For the majority of numbered asteroids, almost nothing is known apart from a few physical parameters. Hundreds of these (See Category:Asteroid stubs) have their own Wikipedia page, where the only information is their name and discovery circumstances plus table of orbital elements and some physical characteristics (often only estimated). An asteroid is a small, solid object in our Solar System, orbiting the Sun. ...

The aim of this page is to provide a reference explaining where the physical data for such generic asteroids comes from.

Please note that due to various ages of the single asteroid articles, the reference below may not be accurate for all asteroid articles.

Dimensions

Data from the IRAS minor planet survey [1] or the Midcourse Space Experiment (MSX) minor planet survey [2] (available at the Planetary Data System Small Bodies Node (PDS) ) is usually used to obtain a diameter. The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. ...

For many asteroids, lightcurve analysis provides estimates of pole direction and diameter ratios. Pre [1995] estimates collected by P. Magnusson are tabulated in the PDS at [3], with the most reliable data being the syntheses labeled in the data tables as "Synth". More recent determinations for several dozens of asteroids are collected at [4], the web page of a finnish research group in Helsinki which is running a systematic campaign to determine poles and shape models from lightcurves. It has been suggested that Hietaniemi beach be merged into this article or section. ...

This data can be used to obtain a better estimate of dimensions. A body's dimensions are usually given in decreasing order as a×b×c. If we have the diameter ratios μ=a/b, ν=b/c from lightcurves, and an IRAS mean diameter d, one sets the geometric mean of the diameters (abc)^1/3 = d for consistency, and obtains the three diameters:

Mass

Barring detailed mass determinations (see e.g. [5]), mass M can be estimated from diameter and (assumed) density values ρ worked out as below.

Such estimates can be indicated as approximate by use of a tilde "~"

Density

Apart from a few asteroids whose densities have been investigated (see e.g. [6]), one has to resort to enlightened guesswork.

For many asteroids a value of ρ~2 g/cm³ has been assumed.

However, a better guess can be obtained by taking into account the asteroid's spectral type. A recent paper [Krasinsky, Icarus, Vol. 158, p. 98 (2002)] gives calculations for the mean densities of C, S, and M class asteroids as 1.38, 2.71, and 5.32 g/cm³. (here "C" included Tholen classes C,D,P,T,B,G, and F), while "S" included Tholen classes S,K,Q,V,R,A,E). Assuming these values (rather than the present ~2 g/cm3) is a better guess.

Surface gravity

This is given by

where the G = 6.6742×10^-11 m³s^-2kg^-1 is the Gravitational constant, M is the mass of the asteroid, and d its diameter. According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ...

However, for irregular bodies, this is approximate and there is a question of which diameter to use. Using the largest diameter as per

seems the most consistent since then at least the entire mass of the asteroid is attracting.

Escape velocity

This is given by with the same issues of which diameter to use as for surface gravity.

Rotation period

Usually taken from lightcurve parameters at the PDS [7]

Spectral class

Usually taken from the Tholen classification at the PDS [8]

Absolute magnitude

Data from the IRAS minor planet survey [9] or the MSX minor planet survey [10] (available at the PDS) is usually used. The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. ...

Albedo

Data from the IRAS minor planet survey [11] or the MSX minor planet survey [12] (available at the PDS) is usually used. The Infrared Astronomical Satellite (IRAS) was a space-based observatory that performed a survey of the entire sky at infrared wavelengths. ...

Mean surface temperature

The formula used appears to be the one given at User:Urhixidur

Where is the asteroid albedo, its semi-major axis, is the solar luminosity (3.827E26 W), is the Stefan-Boltzmann constant (5.67040238774897E-08 W/m²K⁴), and is the asteroid's infra-red emissivity. The standard value of 0.9 is used. The albedo is a measure of reflectivity of a surface or body. ... In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolas. ... The Stefan-Boltzmann constant (also Stefans constant), denoted with a Greek letter σ, is a derivable physical constant, the constant of proportionality between the total energy radiated per unit surface area of a black body in unit time and the fourth power of the thermodynamic temperature, as per the...

Other common data

Soem other information for large numbers of asteroids can be found at the Planetary Data Syetem Small Bodies Node [13]. Up-to date information on pole orientation of several dozen asteroids is at [14], and can be used to determine axial tilt. Axial tilt is an astronomical term regarding the inclination angle of a planets rotational axis in relation to its orbital plane. ...