May 1, 2005

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Asteroid (and Comet) Groups

Release 2.0

Petr Scheirich, 2005
Petr.Scheirich(at)centrum.cz

At this page I show distinctions between various asteroid and comet groups (up to date Apr. 7, 2005) in a graphical mode. The descriptions of the individual groups can be found at Gérard Faure's excellent page DESCRIPTION OF THE SYSTEM OF ASTEROIDS.

The properties and members of main comet groups are summarized at Yan Fernandez's page List of Jupiter-Family and Halley-Family Comets. Orbital elements of comets are taken from Roman Maňák's catalogue.

The main asteroid groups are distinguished by colours introduced in a legend at the top left corner of every image. Asteroids positions are computed for Apr. 7, 2004 and their orbital elements are taken from the MPCOrb database. There are three general representations of the groups below: views of the solar system with respect to an external observer, animations showing the particular groups individually, and positions of asteroids in an orbital elements space, respectively. For clarity, all pictures and animation are separated for inner and outer part of the solar system.
On the majority of images, pointing the mouse cursor out some objects will show its name or provisional designation.

The pictures are thumbnails only - clicking on them will open large versions.

Many thanks to Gérard Faure and Bill Allen for their remarks and recommendations to this web.


If your browser does not support saving animated gifs, you can download all animations in zipped form here.

News in release 2.0:

Contents:


Inner solar system - views from outside

Two groups at these views have specific distribution in space - Trojans and Hilda group.
Trojan asteroids lie in regions around Jupiter-Sun Lagrangian points, 60° ahead and behind of Jupiter. In Lagrangian points gravitational forces of two bodies combined with the centrifugal force of co-orbiting third small body are in balance. Hilda asteroids are in a 3:2 resonance of mean motion with Jupiter (that means the orbital period of asteroids and that of Jupiter have ratio of 2:3). This enables them to have aphelia up to the distance of Jupiter and not beeing scattered. They form a typical triangle, visible best in the animations:
Animation showing Hildas and Trojans orbiting the Sun (2.2 MB),
Animation showing Hildas orbiting the Sun, with 3 orbits indicated (1.9 MB),
Animation showing Hildas and Trojans in Jupiter co-orbiting frame (1.7 MB).
(If the animations are slow on your browser, download them and open with some common image viewer, e.g. XnView.)
Orbital properties of Hildas can be better understanded looking at the image showig longitude of perihelion versus time of perihelion passage.

You can watch the analogical animations for Cybele group:
Animation showing Cybeles orbiting the Sun (1.2 MB),
Animation showing Cybeles orbiting the Sun, with 2 binaries (Sylvia and Hermione) indicated (1.5 MB),
Animation showing Cybeles in Jupiter co-orbiting frame (0.7 MB).

Top view


Animation showing particular groups.
General view


Animation showing particular groups.
Side view


Animation showing particular groups.
Top view
with some best known objects indicated.

General view
with some best known objects indicated.

See also animations of comets in inner solar system: top view, side view.


Near-Earth asteroids - views from outside

Top view


Animation for the next two years.
General view


Animation for the next two years.
Side view


Animation for the next two years.
Animation showing NEAs for the next two years in Earth co-orbiting frame.
Note some "quasi-moons" from Aten group which are moving in the vicinity of the Earth.


Inner solar system - absolute magnitudes

Absolute magnitude is measure of an object size. For a conversion between absolute magnitude, albedo (fraction of light which object reflects) and a diameter see here.

All objects


Perihelion distance vs. absolute magnitude


Near-Earth Asteroids


Note the observational bias towards larger objects at farther distances from the Sun (at "All objects" and "q vs. H" views).


Inner solar system - orbital elements space

The distinctions between particular groups are fuzzy in the real space (see above) but sharply bounded (by definiton) in orbital elements space, as is shown below.

Semimajor axis vs. eccentricity
Curves for constant perihelion distance q=a(1-e) and aphelion distance Q=a(1+e) are drawn.

Semimajor axis vs. eccentricity
(without curves)

Semimajor axis vs. inclination


Semimajor axis vs. eccentricity
with some best known objects indicated.

Semimajor axis vs. inclination
with some best known objects indicated.

Also interesting are scatter diagrams of the length of ascending node (W) versus inclination (i) for the three main belt zones:

MB Zone I and Hungaria family: W vs. i

MB Zone II: W vs. i

MB Zone III, Cybele and Hilda group: W vs. i

A "wave" in MB Zone III could be due to symmetry of main belt not to the ecliptic but to Jupiter orbital plane. When showing the inclinations between asteroids' and Jupiter's orbits (i_J) instead of inclinations between asteroids' orbits and ecliptic (i) the "wave" disappear. However, this explanation doesn't work for Main Belt Zone II, I, and Hungaria family (neither for inclinations relative to orbit of Mars). If someone know the right explanation, please let me know.

