arxiv: 2604.09020 · v1 · submitted 2026-04-10 · 🌌 astro-ph.IM · astro-ph.EP

Recognition: unknown

Recent development in high-precision high-fidelity spectrographs for exoplanet research and characterization

Fran\c{c}ois Bouchy , Francesco Pepe , Xavier Dumusque , Tobias Schmidt , Christophe Lovis , St\'ephane Udry

Authors on Pith no claims yet

Pith reviewed 2026-05-10 17:22 UTC · model grok-4.3

classification 🌌 astro-ph.IM astro-ph.EP

keywords exoplanetsradial velocityspectrographsprecision measurementsplanet detectionhigh fidelityinstrument developmentstellar variability

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The pith

ESPRESSO, NIRPS, ANDES and RISTRETTO are designed to deliver sub-m/s radial velocity precision for detecting Earth-mass exoplanets.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Detecting Earth-mass exoplanets requires measuring stellar radial velocities to a precision of less than one meter per second. This level of accuracy can only be reached by minimizing every instrumental imperfection and accounting for stellar surface variations. The paper outlines the design and capabilities of four new spectrographs developed specifically for this challenge. ESPRESSO operates in the visible, NIRPS in the near-infrared, ANDES is planned for a future extremely large telescope, and RISTRETTO focuses on high-contrast targets. Together they represent the current state of the art in precision instrumentation for exoplanet research.

Core claim

The paper presents the recent development of four high-precision high-fidelity spectrographs—ESPRESSO, NIRPS, ANDES, and RISTRETTO—that are designed to overcome all sources of instrumental and stellar instabilities, thereby achieving the sub-m/s radial-velocity precision essential for detecting and characterizing Earth-mass exoplanets.

What carries the argument

High-fidelity spectrographs that combine extreme environmental stability, precise wavelength calibration, and advanced data reduction to extract radial velocities at the sub-meter-per-second level.

If this is right

Terrestrial planets can be discovered around Sun-like stars in their habitable zones.
Accurate masses for transiting planets will reveal their bulk densities and compositions.
Exoplanet population statistics will improve with detections down to Earth masses.
These instruments will support follow-up observations for planets found by transit surveys.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Parallel progress in modeling stellar jitter will be necessary to extract the smallest planetary signals.
Data from these spectrographs could be combined with astrometry or direct imaging for complete system characterizations.
Long-term monitoring programs will test whether the precision holds over years of operation.

Load-bearing premise

The new spectrographs will in practice reach and sustain the sub-m/s radial velocity precision once all instrumental and stellar instabilities are addressed.

What would settle it

A demonstration that the radial velocity scatter on inactive stars remains above 1 m/s after applying all corrections would show that the precision target has not been met.

Figures

Figures reproduced from arXiv: 2604.09020 by Christophe Lovis, Fran\c{c}ois Bouchy, Francesco Pepe, St\'ephane Udry, Tobias Schmidt, Xavier Dumusque.

**Figure 1.** Figure 1: (Left) ESPRESSO vacuum chamber delivered on the VLT platform (Credit: Francesco Pepe). (Right) ESPRESSO team during a commissioning phase (Credit: ESO/Giorgio Calderone). 2.2 Observing with ESPRESSO The main instrument characteristics in the various observing configurations and instrument modes are summarized in [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗

**Figure 2.** Figure 2: (Left) Vaccum vessel of NIRPS spectrograph in the Coude Room of the 3.6m telescope. ´ (Right) Screenshot of the NIRPS first light made on 17 May 2022 showing a portion of the raw spectra, the guiding camera and the AO wave-front sensor (Credit: Franc¸ois Bouchy). 3.1 A dedicated design for high-fidelity nIR spectroscopy The NIRPS instrument includes a Front-End at the Cassegrain focus, linked via optical … view at source ↗

**Figure 3.** Figure 3: (Left) Picture of the construction of ELT@ESO (Credit: ESO). (Right) ANDES architectural design (from Marconi et al, 2024). 4.2 The ELT-ANDES project ANDES (ArmazoNes high-Dispersion Echelle Spectrograph), previously known as HIRES, is the optical/near-IR high-resolution spectrograph for the ELT (Marconi et al, 2022, 2024). It is made of three fiber-fed spectrographs spanning the BV, RIZ and YJH wavelength… view at source ↗

**Figure 4.** Figure 4: Schematic of the RISTRETTO instrument (from Lovis et al, 2022) 5.2 Exoplanets in reflected light Over the past three decades, RV surveys have discovered many exoplanets orbiting very nearby stars. Some of them reach angular separations at maximum elongation that are large enough to make them resolvable by 8-m-class telescopes in the visible. We used the NASA Exoplanet Archive and the RISTRETTO simulator to… view at source ↗

