Planetary Coordinate Systems & Small Body Mapping Needs

Brent Archinal

U. S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA, [email protected]

Northern Arizona Planetary Science Alliance

Flagstaff, AZ 2015 February 24 Planetary Coordinate Systems (Frames) As recommended by IAU Working Group on Cartographic Coordinates and Rotational Elements

. WGCCRE issues reports recommending coordinate systems WGCCRE web site and related parameters for making cartographic products of solar system bodies . Starting in 1979 (Davies et al., 1980), reports every three years . Current “2009” report published 2011 (Archinal et al., 2011, CDMA; erratum, 2011) . “2015” (delayed from 2012) report in progress . Makes recommendations, open to further modification when needed, intended to facilitate the use and comparison of multiple datasets . Setting up coordinate systems . Updating coordinate systems . Prime meridian . Orientation (spin, pole position) . Shape (for map scale, map projection, orthoprojection of data) . Promotion of the use of a standardized set of mapping parameters . “High level” system recommendations, not about products and mapping standards, etc. . Web site: . http://astrogeology.usgs.gov/groups/IAU-WGCCRE

WGCCRE 2009 Report (pub. 2011) Two Recommended Systems: Planets & Satellites vs. “Small Bodies”

Planets and Planetary Satellites Dwarf planets, asteroids, comets . Planetographic - Right handed system . Longitude increases as viewed from . Longitude is right handed (positive, Earth (west or east) negative) . Latitude defined relative to ecliptic . Latitude is right handed (positive, (north or south) negative) . Planetocentric . No reliance on Earth or ecliptic . Longitude toward east . Adopted 2003 . Latitude same as planetographic . Classical system . Kept for historical reasons

Definition of Longitude – Mars example

. WG has reiterated 1979 (Davies et al., 1980) recommendation: Once an observable reference feature at a defined longitude is chosen, the longitude definition origin should not change except under unusual circumstances . Recent questions relative to Moon, Mercury, satellites of Jupiter and Saturn, Vesta, Lutetia . No clear advantage seen in creating multiple prime meridians and Transfer of Mars 0° longitude from Meridiani Sinus cartographic systems – alternate systems (left) to Airy-0 (right) in 1973. Left: USAF 1962 Mars map (ESA/DLR/FU Berlin (G. Neukum / Google Earth); Right: Mariner 9 image of Airy and (e.g. dynamic) considered more useful Airy-0, no. 533B03 . Examples at right: Airy-0 on Mars (de Vaucouleurs et al., 1973); Hun Kal on Mercury Left: Longitude origin for Mercury was transferred in 1979 from dynamical one (long principal axis at 0°) to surface feature, crater Hun Kal (“twenty” in Mayan) at 20° west longitude. Definition of Longitude on Small Bodies

Guidelines: Cases so far: name) . Initially, use arbitrary meridian, e.g. W = 0° . No feature chosen, W = 0° . Tempel 1 (unnamed crater 0 0 near impact) at J2000.0 or observation epoch . Itokawa, Borrelly . Feature near long axis set to 0° . No feature chosen, arbitrary W . When surface first mapped chose “small” 0 . Ida (Afon crater) . Davida feature near equator, set longitude (e.g. 0°), . Considered for Wild 2? calculate W . Arbitrary W0, based on light 0 curve . Long axis of shape model chosen at 0° . Maintain definition into future, as new data . Lutetia (in WG report) . Pallas obtained (pick new feature if necessary, modify . Arbitrary (obvious) feature . Synchronous rotation defines W W0 within accuracy limits as necessary) chosen at 0° 0 . Pluto and Charon . Specify second feature for chaotic (“tumbling”) . Ceres (unnamed bright spot) rotation bodies (none yet) . Vesta (“Olbers Regio”, informal name); Now also . *** Very long story – Dawn Claudia crater at 146 °*** mission has used several other . Eros (unnamed crater) non-standard systems. Use . Gaspra (Charax crater, near caution… long axis) . Šteins (“Spinel”, informal

Tempel 1 example: unnamed prime meridian crater (center) (Deep Impact; Thomas et al., 2007, Fig. 3) Gaspra example: prime meridian crater Charax (no. 17) (Galileo; Davies et al., 1994, Fig. 1) Small Bodies in Current Report

