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This system is an archive (data base) of published mass and diameter estimates of minor bodies of our Solar System (mainly asteroids, but also some comets, TNOs and dwarf planets). Currently 1760 mass and 4094 diameter estimates for 428 objects are archived.

Status: The archive is yet not complete, especially volume-equivalent diameter from DAMIT has to be added and masses from some planetary ephemerides.


Enter in the form above the name of an asteroid (like for example Hermione or Psyche) or select an object from the drop down list.

The average mass and diameter values are calculated interactively from the list of values in the tables. You can select / deselect entries (except there is only one value given) and (re-)calculate the average mass and / or the average diameter by clicking the "Update" button. The corresponding plot will be updated as well. Unselected values will be shown in light grey in the plot and are not used for the average calculation. The derived mean bulk density will be recalculated as well after you re-calculated either the average mass or the average diameter.

The average mass and diameter values are calculated using the "Expected Value Method (EVM)" [1]. For comparison the summary table also gives the values derived using the well-known weighted average (w.avg). The disadvantage of the latter method is that a single estimate with underestimated errors can bias the average because of the strong weight it gets (w = 1/err^2).

All errors are 1σ. Concerning the treatment of asymmetric errors for diameter and / or mass estimates here in SiMDA please refer to the info page.


Kretlow, M., 2020: Size, Mass and Density of Asteroids (SiMDA) - A Web Based Archive and Data Service. EPSC Abstracts Vol. 14, EPSC2020-690.

The calculated bulk density (ρ) is based on the averaged values of the mass (M) and of the diameter (D), from which a volume of a sphere is calculated. Derived densities can be unrealitstic. Currently, the uncertainty of the mass estimate is in many cases the limiting factor for the reliability of the bulk density ρ, but if the mass estimate is accurate to ≈20%, the contribution of the uncertainty of the volume-equivalent diameter can overwhelm that of the mass. See [2] and also here.


As the volume V of the object is ~D3 (D: volume-equivalent diameter), the derived density is sensitive to the (volume-equivalent) diameter D. Not all methods provide volume-equivalent diameters, like for example stellar occcultation profile fits. But combining them with 3D shape models yields to volume-equivalent sizes.

Dyn and Tax

Dynamical (orbit) classes (Dyn) used here are: COM, MBA (IMB, OMB, MCA etc.), NEA, CEN and TNO. Taxanomic classes (Tax) used here corresponds to the Tholen (1984+) scheme, the SMASSII Bus and Binzel (2002), the S3OS2 Lazarro+5 (2004), and the DeMeo+3 (2009) scheme. The data are taken from PDS (v4), and are given in the T.T, T.B , T.L (T:Tholen | B:Bus) and T.D columns of the summary table for the object.


If you are missing a mass or size estimate which should be added into this data base please send me an email with the reference. If you find a bug please inform me as well. Thank you!


[1] M. Birch, B. Singh. Method of Best Representation for Averages in Data Evaluation. Nucl. Data Sheets 120, 106 (2014). DOI.
[2] Carry, B., 2012 : Density of asteroids. Planetary and Space Science, Volume 73, Issue 1, p. 98-118. ADS.