For a quick visual view of asteroids, close approaches and mission trajectories, start with NASA/JPL’s Eyes on Asteroids. For the data behind an object’s orbit, use the Small-Body Database (SBDB); for positions over a chosen time span, use Horizons. The key distinction: orbital elements describe an orbit at an epoch, while an ephemeris gives calculated quantities over time. Check a spacecraft trajectory’s revision date and comments before using it as a current mission-status indicator or for precision work.
Choose the right NASA/JPL tool
| Tool | Best for | What it provides | Important qualification |
|---|---|---|---|
| Eyes on Asteroids | Visual orientation: exploring asteroids, comets, close approaches and missions | Interactive visualizations of thousands of asteroids and comets, and past, present and future missions; it also shows the next five close approaches | It uses CNEOS data and is an accessible overview, not a substitute for a specified numerical data product. NASA/JPL CNEOS computes high-precision orbits for near-Earth objects. |
| SBDB Lookup | Identifying a small body and inspecting its record | Orbital elements and uncertainties where available, orbit diagrams, physical parameters, close-approach details, radar astrometry, discovery circumstances and alternate designations | The built-in orbit viewer uses two-body methods; JPL cautions against using it for accurate long-term trajectories or planetary encounter circumstances. |
| Horizons | Calculating time-dependent positions or requesting other numerical outputs | Ephemerides, orbital elements and SPK files for supported bodies and requests | Spacecraft trajectories supplied externally may lag maneuvers or planning changes. Check the data-sheet revision date and comments. |
These tools serve different purposes; the cited documentation does not establish a controlled performance comparison among them. Use Eyes on Asteroids to see the mission picture, SBDB to look up the body and its orbit record, and Horizons when you need values calculated for particular times or an observing location.
Track a mission and find its target
Start with the visual overview
- Open Eyes on Asteroids and explore the object, close approach or mission of interest.
- Use the visualization to understand the general relationship among an asteroid, its orbit and a mission trajectory. Treat it as orientation rather than a precision forecast.
- For a concise mission-target index, consult JPL’s selected small-body mission-target table. It lists target, mission type, arrival, mission name, launch and status, with links to SBDB and mission pages where available. Its status and dates can change, so check the live table before relying on them.
Identify the asteroid unambiguously
In SBDB Lookup, search by an IAU number, formal designation, name or JPL SPK-ID. Prefer a number or formal designation if a common name could refer to more than one object. Once you have the right record, inspect its orbital elements and any available uncertainties or related observations.
Choose between orbital elements and an ephemeris
Orbital elements and ephemerides answer different questions. Elements are a compact description of an orbit or state at a specified epoch and relative to a selected reference. An ephemeris is calculated output over time; observer ephemerides can include sky position and rates for a specified observing location. Horizons can also produce SPK files when downstream software needs a binary trajectory file.
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- Use orbital elements to describe orbit geometry or state at an epoch, making sure to retain the epoch, reference plane or frame, coordinate system and units.
- Use an observer ephemeris to ask where an object will appear over a time interval from a particular observing location.
- Use an SPK file when compatible downstream software requires a binary trajectory product.
Horizons requests depend on the selected command, center, time interval, step size and output quantities. JPL’s API documentation describes programmatic requests and output classes, including observer ephemerides, orbital elements and SPK. Follow its URL-encoding requirements when constructing a request.
Read orbital elements in context
Horizons describes osculating elements as an instantaneous representation relative to a selected body or barycenter. Depending on the requested output, fields can include:
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- Epoch: the time to which the element set applies.
- Eccentricity and semimajor axis: shape and scale of the orbit, when those values are part of the selected output.
- Periapsis distance: the closest orbital distance to the reference center.
- Inclination, longitude of ascending node and argument of periapsis: orientation of the orbit in the stated reference system.
- Mean anomaly and true anomaly: measures of the body’s position along the orbit at the epoch.
- Period: orbital period when included in the output.
Do not treat these values as timeless constants. Include the epoch and the output’s reference plane or frame, coordinate system and units when recording or sharing them. SBDB provides uncertainties for orbital elements where available; those are part of the result, not optional decoration.
NEO orbit solutions are fitted to astrometric observations using debiasing, weighting, perturbation models and numerical methods. As observations accumulate, an orbit solution can improve. For a value that may change, identify the solution or retrieval date rather than presenting it as permanently fixed. See CNEOS’s explanation of how near-Earth-object orbits are determined.
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Check spacecraft trajectory freshness before relying on it
A spacecraft trajectory in Horizons is not necessarily a live navigation solution. JPL’s Horizons manual warns that externally produced spacecraft trajectories may be updated less regularly than small-body solutions; maneuvers or planning changes can make a trajectory obsolete.
- Open the spacecraft’s Horizons data sheet.
- Check the revision date in the upper-left corner to see when the trajectory was last updated.
- Read the data-sheet comments for mission-status information.
- If revision status is uncertain and the work is a high-precision interplanetary application, JPL advises contacting Solar System Dynamics.
An old trajectory alone is not evidence that a mission is still following its planned path. The manual version identified by JPL is 4.98e, dated August 25, 2026; consult the live manual for current instructions.
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Interpret close-approach and hazard information carefully
JPL defines a potentially hazardous asteroid as one more than about 460 feet (140 meters) in size whose orbit brings it within 4.6 million miles (7.5 million kilometers) of Earth’s orbit around the Sun. This classification, as described on NASA/JPL’s Asteroid Watch page, does not mean the object is on an impact trajectory. Close-approach listings and hazard classifications are useful context, but they are not interchangeable with an impact prediction.
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