# Exploring the architectures of nearby exoplanetary systems using high-precision space astrometry

Fabien Malbet, M. Lizzana, A. Léger, G. Mamon, L. Labadie, A. Sozzetti, T.

Lépine, R. Goullioud

► To cite this version:

Fabien Malbet, M. Lizzana, A. Léger, G. Mamon, L. Labadie, et al. Exploring the architectures of nearby exoplanetary systems using high-precision space astrometry. Exoplanets 5, Jun 2024, Leiden, Netherlands. . hal-04704208

HAL Id: hal-04704208

https://hal.science/hal-04704208v1

Submitted on 20 Sep 2024

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# Exploring the architectures of nearby exoplanetary systems using high-precision space astrometry

F. Malbet (1), M. Lizzana (1,2), A. Léger (3), G. Mamon (4), L. Labadie (5), A. Sozzetti (6), T. Lépine (7), R. Goullioud (8), and Theia collaboration (9)

See poster 1180 (M. Lizzana)
for instrumental results

## Principle of Theia : relative and precise differential astrometry

<figure><img src="image_5.png" /></figure>

* The science target is at the center of the FOV

* We measure the offset angles between the target object (in **black**) and the reference stars (other stars in **red** and **blue**)

* 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

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

## Improvement compared to Gaia

<table><thead><tr><th></th><th>Gaia post-launch</th><th>Theia</th><th>improvement</th></tr></thead><tbody><tr><td>Telescope Aperture</td><td>1.49 x 0.54 = 0.80 m²</td><td>0.8 → 0.50 m²</td><td>0.62</td></tr><tr><td>Field of view</td><td></td><td>0.5 deg</td><td></td></tr><tr><td>Coverage</td><td>Survey</td><td>Pointed</td><td></td></tr><tr><td>Astrometry</td><td>Global</td><td>Differential</td><td></td></tr><tr><td>Exposure time per field</td><td>76 x 9 (CCD) x 4.4 sec = 0.84 hr</td><td>25 x 40 hr = 1000 hr</td><td>1200</td></tr><tr><td>Additional factors</td><td colspan="3">2D vs 1D astrometry: 1.4, Gaia Stray light: 1.9</td></tr><tr><td>Proper motion accuracy G=10 star</td><td>3.5 µas/yr</td><td>0.11 µas/yr</td><td>30</td></tr><tr><td>Proper motion accuracy G=15 star</td><td>14 µas/yr</td><td>0.4 µas/yr</td><td>35</td></tr><tr><td>Proper motion accuracy G=20 star</td><td>330 µas/yr</td><td>5 µas/yr</td><td>66</td></tr></tbody></table>

<figure><img src="image_8.png" /></figure>

## Exoplanets primary goal : Earth-mass planets in HZ in the vicinity of the Sun

<figure><img src="image_9.png" /><figcaption>Complete census of exo-Earths, superEarths and mini-Neptune (M< 5 M_Earth) orbiting our 50 nearest Solar-type stars</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Averaging 10000 random exoplanets distributions around the 50 target stars (Crouzier 2014).</figcaption></figure>

## Theia mission profile

* ESA-led, ESA-operated mission with consortium funded payload (this is the normal type of ESA mission)

* Submitted for the **ESA M7 call** as an Ariane 6.02 launch

* Spacecraft dry mass with margin: 1063 kg. Total launch Mass: 1325 kg

<figure><img src="image_11.png" /></figure>

<table><tr><td>Launch date</td><td>No constraints, allowing launch date in 2037</td></tr><tr><td>Orbit</td><td>Large Lissajous in L2</td></tr><tr><td>Lifetime</td><td><ul><li>4 years of nominal science operations</li><li>Technical operations: 6 months orbit transfer plus instrument commissioning and 1 month decommissioning</li></ul></td></tr><tr><td>Concept</td><td>Single spacecraft, single telescope in the PLM, single camera in the focal plane, metrological monitoring of PLM</td></tr><tr><td>Communication architecture</td><td>75 Mbps, 4h/day</td></tr></table>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

## Affiliations

1. Univ. Grenoble Alpes CNRS IPAG, Grenoble, France

2. CNES, Paris, France

3. Univ. Paris Saclay CNRS IAS, Orsay, France

4. Sorbonne Univ. CNRS IAP, Paris, France

5. Univ. Cologne, Cologne, Germany

6. INAF Oss. Di Torino, Turin, Italy

7. Univ. Jean Monnet, CNRS, IOGS, Curien lab, Saint Etienne, France,

8. JPL, Pasadena, USA

9. http://theia.phyip3.dur.ac.uk/

## Astrometry: parallax, proper motion and reflex motion

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

Proper Motion + Parallax → Residuals where (a) plots RA and DEC positions while (b,c) are positions with time and (d, e) are period-aram for each direction

<figure><img src="image_17.png" /></figure>

Unwin et al. (2008) ; Malbet et al. (2012)

## Theia's main science based on high precision astrometry

<figure><img src="image_18.png" /></figure>

## Advantages and limitations of high precision astrometry

<figure><img src="image_19.png" /><figcaption>Sun's astrometric position due to activity (1996-2007)</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>Earth astrometric signature @10pc</figcaption></figure>

<figure><img src="image_21.png" /><figcaption>Earth astrometric signature @10pc</figcaption></figure>

Detection limits have been revisited by Meunier & Lagrange (2023) through a blind test method and found lower detection limits, except for a handful of stars,

showing that it is probably possible to reach lower masses.

<figure><img src="image_22.png" /></figure>

## Theia instrumental concept

Specifications
Diffraction-limited 0.5° FOV
~ 30,000 x 30,000 pixels
≤ 1 billion pixels

### Proposed implementation (M7)

<figure><img src="image_23.png" /></figure>

But new large CMOS detectors with smaller pixels !

<figure><img src="image_24.png" /><figcaption>Fig. 14. A huge area, 203 mm x 179 mm, 1.8 Billion pixels CIS (Left: A photograph of the exposure shot map placement and the sensor fabricated on 12 inch; Right: the corresponding wafer image.) Zhu et al. (2016)</figcaption></figure>

Pixels of ~4µm
=≈ array of 12 cm x 12 cm,
(i.e. 30k x 30k detector)
can be manufactured on a wafer of 12" (300mm)

## References

- Crouzier, A., Malbet, F., Henault, F., et al. 2016, A&A, 595, A108

- Malbet, F., Boehm, C., Krone-Martins, A., et al. 2021, Experimental Astronomy 51, 845

- Malbet, F., Labadie, L., Sozzetti, A., et al. 2022, in Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series, Vol. 12180, Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave, eds. L. E. Coyle, S. Matsuura, & M. D. Perrin, 121801F

- Shao, M., Zhai, C., Nemati, B., et al. 2023, PASP, 135, 074502 527