---
title: 'CODE Catalogue: Comet Orbit Dynamics'
url: https://www.emergentmind.com/topics/code-catalogue
type: topic
---

# CODE Catalogue: Comet Orbit Dynamics

Searching arXiv for the cited catalogue papers and the cometary CODE updates to ground the article in the literature.
CODE, the **Catalogue of Cometary Orbits and their Dynamical Evolution**, is a curated dynamical database of long-period comets (LPCs), especially Oort Cloud and Oort spike objects, designed to provide not only osculating orbits but also the original, future, previous, and next stages of a comet’s trajectory together with uncertainty information and dynamical classification [2005.09698]. Its distinguishing feature is that it treats comet cataloguing as a long-baseline orbital-evolution problem rather than as a static list of orbital elements: the catalogue links a comet’s observed apparition to its inferred motion before planetary entry and after planetary exit, and in later versions it does so in both a Galactic-tide-only model and a Galactic-plus-stellar-perturber model [2311.04063][2508.20780].

## 1. Historical development and scope

The original 2020 release announced a catalogue containing data for **277 LPCs**, described as **almost 300 LPCs discovered before 2018**, with emphasis on comets having **original semimajor axis greater than 10,000 au** for a purely gravitational orbit; these were identified as **Oort spike comets** [2005.09698]. The catalogue was intended to be nearly complete for LPCs discovered in **1885–2017** satisfying that criterion, apart from a small set of about **twenty Oort-spike comets with \(q<3.1\) au discovered in 2013–2017** that were still absent at that stage [2005.09698].

The 2023 update described a broader and nearly complete sample of Oort spike comets discovered through **January 2021**. At that point, CODE contained **312 LPCs** with **766 sets of orbits**, including **258 Oort Cloud comets**, and explicitly added the complete sample of **29 Oort Cloud comets discovered in 2018, 2019, 2020, and January 2021**, plus **4 other LPCs** from the same period [2311.04063].

The 2025 update expanded the database further to **983 orbital solutions** for **369 comets** with full uncertainty estimates and dynamical classifications. It stated that the catalogue covers **nearly all comets with original semi-major axes exceeding 10,000 au and discovered before 2022**, as well as **all LPCs discovered beyond 10 au from the Sun during this period**, and **over 80% of the known LPCs with perihelion distances beyond 7 au** [2508.20780].

| Version | Scope stated in the paper | Size |
|---|---|---:|
| 2020 [2005.09698] | LPCs discovered before 2018; nearly complete for 1885–2017 Oort-spike sample | 277 LPCs |
| 2023 [2311.04063] | Nearly complete sample of Oort spike comets through January 2021 | 312 LPCs; 766 orbit sets |
| 2025 [2508.20780] | Nearly all relevant pre-2022 Oort-Cloud/LPC cases, plus all LPCs discovered beyond 10 au | 369 comets; 983 solutions |

This progression shows that CODE evolved from a standardized Oort-spike catalogue into a more general-purpose, dynamically homogeneous LPC database. A plausible implication is that its scientific role shifted from cataloguing a specific dynamical population to supporting broader inference on comet origin, dynamical age, and outer-Solar-System structure.

## 2. Orbital architecture and the five-stage representation

A central design feature of CODE is that it stores each comet in **five snapshots** of orbital evolution: **previous**, **original**, **observed**, **future**, and **next** [2005.09698]. These five stages are arranged so as to cover **three successive passages through the perihelion**: the perihelion before the observed apparition, the observed perihelion, and the subsequent perihelion.

In the 2020 definition, the **observed** snapshot is the osculating heliocentric orbit determined from positional observations near the center of the observed data arc, typically near perihelion. The **original** and **future** snapshots are obtained by propagating the motion to **250 au** from the Sun, where planetary perturbations are negligible and the orbit is considered in the barycentric frame. The **previous** and **next** snapshots are obtained by propagating farther backward and forward under Galactic and stellar perturbations, to the previous and next perihelion respectively; for hyperbolic or extremely elongated cases, the stopping point is instead the **escape limit** of **120,000 au** [2005.09698].

| Stage | Meaning in CODE | Dynamical context |
|---|---|---|
| Previous | Orbit at previous perihelion, or at 120,000 au in special cases | Long-term backward evolution |
| Original | Orbit at 250 au before strong planetary perturbations | Barycentric pre-entry state |
| Observed | Osculating orbit from the observed arc | Near-apparition state |
| Future | Orbit at 250 au after planetary perturbations | Barycentric post-exit state |
| Next | Orbit at next perihelion, or at 120,000 au in special cases | Long-term forward evolution |

From the 2023 update onward, the **previous** and **next** stages are supplied in **two variants**: one including the **full Galactic tide only**, and another including the **full Galactic tide + all known stellar perturbers** [2311.04063]. The 2025 update states that these are exposed in the interface as `previous`, `next` and `previous_g`, `next_g` [2508.20780]. This dual representation is methodologically important because it isolates the contribution of stellar encounters to long-term orbital history.

