How space works
How to read an exoplanet measurement table
A useful planet profile tells you where its numbers came from, what the units mean, and what remains unmeasured. A complete-looking table is not always a trustworthy one.
Updated
One planet can have several published solutions
Researchers may publish different estimates as new observations and methods become available. The NASA Exoplanet Archive's Planetary Systems table, abbreviated PS, keeps rows associated with individual references. A default flag identifies the archive's selected default solution. A default is a documented selection, not a guarantee that all other research agrees.
Space Pixel's profiles use that PS default row and preserve a link to its planetary reference. The archive's composite table serves a different purpose: it fills more parameters by drawing on multiple sources and can contain values that are not mutually self-consistent. Keeping those table types distinct helps avoid calculating a density from incompatible mass and radius estimates.
Units carry part of the meaning
An Earth radius and an Earth mass compare different properties. An AU measures orbital size, days measure period, kelvin measures temperature, and grams per cubic centimeter measure density. Stellar masses and radii are commonly expressed relative to the Sun. A distance in parsecs is converted to light-years only after its original meaning is preserved.
Some quantities are logarithmic. Stellar luminosity in log10 solar units must be converted with 10 raised to the tabulated value before a direct luminosity ratio is calculated. Metallicity such as [Fe/H] is also logarithmic and depends on the abundance definition. The profiles label the raw quantity rather than silently changing its interpretation.
Uncertainty, limits, and missing data differ
A value with an upper and lower error describes an uncertainty interval in the cited work. The two sides can be unequal. A limit flag means the entry is an upper or lower bound, rather than an ordinary central estimate. Some model parameters may have been held fixed. No displayed uncertainty should be invented when the archive does not supply one.
Missing does not mean zero. A missing radius means the selected record does not provide that radius, even if another paper may discuss one. A missing atmosphere entry does not prove that the planet is airless. The Codex uses explicit unavailable labels and keeps bounds visible so that a clean layout does not erase those distinctions.
Minimum mass needs its own label
Radial-velocity work can provide M sin i, where i is orbital inclination. Unless inclination is known, this is a minimum mass. The actual mass can be higher. The archive's mass-provenance field distinguishes true mass, minimum mass, and other available definitions; the profiles show that field beside the number.
For an ordinary measured mass and radius, their ratio gives a bulk-density clue, but composition remains model dependent. The profiles do not calculate a surface gravity from minimum mass and present it as a measurement. Derived comparisons are identified separately, including period ratios, distance conversions, and radius comparisons.
Understand this edition's selection
The reference collection selects nearby, noncontroversial archive entries with a reported orbital period, a distance, and enough numerical parameters to support a useful profile. It is a curated subset, not a complete catalog of every confirmed planet. The timestamp records when the archive was fetched, while a paper's publication date describes a different event.
The collection is separate from the sponsor-supported 3D atlas. A reference profile does not create a purchasable placement or imply that its planet has been added to the explorer. The source table, selection rule, and missing-data handling are provided so readers can check a number and follow it back to the research.