Radar observations of 1999 MN


We described the motivation for observing near-Earth asteroids in Icarus-like orbits in this paper. By obtaining precise radar astrometry for a number of objects at several apparitions, we can disentangle Yarkovsky, GR, and solar J2 perturbations on the orbit.

1999 MN is a 200-m diameter asteroid that has been designated as potentially hazardous by the Minor Planet Center. Its orbital elements (a = 0.674, e = 0.665, i = 2.06 deg) make it one of the most suitable candidates for the measurement of perihelion shift (18 arcsecond/cy) due to general relativistic effects and the oblateness of the Sun. 1999 MN is also a prime candidate for the measurement of Yarkovsky orbital drift which can be used to place constraints on an asteroid mass and thermal properties. We obtained good data in 2004 and 2005, but the 2009 and 2010 observations were cancelled due to observatory equipment failure.

GR plot

Figure 1: Predicted rates of perihelion shift due to GR alone for a number of newly discovered NEOs, compared to that of 1566 Icarus.


Figure 2: Trajectories of 1999 MN (solid) and Earth (dashed) looking down on the ecliptic plane (2004-JUL-11 to 2005-JUN-02, counter-clockwise). The Sun is at the origin and the vernal equinox is in the positive X-direction. The longitude of perihelion of the asteroid is 90.6 deg, and the 0.16 arcsec shift due to GR during this period corresponds to a range difference of ~115 km at 1 AU, mostly aligned with the line of sight.

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