# Theia and HWO astrometric power for Giant Exoplanets around solar-type stars

Fabien Malbet, L. Labadie, A. Sozzetti, P.-O. Lagage, M. Lizzana, A. Léger, H. Rousset, F. Pancher, S. Soler, T. Lépine, et al.

► To cite this version:

Fabien Malbet, L. Labadie, A. Sozzetti, P.-O. Lagage, M. Lizzana, et al. Theia and HWO astrometric power for Giant Exoplanets around solar-type stars. 30th anniversary of the discovery of planet 51 Peg b, cool giant planets and their systems, Boisse, Isabelle; Vigan, Arthur, Oct 2025, Observatoire Haute Provence, France. hal-05304690

HAL Id: hal-05304690

https://hal.science/hal-05304690v1

Submitted on 8 Oct 2025

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Distributed under a Creative Commons Attribution 4.0 International License
# Theia and HWO astrometric power for Giant Exoplanets around solar-type stars

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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51 Peg
G2IV,
G=5.3 mag

Earth-mass planet around a Solar-type star @ 15pc

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# How to find planetary systems around nearby solar-type stars ?

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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, a, i, e, ω, Ω, T₀ → M_P

Mostly limited by the mission duration for cool giant exoplanets!
# What planetary components are we missing?

<figure><img src="image_9.png" /><figcaption>## Exoplanets found around nearby stars</figcaption></figure>

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# What planetary components are we missing?

<figure><img src="image_11.png" /><figcaption>## Exoplanets found around nearby stars</figcaption></figure>

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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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<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

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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
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# Reaching Technical Readiness Level 3 for future astrometry focal plane instruments

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# Astrometric error budget for bright targets with Theia and HWO

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Unwin et al. (2008)
# Conclusion

<figure><img src="image_33.png" /><figcaption>Theia</figcaption></figure>

<figure><img src="image_34.png" /><figcaption>HWO</figcaption></figure>

**Science**: high precision astrometry can probe Giant Exoplanets

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

- Sensitive to relatively **wide orbits** ($a > 3$ AU) depending on mission duration

- Census of cool giant 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**: same focal plane architecture and calibration system

- Both 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

<figure><img src="image_35.png" /><figcaption>Focal plane</figcaption></figure>