Bidang ajeg

+Gumiwanging orbit tumrap bidang ajegé raseksa gas:taunJupiterSaturnusUranusNeptunus2009 0.32°0.93°1.02°0.72°142400  (produced with Solex 10)0.48°0.79°1.04°0.55°168000  (produced with Solex 10)0.23°1.01°1.12°0.55°

Bidang ajeg (basa Inggris : invariabel plane), uga diarani bidang ajeg Laplace, ya iku bidang sing ngliwati  barisentrum (punjer massa), jejeg karo vektor momentum sudut sawijining planit. Ing Tata Surya, udakara 98% bidang ajeg diasilaké dening momentum sudut orbit saka patang planit jovian (Jupiter, Saturnus, Uranus, lan Neptunus). Bidang iki adohé kurang luwih 0,5° saka bidang orbit Jupiter,  lan dianggep bobot rata-rata sakabehing bidang orbit lan bidang rotasi planit ing Tata Surya.

Bidang iki kadhangkala karan "Laplacian" utawa "bidang ajeg Laplace", sanajan ora padha karo bidang Laplace, ya iku papan orbité planit sing ngalami presesi. S. Tremaine, J. Touma, and F. Namouni (2009). Satellite dynamics on the Laplace surface, The Astronomical Journal 137, 3706–3717. Kaloro bidang kuwi dijenengi miturut ahli astronomi Prancis, Pierre Simon Laplace. La Place, Marquis de (Pierre Simon Laplace). Mécanique Céleste, translated by Nathaniel Bowditch. Boston: 1829, in four volumes (1829–1839). See volume I, chapter V, especially page 121. Originally published as Traite de mécanique céleste (Treatise on Celestial Mechanics) in five volumes, 1799–1825. Bidang ajeg dicacah miturut jumlah momentum sudut ing sakabehing tata kaplanitan, dene bidang Laplace dicacah miturut jumlah barang akasa sing ngorbit ing tata planit Laplace ngarani bidang ajeg kanthi jeneng "bidang area maksimum"; wilayah kuwi diitung saka jari-jari lan bedané wektu diferensial dR / dt, utawa kanthi cara ngaleaké kacepatan karo massa.