## 3. Orbit determination, nongravitational modeling, and multiple solutions

CODE uses a uniform orbit-determination procedure for its osculating solutions, with consistent data-selection and weighting choices emphasized as essential for statistical studies of the **Oort spike maximum**, that is, the distribution of original reciprocal semimajor axes \(1/a\) [2005.09698]. The catalogue is not limited to one orbit per comet. For many objects it contains several acceptable solutions, differing by force model, data subset, or both [2005.09698][2311.04063].

For about **one third** of the LPCs in the 2020 catalogue, detectable **non-gravitational (NG) accelerations** were found, and in the subsample with **\(q<3.1\) au** NG solutions were found for **more than 60%** of objects [2005.09698]. The 2025 update similarly states that **more than 40%** of all LPCs in CODE show detectable residual trends, rising to **over 60%** for small-perihelion comets with \(q<3.35\) au [2508.20780]. When NG effects are significant, CODE stores both an NG solution and, for comparison, a purely gravitational solution.

The standard NG acceleration model follows the Marsden et al. formalism,
$$
F_i = A_i\,g(r), \qquad A_i=\mathrm{const\ for}\ i=1,2,3,
$$
with
$$
g(r)=\alpha (r/r_0)^m\left[1+(r/r_0)^n\right]^k,
$$
where \(F_1,F_2,F_3\) are the radial, transverse, and normal components of the NG acceleration [2005.09698]. CODE uses both a **water-sublimation law** and a **CO-sublimation law**, and in some cases a more specialized force model or a fourth NG parameter representing a time shift of the \(g(r)\) maximum relative to perihelion, allowing **asymmetric NG solutions** [2005.09698]. The 2023 update adds that CODE may also use **subsolar-point water sublimation**, again in symmetric or asymmetric form [2311.04063].

Multiple solutions are also generated from different observational subsets: the **entire data arc**, **pre-perihelion data only**, **post-perihelion data only**, or sometimes only data at large heliocentric distance [2005.09698][2311.04063]. This is especially relevant when outbursts, splitting, or disintegration make a single constant-NG model inadequate. The 2023 paper is explicit that the **preferred orbit** is ordinarily the **NG orbit**, or the **GR orbit if NG effects are not detectable**, and that it is derived from the **longest possible data arc**, except in unusual cases such as disintegrating comets [2311.04063]. The same paper also stresses that the preferred orbit is **not always best** for dynamical-history studies. This is a substantive methodological caution rather than a minor implementation detail.

## 4. Monte Carlo propagation, perturbation models, and uncertainty reporting

To construct the **original** and **future** orbits, CODE generates a swarm of **5001 virtual comets (VCs)**, including the nominal orbit, by a Monte Carlo method and integrates them backward and forward until each reaches **250 au** [2005.09698]. For the **previous** and **next** stages, the same swarms are propagated farther under the action of the **Galactic potential** and perturbations from nearby stars [2005.09698]. The 2025 update reiterates that CODE uses full Monte Carlo virtual-comet swarms and notes that dynamical classification propagates the nominal orbit together with **5000 additional VCs** [2508.20780].

In the 2020 release, the stellar-perturber model used a list of **643 stars or stellar systems** that may pass within **4 pc** of the Sun during the relevant time intervals [2005.09698]. The 2023 and 2025 updates replaced this with the **StePPeD** database of potential stellar perturbers, built from Gaia-era astrometry and radial velocities; the 2023 paper identifies the latest version it mentions as **StePPeD v3.3**, released on **2023 June 28** [2311.04063]. The introduction of separate Galactic-only and Galactic-plus-stellar variants reflects the authors’ judgment that stellar-encounter data remain materially uncertain.

CODE also formalizes the distinction between **returning**, **escaping**, and **hyperbolic** virtual comets. For hyperbolic or extremely elongated elliptic orbits, **120,000 au** is adopted as an escape limit; VCs not going beyond this are counted as returning, while those that do are escaping, with hyperbolic cases counted separately [2005.09698]. The catalogue records, for previous and next orbits, the number of returning \([R]\), escaping \([E]\), and hyperbolic \([H]\) VCs, which group contains the nominal orbit, and statistics of reciprocal semimajor axis, aphelion distance, and time interval to perihelion [2005.09698].

The uncertainty summaries are distribution-aware. In the 2020 design, if a parameter distribution is close to Gaussian, CODE reports the **mean** and **standard deviation**; otherwise it reports the **10th, 50th (median), and 90th percentiles** [2005.09698]. The 2023 update places stronger emphasis on the decile representation, noting that previous/next-orbit distributions are often non-Gaussian and are therefore given as the **10th percentile**, **median**, and **90th percentile** [2311.04063].