**Figure 5.** Figure 5: Chromatic drift of the ESPRESSO FP etalon, as inferred from the ThAr calibration, over a period of 900 days (top). Difference of inferred stellar RVs from two nights separated by 1078 days (bottom). Using the old data reduction system, which did not yet take this effect into account, the measurements exhibit a chromatic pattern that clearly resembles the inverse of the FP drift. In the new DRS, the FP is f… view at source ↗

**Figure 6.** Figure 6: Comparison between ESPRESSO ThAr/FP and LFC wavelength solutions from Schmidt and Bouchy (2024). Assuming a Gaussian LSF (light colors in the background) leads to significant intra-order modulations and discrepancies between fibers and slices up to 30 m/s, in particular for the blue arm. Using the accurate, non-parametric LSF model (strong colors) one achieves an excellent agreement between fibers and slic… view at source ↗

**Figure 7.** Figure 7: this solar telescope started operating in July 2015 and has now obtained 10 years of nearly continuous data, with several hours of observations per day (Collier Cameron et al, 2019; Dumusque et al, 2021; Al Moulla et al, 2023, Dumusque et al. 2025 in prep.). Attempts to observe the Sun with a lens directly focusing the solar disk into an optical fiber showed clearly guiding limitations at the m s−1 level (… view at source ↗

read the original abstract

High-precision high-fidelity spectrographs are the most powerful instruments for exoplanets detection and characterization. The sub-m/s radial-velocity precision, required to detect Earth-mass exoplanets, necessitates tackling all the sources of instrumental and stellar instabilities. We present the new high-precision high-fidelity spectrographs ESPRESSO, NIRPS, ANDES and RISTRETTO designed, developed, and operated with support of PlanetS.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This is a descriptive status report on four RV spectrograph projects with no performance data or new measurements.

read the letter

The paper compiles basic design and development details for ESPRESSO, NIRPS, ANDES, and RISTRETTO, all tied to the PlanetS effort and aimed at sub-m/s radial-velocity work for exoplanets. It frames them as responses to the need for higher precision to find Earth-mass planets, but stays at the level of project overviews and goals. What it does reasonably is gather the current status of these instruments into one short document, which saves time for anyone tracking instrumentation in the field. The descriptions appear straightforward and cite the supporting collaboration without obvious overclaims in the abstract. The soft spot is the complete absence of actual performance numbers, error budgets, on-sky tests, or verification against the sub-m/s target. Without those, the central point reduces to stating that the instruments exist and are being developed, which is not a new technical result. The underlying spectrograph approach itself is already established in prior work, so the novelty is limited to the specific project updates. This kind of paper is mainly useful for instrument teams, observatory planners, or exoplanet observers who need a quick reference on what hardware is coming online. It does not contain derivations, data, or predictions that would require heavy scrutiny. I would send it to peer review if the journal accepts instrument-status pieces, mainly to check for missing details on timelines and achieved precisions rather than to evaluate a scientific claim.

Referee Report

0 major / 1 minor

Summary. The manuscript provides an overview of recent developments in high-precision spectrographs for exoplanet research, focusing on ESPRESSO, NIRPS, ANDES, and RISTRETTO. These instruments are presented as designed, developed, and operated with PlanetS support to achieve the sub-m/s radial-velocity precision necessary for detecting Earth-mass exoplanets by addressing instrumental and stellar instabilities.

Significance. If the instrument descriptions are accurate, this work is significant as a status report documenting key projects that could enable detection of Earth-like exoplanets. It contributes to the field by summarizing technical approaches to high-fidelity spectroscopy and PlanetS-supported initiatives, serving as a useful reference for the community.

minor comments (1)

The abstract states that the instruments tackle 'all the sources of instrumental and stellar instabilities' but provides no quantitative error budget or verification approach; adding a brief summary of design mitigations would strengthen the presentation.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript and for recommending minor revision. The report correctly identifies the paper as an overview of PlanetS-supported high-precision spectrographs (ESPRESSO, NIRPS, ANDES, and RISTRETTO) aimed at sub-m/s radial-velocity precision for exoplanet detection. No specific major comments were raised in the report.

Circularity Check

0 steps flagged

No significant circularity in descriptive instrument overview

full rationale

The paper is a descriptive overview of four spectrograph projects (ESPRESSO, NIRPS, ANDES, RISTRETTO) and their development with PlanetS support. It contains no derivations, equations, fitted parameters presented as predictions, or load-bearing self-citations. The central content is factual presentation of instrument design and status rather than any claim that reduces to its own inputs by construction. This is a standard non-circular finding for purely descriptive instrument papers with no mathematical chain.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The abstract contains no mathematical model, free parameters, axioms, or invented physical entities.

pith-pipeline@v0.9.0 · 5382 in / 976 out tokens · 33863 ms · 2026-05-10T17:22:49.183470+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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