PLATOSpec Instrument: Design & Exoplanet Research

• PLATOSpec instrument is a high-precision photometric and spectroscopic system designed to detect exoplanets and analyze stellar oscillations.
• It features a modular design with 26 onboard cameras and advanced ground-based echelle spectrographs, enabling ultra-high precision imaging and radial velocity measurements.
• Its integrated data processing, simulation, and calibration tools facilitate detailed analysis of planetary transits, stellar activity, and exoplanet dynamical architectures.

The PLATOSpec instrument refers collectively to specialized high-precision photometric and spectroscopic instrumentation that forms a central component of ESA’s PLATO space mission, as well as a series of dedicated ground-based spectrographs designed for complementary exoplanet characterization. The instrument’s principal objectives are the detection and characterization of extrasolar planets via space-based ultra-high precision photometry and the measurement of stellar parameters and architecture through asteroseismology and dynamical studies. PLATOSpec’s evolving design—spanning 26 modular cameras aboard the PLATO spacecraft and modern fiber-fed echelle spectrographs at sites like La Silla Observatory—reflects the technological and scientific requirements for large-scale exoplanet surveys, high-fidelity light curve analysis, and the combined use of radial velocity and spin–orbit diagnostics.

1. Instrument Architecture and Technical Design

PLATOSpec on-board PLATO spacecraft consists of 26 cameras: 24 “normal” units dedicated to wide-field photometric surveys and two “fast” cameras for high-cadence photometry and color information (Rauer et al., 8 Jun 2024). Each camera features a 12-cm aperture and a six-lens optical system with central CaF₂ lens and anti-reflection coatings optimized for 500–1000 nm. The focal plane in each normal camera comprises four full-frame CCDs (4510 × 4510 pixels, 15 arcsec/pixel), contributing to an overall field-of-view of ca. 2132 deg². The fast cameras operate with 2.5-second cadence in two color bands, serve bright target regimes (V = 4–8.2), and provide pointing error signals for the Fine Guidance System (FGS).

Mechanical and thermal stability is achieved via independent thermal control systems per camera (setpoint –80 °C; ±10 mK stability/14 hr), athermal optical tubes, and bipod mountings to decouple payload from spacecraft mechanical stresses. On-ground, PLATOSpec refers to a high-resolution (R ≈ 70,000) fiber-fed echelle spectrograph for the ESO 1.5m telescope, optimized for the blue-UV (360–680 nm) and engineered for CaII H&K chromospheric activity measurements and RV follow-up (Guenther et al., 2021, Zak et al., 13 Aug 2025).

2. Data Handling, Onboard Processing, and Network Infrastructure

Due to massive raw data volumes (hundreds of terabits daily), PLATOSpec’s data flow relies on a distributed processing architecture. Pairs of cameras feed into Data Processing Units (DPUs), which perform photon-event detection, stellar centroiding, and photometry using “imagettes” extracted at 25 s cadence (normal) or 2.5 s for fast cameras (Focardi et al., 2018). The DPUs reduce the outgoing science data by a factor >1000 before transfer.

Communications between Focal Plane Electronics, DPUs, and the Instrument Control Unit (ICU) are managed by a 100 MHz SpaceWire network in a cold-redundant topology; routing is controlled using RMAP and CCSDS/PUS protocols and dynamically reconfigured by the ICU's application software. Compression and time-synchronization are performed prior to transmission to the spacecraft Service Module and ultimately downlink to Earth.

A simplified data flow can be represented as:

Stage	Hardware	Processing Actions
CCD Detectors	FPA/Front-End Electronics	Signal digitization, temperature control
DPUs	Normal/Fast DPUs	Windowing, cropping, imagette extraction, preliminary photometry
ICU	18-channel SpW Router	Aggregation, compression, re-routing, time-tagging
Spacecraft Computer	Service Module	Final data handling, telemetry

3. Simulation, Optical Characterization, and Noise Modeling

End-to-end simulation of PLATOSpec performance is managed by PLATO Simulator/PLATOSim tools (Zima et al., 2010, Marcos-Arenal et al., 2014). These model CCDs, electronics, optics, stellar fields, jitter, and natural/instrumental noise sources. A key formalism for stellar photon counts is:

$$F_{\rm phot} = t_{\rm exp} \, F_0 \, T_\lambda \, Q_\lambda \, A \, 10^{-0.4m_\lambda}$$

Modeling incorporates:

• Photon shot noise ($\sigma_{\rm photon} = \sqrt{N_{\rm photon}}$),
• Readout noise, bias, dark current,
• Frame-transfer readout smearing,
• PRNU (with $1/f$ spatial power spectrum),
• Jitter displacements (with subpixel movements sampled from time-series),
• Crowding/confusion, saturation, charge-transfer inefficiency, cosmic ray impacts.

