Calculating Diameter
When requested by the user by selecting
Calculation Models : H→ Diameter, neoproperties will calculate a best estimate for diameter based on the absolute magnitude
§ (H) and information available. The method used to calculate the best estimate will depend on the information available for each object. In order of precedence:
- If the object has a measured geometric albedo (pv) then diameter is calculated‡ as D(km) = 1329 * 10^(-0.2*H) / sqrt(pv) .
- If the object has a taxonomic complex but no albedo, then the table below is used to look up an albedo for the taxonomic complex, and the equation in method #1 is used.
- If there is no taxonomic complex and no albedo, then assume the albedo = 0.17 +/- 0.13. (See discussion of broad albedo range below.)
Taxonomic Complex → Albedo
The lookup table below is based heavily on the debiased albedos for taxonomic complexes published by
Stuart & Binzel 2004 (S+B 2004). When there was not a value for a particular complex, but there was a value for a strongly related complex, we used the albedo for the related complex. When there were no equivalent complexes, we used our broad albedo range (= 0.17 +/- 0.13).
Table specifying how Taxonomic Complex relates to Albedo.
| Taxonomic Complex |
Debiased Albedo |
+/- |
reference |
| &A |
0.200 |
0.020 |
S+B 2004 |
| &B |
0.101 |
0.027 |
S+B 2004 value for &C |
| &C |
0.101 |
0.027 |
S+B 2004 |
| &D |
0.042 |
0.013 |
S+B 2004 |
| &K |
0.239 |
0.044 |
S+B 2004 value for &S |
| &L |
0.239 |
0.044 |
S+B 2004 value for &S |
| &O |
0.520 |
0.156 |
S+B 2004 |
| &Q |
0.247 |
0.060 |
S+B 2004 |
| &R |
0.340 |
0.034 |
S+B 2004 |
| &S |
0.239 |
0.044 |
S+B 2004 |
| &U |
0.170 |
0.130 |
broad albedo range |
| &V |
0.417 |
0.147 |
S+B 2004 |
| &X |
0.072 |
0.025 |
S+B 2004 |
| &C;&B |
0.101 |
0.027 |
S+B 2004 value for &C |
| &C/X |
0.088 |
0.041 |
S+B 2004 combination of ranges for &C and &X |
| &S;&Q |
0.247 |
0.060 |
S+B 2004 value for &Q |
Broad Albedo Range In the absence of an albedo measurement or a taxonomic complex, neoproperties uses an albedo = 0.17 +/- 0.13. This value was determined by taking the distribution of albedos measured in
Mainzer et al 2011 and fitting a single gaussian to the reported distribution. The underlying distribution is bi-modal, but in order to facilitate computation tractability for diameter estimates, a single distribution was assumed.
§ H magnitudes are adopted from the Minor Planet Center (
http://www.minorplanetcenter.net/iau/MPCORB/NEA.txt).
‡ Equation 2, Harris and Harris (1997) (
http://dx.doi.org/10.1006/icar.1996.5664)
