Non-Gravitational Accelerations in 3I/ATLAS: Marsden Model Analysis

 




Non-Gravitational Acceleration and Physical Activity in Interstellar Objects: Insights from 3I/ATLAS (C/2025 N1)

Deviations from purely gravitational motion provide some of the most direct evidence for physical activity in interstellar objects, linking observed orbital behavior to sublimation-driven processes on the nucleus. For 3I/ATLAS (C/2025 N1), non-gravitational acceleration modeling establishes a quantitative connection between high-precision astrometry and cometary activity, allowing physical interpretation to be grounded firmly in orbital dynamics.

Full text (open access):
https://www.researchgate.net/publication/398431066

Why Non-Gravitational Forces Matter for Interstellar Comets

In an idealized dynamical framework, small bodies follow purely Keplerian orbits governed by gravity alone. In reality, outgassing-driven recoil forces introduce subtle but measurable accelerations that modify an object’s trajectory. For interstellar objects, detecting and modeling these effects is essential because:

  • They provide direct evidence of sublimation and volatile release
  • They constrain activity strength and distribution on the nucleus
  • They distinguish physical processes from purely dynamical anomalies

Non-gravitational modeling therefore acts as a diagnostic bridge between orbital mechanics and surface physics.

Detecting Deviations from Keplerian Motion in 3I/ATLAS

The trajectory of 3I/ATLAS exhibits small but statistically significant departures from a strictly gravitational orbit. These deviations were detected thanks to dense, high-quality astrometric coverage, enabling residual patterns to be distinguished from noise and catalog systematics.

Such departures are subtle, but when consistently aligned with solar geometry, they indicate real physical acceleration rather than fitting artifacts.

The Marsden Non-Gravitational Force Model

To interpret these deviations, the classical Marsden non-gravitational force model was applied. This framework parameterizes acceleration components in three orthogonal directions relative to the Sun–object line:

  • Radial (A₁): Directed away from the Sun
  • Transverse (A₂): Along the orbital velocity
  • Normal (A₃): Perpendicular to the orbital plane

Applied to the refined astrometric dataset of 3I/ATLAS, this model enabled statistically meaningful detection of non-gravitational effects during the inbound phase of the object’s trajectory.

Radial Acceleration and Sublimation-Driven Activity

Model fits indicate that the dominant non-gravitational contribution lies in the radial component, a signature consistent with asymmetric outgassing driven by solar heating. As volatiles sublimate preferentially from the sunward hemisphere, recoil forces naturally act along the Sun–object line.

This behavior supports a thermally driven activity model, in which sublimation responds smoothly to increasing insolation rather than arising from impulsive or non-physical mechanisms.

Weak Transverse and Normal Components: Implications for Rotation

The transverse and normal acceleration components inferred for 3I/ATLAS are comparatively weak. This has important physical implications:

  • Limited torque acting on the nucleus
  • Absence of strong rotational spin-up
  • A dynamically stable rotational state

Such characteristics suggest a physically ordinary cometary body, rather than one undergoing extreme or exotic dynamical evolution.

Comparison with Earlier Interstellar Objects

The magnitude of the inferred non-gravitational accelerations for 3I/ATLAS (C/2025 N1) is significantly weaker than those reported for 1I/‘Oumuamua. This contrast is crucial, as it aligns 3I/ATLAS with moderate, volatile-driven activity rather than requiring non-standard propulsion hypotheses.

The comparison reinforces the interpretation of 3I/ATLAS as an extrasolar comet behaving in a physically familiar way, despite its interstellar origin.

Classical Models in the Era of Precision Astrometry

The Marsden analysis of 3I/ATLAS demonstrates that classical cometary force models remain effective when paired with modern statistical treatment and high-precision astrometric datasets. Dense observational coverage transforms subtle accelerations into interpretable physical signals.

As interstellar detections increase, systematic application of non-gravitational modeling will be essential for:

  • Separating physical activity from dynamical signatures
  • Quantifying sublimation efficiency
  • Establishing population-level trends in interstellar comet behavior

This Article Examines

  • How non-gravitational forces are modeled using the Marsden framework
  • What radial acceleration signatures reveal about sublimation activity
  • Why weak transverse components imply rotational stability
  • The role of non-gravitational modeling in interpreting interstellar comet dynamics

Reference (APA 7):
Kodiyatar, N., & Shamala, A. (2025). Scientific understanding of 3I/ATLAS (C/2025 N1): Authentic data, observational insights, and information ethics. Nohil Kodiyatar & Abhay Shamala. https://doi.org/10.5281/zenodo.17851223

#InterstellarObjects #3IATLAS #OrbitalDynamics #NonGravitationalForces #Astrophysics #PlanetaryScience #ComputationalAstronomy #OpenScience

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