{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.682","julian_year":2026.682,"time":"2026-09-06T23:34:44.496Z","years_from_j2000":26.682,"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-257-d","name":"Kepler-257 d","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":2544.8547065175535,"distance_method":"NASA Exoplanet Archive sy_dist (TICv8, 2019AJ....158..138S)","ra_deg":297.3159994,"dec_deg":46.0232642,"epoch_ra_deg":297.521376,"epoch_dec_deg":46.090101,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":"Kepler-257","semi_major_axis_km":23935659.312,"periapsis_km":null,"mass_kg":1.2959604273107292e+26,"mass_msun":0.0000651757,"constellation":"Cygnus","discovered":"2014","featured":false,"url":"https://spacecatalog.org/object/kepler-257-d","radius_km":31571.595,"radius_kind":null,"data_quality":null,"description":null,"properties":{"host_star":"Kepler-257","host_v_mag":15.652,"eccentricity":0,"uncertainties":{"radius_km":[15817.688,15817.688],"distance_ly":[54.79100989263573,57.20782865151679],"host_mass_solar":[0.017,0.017],"host_radius_solar":[0.518,0.518],"host_temperature_k":[200,200],"orbital_period_days":[0.000051,0.000051]},"host_mass_solar":0.916,"inclination_deg":88.98,"stars_in_system":1,"discovery_method":"Transit","host_radius_solar":1.037,"planets_in_system":3,"discovery_facility":"Kepler","host_temperature_k":5180,"orbital_period_days":24.664551,"transit_midpoint_bjd":2455022.02052,"equilibrium_temperature_k":567},"designations":[{"catalog":"Exoplanet","designation":"Kepler-257 d"}],"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."}