{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.653","julian_year":2026.653,"time":"2026-08-27T16:20:14.999Z","years_from_j2000":26.653,"frame":"date","applied":"Proper motion, then precession and nutation. The catalogued J2000 position is carried along the great circle the object's own published motion puts it on, at a constant velocity, and the result is referred to the true equator and equinox of this instant. Those are separate things: the motion moves the object, and the rotation turns the grid under it by about fifty arcseconds a year, with nutation adding up to another seventeen.","excluded":"Parallax, the radial-velocity perspective term, aberration and refraction; each is below the accuracy of the catalogued positions themselves. An object with no published proper motion comes back where the catalogue has it rather than at a fabricated zero, and says so with a null pm_ra_mas_yr. A body with no fixed position is not propagated at all — its place comes from an ephemeris, which is what /api/v1/visible answers with."},"slug":"k2-18-b","name":"K2-18 b","class":"neptune_like_planet","category":"exoplanet","object_type":"Neptune-like planet","mag":null,"mag_band":null,"abs_mag":null,"abs_mag_band":null,"distance_ly":124.02618112883516,"distance_method":"NASA Exoplanet Archive sy_dist (TICv8, 2019AJ....158..138S)","ra_deg":172.560141,"dec_deg":7.5878315,"epoch_ra_deg":172.906879,"epoch_dec_deg":7.43988,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":"K2-18","semi_major_axis_km":21377535.723029997,"periapsis_km":null,"mass_kg":5.32717373806991e+25,"mass_msun":0.0000267911,"constellation":"Leo","discovered":"2015","featured":true,"url":"https://spacecatalog.org/object/k2-18-b","radius_km":15116.097000000002,"radius_kind":null,"data_quality":null,"description":"A sub-Neptune where water vapour was detected in 2019 and carbon-bearing molecules in 2023, making it one of the most closely watched planets for signs of habitability.","properties":{"host_star":"K2-18","host_v_mag":13.477,"eccentricity":0.2,"uncertainties":{"mass_kg":[9.555468588466207e+24,1.0152685375245345e+25],"radius_km":[1403.182,1403.182],"distance_ly":[0.2594573984736694,0.2594573984736694],"eccentricity":[0.08,0.08],"host_mass_solar":[0.047,0.047],"inclination_deg":[0.0088,0.0079],"host_radius_solar":[0.038,0.038],"host_temperature_k":[39,39],"semi_major_axis_km":[972386.1595499999,897587.2241999999],"orbital_period_days":[0.0001,0.000095],"argument_of_periastron_deg":[33.8,46.4]},"host_mass_solar":0.359,"inclination_deg":89.5785,"stars_in_system":1,"discovery_method":"Transit","host_radius_solar":0.411,"planets_in_system":2,"discovery_facility":"K2","host_spectral_type":"M2.5 V","host_temperature_k":3457,"orbital_period_days":32.939623,"transit_midpoint_bjd":2457264.39144,"equilibrium_temperature_k":284,"argument_of_periastron_deg":-5.7},"designations":[{"catalog":"Exoplanet","designation":"K2-18 b"},{"catalog":"Host star","designation":"K2-18"}],"source":{"id":"exoplanet_archive","name":"NASA Exoplanet Archive (Planetary Systems Composite Parameters)","url":"https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=PSCompPars","license":"Public domain (NASA)"},"updated_at":"2026-08-27T16:03:54.983Z","attribution":"Data from SpaceCatalog.org. Individual records carry their source and license in `source`; attribution is required for CC-BY and CC-BY-SA rows."}