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1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minuteTo read an exoplanet discovery, first identify how the planet was found, then check what each reported number represents and where it came from. A discovery-method label records how a planet was first identified—not every technique used to study it. Radius, orbital period, distance, and age also have different meanings, and some catalog values are inferred or calculated rather than directly measured.
Start with the source and the discovery-method label
In the NASA Exoplanet Archive, “Discovery Method” means the method by which a planet was first identified. It is an origin label, not a complete account of the evidence gathered afterward. A planet first detected by one method may later be observed or characterized with another. The Archive cautions that the discovery-method field alone does not show every technique used, including for transiting planets. See the Archive FAQ and its Planetary Systems field definitions.
Detection methods observe different signals and favor different kinds of planetary systems. The method is useful context, but it is not an unbiased inventory of what planets exist.
Transit
A transit occurs when a planet passes in front of its star from our viewpoint, causing a small dip in the star’s light. Repeated dips can reveal the orbital period. The dip’s depth constrains the planet-to-star radius ratio; the star’s size is needed to estimate the planet’s radius. A transit is not an image of the planet. NASA’s transit explainer describes the signal.
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Radial velocity
A planet’s gravity makes its star move. Radial-velocity observations measure changes in the star’s motion along our line of sight. The signal can constrain a planet’s mass, but interpretation depends on the orbit’s inclination and what is known about the star. NASA outlines this and other methods in How We Find and Characterize.
Gravitational microlensing
When a foreground star passes in front of a more distant background star, its gravity can magnify the background star’s light. A planet orbiting the foreground star can add a distinct signal to that brightening. Microlensing samples systems differently from transit and radial-velocity searches.
Direct imaging
Direct imaging attempts to separate a planet’s light from the much brighter light of its host star. NASA notes that directly imaged planets are often young, large, and widely separated: those traits reflect the method’s observational selection, not a general description of all exoplanets. The Archive provides more detail in its Directly Imaged Planet Resources.
Astrometry
Astrometry tracks a star’s position on the sky to detect the motion caused by an orbiting planet. Like other methods that rely on precise knowledge of the host star, it reveals a signal from the system rather than a direct view of the planet.
Read the planet’s size as a specific measurement
Check which size field is reported and its units. Radius may be given in Earth radii or Jupiter radii. Read the uncertainty and any upper- or lower-limit marker alongside the central value; the NASA Exoplanet Archive lists these fields in its Confirmed Planets table columns and Extended Planet Data table columns.
How the radius was obtained matters. For a transit record, the light dip constrains a ratio between the planet’s and star’s radii. The host star’s diameter is needed to infer the planet’s radius, so the result depends in part on the adopted stellar parameters.
Also check whether a catalog value is empirical or calculated. In the Archive’s composite data, a radius may be calculated from a mass–radius relation when an empirical radius is unavailable. That is a derived value, not an independent radius measurement; see the Archive’s composite parameter calculations.
Radius alone does not establish mass, density, composition, or whether a planet is “Earth-like.” Those are separate properties requiring their own evidence.
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Separate orbital period from orbital scale
Orbital period is the time a planet takes to complete one orbit. Semi-major axis describes the characteristic scale of an elliptical orbit. They are related, but they are not interchangeable fields: a period is a duration, while a semi-major axis is a distance.
There is an important Archive caveat: for some microlensing and directly imaged planets, the value shown in the semi-major-axis field may instead be a projected separation in the plane of the sky. Check the field definition, units, uncertainty, and any limit marker before interpreting it. The Archive documents these fields in the Confirmed Planets table and Extended Planet Data table.
- Eccentricity describes how much an orbit departs from a circle.
- Inclination describes the orbit’s orientation relative to our line of sight.
Do not translate a period directly into “close” or “far.” How long an orbit takes depends on the host star as well as the orbital scale; a period by itself is not a universal distance label.
Treat age as an estimate tied to the host star
A listed planet age is often based on an estimate of the age of its host star. NASA explains that stellar ages can be used to estimate planet ages in Know the Star, Know the Planet. A practical reading is: the listed age is an estimate for the host star, used as a guide to the planet’s age.
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Age is not a direct measurement of when the planet formed. The method and uncertainty depend on the cited source, so consult the planet’s reference before treating a number as precise or comparing it with another catalog entry. The Archive’s field documentation includes age and reference fields, but there is no single age-dating method or precision that can safely be assumed for every entry.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Compare catalog values by provenance, not just by number
Different values for the same planet do not automatically mean one source is wrong. Catalogs can draw on peer-reviewed papers, mission data, candidate pipelines, or calculated quantities. NASA’s Archive says its confirmed-planet parameters come from accepted peer-reviewed literature and additional Kepler and TESS mission deliveries. It assesses parameter sets and, in some tables, chooses a consistent set from one publication rather than combining values derived under incompatible assumptions. Other views may include more parameters but be less internally consistent. The FAQ, updated 1 July 2026, explains these choices.
When two entries differ, compare the details in this order:
- Table and status: Check whether each value belongs to a confirmed planet or a candidate, and whether it comes from a pipeline or a later publication.
- Reference: Follow the citation attached to the specific parameter, not only the planet’s discovery paper. Record the publication date or catalog version when reporting it.
- Parameter set: Find out whether the values come from one internally consistent publication or from a composite of sources.
- Uncertainty and limits: Compare the full error bars, including asymmetric uncertainties and upper or lower limits, rather than only the central numbers.
- Measurement status: Establish whether the value is empirical, inferred from another measured quantity, or calculated by the catalog.
For an individual planet, the paper cited for the value is the best guide to its assumptions and interpretation. Archive entries can change as the literature and mission data are updated.
Quick Recap
A quick checklist for a discovery story
- What method first identified the planet, and is the article describing that discovery or later follow-up?
- Does “size” mean radius, and is it measured empirically or derived?
- Is the orbit number a period, a semi-major axis, or—in some records—a projected separation?
- Are units, uncertainties, and limits shown with the values?
- Is the age an estimate for the host star, and what source supports it?
- Which paper, mission delivery, or catalog version supplied each number?
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