Rotational Elements (Orientation) Size and Shape Radius, principal axes defined for: α0, δ0, and W 0 defined* for: (1) Ceres (134340) Pluto (1) Ceres (4179) Toutatis (2) Pallas (134340) Pluto : I (4) Vesta (25143) Itokawa (4) Vesta Charon (21) Lutetia (134340) Pluto (21) Lutetia 9P/Tempel 1 (243) Ida (134340) Pluto: I Charon (243) Ida 19P/Borrelly (253) Mathilde 1P/Halley (433) Eros * Only “mapped” bodies – (433) Eros 9P/Tempel 1 (511) Davida no photometric only (511) Davida 19P/Borrelly definitions (951) Gaspra (951) Gaspra 81P/Wild 2 (2867) Šteins (2867) Šteins (25143) Itokawa

Ceres example: rotation of prime Pallas example: positive meridian polar projection K band bright spot map of shape model, with (HST images; 0° (long axis) at bottom Thomas, et (from Keck II and VLT al., 2005, Fig. images; Carry, et al., 2010) 1) Changing topics… Small Bodies Mapping Needs

. NASA and International Planning Issues need to be addressed . Active efforts to use existing data, new data from currently active and planned missions, and data from future robotic and human asteroid missions for development of cartographic products must begin ASAP . Better coordination and education is needed to ensure compliance with existing standards for mapping . For example, Dawn mission at Vesta . Use of many non-standard coordinate systems . Confusion on geologic mapping standards . Better coordination of and education on cartographic & mapping standards needed! . “Cartography Research and Assessment Group” (CRAG), being created to support NASA Planetary Science Division . At our urging . Should begin to again address NASA Cartography Planning, including for small bodies . Town Hall meeting at LPSC meeting next month

Small Bodies Mapping Needs, continued

. General Technical issues require substantial investment and development . The “state of the art” of mapping irregular small bodies is uncertain and currently poorly developed . Significant algorithm & software development is required for mapping small and irregular bodies . Accuracy verification---an essential element of development of precise, high-quality products for planetary exploration---is essential . And yet is not currently planned for most techniques . Needs demonstrated, applied to the novel image geometries that arise with small bodies . Algorithm and software development for efficient processing of small body data sets (including large numbers of images with complex geometries) Small Bodies Mapping Needs, continued

. Specific Technical Issues as examples of current needs . Development of a tool or tools to create a data catalog to be used for data registration, comparison between data sets, and assessment of the registration accuracy; . Rigorous combination of stereo imaging and lidar data, possibly as part of orbit and gravity field determination; . Improved accuracy solutions for photoclinometry (shape from shading) and stereo photoclinometry by combining stereo and shape from shading techniques and using well determined photometric models; . Rigorous accuracy estimation for absolute scale and relative coordinates, based on simulation, analog experiments, and direct comparison of redundant (stereo vs. lidar) observations; . Tools for mapping of irregular bodies in true 3D where views are occluded by topography, and for display of surface data on irregular objects; . Development and conversion between shape models in multiple formats; . Integration of rover, lander, descent, and orbital/station keeping data; . Near real-time or real-time mapping; . Conversion and testing of software for on board spacecraft use Resources . NASA Ames white paper . tiny.cc/mapping-small-bodies . January 2014 SBAG presentation . http://www.lpi.usra.edu/sbag/meetings/jan2014/pr esentations/09_1135_Nefian_2014_01_09_sb_map ping_SBAG.pdf . Need for NEO Close Mapping . ftp://ftpext.usgs.gov/pub/wr/az/flagstaff/barchinal/ Carto-Planning/IAA-PDC13-03-01P%20Archinal.pdf . NASA Planetary Cartography Planning . Many articles and presentations about needs for planetary mapping and planning, etc. . http://astrogeology.usgs.gov/groups/nasa- planetary-cartography-planning

Summary

. Coordinate Systems . Where mapping has been done, recommendations made by IAU WGCCRE . Small bodies use a right handed system . See current (“2009”, soon 2015) WG report . Small Body Mapping Needs . Substantial general planning issues need considered, prioritized, and addressed . Many specific technical questions and developments need addressed . See links for details, examples Backup IAU Working Group Operation

