Asteroids are small rocky bodies primarily in orbit between Jupiter and Mars
Those observed range in diameter from 948 km (1 Ceres)
to a few meters.
Near-Earth asteroids (NEAs) are a subset of asteroids whose orbits
approach and/or cross the Earth's orbit.
Please visit our sister-site dedicated to
near-Earth objects (NEOs)
for more information on NEAs.
We include Trojans (bodies captured in Jupiter's 4th and 5th Lagrange points),
Centaurs (bodies in orbit between Jupiter and Neptune),
and trans-Neptunian objects (orbiting beyond Neptune)
in our definition of "asteroid" as used on this site,
even though they may more correctly be called "minor planets" instead of asteroids.
The largest trans-Neptunian object (over 2000 km in diameter)
is substantially larger than the biggest main-belt asteroid, 1 Ceres
These outer "asteroids" tend to be less rocky and more icy in composition
since they formed farther from the sun.
In fact, a group of these objects known as the Kuiper-belt
is thought to be the reservoir for short-period comets.
The distinction between asteroid and comet
has become increasingly difficult to characterize
as we learn more about these primordial building blocks
of our solar system.
The first asteroid (1 Ceres) was discovered January 1, 1801
by Giuseppe Piazzi at Palermo, Sicily.
Read this short article by Don Yeomans
to learn why asteroids are particularly interesting and
why we should study these primitive bodies.
Orbits: Diagrams & Elements
The orbit of any asteroid (or comet) can be viewed
using our java-based orbit applet.
Start with our small-body browser to find the asteroid of interest,
then select the Orbit Diagram link.
For example, here is the
orbit diagram for asteroids 1 Ceres.
Orbital elements and related parameters are also
available for any asteroid (or comet) using our small-body browser.
In addition, custom tables of orbital elements and/or physical parameters
are available using our
small body database search engine.
We also provide fixed-format ASCII tables of elements.
In addition, there are diagrams showing the distribution of orbital elements for
most known inner solar system asteroids and comets.
The following diagrams are available:
Physical parameters for asteroids are not well known primarily because these bodies are
so small and there are so many.
The only parameter determined for nearly all asteroids is the absolute magnitude (H)
which can be used to obtain a very rough estimate of an asteroid's size.
However, a few asteroids have other parameters determined including
colors (B-V, U-B, I-R),
spectral taxonomic type,
and bulk density.
Known physical parameters for any given small body are
are available from our small-body browser.
Asteroid ephemerides are available using JPL's HORIZONS system.
Asteroid discovery circumstances are also available using our small-body browser.
Discovery data are available for only numbered asteroids
and include the date of discovery, who discovery the asteroid, and where it was discovered.
In addition, for most officially named asteroids, the citation issued for the name
Spacecraft missions to small-bodies provide
valuable scientific data ultimately improving our understanding
of these primitive solar system bodies.
A list of asteroids and comets
targeted by spacecraft missions (past, present, and future)
is presented on this page.
Radar astrometry for selected asteroids
is available in tabular format. A table showing data for only
asteroids is presented on this page.