PSF modeling employs microscanning techniques that combine subpixel-displaced exposures via inverse methods (e.g., Landweber iteration) to reconstruct super-resolved PSFs (Ouazzani et al., 2014). The microscanning sequence is performed as an Archimedean spiral, optimizing calibration and achieving the subpixel knowledge necessary for weighted mask photometry and jitter correction. Onboard photometric extraction uses either aperture or weighted mask algorithms, with trade-offs between noise minimization and contamination mitigation.

4. Photometric and Stellar Simulation Tools

PLATO Solar-like Light-curve Simulator (PSLS) synthesizes time-domain light curves by building power spectral density (PSD) models including oscillatory, granulation, and magnetic activity components—a typical PSD is

$$\overline{\mathcal{P}}(\nu) = \mathcal{A}(\nu) + G(\nu) + O(\nu)$$

where $\mathcal{A}(\nu)$ (activity) and $G(\nu)$ (granulation) are Lorentzian and pseudo-Lorentzian profiles, and $O(\nu)$ (oscillations) comprises resolved Lorentzian or unresolved sinc$^2$ modes (Samadi et al., 2019). Instrumental effects simulated at the pixel level include:

• Jitter-induced noise,
• CCD systematics (charge transfer inefficiency, Brighter Fatter Effect, etc.),
• Mask update artifacts,
• Long-term stellar drift,
• PSF-induced variability (corrected via microscanning-based PSF inversion).

Simulated and real light curves (e.g., Kepler targets) display basic agreement in frequency domains relevant for asteroseismology and planetary transit detection.

5. Spectroscopic Follow-up and Stellar Activity Diagnostics

PLATOSpec at La Silla Observatory offers medium-precision RV (with ThAr lamp, <8 m/s stability; improvement possible to 4–5 m/s) and high-precision RV using an iodine cell (3 m/s for bright targets), designed to support transit-confirming and atmosphere-probing campaigns (Guenther et al., 2021, Zak et al., 13 Aug 2025).

The spectrograph configuration provides high throughput around 393–397 nm for Ca II H&K chromospheric lines, enabling indirect XUV radiation inference via empirical scaling relations such as

$\log F_{\rm XUV} = a\,\log F_{\rm Ca\,II} + b$

Ground-based Ca II H&K monitoring yields proxies for energetic stellar output, which influences exoplanet atmosphere photochemistry and erosion. Scheduling flexibility on modest aperture telescopes allows extensive monitoring, bridging to large-telescope programs (e.g., CUBES at VLT) capable of targeting fainter stars.

6. Exoplanet Dynamical Architectures: Rossiter–McLaughlin Measurements

With the commissioning of PLATOSpec, RV capabilities now allow precise spin–orbit angle measurements via the Rossiter–McLaughlin (RM) effect (Zak et al., 13 Aug 2025). High-cadence spectroscopy during transit is modeled to extract the projected angle ($\lambda$) and, with knowledge of orbital and stellar inclination, the true obliquity ($\psi$):

$$\cos\psi = \sin i_* \sin i \cos\lambda + \cos i_* \cos i$$

Recent first-light results include:

• WASP-35b: $\lambda = 1^{+19}_{-18}$° (aligned),
• TOI-622b: $\lambda = -4 \pm 12$°, $\psi = 16.1^{+8.0}_{-9.7}$° (aligned),
• K2-237b: $\lambda = 91 \pm 7$°, $\psi = 90.5^{+6.8}_{-6.2}$° (polar).

These observations indicate a mix of disc-driven and dynamical migration histories, with implications for the prevalence of polar orbits among close-in exoplanets, particularly for planets above the Kraft break and sub-Jovian mass regime (editor's term for the high-mass transition in host stars).

7. Scientific Impact, Challenge Areas, and Future Directions

PLATOSpec’s technical architecture and software simulations have enabled unprecedented photometric precision (50 ppm/hr for bright targets), robust seismic characterizations, and statistical analyses of planetary radii ($<$5%), masses ($<$10%), and ages ($<$10%) (Rauer et al., 8 Jun 2024). Multi-telescope observations and high-cadence data acquisition support nearly continuous complex datasets free of atmospheric and diurnal artifacts.

Challenges remain in systematic error minimization (jitter correction, crowding, long-term drifts), the inclusion of all relevant CCD effects, and capturing instrumental diversity among all cameras and ground-based spectrographs. Ongoing work extends simulation models, adaptive mask extraction, and empirical proxies for stellar activity and migration physics. The synergy between space-based PLATOSpec datasets and ground-based spectroscopic follow-up is central to planned comparative exoplanetology and population-level theories of planet formation and evolution.

In conclusion, PLATOSpec embodies a modular, stable, and high-precision instrumentation approach enabling both the large-scale statistical paper of exoplanets and host-star astrophysics, with rigorous foundation in simulation, calibration, and performance validation. The instrument continues to shape the scientific landscape of exoplanet research and stellar physics and remains a benchmark for the integration of space and ground-based observational resources.