GECKOS Program Overview

• The GECKOS Program is a multidisciplinary initiative that integrates bio-inspired reversible adhesion with extragalactic astronomy to advance both engineering and astrophysical understanding.
• It drives innovation through gecko-inspired adhesive grippers and feedforward gravity compensation, enhancing robotic perching, climbing, and space operations.
• In astrophysics, GECKOS employs advanced spectroscopic surveys, JAM modeling, and kinematic mapping to unravel the chemo-kinematic assembly histories of edge-on disk galaxies.

The GECKOS Program refers to a set of interconnected research initiatives spanning both bio-inspired engineering and extragalactic astronomy. While the acronym “GECKOS” has been explicitly applied to several major galaxy evolution surveys, foundational studies in adhesion mechanics and robotics also contribute core concepts and technologies that underpin the program. Thematic unity derives from a focus on understanding and replicating the principles of reversible adhesion (as exemplified by geckos) and unraveling the structural and dynamical complexity of galactic systems.

1. Theoretical Foundations: Cohesion-Decohesion Asymmetry in Gecko Adhesion

The foundational theoretical model of gecko adhesion and detachment (Puglisi et al., 2013) presents a mechanical explanation for how geckos reconcile strong surface attachment with effortless release. The model describes the adhesive pad as a chain of elastic elements (fibrillar units) interconnected by shear springs. Each element attaches to the substrate via a breakable cohesive bond modeled by a piecewise quadratic potential. The total system energy comprises both the adhesive energy of individual bonds and elastic coupling between adjacent units.

A central analytic result is the critical force threshold for detachment in the continuum limit: $$f_m(G) = \sqrt{2\gamma b G}~\tanh\left(L \sqrt{k}/\sqrt{G}\right),$$ where $G$ is shear stiffness (muscle-controlled), $k$ extensional stiffness, $\gamma$ adhesion energy density, $b$ out-of-plane length, and $L$ the pad length. The key insight is that the detachment force depends not only on properties of the adhesive units but on their cooperative elastic interaction (via $G$). By actively modulating $G$ through muscle activity, geckos switch reversibly between high-force “peeling” (localized adhesion) and low-force “pull-off” (delocalized adhesion). This model not only explains biological adhesion asymmetry but also motivates bio-inspired device design.

2. Bio-Inspired Robotic Applications: Gecko Adhesion Grippers

Emerging from the theoretical understanding of gecko adhesion, the GECKOS Program encompasses engineering efforts to realize synthetic adhesion in robotic platforms. For example, the design and development of a gecko-inspired adhesive gripper for the Astrobee free-flyer robot (Cauligi et al., 2020) implements dry adhesive technology based on microstructured elements that mimic gecko setae.

Key features include:

• Hierarchical compliance and adaptability to varied surface topography,
• Passive (low-energy) engagement and rapid reversible attachment,
• Tendon-driven and spring-loaded actuation to modulate contact area,
• Software integration with space robot avionics via ROS modules.

Ground tests demonstrate robust attachment and perching in simulated microgravity conditions. By enabling perching and manipulation on featureless surfaces, the device augments satellite servicing, debris capture, and autonomous space operations. Integration with Astrobee leverages control interoperability, and further enhancements—such as closed-loop feedback for surface adaptation and extended flight testing—are being developed within the GECKOS framework.

3. Geckos-Inspired Gravity Compensation in Climbing Robots

Feedforward gravity compensation (FGC) extends bio-inspired adhesion principles to improve the stability of multi-legged climbing robots (Wang et al., 4 May 2024). In low-stiffness robotic legs, gravitational forces produce posture deviations and misaligned adhesive contact. FGC employs an enhanced mechanical stiffness model (based on Denavit–Hartenberg kinematic chains) and offline quadratic programming to pre-compute joint angle corrections, maintaining optimal footpad attachment angles even on inverted surfaces.

Experimental validation with a quadrupedal robot (EF-I platform) reveals:

• Success rate improvement from 30% (no FGC) to 100% (with FGC) in ceiling climbing,
• Reduction in body attitude oscillations by factors of 2.6–3.18,
• Stable kinematic performance without loss of locomotion speed.

FGC demonstrates that feedforward mechanical compensation—rather than hardware reinforcement—enables stable, reliable adhesion in challenging postures, a concept central to the GECKOS Program’s engineering thrust.

4. GECKOS Survey: Edge-On Galaxy Chemo-Kinematics

The “GECKOS” acronym is formally adopted in galaxy evolution research, specifically for the ESO VLT/MUSE large program “Generalising Edge-on galaxies and their Chemical bimodalities, Kinematics, and Outflows out to Solar environments” (Sande et al., 2023). The survey’s primary aim is to dissect the chemodynamical assembly history of disk galaxies by leveraging the vertical resolution afforded by edge-on orientations.

Salient components:

• A sample of 35 edge-on, Milky Way-mass disk galaxies (15–70 Mpc distance; i > 85°; star formation rate range spans 2 dex),
• Integral field spectroscopic mapping of stellar ages, abundances ([M/H], α-enhancements), ionized gas properties, and velocity dispersions,
• Use of methods refined by Galactic Archaeology (chemical tagging, kinematic analysis),
• Observational depth (signal-to-noise S/N > 40 at μ₍g₎ = 23.5 mag arcsec⁻²) and vertical mapping of outflows up to 10 kpc above the disk.

