Planetary Coordinate Systems & Small Body Mapping Needs

Brent Archinal U. S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001, USA, barchinal@usgs.gov

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 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)

WGCCRE web site

Two Recommended Systems: Planets & Satellites vs. “Small Bodies”

Planets and Planetary Satellites Planetographic

Longitude increases as viewed from Earth (west or east)

Latitude defined relative to ecliptic (north or south)

Planetocentric Longitude toward east Latitude same as planetographic

Classical system Kept for historical reasons

Dwarf planets, asteroids, comets - Right handed system

Longitude is right handed (positive, negative)

Latitude is right handed (positive, negative)

No reliance on Earth or ecliptic Adopted 2003

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 cartographic systems – alternate systems (e.g. dynamic) considered more useful

Examples at right: Airy-0 on Mars (de Vaucouleurs et al., 1973); Hun Kal on Mercury

Transfer of Mars 0° longitude from Meridiani Sinus (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 Airy-0, no. 533B03

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: Initially, use arbitrary meridian, e.g. W0 = 0°

at J2000.0 or observation epoch When surface first mapped chose “small”

feature near equator, set longitude (e.g. 0°), calculate W0

Maintain definition into future, as new data obtained (pick new feature if necessary, modify W0 within accuracy limits as necessary)

Specify second feature for chaotic (“tumbling”) rotation bodies (none yet)

Cases so far: No feature chosen, W0 = 0°

Itokawa, Borrelly No feature chosen, arbitrary W0

Davida Arbitrary W0, based on light

curve Lutetia (in WG report)

Arbitrary (obvious) feature chosen at 0° Ceres (unnamed bright spot) Vesta (“Olbers Regio”,

informal name); Now also Claudia crater at 146 °***

Eros (unnamed crater) Gaspra (Charax crater, near

long axis) Šteins (“Spinel”, informal

name) Tempel 1 (unnamed crater

near impact) Feature near long axis set to 0°

Ida (Afon crater) Considered for Wild 2?

Long axis of shape model chosen at 0° Pallas

Synchronous rotation defines W0 Pluto and Charon

*** Very long story – Dawn

mission has used several other non-standard systems. Use caution…

Gaspra example: prime meridian crater Charax (no. 17) (Galileo; Davies et al., 1994, Fig. 1)

Tempel 1 example: unnamed prime meridian crater (center) (Deep Impact; Thomas et al., 2007, Fig. 3)

Small Bodies in Current Report

Rotational Elements (Orientation) α0, δ0, and W0 defined* for: (1) Ceres (2) Pallas (4) Vesta (21) Lutetia (243) Ida (433) Eros (511) Davida (951) Gaspra (2867) Šteins (25143) Itokawa

(134340) Pluto (134340) Pluto : I

Charon 9P/Tempel 1 19P/Borrelly * Only “mapped” bodies –

no photometric only definitions

Size and Shape Radius, principal axes defined for:

(1) Ceres (4) Vesta (21) Lutetia (243) Ida (253) Mathilde (433) Eros (511) Davida (951) Gaspra (2867) Šteins

(4179) Toutatis (25143) Itokawa (134340) Pluto (134340) Pluto: I Charon 1P/Halley 9P/Tempel 1 19P/Borrelly 81P/Wild 2

Ceres example: rotation of prime meridian bright spot (HST images; Thomas, et al., 2005, Fig. 1)

Pallas example: positive polar projection K band map of shape model, with 0° (long axis) at bottom (from Keck II and VLT images; Carry, et al., 2010)

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_mapping_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 Currently 19 members from 6 countries Considers new published coordinate system

related determinations Recommends standards based on consensus No independent resources of its own Does not “bless” or “enforce”

recommendations – value is only from reflection of general consensus and use

Recommendations primarily for mapping – other uses (e.g. dynamical) possible

Does not deal with formats, “lower level” mapping standards There is a need for missions and space

agencies to develop and maintain such standards

E.g. International Planetary Data Alliance, Planetary Data System, Mars Geodesy and Cartography WG (Duxbury et al., 2002), Lunar Geodesy and Cartography WG (Archinal and LGCWG, 2009), Cassini Icy Satellites Cartography WG

B.A. ARCHINAL (CHAIR) U.S. Geological Survey, Flagstaff, AZ, U.S.A. C.H. ACTON Jet Propulsion Laboratory, Pasadena, CA, U.S.A. M.F. A’HEARN University of Maryland, College Park, MD, U.S.A. A. CONRAD Max Planck Institute for Astronomy, Heidelberg, Germany G.J. CONSOLMAGNO Vatican Observatory, Vatican City State T. DUXBURY George Mason University, Fairfax, VA, U.S.A. D. HESTROFFER IMCCE, Observatoire de Paris, CNRS, Paris, France J.L. HILTON U.S. Naval Observatory, Washington D.C., U.S.A. L. JORDA Laboratoire d'Astrophysique de Marseille, Marseille, France R. Kirk U.S. Geological Survey (emeritus), Flagstaff, AZ, U.S.A.

S.A. KLIONER Technische Universität Dresden, Lohrmann Observatory, Dresden, Germany D. McCARTHY U.S. Naval Observatory (retired), Washington, DC, U.S.A. K. MEECH Institute for Astronomy, Honolulu, HI, U.S.A. J. OBERST DLR Berlin Adlershof, Berlin, Germany J. PING Shanghai Astronomical Observatory, Shanghai, China P.K. SEIDELMANN University of Virginia, Charlottesville, VA, U.S.A. D.J. THOLEN University of Hawaii, Honolulu, HI, U.S.A. P.C. THOMAS Cornell University, Ithaca, NY, U.S.A. I.P. WILLIAMS Queen Mary, University of London, London, U.K.

Current WGCCRE Membership

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 previous usage by the planetary community and the WG’s previous recommendations 2012: Unfortunately the mission began publishing results using their rotated system, resulting in substantial confusion Fortunately, the NASA Planetary Data System

requires that data products archived to it follow various international and NASA standards, including those of the IAU

The mission therefore proposed using a new system, which the PDS did accept as agreeing with IAU recommendations. This system is (now) as described in the Dawn PDS archive (with W0=285.39°)

2012 November: The mission asked the WG for concurrence on the suitability of this latest system, and it provided that. The WG also recommended that to avoid further confusion, maps and scientific publications should henceforth use the same primary system as the data archives The DAWN mission has been delivering data to the PDS using the new compliant system where it has been reviewed and is available for public use 2013 November: WG formally recommends use of compliant coordinate system

Dawn image of Vesta with HST and Dawn derived prime meridians shown

HST image of Vesta and “Olbers Regio” at 25 km resolution (Zellner et al. 1997, Figure 1)

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)