{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.679","julian_year":2026.679,"time":"2026-09-05T22:12:35.243Z","years_from_j2000":26.679,"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":"k2-21-b","name":"K2-21 b","class":"super_earth","category":"exoplanet","object_type":"Super-Earth","mag":null,"mag_band":null,"abs_mag":null,"abs_mag_band":null,"distance_ly":272.8128498284146,"distance_method":"NASA Exoplanet Archive sy_dist (TICv8, 2019AJ....158..138S)","ra_deg":340.3037846,"dec_deg":-14.4893256,"epoch_ra_deg":340.661361,"epoch_dec_deg":-14.349139,"epoch_moved_arcsec":null,"pm_ra_mas_yr":null,"pm_dec_mas_yr":null,"orbits":"K2-21","semi_major_axis_km":11369438.173199998,"periapsis_km":null,"mass_kg":2.412755818587717e+25,"mass_msun":0.0000121341,"constellation":"Aquarius","discovered":"2015","featured":false,"url":"https://spacecatalog.org/object/k2-21-b","radius_km":11735.704000000002,"radius_kind":null,"data_quality":null,"description":null,"properties":{"host_star":"K2-21","host_v_mag":12.851,"eccentricity":0.1,"uncertainties":{"radius_km":[637.8100000000001,637.8100000000001],"distance_ly":[0.8639882445716534,0.8692067466151212],"eccentricity":[0.084698,0.148654],"host_mass_solar":[0.067602,0.067602],"inclination_deg":[0.31,0.5],"host_radius_solar":[0.028216,0.028803],"host_temperature_k":[84.41,88.15],"semi_major_axis_km":[448793.61209999997,299195.7414],"orbital_period_days":[0.000403,0.000379],"argument_of_periastron_deg":[133.739,101.8842]},"host_mass_solar":0.676023,"inclination_deg":88.98,"stars_in_system":1,"discovery_method":"Transit","host_radius_solar":0.646783,"planets_in_system":2,"discovery_facility":"K2","host_spectral_type":"M0.0","host_temperature_k":4222.06,"orbital_period_days":9.325038,"transit_midpoint_bjd":2456989.422,"equilibrium_temperature_k":500,"argument_of_periastron_deg":34.48},"designations":[{"catalog":"Exoplanet","designation":"K2-21 b"},{"catalog":"Host star","designation":"K2-21"}],"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."}