Asteroids

Asteroids are small rocky bodies primarily in orbit between Jupiter and Mars(i.e. main-belt).Those observed range in diameter from 948 km (1 Ceres)to a few meters.Near-Earth asteroids (NEAs) are a subset of asteroids whose orbitsapproach and/or cross the Earth's orbit.Please visit our sister-site dedicated tonear-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.

Asteroids are rocky objects primarily found in the asteroid belt, a region of the solar system that lies more than 2 ½ times as far from the Sun as Earth does, between the orbits of Mars and Jupiter. These objects are sometimes called minor planets or planetoids.
Asteroids range in size from Vesta—the largest at about 329 miles (530 kilometers) in diameter - to bodies that are less than 33 feet (10 meters) across. The total mass of all the asteroids combined is less than that of Earth's Moon. Most asteroids are irregularly shaped, though a few are nearly spherical, and they are often pitted or cratered.
Asteroids are small rocky bodies primarily in orbit between Jupiter and Mars (i.e. 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.
Asteroids often collide with each other. Upon collision, smaller ones can break and end up as dust on the larger ones. This dust is known as regolith. It is not necessary that asteroids will collide only with other asteroids. Any object that crosses their path can collide. Asteroids are pretty dangerous.

Asteroids are somewhat arbitrarily differentiated from comets and meteoroids. In the case of comets, the difference is one of composition: while asteroids are mainly composed of mineral and rock, comets are primarily composed of dust and ice. Furthermore, asteroids formed closer to the sun, preventing the development of cometary ice.

The largest trans-Neptunian object (over 2000 km in diameter)is substantially larger than the biggest main-belt asteroid, 1 Ceres(948 km).These outer 'asteroids' tend to be less rocky and more icy in compositionsince they formed farther from the sun.In fact, a group of these objects known as the Kuiper-beltis thought to be the reservoir for short-period comets.The distinction between asteroid and comethas become increasingly difficult to characterizeas we learn more about these primordial building blocksof our solar system.

The first asteroid (1 Ceres) was discovered January 1, 1801by Giuseppe Piazzi at Palermo, Sicily.Read this short article by Don Yeomansto learn why asteroids are particularly interesting andwhy we should study these primitive bodies.

Orbits: Diagrams & Elements

Asteroids Hitting Earth

The orbit of any asteroid (or comet) can be viewed.Start with our small-body browser to find the asteroid of interest,then select the Orbit Diagram link.For example, here is theorbit diagram for asteroids 1 Ceres.

Orbital elements and related parameters are alsoavailable for any asteroid (or comet) using our small-body browser.In addition, custom tables of orbital elements and/or physical parametersare available using oursmall body database search engine.We also provide fixed-format ASCII tables of elements.

Distribution Diagrams

In addition, there are diagrams showing the distribution of orbital elements formost known inner solar system asteroids and comets.The following diagrams are available:

Distribution of elements (a vs. e) for comets and asteroids
Distribution of elements (a vs. e) for asteroids only
Distribution of semimajor axis (histogram of a) for asteroids only

Physical Parameters

Physical parameters for asteroids are not well known primarily because these bodies areso 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 includingrotation period,geometric albedo,colors (B-V, U-B, I-R),spectral taxonomic type,mass (GM),and bulk density.Known physical parameters for any given small body areare available from our small-body browser.

Ephemerides

Asteroid ephemerides are available using JPL's HORIZONS system.

Discovery Circumstances

Asteroids Definition

Asteroid discovery circumstances are also available using our small-body browser.Discovery data are available for only numbered asteroidsand 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 nameis available.

Mission Targets

Spacecraft missions to small-bodies providevaluable scientific data ultimately improving our understandingof these primitive solar system bodies.A list of asteroids and cometstargeted by spacecraft missions (past, present, and future)is presented on this page.

Radar Astrometry

Radar astrometry for selected asteroidsis available in tabular format. A table showing data for onlyasteroids is presented on this page.

General Information

Missions to Asteroids

Current and Past Missions

OSIRIS-REx - Sample Return Mission to Asteroid Bennu (2016)
Hayabusa2 - JAXA Sample Return Mission to Asteroid Ryugu (2014)
PROCYON - JAXA Small Satellite Asteroid Flyby Mission (2014)
Dawn - NASA Orbiter of Asteroids Ceres and Vesta (2007)
Rosetta - ESA Comet Mission, flew by asteroids Steins and Lutetia (2004)
Hayabusa (Muses-C) - ISAS (Japan) Sample Return Mission to Asteroid 25143 Itokawa (2003)
Genesis - NASA Discovery Solar Wind Sample Return Mission (2001)
Stardust - NASA Comet Coma Sample Return Mission, flew by asteroid AnneFrank (1999)
Deep Space 1 - NASA Flyby Mission to asteroid Braille (1998)
Cassini - NASA/ESA Mission to Saturn through the Asteroid Belt (1997)
NEAR - NASA Near-Earth Asteroid Rendezvous with 433 Eros
Galileo - NASA Mission to Jupiter via asteroids Gaspra and Ida

Future Missions

Double Asteroid Redirection Test (DART) - Kinetic Impact Test Mission to Asteroids Didymos and Dimorphos (2021)
Lucy - Flyby Mission to Multiple Trojan Asteroids (2021)
NEA Scout - Flyby CubeSat Mission to Near Earth Asteroid (2021)
Psyche - Orbital Mission to Main Belt Asteroid 16 Psyche (2022)
Hera - Follow-up Mission to Asteroids Didymos and Dimorphos(2024)

Data

Images of Asteroids (Catalog of Spaceborne Imaging)
Images of Asteroids (NSSDCA Photo Gallery)
Asteroid Data Tables - PDS compilations of asteroid data

Press Releases

NASA's asteroid sample return mission moves into development - NASA Press Release, 16 May 2013
NASA to launch new science mission to asteroid in 2016 - NASA Press Release, 25 May 2011
Press briefing Dawn mission July 7 launch - NASA Press Release, 20 June 2007
OSIRIS asteroid sample return mission chosen for concept study - NASA Press Release, 30 October 2006
Arecibo radar images of asteroid 216 Kleopatra - NASA Press Release, 4 May 2000
Moon discovered orbiting asteroid 45 Eugenia - Announcement of discovery made in November 1998
Asteroid 1997 XF₁₁ - Information on the close approach in 2028
New masses calculated for 3 largest asteroids - U.S. Naval Observatory press release, 7 January 1998
Crater on Vesta imaged by HST - Press release (4 Sept. 1997)