## 5. Dynamical status, perihelion history, and the role of stellar perturbations

The scientific core of CODE is the inference of a comet’s **dynamical status** from its earlier orbital history. In the 2020 catalogue, the previous-perihelion summary includes the fraction of VCs with perihelion distance **smaller than 10 au**, **between 10 and 20 au**, and **greater than 20 au**; for the **previous orbit**, these bins are interpreted respectively as **dynamically old**, **uncertain status**, and **dynamically new** [2005.09698]. The 2025 update makes the same logic explicit as thresholds on \(q_{\rm prev}\):
$$
q_{\rm prev} > 20~\mathrm{au} \Rightarrow \text{dynamically new},
$$
$$
q_{\rm prev} < 10~\mathrm{au} \Rightarrow \text{dynamically old},
$$
$$
10~\mathrm{au} < q_{\rm prev} < 20~\mathrm{au} \Rightarrow \text{dynamically uncertain}
$$
[2508.20780].

A recurring conclusion of the later papers is that **\(1/a_{\rm ori}\) alone is not enough** to determine whether a comet is dynamically new [2508.20780]. The 2025 update proposes a better approximate proxy only when \(q_{\rm prev}\) cannot be computed: use
$$
1/a_{\rm ori} < 55~\mathrm{au}_{-6}
$$
as a rough criterion for a dynamically new comet, **provided stellar perturbations are included** [2508.20780]. The same paper explicitly cautions against relying on the older **\(1/a_{\rm ori}=100\) au\(^{-6}\)** cutoff as a universal boundary.

The importance of stellar perturbations is one of the strongest quantitative results in the 2025 update. For **222 comets** with fully returning swarms in both force models, the median \(q_{\rm prev}\) is **6.9 au** **without stars** and **59.0 au** **with stars** [2508.20780]. For the subset with **\(1/a_{\rm ori}<55\) au\(^{-6}\)**, comprising **118 comets**, the median \(q_{\rm prev}\) changes from **12.7 au** without stars to **643.1 au** with stars [2508.20780]. Within that subset, using the **\(q_{\rm prev}=20\) au** threshold, **115** comets become dynamically new when stars are included, **0** are dynamically old, and **3** are uncertain; without stellar perturbations, only **36** would have been classed as dynamically new [2508.20780]. This result directly supports the catalogue’s later two-variant design.

Specific objects illustrate the classification logic. In the 2020 paper, the preferred solution for **C/2002 T7 LINEAR** yields a previous perihelion distance of about **150 au**, placing it outside the planetary region and therefore identifying it as **dynamically new** [2005.09698]. The 2023 update shows how dynamical inference can remain sensitive to NG law and data treatment in objects such as **C/2015 O1 (PanSTARRS)**, for which different acceptable solutions yield different \(1/a_{\rm ori}\) values, even if the broad dynamical interpretation remains comparable [2311.04063].

## 6. Interfaces, scientific uses, and limitations

CODE is designed for both inspection and statistical analysis. The 2020 paper describes two public interfaces: **Browse**, which lists comets and by default shows one preferred orbit per comet, and **Search**, which allows filtering by nearly all orbital and observational parameters, with results downloadable in full precision together with uncertainties [2005.09698]. The 2023 update notes an interface restriction: the **Search** option works only with **previous** and **next** orbits obtained from the **full dynamical model** including both stars and Galactic tide [2311.04063].

The catalogue is intended to support studies of the **origins and evolution** of LPCs and the **Oort Cloud**, analyses of how NG effects alter osculating and original orbits, investigations of the **\(1/a_{\rm ori}\)** distribution and the **Oort spike**, classification of comets as dynamically new or old, and examination of the effects of Galactic tides and stellar encounters on past and future trajectories [2005.09698]. The 2025 update adds that CODE is meant to support the study of the **6D distribution** of orbital elements relevant to the outer Solar System [2508.20780].

The papers also state several limitations. The catalogue reflects the **current state of knowledge** and can change if new positional data become available or if old data are re-reduced with better star catalogues [2005.09698]. The 2020 release was still missing some small-perihelion Oort-spike comets from **2013–2017** [2005.09698], although the 2025 update later reports that it added a complete sample of **24 LPCs discovered in 2013–2017 with \(q<3.1\) au** [2508.20780]. Previous and next orbits depend on the adopted stellar-perturber list, and the 2023 paper cites **HD 7977** as an example of a potentially strong perturber whose Gaia data remain inconclusive [2311.04063]. The 2020 paper also notes that original and future orbits might be slightly affected by unmodeled influences, including a hypothetical **Planet Nine** [2005.09698].

These caveats do not reduce the catalogue to a provisional ephemeris list. Rather, they define its character as a living dynamical atlas whose principal scientific value lies in the combination of standardized orbit determination, alternative physical models, uncertainty propagation through virtual-comet swarms, and explicit tracking of how Galactic and stellar perturbations reshape LPC histories over Myr timescales [2005.09698][2508.20780].

Source: https://www.emergentmind.com/topics/code-catalogue