Exploration: How We Know About Small Bodies
The tools, the methods and the people behind every number you read about asteroids and comets.
Almost everything we know about small bodies comes from indirect measurements. A dwarf planet at the edge of the Solar System is a faint dot. A comet's nucleus hides inside its own cloud. Astronomers learn the size, shape, makeup and path of these objects by combining many kinds of observations, and each guide in this category explains one of those tools.
Discovery comes first. Sky surveys photograph the same patches of sky night after night, and software looks for points of light that move against the stars. Candidates are reported to the Minor Planet Center, which collects the measurements, assigns a provisional designation and publishes the orbit. Names come later, and only after an orbit is well known. The International Astronomical Union has rules for them.
Orbits are the language of the field. A few numbers, such as eccentricity and inclination, describe the whole path of an asteroid or comet. One guide shows how to read them and how to look up any object in NASA's Small-Body Database.
Telescopes on the ground and in space measure brightness, color and heat. When a distant body passes in front of a star, the star's light blinks out, and the timing gives a precise size. Spacecraft then confirm or overturn those estimates. A timeline guide lists the missions that have visited asteroids, comets and dwarf planets, and another explains how scientists work out what an asteroid is made of.
You can also take part. Several projects accept help from the public, from classifying images to timing occultations, and one guide lists what is open and what you need to start.
Begin with how minor planets are discovered or jump to the mission timeline.
The nine guides
How Minor Planets Are Discovered, From Blink Plates to Sky Surveys
A minor planet is found when a dot drifts against fixed stars. Here is the path from first image to confirmed orbit, official designation and credit.
How Asteroids and Comets Get Their Names and Designations
A provisional code, a permanent number and an approved name are three separate steps. This guide decodes each one for asteroids and for comets.
How to Read an Orbit: Eccentricity, Inclination and More
Six numbers describe where a small body travels. This guide explains each one in plain words and uses real asteroids and comets to show how to read them.
How to Use the JPL Small-Body Database and Horizons
Enter an object's number or code into a public JPL tool and get orbit, size and discovery data. This guide shows each field and how to find a body's sky position.
Missions to Asteroids, Comets and Dwarf Planets: A Timeline
Forty years of spacecraft visits, from comet flybys to sample returns and an asteroid impact test. Every entry has a date and a mission type.
The Telescopes That Find and Study Small Bodies
Some instruments find new objects and others measure size, shape or makeup. Here is what each major facility is good at, with its status as of November 2026.
Citizen Science for Asteroids and Comets: How to Take Part
Several NASA-listed projects invite the public to review telescope images, and amateurs can report measurements. Here is what each involves as of November 2026.
Stellar Occultations: Measuring Worlds by Their Shadows
When a distant body hides a star for a few seconds, the shadow measures it better than most telescopes can. Here is how the method works and who takes part.
How Do We Know What Asteroids Are Made Of?
No single measurement identifies an asteroid's makeup. Scientists combine reflected light, density, radar, meteorite matches and returned samples to check one another.