Use NASA/JPL’s Eyes on Asteroids to see asteroids, close approaches and mission trajectories, then use JPL’s Small-Body Database (SBDB) for an object’s orbit data and Horizons for positions over time. The key distinction: orbital elements describe an orbit at a particular epoch; an ephemeris gives calculated positions or other quantities across a chosen time span. For spacecraft, check the trajectory’s revision date and comments before relying on it.
Which NASA/JPL tool should you use?
| Tool | Best for | What it provides | Important limitation |
|---|---|---|---|
| Eyes on Asteroids | Visual orientation: exploring asteroids, comets, close approaches and missions | An interactive view of thousands of small bodies and past, present and future missions; it uses data from CNEOS. | Use it to understand the broad picture, not as a substitute for a specific numerical query. |
| JPL Small-Body Database Lookup | Finding a small body and inspecting its record | Orbital elements, uncertainties where available, diagrams and related object information. | Its orbit viewer uses two-body methods; JPL cautions against using it for accurate long-term trajectories or planetary encounter circumstances. |
| JPL Horizons | Getting calculated values for a chosen time interval or downstream software | Time-dependent ephemerides, orbital elements and SPK trajectory files. | Spacecraft trajectories can become outdated; verify their data-sheet revision date and comments. |
The services answer different questions rather than compete in a controlled performance comparison. Start with the visual view, identify the object in SBDB, then use Horizons when you need calculated positions or a file for another tool.
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How to track an asteroid mission
- Explore the mission visually. Open Eyes on Asteroids to orient yourself to an asteroid, its close approaches or a mission trajectory. JPL describes it as an interactive visualization using CNEOS data; CNEOS computes high-precision orbits for near-Earth objects. Treat the display as an accessible overview.
- Identify the target precisely. Search for the object in SBDB Lookup using its IAU number, formal designation, name or JPL SPK-ID. If a name may be ambiguous, use a number or formal designation. The record may include alternate designations, discovery information, physical parameters, close approaches and radar astrometry.
- Choose a data product for the question. Use SBDB to inspect the object’s orbit solution and uncertainties. Use Horizons to calculate positions and other ephemeris quantities over a specified interval and, for observer ephemerides, from a specified observing location. Request an SPK file when downstream software needs a binary trajectory file.
- Check spacecraft data freshness. If the question is where a spacecraft is or whether its route reflects a mission change, inspect its Horizons data sheet before interpreting the trajectory. The revision date and comments matter because externally produced spacecraft trajectories may not be updated as regularly as small-body solutions.
For a quick list of selected mission targets, JPL’s small-body mission-target table includes target, mission type, arrival, mission name, launch and status, with links where available. Its entries are dynamic; verify the page for current status and dates rather than treating a listed arrival or status as a live navigation update.
Orbital elements and ephemerides are not the same
An orbital-element set is a compact description of orbit geometry or state at an epoch, relative to a selected body or barycenter and within a stated reference plane or frame. An ephemeris is a sequence of calculated quantities over time—for example, sky position and rates for a selected observer. Use elements to understand the orbit’s parameters; use an ephemeris to ask where an object is expected to appear over a particular interval and viewpoint.
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Horizons can provide both kinds of output, so check the selected output type rather than assuming that every result is a forecast table. Its manual describes observer ephemerides and osculating elements; its API documentation covers observer ephemerides, orbital elements and SPK output for programmatic requests.
How to read an orbital-elements output
Horizons describes osculating elements as an instantaneous representation. Depending on the output, fields can include:
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- Epoch: the date and time to which the listed elements apply.
- Eccentricity: a measure of how far the orbit’s shape departs from a circle.
- Periapsis distance and semimajor axis: measures describing the orbit’s scale and closest point to its central body.
- Inclination: the tilt of the orbital plane relative to the stated reference plane.
- Longitude of ascending node and argument of periapsis: angles that orient the orbit in its reference plane and locate periapsis within it.
- Mean anomaly and true anomaly: angular measures of the body’s position along its orbit.
- Period: the stated orbital period, when included.
Read these values together with the epoch, reference plane or frame, coordinate system and units. They are not timeless constants. SBDB provides uncertainties where available; those matter when judging how tightly an orbit is known. CNEOS explains that near-Earth-object orbit solutions are fitted to astrometric observations using debiasing, weighting, perturbation models and numerical methods. Additional observations can improve an orbit solution, so note which solution or retrieval date you are using if quoting changing values.
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Horizons supports web queries and an API. Before submitting a request, decide which body or object to query, the center or observer, the start and end times, step size and output quantities. API requests also require correctly URL-encoded parameters; select the command and output class that match the question—observer ephemeris, orbital elements or SPK—rather than treating them as interchangeable. Consult the API documentation for parameter details and the Horizons manual for output interpretation.
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Check spacecraft trajectories before relying on them
A spacecraft path in Horizons is not necessarily a live mission-navigation feed. The Horizons manual warns that externally produced spacecraft trajectories may not be updated regularly; maneuvers or planning changes can make a stored trajectory obsolete. Check the revision date in the upper-left corner of the spacecraft data sheet and read its comments for mission-status information. If revision status is uncertain and the work requires high-precision interplanetary data, JPL advises contacting Solar System Dynamics. Do not infer that a spacecraft is following its planned route from an old trajectory alone.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What “potentially hazardous asteroid” means
NASA/JPL Asteroid Watch defines potentially hazardous asteroids as objects more than about 460 feet (140 meters) in size whose orbits bring them within 4.6 million miles (7.5 million kilometers) of Earth’s orbit around the Sun. This is a classification definition, not a claim that every object meeting it is on an impact trajectory. See Asteroid Watch for JPL’s explanation.
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