Solar System processing (SSP)#
Solar System Processing includes both the association of known Solar System Objects (SSOs) during nighttime observations (see the Source Association page) as well as the discovery of new SSOs by linking unassociated DiaSources during daytime processing.
All Rubin SSO observations and discoveries are reported to the Minor Planet Center (MPC).
In addition, Rubin interfaces with the Minor Planet Center (MPC) for physical parameter derivation and orbit fitting.
General overview of SSP#
Solar System processing#
Solar System processing consists of two key components: the association of observations (sources) with known solar system objects, and the discovery of previously unknown objects by linking sets of tracklets, where a tracklet is defined as two or more observations taken in close succession in a single night.
To generate expected positions for known objects, ephemerides are computed for all objects found in the Minor Planet Center orbit catalog using the Sorcha survey simulation toolkit (Merritt et al., in press).
To enable fast lookup of objects potentially present in an observed visit, Sorcha uses the mpsky package (M. Juric 2025).
In each difference image resulting from Difference image analysis (DIA) processing, the closest DIASource within 1 arcsecond of a known solar system object’s predicted position is associated to that object (for details, see the Source Association page).
Solar system object discovery uses the heliolinx package of asteroid identification and linking tools (A. Heinze et al. 2023).
The suite consists of the following tasks:
Tracklet creation with
make_trackletsMulti-night tracklet linking with
heliolincLinkage post processing (orbit fitting, outlier rejection, and de-duplication) with
link_purify
Tracklet creation with make_tracklets uses an upper limit angular velocity of 1.5 deg/day, faster than any main belt asteroid and in the range of many NEO discoveries.
To avoid excessive false tracklets from fields observed many times per night, the minimum tracklet length is set to three and the minimum on-sky motion for a valid tracklet is set to five arcseconds.
The heart of the discovery pipeline is the heliolinc task, which connects (“links”) tracklets belonging to the same object over a series of nights.
It employs the HelioLinC3D algorithm (S. Eggl et al. 2020; A. Heinze et al. 2022), a refinement of the original HelioLinC algorithm of M. J. Holman et al. (2018).
The heliolinc run tests each tracklet with 324 different hypotheses spanning heliocentric distances from 1.5 to 9.8 au and radial velocities spanning the full range of possible bound orbits (eccentricity 0.0 to nearly 1.0).
This range of distances encompasses all main belt asteroids and Jupiter Trojans, as well as many comets and Mars-crossers and some NEOs.
Smaller heliocentric distances are not attempted, because nearby objects move rapidly across the sky and hence were not likely to remain long enough in the field to be discovered.
A clustering radius is chosen corresponding to \(1.33 \times 10^{-3}\) au at 1 au from Earth.
Linkages produced by heliolinc are post-processed with link_purify into a final non-overlapping set of candidate discoveries, ranked from highest to lowest probability of being a real asteroid based on astrometric orbit-fit residuals and other considerations.