Revisions from previous version

The correct and final IAU names are listed for all craters.

I reconciled the database with other existing crater databases and I list discrepancies.

I removed some of the entries that I thoght were either not useful or too difficult to consistently categorize.

I updated the database to correct errors and to include craters missed in previous version.

Entries in Main Database

Below I summarize measurements made on each crater in the database. Parentheses indicate notation used in tables. In the tables, blank entries indicate that not enough data was available to make the measurement. An "x" as an entry indicates the feature does not exist or cannot be measured. All distance and location measurements were made with digital images at C1-MIDR resolution (225 m/pixel). The minimum possible error of any distance measurement is therefore 122.5 m. However, the choice of endpoints for a particular measurement is subjective, and the repeatability of this choice dictates the true error in a measurement. To assess this I repeated the analysis several times for a subsample of the database and then found the standard deviation for each measurement type. If the error was constant with increasing crater diameter then we give the absolute average standard deviation below. However, some measurements had errors that systematically increased with increasing crater diameter, so that it is more appropriate to give the average percentage deviation.

Reference number (#). For reference purposes, each crater is assigned a diferent number.

Name. Official IAU name.

Latitude (Lat) of crater center. Error is ± 0.05°.

Longitude (Lon) of crater center. Error is ± 0.05°.

Rim-to-rim diameter (D). Value is diameter of a circle with an area equivalent to the crater's. I measured the area digitally by outlining the rim and counting the number of enclosed pixels. For craters with terracing, the rim is defined by the outermost boundary of the observable terraces. Most previous studies on other planets were made with photographic products rather than digital data, and typically involved measuring diameter using a set of rim-to-rim measurements or by fitting circle templates to the craters. In most cases the end result is nearly the same. Error is ± 2%. For crater fields, the equivalent single crater diameter (SD) entry of the multiple impacts database is used for D.

Confidence level (Co) that structure is an impact crater. Possible values are 1 (almost certain, 80 to 100% confidence), 2 (probable, 30% to 80% confidence), and 3 (cannot be ruled out as an impact structure, <30% confidence). Confidence levels are subjective, but are generally based on the presence or absence of such features as "hummocky" ejecta, well-defined ejecta deposits, rough walls, terracing (larger craters only), and a central peak or peak ring (larger craters only). Volcanic structures, the features most often confused with impact craters, usually are steep-sided, have smooth inner walls, and have smaller, less complete (if any) ejecta deposits than impact craters.

Elevation (Ev) of surrounding terrain. Made by taking 4-point average of global topography data (5 km/pixel sampling) located 3 diameters away from the crater center.

Crater density at a crater's location (Rho). Value is the density of craters in the neighborhood of the specified crater. This is calculated by counting the number of craters (including the specified crater) within a 1000 km radius circle, and normalizing to give the number of craters per 1 x 10 6 km2.

Twenty-five pixel averages of the DN values (an 8 bit, unsigned integer for each pixel in the SAR image) of a representative location on the crater floor (dni) and a location in the terrain surrounding the crater (dno). A representative location in the crater floor is similar in brightness to the majority of the crater floor. A representative location in the terrain surrounding the crater is a piece of terrain near the crater that is similar in character to the terrain that the crater formed on but that is unaffected by the crater. Within the crater we chose a piece of floor that appeared to be similar in brightness to the majority of the floor material. The difference between these values (dnd) gives an estimate of the relative radar brightness of the crater interior. Individual DN values can be converted to radar cross section in decibels by the formula

The average DN is the average of the logarithm of the backscatter at each pixel location. This calculation was only made for craters > 16 km in diameter.

Maximum distance of radar-bright continuous ejecta (Ce) from the rim. This does not include ejecta that was obviously emplaced as long run-out flows. Error is ± 0.9 km.

Maximum distance from rim of all flow units (Fl) extending from the ejecta blanket. Error is ± 0.3 km.

Approximate diameter of dark halo (Dh) surrounding crater. Error is ± 5%.

Completeness of ejecta deposits (Ec) around the rim as a fraction of 1. Error is ± 0.05.

Completeness of the rim (Rc) as a fraction of 1. Error is ± 0.05.

Planform of the crater rim (Pl): (c)ircular, (e)longate, (i)rregular, and (p)olygonal

Morphologic class (Mo) : (1) bowl-shaped; (2) knobby base; (3) central peak; (4) multiple peaks; (5) peak rings; (6) multiple rings; and (0) indistinguishable flat-floored feature, albedo line, etc.