MB Zone I and Hungaria family: W vs. i_J

MB Zone II: W vs. i_J

MB Zone III: W vs. i_J


Inner solar system - Tisserand parameter

Tisserand parameter of orbit with regard of Jupiter is defined by

where a, e, and i are semimajor axis, eccentricity, and inclination, resp., and aJ is semimajor axis of Jupiter's orbit. The parameter is integral of motion for bodies orbiting under influence of Sun and Jupiter. Typical asteroidal orbits have TJ > 3 and typical cometary orbits have TJ < 3. Bellow are scatter diagrams of Tisserand parameter and other elements. There are indicated objects from interesting Damocliod group - the group of asteroids on cometary orbits (called sometimes as "asteroids from Oort cloud").

Tisserand parameter vs. eccentricity

Tisserand parameter vs. inclination

Semimajor axis vs. Tisserand parameter

See also scatter diagram of TJ vs. TN for whole Solar System below.


Main belt - proper elements and families

All above images shows osculating elements describing instantaneous orbit of the objects, which are continuously perturbed by major planets. A complex structure of the Main Belt could be better represented by so called proper elements. They are some sort of quasi-integral of motion (nearly constant in time) and represent "average" characteristics of osculating elements.

There are many clusters visible in proper elements space, which are called asteroid families. Objects belonging to the families usually originate from past collisions between asteroids.

The family-members at these images are taken from Zappala et al. (1995) (could be downloaded from NASA PDS) and proper elements taken from AstDyS. The largest families (with number of identificated members greater than 50) are coded by color, the others by name of the family (named after the lowest-numbered member) shown near the "cluster".

Proper a vs. proper e


Proper a vs. proper i


Proper e vs. proper i


Proper a vs. proper e + families
Largest families are indicated by color, smaller by name


Animation showing thin cross-sections in proper i.
Proper a vs. proper i + families
Largest families are indicated by color, smaller by name


Animation showing thin cross-sections in proper e.
Proper e vs. proper i + families
Largest families are indicated by color, smaller by name


Animation showing thin cross-sections in proper a.

3D animation showing main families in a - e - i space.


The clustering of the family members almost disappear if projected onto the orbital elements space...

Osculating a vs. e + families
Largest families are indicated by color.

Osculating a vs. i + families
Largest families are indicated by color.

Osculating e vs. i + families
Largest families are indicated by color.


Main belt families - views from outside

The family members are not clustered in the real space as is shown below, where their instantaneous positions are indicated.

Top view

General view

Side view


Inner Solar System - Taxonomic classes and Albedos

Asteroid taxonomic classes and albedos are taken from NASA PDS. Asteroids are coded by colors which correspond to Tholen classes (SMASSII clases K and L are added) - if Tholen class is not available, it is determined from other classes (Barucci, Tedesco, Howell, SMASS, SMASSII) using Table 1 in S.J. Bus, F. Vilas, M.A. Barucci, Visible-Wavelength Spectroscopy of Asteroids, in Asteroids III.

Semimajor axis vs. eccentricity

Proper semimajor axis vs. proper eccentricity

Proper semimajor axis vs. proper inclination

Note the compositional diversity of the main belt as a whole (as is visible on images below too) and the diversity of asteroid families.

Semimajor axis vs. albedo

Semimajor axis vs. albedo
with asteroids coded by taxonomical classes


Outer solar system - views from outside

These views notably show some observational biases. First of all is seen the lack of the objects in the Milky Way areas, as well as straight "chainlets" of objects originated in pencil-beam surveys.

Top view


Animation showing particular groups.
General view

Click for large version
Animation showing particular groups.
Side view


Animation showing particular groups.
Top view
with some best known objects indicated.

General view
with some best known objects indicated.


Outer solar system - absolute magnitudes

Top view

Perihelion distance vs. absolute magnitude


Outer solar system - orbital elements space

Semimajor axis vs. eccentricity
Curves for constant perihelion distance q=a(1-e) and aphelion distance Q=a(1+e) are drawn.

Semimajor axis vs. eccentricity
(without curves)

Semimajor axis vs. inclination


Semimajor axis vs. eccentricity
with some best known objects indicated.

Semimajor axis vs. inclination
with some best known objects indicated.

Outermost a vs. e
Curves for constant perihelion distance q=a(1-e) and aphelion distance Q=a(1+e) are drawn.

Outermost a vs. i



Outer solar system - Tisserand parameter

Tisserand parameter of obrit with regard of Neptun is defined by

where a, e, and i are semimajor axis, eccentricity, and inclination, resp., and aN is semimajor axis of Neptun's orbit. The parameter is integral of motion for bodies orbiting under influence of Sun and Neptun. Typical asteroidal orbits have TN > 3 and typical cometary orbits have TN < 3. Bellow are scatter diagrams of Tisserand parameter and other elements. There are indicated objects from interesting Damocliod group - the group of asteroids on cometary orbits (called sometimes as "asteroids from Oort cloud").

Tisserand parameter vs. eccentricity

Tisserand parameter vs. inclination

Semimajor axis vs. Tisserand parameter

See also scatter diagram of TJ vs. TN for whole Solar System below.


Whole solar system - Tisserand parameters

All asteroids of Solar System are shown bellow in scatter diagram showing Tisserand parameter with regard of Jupiter (TJ) versus Tisserand parameter with regard of Neptun (TN). The Damocliod group is also indicated.

TJ vs. TN

TJ vs. TN - detailed description

3D animation showing all objects in TJ - TN - i space.