Description of the Roberts Eros Ponds Catalog bundle V1.0 ========================================================= Bundle Generation Date: 2020-07-07 Peer Review: 2019 Asteroid Review Discipline node: Small Bodies Node Content description for the Roberts Eros Ponds Catalog bundle ============================================================= OVERVIEW -------- Ponds or "ponded deposits" are smooth deposits tens of meters in diameter that are interpreted to consist of fine-grained material (VEVERKAETAL2001; ROBINSONETAL2001). Over 300 of these landforms have been identified on (433) Eros, and are typically located at the bottoms of topographic depressions and sharply embay the bounding depressions in which they lie (VEVERKAETAL2001; ROBINSONETAL2001; CHENGETAL2002B). The ponds are found at all latitudes, but are largely concentrated near the equator at the ends of the long axis of the asteroid. NEAR MSI spectra of the deposits appear blue relative to the surrounding terrain, and are thus interpreted to consist of fine-grained material (ROBINSONETAL2001). The ponds have also been interpreted to lie on geopotential surfaces (ROBINSONETAL2001; VEVERKAETAL2001B). However, because the coverage of altimetry data is limited (ZUBERETAL2000B; CHENGETAL2001B; CHENGETAL2002B), the flatness of few ponds can be measured directly (ROBERTSETAL2014). The apparent distribution of ponds has been used to evaluate some of the mechanisms that have been proposed for their formation. Because the long ends of the asteroid are furthest from the center of mass, the gravity is the lowest at these places (THOMASETAL2002), and has been interpreted (ROBINSONETAL2001) as supporting a formation method that works best when the gravity is low, e.g. electrostatic levitation and transport of fine-grained material (Lee, 1996). The distribution of ponds (especially those containing boulders) also correlates with the regions of the asteroid that spend more time near the terminator. Repeated terminator crossings are important for the electrostatic levitation hypothesis, but has also been interpreted (Dombard et al. 2010) to support formation of ponds by thermal disaggregation of boulders. Analysis of the distribution of ponds (ROBERTSETAL2014) indicates that it is correlated with spatial resolution of the imaging data, and may be affected by an observational bias, particularly at smaller sizes (< 30 m diameter). Because the pond distribution has been used to evaluate the above formation hypotheses, it is important that the ponds be accurately located with respect to the background topography. The known pond locations were originally referenced to a shape model derived with classical stereogrammetry. However, the highest resolution shape model had been produced using stereophotoclinometry (SPC), but was produced with a fraction of the available MSI images (GASKELLETAL2008) and only the 55 ponds contained in those images could be accurately located on that shape model (ROBERTSETAL2014B). Now that the full set of NEAR MSI images have been registered to the SPC shape model, we have updated the locations of all previously identified ponds, to enable future mapping tasks. DATA ---- This data set consists of two tables describing the body-fixed location and diameter of 334 ponds on asteroid (433) Eros. These ponds were identified by Peter Thomas, who provided an unpublished database referenced in ROBINSONETAL2001 containing the MSI image number and pixel coordinates of the center of each pond. The MSI images containing the pond locations were projected onto the shape model (GASKELL2008) using the Small Body Mapping Tool (ERNSTETAL2018) to determine the IAU_EROS coordinates corresponding to the Thomas pixel coordinates. The IAU_EROS reference frame is defined in near_coordinate_systems.pdf located in the document directory. The orientation of this frame is computed by evaluating the rotation constants provided in SPICE kernel file eros_alex.tpc, available in the document directory of the PDS data set NEAR-A-MSI-5-EROSSHAPE-V1.0 (GASKELL2008). Although the ponds are generally not circular, Thomas provides a characteristic radius for each pond. The pond diameter in the tables is taken directly from the Thomas database. Table "erosShiftedPonds_20190226_circles.csv" consists of the following columns: 1) pond number 2) x coordinate (km) of pond center in IAU_EROS frame 3) y coordinate (km) of pond center in IAU_EROS frame 4) z coordinate (km) of pond center in IAU_EROS frame 5) north latitude (deg) of pond center 6) east longitude (deg) of pond center 7) distance (km) between Eros center and pond center 8) pond diameter (km) Table "erosShiftedPonds_20190226_sbmt.tab" is formatted for ingestion into the Small Body Mapping Tool (SBMT) as a "Circles" or "Ellipses" type "Structures" file. It provides the same information as table "erosShiftedPonds_20190226_circles.csv", plus additional columns required by SBMT for display purposes. 1) pond number 2) SBMT internal name of structure 3) x coordinate (km) of pond center in IAU_EROS frame 4) y coordinate (km) of pond center in IAU_EROS frame 5) z coordinate (km) of pond center in IAU_EROS frame 6) north latitude (deg) of pond center 7) east longitude (deg) of pond center 8) distance (km) between Eros center and pond center 9) SBMT internal value 10) SBMT internal value 11) SBMT internal value 12) SBMT internal value 13) pond diameter (km) 14) SBMT internal flattening 15) SBMT internal value 16) SBMT pond color RGB 17) SBMT structure label Caveats to the data user ======================== The ponds are generally not circular, but Thomas provides a characteristic radius for each pond. A future update to this archive will re-characterize the pond outlines as best-fit ellipses. Not all of the ponds in the Thomas database are distinct deposits. There are cases where multiple circular ponds comprise a single, elongated continuous deposit. These continuous deposits are not identified in this data set. Such identification would require re-characterizing the pond outlines as polygons.