Central structure diameter (Cd). Value is actually diameter of a circle with an area equivalent to that encompassing any central structure; measured in the same manner as rim-to-rim diameter. Previous studies have measured peak ring diameter by fitting a circle to the peaks of the ring massif (e.g., Pike and Spudis 1987, EM &P, v. 39, 129). For the sake of interplanetary comparisons in the text we also used this older technique to measure peak ring diameters for single- and double-ring basins. Peak ring diameters using this second technique are in the separate sheet. Error for central peak or peak ring diameter using the equivalent area technique is ± 6%. Error for peak ring diameter using the circle-fitting technique is ± 1.7 km.

Wall (Wa) terracing. Denotes whether the wall appears (u)nterraced or (t)erraced at C1-MIDR resolution.

Wall width (Ww) (Fig. 10). To minimize distortion resulting from SAR effects, horizontal distance from rim to floor was measured in the N - S direction. If no clear break between wall and floor could be discerned, this measurement was not made. Error is ± 10%.

Multiples (Mu). Impact event is classified as either a (s)ingle crater, one with (m)ultiple floors and a single rim, or a (f)ield of craters.

Floor reflectivity (Fr). In qualitative terms, does the floor appear (b)right, (i)ntermediate or (d)ark.

Parabolic feature (Pf) associated with crater -- yes, no, maybe. We used only definitely parabolic features in SAR images that could not be attributed to processes other than crater formation.

Apparent projectile direction of travel (Pd). A qualitative assessment based on crater shape and orientation of ejecta deposits.

Multiple asteroid (Ma). A few impact craters are unusually close together, but too large and too far apart to be from a single impactor. These are assumed to be the result of binary (or more) asteroids (or comets) striking simultaneously. The individual craters of these events are listed separately, but are linked by an identical number in this column.

Terrain type that crater lies on: undistinguished plains (p), fractured plains (pf), Lakshmi planum (lp), tessera and mountain belts (t), corona (c), volcanic regions (v), ridge belt (r), and rift (ri).

Interior flat floor (If) -- yes, no, maybe. The crater floor has an areally extensive flat surface as if emplaced by a fluid that then cooled in situ, without obvious breaching or overflowing of the rim by exterior processes.

Embayment and/or filling of crater or its ejecta blanket by obviously exterior processes (Ee) -- yes, no, maybe.

Tectonic deformation (T) of crater by exterior processes -- yes, no, maybe.

Degradation state (De) as defined in Basilevsky et al. (1987, JGR v.92, 12,869): (1) pristine, apparently intact ejecta deposits; (2) degraded, small amount of ejecta; and (3) highly degraded, can barely tell it's a crater.

Entries in Multiple Impacts Database

Some entries are taken directly from the main database. See above for descriptions of Name, Lat, Lon, Co, Mo, and Mu. The other entries are as follows, and were only measured for Confidence Level (Co) 1 and 2 craters:

Diameter (D). An equivalent diameter of the entire area encompassed by the multiple-floored crater or crater field. Measured as D is for the main database. NOTE: For crater fields, the equivalent single crater diameter (SD) is used for D in the main database and the HTML version of the Multiple Impacts database.

Properties (Pr). Properties of the ejecta blanket and shape of the crater(s) indicative of impact angle: (1) asymmetric ejecta blanket (45-60 degrees), (2) missing ejecta uprange (30-45 deg.), (3) partially missing ejecta downrange (15-30 deg.), (4) butterfly ejecta pattern (0-15 deg.), (5) steepening of crater walls uprange (15-30 deg.), (6) elongate crater shape (0-15 deg.), (7) ricochet fragments (0-15 deg.), and (8) single ricochet crater (0-15 deg.). Classification based primarily on Gault and Wedekind (1978, Proc. LPSC 9, 3843).

Impact angle (Ia). Based on properties of the ejecta blanket and crater shape, Impact angle is assessed in 15 degree increments: (1) 0-15 deg., (2) 15-30 deg., (3) 30-45 deg., (4) 45-60 deg., (5) > 60 deg..

Largest crater's diameter (Ld) and other craters' diameters (2-6).

Equivalent single crater diameter (SD). Using the diameters of the individual craters and a simple crater scaling law, calculates the equivalent diameter crater that would have been produced had the incoming meteoroid not broken apart.

Maximum downrange separation (Md) of craters.

Maximum crossrange separation (Mx) of craters.

Maximum total separation (Mt) of craters.

Number of crater farthest downrange (Dr).

Number of crater farthest from the largest crater (Cf).

Diameter of crater farthest from the largest crater (Fd).

Entries in Rings Database

This database lists the measurements of ring diameters for peak-ring craters and multi-ring basins. Ring diameters are measured from the diameter of the best-fit circle that runs along the rim crest of craters. As described in the main database, we also measure the area encompassing the central structure and calculate an equivalent diameter (Cd).