.; Seu, R.; Kempf, S. D.; Choudhary, P.; Young, D. A.; Putzig, N. E.; Biccari, D.; Gim, Y. (2008). "Radar Sounding Evidence for Buried Glaciers in the Southern Mid-Latitudes of Mars". Science. 322 (5905): 1235–1238. Bibcode:2008Sci...322.1235H. doi:10.1126/science.1164246. PMID 19023078. S2CID 36614186.
  4. ^ 4.0 4.1 Staff (November 22, 2016). "Scalloped Terrain Led to Finding of Buried Ice on Mars". NASA. Retrieved November 23, 2016.
  5. ^ 5.0 5.1 "Lake of frozen water the size of New Mexico found on Mars – NASA". The Register. November 22, 2016. Retrieved November 23, 2016.
  6. ^ 6.0 6.1 "Mars Ice Deposit Holds as Much Water as Lake Superior". NASA. November 22, 2016. Retrieved November 23, 2016.
  7. ^ Foss, F., et al. 2017. 3D imaging of Mars'polar ice caps using orbital radar data. The Leading Edge: 36, 43-57.
  8. ^ "NASA Spacecraft Reveals Dramatic Changes in Mars' Atmosphere". Archived from the original on February 2, 2013.
  9. ^ Phillips, R., et al. 2011. Massive CO2 ice deposits sequestered in the south polar layered deposits of Mars. Science: 332, 638-841
  10. ^ Bierson, C., et al. 2016. Stratigraphy and evolution of the buried CO2 depositin the Martian south polar cap. Geophysical Research Letters: 43, 4172-4179

Further reading

External links

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