We measure the mid-plane of the main asteroid belt by using the observational data of a nearly complete and unbiased sample of asteroids , and find that it has inclination \bar { I } = 0.93 \pm 0.04 degrees and longitude of ascending node \bar { \Omega } = 87.6 \pm 2.6 degrees ( in J2000 ecliptic-equinox coordinate system ) .
This plane differs significantly from previously published measurements , and it is also distinctly different than the solar system ’ s invariable plane as well as Jupiter ’ s orbit plane .
The mid-plane of the asteroid belt is theoretically expected to be a slightly warped sheet whose local normal is controlled by the gravity of the major planets .
Specifically , its inclination and longitude of ascending node varies with semi-major axis and time ( on secular timescales ) , and is defined by the forced solution of secular perturbation theory ; the \nu _ { 16 } nodal secular resonance is predicted to cause a significant warp of the mid-plane in the inner asteroid belt .
We test the secular theory by measuring the current location of the asteroids ’ mid-plane in finer semi-major axis bins .
We find that the measured mid-plane in the middle and outer asteroid belt is consistent , within 3– \sigma confidence level , with the prediction of secular perturbation theory , but a notable discrepancy is present in the inner asteroid belt near \sim 2 AU .