The Effect of Light Deflection by Solar System Objects on High-precision Square Kilometre Array Astrometry

Abstract

We have computed the deflection angles caused by 195 objects in the solar system, including 177 satellites, and eight asteroids; 21 satellites and six asteroids can bend light from distant compact extragalactic sources by more than 0.1 μas, and 14 satellites, and the asteroid Ceres can deflect light by more than 1.0 μas. We calculated the zones and durations of perturbations posed by the gravitational fields of five planets (excluding Earth, Jupiter, and Saturn), Pluto, and Ceres, where the perturbations would affect astrometry measured with the Square Kilometre Array (SKA). Perturbed zones with deflection angles larger than 0.1 and 1.0 μas appear as ribbons. Their widths range from dozens of degrees for Uranus, Neptune, and Venus to several degrees or less for other objects at 0.1 μas, and from ∼16° for Venus to several degrees or less for other objects at 1.0 μas. From the calculated perturbation durations, the influence of the gravitational fields of selected objects can be divided into four levels: (i) hardly affects SKA astrometry, (ii) may have little effect, (iii) may have a great effect on single-epoch astrometry, and (iv) may greatly affect both single- and multiepoch astrometry. The objects corresponding to these levels are (i) Ceres, (ii) Pluto, (iii) Mercury and Mars, and (iv) other objects.

VLBI with SKA: Possible Arrays and Astrometric Science

“…Light deflection and the underlying theory (e.g., relativistic gravity, gravitational lensing theory, etc.) have become important tools for both astronomy and cosmology (Will 2015), while light deflection by solar system objects will pose a nonnegligible restraining factor in astrometry by SKA-VLBI, affecting positional accuracies at the level 1 μas (Li et al 2022b).…”

“…Both methods will already help removing the bulk of the systematics, although it is true that the final astrometric precision will depend on various factors (like the brightness, compactness, the number, and the distribution of these calibrators) and may reach routinely below 10 μas, even challenging 1 μas. It should be noted that extremely highprecision astrometry (e.g., SKA μas astrometry) will face the challenge of light deflection under the gravitational fields of celestial bodies in the solar system (e.g., Li et al 2022b). In any case, there is now a realistic possibility of carrying out μas radio astrometric surveys of exquisite detail for large samples of objects, which will advance our understanding of different astrophysical phenomena and classes (Rioja & Dodson 2020).…”