# Unveiling Habitable Worlds with high precision astrometry for next-generation Direct Imaging missions like LIFE

Fabien Malbet, Lucas Labadie, Alessandro Sozzetti, Pierre-Olivier Lagage, Manon Lizzana, Alain Léger, Hugo Rousset, Fabrice Pancher, Sébastien Soler, Thierry Lépine, et al.

► To cite this version:

Fabien Malbet, Lucas Labadie, Alessandro Sozzetti, Pierre-Olivier Lagage, Manon Lizzana, et al. Unveiling Habitable Worlds with high precision astrometry for next-generation Direct Imaging missions like LIFE. Science and Technology for the Era of LIFE, Sascha Quanz; Ignasi Ribas, Nov 2025, Barcelone, Spain. **hal-05379383**

HAL Id: hal-05379383

https://hal.science/hal-05379383v1

Submitted on 24 Nov 2025

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Distributed under a Creative Commons Attribution 4.0 International License
# Unveiling Habitable Worlds with high precision astrometry for next-generation Direct Imaging missions like LIFE

F. Malbet (IPAG), L. Labadie (University. Cologne), A. Sozzetti (Obs. Torino/INAF), P.-O. Lagage (CEA Saclay), M. Lizzana (IPAG/CNES/CNRS), A. Léger (IAS), H. Rousset (IPAG), F. Pancher (IPAG), S. Soler (IPAG), T. Lépine (IOGS), M. Pinamonti (Obs. Torino), J. Amiaux (CEA Saclay), F. Ardellier (CEA Saclay).

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# Principle : relative and precise differential astrometry

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* The science target is at the center of the FOV

* We measure the offset angles between the target object (in the center) and the many reference stars

* The single measurement is repeated several times over the mission lifetime to reach the required accuracy on the target motion

* The detector calibration is done using interferometric modulated Young's fringes

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# Astrometry ultimate accuracy

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$$ \alpha = 0.33 \left( \frac{M_P}{1 M_\oplus} \right) \left( \frac{a_P}{1 \text{ AU}} \right) \left( \frac{M_\star}{1 M_\odot} \right)^{-1} \left( \frac{D}{10 \text{ pc}} \right)^{-1} \mu\text{as} $$

Solar system

<table><thead><tr><th rowspan="2"></th><th colspan="2">Giants planets</th><th colspan="2">Terrestrial planets</th></tr><tr><th>Jupiter@10pc</th><th>Saturn@20pc</th><th>Super Earth@5pc</th><th>Earth@10pc</th></tr></thead><tbody><tr><th>M<sub>P</sub> (M<sub>E</sub>)</th><td>300</td><td>100</td><td>3</td><td>1</td></tr><tr><th>a<sub>P</sub> (AU)</th><td>5</td><td>10</td><td>1</td><td>1</td></tr><tr><th>P (yr)</th><td>11</td><td>30</td><td>1</td><td>1</td></tr><tr><th>α (in μas)</th><td>500</td><td>170</td><td>2</td><td>0.3</td></tr></tbody></table>

Astrometry measures *P*, *α*, *i*, *e*, *ω*, *Ω*, *T*₀ → *M*<sub>P</sub> complementary to radial velocity measurements
# Effect of stellar activity

## Astrometrical signals

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### Expectations from the Sun located at 10pc

### Radial velocities

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Daily variations of the solar total irradiance (top panel), photocenter position in the east-west dimension (mid panel) and south-north dimension (lower panel) during 1996 -- 2007

Makarov et al. (2009, ApJ 707, L73); Lagrange, Desort, & Meunier (2010, A&A 512,

Astrometric jitter of a solar analog at 10 pc in the **equatorial dimension** : **0.052 µas**
- negligible compared to the Earth signal 0.3 µas

**Astrometry is not limited by stellar activity with stars x5 more active than the Sun**
# The need of Earth-like planets mass determination

Knowledge of the exoplanet mass with a precision better than 10% is required to retrieve in an unambiguous manner the composition of the atmosphere (presence of biosignatures) from the spectrum of the reflected light from an Earth like exoplanet (Damiano et al. 2025, AJ 169, 97).

Simulated spectra and data models for the
Modern and Archean Earth-like scenarios

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Posterior distribution functions for planetary mass, radius, and surface pressure for the Modern (left) and Archean (right) Earth-like planets

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The best way to get Earth-like mass is **astrometry, the most robust technique against the effect of stellar activity** and to determine the **true mass**.
# Star list for detecting biosignatures on possible Earth-like planets

## HWO candidate star lists

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## Detection techniques

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Built on existing direct imaging target lists and the results of yield calculations.

**Defined priority tiers of objects:**

- **Tier 1:** Most accessible targets for exoEarth direct imaging (164 stars)

- **Tier 2:** Targets with a med-to-high probability of being selected for survey, (659 stars)

- **Tier 3:** Nearby, bright stars that are potential HWO targets (12,944 stars)
# What has been detected around nearby solar-type stars?