. Membership by invitation or volunteering, with IAU Division approval Current WGCCRE Membership

. Currently 19 members from 6 countries B.A. ARCHINAL (CHAIR) S.A. KLIONER . Considers new published coordinate system U.S. Geological Survey, Flagstaff, AZ, Technische Universität Dresden, Lohrmann U.S.A. Observatory, Dresden, Germany related determinations C.H. ACTON D. McCARTHY . Recommends standards based on consensus Jet Propulsion Laboratory, Pasadena, CA, U.S. Naval Observatory (retired), Washington, U.S.A. DC, U.S.A. . No independent resources of its own M.F. A’HEARN K. MEECH University of Maryland, College Park, MD, . Does not “bless” or “enforce” U.S.A. Institute for Astronomy, Honolulu, HI, U.S.A.

recommendations – value is only from A. CONRAD J. OBERST Max Planck Institute for Astronomy, DLR Berlin Adlershof, Berlin, Germany reflection of general consensus and use Heidelberg, Germany J. PING . Recommendations primarily for mapping – G.J. CONSOLMAGNO Shanghai Astronomical Observatory, other uses (e.g. dynamical) possible Vatican Observatory, Vatican City State Shanghai, China

T. DUXBURY P.K. SEIDELMANN . Does not deal with formats, “lower level” George Mason University, Fairfax, VA, University of Virginia, Charlottesville, VA, mapping standards U.S.A. U.S.A.

D. HESTROFFER D.J. THOLEN . There is a need for missions and space IMCCE, Observatoire de Paris, CNRS, Paris, University of Hawaii, Honolulu, HI, U.S.A. agencies to develop and maintain such France P.C. THOMAS standards J.L. HILTON Cornell University, Ithaca, NY, U.S.A. U.S. Naval Observatory, Washington D.C., . E.g. International Planetary Data U.S.A. I.P. WILLIAMS Queen Mary, University of London, London, Alliance, Planetary Data System, Mars L. JORDA U.K. Laboratoire d'Astrophysique de Marseille, Geodesy and Cartography WG Marseille, France

(Duxbury et al., 2002), Lunar Geodesy R. Kirk U.S. Geological Survey (emeritus), and Cartography WG (Archinal and Flagstaff, AZ, U.S.A.

LGCWG, 2009), Cassini Icy Satellites Cartography WG

Coordinate System for (4) Vesta – Chronology

2011 August: Dawn mission proposes a longitude system with a large (~155°) rotation from the IAU recommended system (based on Thomas et al. 1997 and Li et al 2010), tied to “Olbers” feature. Many reasons expressed for the large departure from the previously used system

2011 & 2012: WG replies in both September and March, after careful and extensive consideration, that the arguments were not compelling enough to ignore HST image of Vesta and Dawn image of Vesta with previous usage by the planetary community and the “Olbers Regio” at 25 km HST and Dawn derived WG’s previous recommendations resolution (Zellner et al. prime meridians shown 1997, Figure 1) 2012: Unfortunately the mission began publishing results using their rotated system, resulting in 2012 November: The mission asked the WG for substantial confusion concurrence on the suitability of this latest system, and it provided that. The WG also recommended that to . Fortunately, the NASA Planetary Data System avoid further confusion, maps and scientific publications requires that data products archived to it follow should henceforth use the same primary system as the various international and NASA standards, including data archives those of the IAU

. The mission therefore proposed using a new system, which the PDS did accept as agreeing with The DAWN mission has been delivering data to the PDS IAU recommendations. This system is (now) as using the new compliant system where it has been described in the Dawn PDS archive (with reviewed and is available for public use

W0=285.39°) 2013 November: WG formally recommends use of compliant coordinate system

Coordinate System for (4) Vesta

. Map here, by Ready et al., from PDS documentation by J. Li . The key point is that the dark “Olbers” feature is kept at/near the 0° meridian . Yellow lines show the approximate location of the original Thomas et al. coordinate system . But not of updated system recommended by the WG in 2011 . Blue and green lines show the location of 0° longitude in other Dawn mission systems . White “X” identifies the small crater Claudia, which the Dawn mission is now using as a longitude reference, in preference to the larger Olbers (as with e.g. Airy-0 vs. Sinus Meridiani on Mars)