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Exoplanets in reflected starlight with dual-field interferometry and a fifth Unit Telescope at VLTI

Óscar Carrión-González, Sylvestre Lacour, Mathias Nowak

TL;DR

The paper addresses the challenge of directly imaging mature exoplanets in reflected light by proposing a VLTI upgrade with a fifth Unit Telescope to enable four ~200 m baselines in the North-West, leveraging dual-field interferometry and GRAVITY/GRAVITY+ to improve inner working angles and contrast. It presents a near-term methodological pathway combining high-contrast interferometry with extended UV coverage to access a larger nearby exoplanet population, supported by simulations showing substantial gains in detectability in band I. Key findings include potential detections of up to 48 of 451 known nearby planets (with some targets reachable in under 3 hours) and the accessibility of Proxima Centauri b, highlighting the synergy with space missions for multi-wavelength orbital characterization. The proposed design aims to deliver practical gains in ground-based high-contrast imaging, enabling complementary follow-up and atmospheric studies across facilities.

Abstract

In this white paper, we propose an upgrade to the Very Large Telescope Interferometer (VLTI) consisting of the addition of a new 8m Unit Telescope (UT5). The primary goal of this upgrade is to optimise the VLTI for exoplanet detection by creating four additional baselines of approximately 200m oriented toward the north-west. The inclusion of this telescope would reduce the inner working angle and improve the achievable contrast of the VLTI, thereby enabling the detection of mature exoplanets in reflected light.

Exoplanets in reflected starlight with dual-field interferometry and a fifth Unit Telescope at VLTI

TL;DR

The paper addresses the challenge of directly imaging mature exoplanets in reflected light by proposing a VLTI upgrade with a fifth Unit Telescope to enable four ~200 m baselines in the North-West, leveraging dual-field interferometry and GRAVITY/GRAVITY+ to improve inner working angles and contrast. It presents a near-term methodological pathway combining high-contrast interferometry with extended UV coverage to access a larger nearby exoplanet population, supported by simulations showing substantial gains in detectability in band I. Key findings include potential detections of up to 48 of 451 known nearby planets (with some targets reachable in under 3 hours) and the accessibility of Proxima Centauri b, highlighting the synergy with space missions for multi-wavelength orbital characterization. The proposed design aims to deliver practical gains in ground-based high-contrast imaging, enabling complementary follow-up and atmospheric studies across facilities.

Abstract

In this white paper, we propose an upgrade to the Very Large Telescope Interferometer (VLTI) consisting of the addition of a new 8m Unit Telescope (UT5). The primary goal of this upgrade is to optimise the VLTI for exoplanet detection by creating four additional baselines of approximately 200m oriented toward the north-west. The inclusion of this telescope would reduce the inner working angle and improve the achievable contrast of the VLTI, thereby enabling the detection of mature exoplanets in reflected light.

Paper Structure

This paper contains 3 sections, 2 figures.

Table of Contents

  1. A journey toward direct imaging of mature exoplanets
  2. Unique questions answered with an extended VLTI
  3. Physical implementation of the fifth UT

Figures (2)

  • Figure 1: Overview of current and predicted contrast limits for present and future direct-imaging instruments. Red squares represent directly detected exoplanets, and blue triangles show the contrast predictions for radial-velocity exoplanets. Figure from lacouretal2025AA...694A.277L, see Fig. 11 therein.
  • Figure 2: Contrast limit of a dual-field interferometer using the current four-UT configuration of the VLTI (left panel), compared to the proposed five-UT configuration (right panel). Figure from lacouretal2025AA...694A.277L.