126 exoplanets discovered around 63 FGK stars at *d* < 20 pc !

<figure><img src="image_19.png" /><figcaption>Number of exoplanet around nearby stars</figcaption></figure>

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Only 12% of nearby stars have known exoplanets so far
and mostly gaseous ones around late-type stars!
# What planetary components are we missing?

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# What planetary components are we missing?

<figure><img src="image_23.png" /><figcaption>## Exoplanets found around nearby stars</figcaption></figure>

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## Theia

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## Two space missions in view

<table><thead><tr><th>Theia</th><th>HWO</th></tr></thead><tbody><tr><td>ESA</td><td>NASA</td></tr><tr><td>Medium (M8)</td><td>Habitable World Observatory</td></tr><tr><td>0.8 m</td><td>7 m</td></tr><tr><td>~2040</td><td>~2040</td></tr><tr><td>L2 lissajous</td><td>L2 lissajous</td></tr><tr><td>[450 nm - 900 nm]</td><td>[450 nm - 900 nm]</td></tr><tr><td>160 mas</td><td>14 mas</td></tr><tr><td>30x30 arcmin<sup>2</sup></td><td>4x3 arcmin<sup>2</sup></td></tr><tr><td>22.500 x 22.500 px<sup>2</sup></td><td>34.300 x 25.700 px<sup>2</sup></td></tr><tr><td>~500 MP</td><td>~900 MP</td></tr></tbody></table>

Missions require a **gigapixel** focal plane

## HWO

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# Which gigapixel detectors ?

## Instrument for relative Astrometry Measurement

### Baseline detector solution:

- 4 Pyxalis CMOS GigaPyx 220 MP

- 3 GigaPyx 14 MP at the center

- ~1 Gigapixel focal plane

**Pyxalis GigaPyx**
sensor family

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GigaPyx (220 MP)

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### Alternative Detectors:

- Teledyne e2V CIS 300: larger pixels (10.0 µm)

- Sony IMX 411: micro-lens array (3,8 µm calibration issue)

- Gpixel GSENSE 1517: larger pixels (15.0 µm)

Teledyne e2v (81 MP)

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Sony (150 MP)

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Gpixel (81 MP)

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# Performance of current Pyxalis GP 46MP detectors

46Mpx Gigapyx already integrated on IPAG testbed, high performance compliant with Pyxalis measurements

Mission calibration currently tested on IPAG bench (optical distortion and focal plane geometry)

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pyxalis
Your Image Sensor Solution

<table><thead><tr><td></td><td>Pyxalis</td><td>IPAG</td></tr></thead><tbody><tr><td>Read out noise</td><td>1.6 e-</td><td>0.8 e-</td></tr><tr><td>Linearity</td><td>&lt; 3%</td><td>0.5%</td></tr><tr><td>Bad pixels</td><td>0.1%</td><td>0.04%</td></tr><tr><td>Response non uniformity</td><td>2%</td><td>0.8%</td></tr><tr><td>Full well (low gain)</td><td>50 000 e-</td><td>-</td></tr></tbody></table>

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Funded by
LabEx
FOCUS

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**Measured performances are compliant** with an astrometric instrument onboard HWO or Theia to detect Earth-like planets
# Telescope calibration : using reference stars to monitor the distortion

<figure><img src="image_43.png" /><figcaption>Distortion can be corrected by fitting the transformation (Sky -> Detector) as calculated by Ray-tracing (Zemax) by a 2D polynomial</figcaption></figure>

<figure><img src="image_44.png" /><figcaption>Simulated field-dependent distortion and fitted position</figcaption></figure>

Error between fitted and true positions

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Simulation results

~100 reference stars in 0.5 deg FOV (ie. $V \le 15$mag) required to reach accuracy better than 5e-6 pix.

Number of stars required to fit the distortion
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# Reaching Technical Readiness Level 3 for future astrometry focal plane instruments

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# Astrometric error budget with Theia and HWO

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Unwin et al. (2008)
# Conclusion

<figure><img src="image_50.png" /><figcaption>Theia</figcaption></figure>

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## Science: high precision astrometry can detect Earth-like planets

- Ultra-precise differential astrometry can detect signals down to a few µas

- Sensitive to relatively wide orbits (up to 3 AU) depending on mission duration

- Census of cool earth-like exoplanets around solar-type stars within ~20 pc

- Characterization of planetary system architectures: mass, inclination, eccentricity

- Measurement of planetary masses is key to formation & structure models

## Technology: focal plane architecture and calibration system

- Theia and HWO missions utilize gigapixel focal planes

- Pyxalis GigaPyx CMOS sensors demonstrate good performance: low noise, excellent linearity and uniformity.

- Calibration system reaches the precision required

- **Goal to achieve TRL-3** with validated focal-plane and metrology testbeds by 2030

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To reach LIFE objective, a precise characterization of target planets is essential: masses and orbital parameters. High precision astrometry can measure these masses and identify targets for LIFE.