Early results reveal clear vertical metallicity and dispersion gradients, indicative of complex assembly histories including radial migration, disk heating, and past accretion events. The survey rigorously tests whether evolutionary paradigms from the Milky Way are universal across the spiral galaxy population.

5. Kinematic Substructure Analysis and Data Pipelines

Follow-up research within the GECKOS program provides systematic kinematic mapping using VLT/MUSE data and proprietary pipelines (notably nGIST) (Fraser-McKelvie et al., 5 Nov 2024). Kinematic substructures—such as boxy-peanut bulges, nuclear disks, and embedded bar features—are identified through resolved maps of mean line-of-sight velocity $V_{\star}$, dispersion $\sigma_{\star}$, and Gauss-Hermite moments $h_3$ (skew) and $h_4$ (kurtosis).

Key findings:

• 8/12 early sample galaxies exhibit boxy/peanut morphology, confirmed by both photometry and kinematic signatures,
• Nuclear disks identified via central $h_3$–$V_{\star}$ anti-correlation, $\sigma_{\star}$ “croissant” depressions, and plateaus in $h_4$,
• The structural and kinematic complexity supports a secular evolution scenario, with many features explainable solely by internal disk processes rather than classical bulge components,
• The nGIST pipeline facilitates robust extraction of kinematic maps in low-S/N regimes via Voronoi binning and pPXF fitting, with analytically calibrated penalization schemes.

This programmatic approach establishes a contemporary view of galaxy morphology, shifting away from the classical “bulge+disk” dichotomy in favor of composite, evolutionarily differentiated components.

6. Advanced Dynamical Modeling: JAM/MGE in Dusty Edge-On Discs

The GECKOS-MUSE survey applies Jeans Anisotropic Multi-Gaussian Expansion (JAM) models to a subset of edge-on disc galaxies (Rutherford et al., 10 Sep 2025). Here, deep near-infrared photometry provides MGE surface brightness models, mitigating direct dust attenuation. Axisymmetric JAM modeling computes the root-mean-square velocity $V_{rms}^2 = V^2 + \sigma^2$ and fits dynamical parameters via MCMC. Dust masking (with $E(B-V)$ thresholds) refines the regions of analysis, demonstrating that global dynamical mass estimates remain constant to within 10% across masking levels.

Residual velocity maps (observed minus JAM) reveal non-axisymmetric substructures:

• Nuclear discs (central velocity residual excess),
• Bars (major-axis velocity excesses),
• Boxy-peanut bulges (X-shaped residual patterns).

Limitations of the method arise from inherent axisymmetry and constant mass-to-light ratio assumptions, partially masking bar-driven dynamics. The results motivate future transitions to orbit-superposition modeling and radiative transfer techniques for comprehensive internal structure recovery.

7. Structural Dissection and Formation Histories in Edge-On Galaxies

A pilot GECKOS paper on PGC 044931 (Fraser-McKelvie et al., 19 Sep 2025) applies rigorous photometric decomposition (VIRCAM H-band, IMFIT) and overlays the resulting dominant components onto resolved kinematic maps from MUSE. Distinct regions (main disc, boxy/peanut bulge, nuclear disc) are identified both photometrically and kinematically, with differentiated distributions in the $(V_{\star}/\sigma_{\star}, h_3)$ parameter space. Analysis of age-metallicity relations across components reveals evolutionary histories:

• Extended disc: ongoing star formation and accretion,
• Bar formation and early buckling: origin of the boxy/peanut bulge,
• Nuclear disc: sustained enrichment tied to inward gas flow post-buckling.

This multimodal approach exemplifies how integral field spectroscopy combined with photometric modeling disentangles overlapping stellar populations and reconstructs composite formation histories.

8. Multiphase Galactic Winds in the GECKOS Program

Resolved multiphase observations of galactic winds (NGC 4666; (Ciraulo et al., 22 Sep 2025)) synthesize VLT/MUSE optical spectroscopy and WALLABY HI imaging to characterize biconical outflows. Notable findings include:

• Ionized wind limbs traced up to $z \sim 8$ kpc; electron density profile with unexpected plateau and rise at large $z$ ($n_e \sim 100-210$ cm$^{-3}$),
• HI phase dominates mass loading (outflow rates $5-13~M_{\odot}~\rm yr^{-1}$ vs. $0.5-5~M_{\odot}~\rm yr^{-1}$ for ionized gas),
• Most expelled cool gas lacks the velocity to escape the galaxy halo, suggesting efficient gas recycling and “galactic fountain” phenomena,
• The necessity for simulations to refine outflow prescriptions and incorporate realistic multiphase, density inhomogeneities.

These resolved observations constrain feedback models and star formation regulation in spiral galaxies.

---

The GECKOS Program, through both biological and galactic research strands, advances the quantitative understanding of reversible adhesion and complex internal structure. By integrating mechanical modeling, device engineering, and galaxy survey analytics, GECKOS provides a comprehensive framework for interpreting asymmetry in attachment systems and chemo-kinematic diversity in galaxies. Applications span bio-inspired robotics, satellite manipulation, and the detailed mapping of the assembly history and mass cycling in galactic discs.