{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.674","julian_year":2026.674,"time":"2026-09-04T02:02:40.099Z","years_from_j2000":26.674,"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":"kepler-538-b","name":"Kepler-538 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":508.6604404319243,"distance_method":"NASA Exoplanet Archive sy_dist (TICv8, 2019AJ....158..138S)","ra_deg":297.4865503,"dec_deg":49.6233975,"epoch_ra_deg":297.673361,"epoch_dec_deg":49.690584,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":"Kepler-538","semi_major_axis_km":53167083.24677999,"periapsis_km":null,"mass_kg":7.704096549450879e+25,"mass_msun":0.000038745,"constellation":"Cygnus","discovered":"2016","featured":false,"url":"https://spacecatalog.org/object/kepler-538-b","radius_km":14127.4915,"radius_kind":null,"data_quality":null,"description":null,"properties":{"host_star":"Kepler-538","host_v_mag":11.27,"uncertainties":{"mass_kg":[1.7319286816595e+25,1.7319286816595e+25],"radius_km":[216.85540000000003,255.12400000000002],"distance_ly":[2.2928793353487062,2.312448718011711],"host_mass_solar":[0.035,0.051],"inclination_deg":[0.06,0.14],"host_radius_solar":[0.0061,0.0064],"host_temperature_k":[61,61],"semi_major_axis_km":[703109.99229,1017265.5207599999],"orbital_period_days":[0.00013,0.00013],"argument_of_periastron_deg":[90,140]},"host_mass_solar":0.892,"inclination_deg":89.73,"stars_in_system":2,"discovery_method":"Transit","host_radius_solar":0.8717,"planets_in_system":1,"discovery_facility":"Kepler","host_temperature_k":5534,"orbital_period_days":81.73778,"transit_midpoint_bjd":2455044.6789,"eccentricity_upper_limit":0.21,"equilibrium_temperature_k":417,"argument_of_periastron_deg":140},"designations":[{"catalog":"Exoplanet","designation":"Kepler-538 b"},{"catalog":"Host star","designation":"Kepler-538"}],"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":"2026-09-02T19:50:56.720Z","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."}