LIRA

Successful separation of the transfer module from the BepiColombo mission

Raphael PERALTA — 2026-09-08T07:22:59Z

After nearly eight years of travelling through the Solar System, BepiColombo is finally beginning its approach to Mercury. A major milestone was reached on 3 September 2026 at 3.49 pm, with the successful separation of the Mercury Transfer Module (MTM) from the MPO and Mio probes. On board these two orbiters, two instruments designed at LIRA are set to explore the surface and magnetic environment of the planet closest to the Sun.

BepiColombo: Unravelling the mysteries of Mercury

Figure 1 - Image taken by a webcam on board BepiColombo, showing the probe during a flyby of the planet.

Credit: ESA

BepiColombo is a joint space mission by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), launched on 19 October 2018 from the Guiana Space Centre in Kourou. Its objective: to reach Mercury, the smallest planet in the Solar System and the closest to the Sun, to unravel its mysteries following several decades of limited exploration.

Due to its proximity to the Sun, which makes any mission particularly complex to design, Mercury remains one of the least studied terrestrial planets. Only two probes had approached it before BepiColombo: Mariner 10, which carried out simple flybys in 1974 and 1975, and MESSENGER, which entered orbit between 2011 and 2015, albeit with limited instrumentation. However, studying Mercury provides a better understanding of the formation of so-called ‘inner' planets, those close to their star – a category to which Earth also belongs.

The BepiColombo mission aims to map the entire surface of the planet in high resolution, to verify the presence of water ice in the polar craters, and to understand the origin of its magnetic field – a feature it shares with Earth amongst the terrestrial planets.

To achieve these objectives, BepiColombo comprises two orbiters: JAXA's Japanese probe Mio (Mercury Magnetospheric Orbiter), equipped with five instruments, and ESA's MPO (Mercury Planetary Orbiter), equipped with 11 instruments. The entire assembly is transported to Mercury by the Mercury Transfer Module (MTM), using its ion propulsion system – employed for the first time on a European interplanetary mission – combined with gravitational assists from various planets during numerous flybys, including Mercury.

Two LIRA instruments set out to explore Mercury

Figure 2 - Artist's impression of the separation of the Mercury Transfer Module (MTM) from the BepiColombo mission

After nearly eight years of travel, 10.2 billion km and nine flybys of planets, including six of Mercury, the MTM, in the foreground, separated from the two scientific orbiters, MPO (ESA) and Mio (JAXA), in the background.

Credit: ESA

LIRA plays a major scientific and technical role in the BepiColombo mission, through the design and manufacture of two of the sixteen instruments on board.

LIRA has developed VIHI (Visual and Infrared Hyperspectral Imager), one of the three channels of the SIMBIO-SYS instrument carried on the MPO probe. This spectro-imager will produce a comprehensive mineralogical map of Mercury's surface between 400 and 2000 nm, with a spatial resolution of up to 100 m in certain targeted areas. By cross-referencing mineralogical composition with surface morphology, these data will provide a better understanding of the processes of differentiation, heating and surface ageing that have shaped the planet throughout its history.

The laboratory has also designed SORBET, a high-frequency radio receiver integrated into the PWI (Plasma Waves Investigation) experiment, carried on board the Mio satellite. Operating between 2.5 kHz and 10 MHz, this instrument will, for the first time, study Mercury's magnetosphere and its interaction with the solar wind using radio frequencies, combining remote and in situ measurements – an approach that will enable the characterisation of both the overall structure of the planet's magnetic field and the local phenomena occurring within it.

Final stage before BepiColombo's arrival

Figure 3 - Photograph of the display screen during the Mercury 2026 symposium, showing the live feed from ESA of the signal sent by the MTM confirming that the two orbiters had separated successfully, 3 September 2026 at 3.49 pm.

Credit: Alain Doressoundiram

After nearly eight years of travel, a major milestone in the BepiColombo mission has just been reached: on 3 September 2026 at 15:49 (see Figure 3), the MTM successfully separated from the two scientific orbiters, MPO and Mio. This manoeuvre marks the start of the mission's arrival phase around Mercury, one of the most complex sequences ever carried out by the European Space Agency.

MPO and Mio are now continuing their journey together, before commencing, in November 2026, a series of manoeuvres designed to place them into orbit around Mercury. This orbital insertion is one of the most delicate phases of the mission: the probe will need to be slowed down sufficiently to be captured by Mercury's gravity, without risking a collision with the planet, all whilst in an environment where the Sun's gravitational pull remains extremely strong.

Once this stage is complete, MPO and Mio will remain attached for a few more weeks, whilst their shared orbit stabilises. They will then separate in December 2026: each will enter its own dedicated scientific orbit, differing in altitude and inclination and tailored to the measurements it is to carry out. This final separation will mark the true start of the mission's scientific phase, scheduled to last for a nominal period of approximately one year.

Adrien Girardot's thesis defence on Tuesday 29 September 2026

Raphael PERALTA — 2026-09-03T09:45:09Z

Adrien Girardot's thesis defence will take place on Tuesday 29 September at 2.00 pm in the Evry Schatzman lecture theatre.

It can be watched live on the LIRA YouTube channel

Thesis title

Development of spectropolarimeters for the near to far ultraviolet: from design to experimental validation.

Composition of the jury

Antonella Barucci (Astronome, LIRA) : President of the jury
Thierry Lépine (Professeur associé, Institut d'Optique) : referee
Frans Snik (!Professeur associé, Leiden University) : referee
Evelyne Alecian (chercheur CNRS, IPAG) : examiner
Jean-Claude Bouret (Directeur de recherche CNRS, LAM) : examiner
Juan Larruquert (Professeur, CSIC) : examiner
Frank Brachet (CNES) : invited
Coralie Neiner (CNRS Directrice de recherche , LIRA) : supervisor
Jean-Michel Reess (Ingénieur de recherche, LIRA) : co-supervisor

Abstract

Spectropolarimetry (the measurement of the intensity and polarisation of light as a function of wavelength) enables unique measurements in astrophysics: among other things, it gives access to stellar magnetic fields through the Zeeman and Hanle effects, to the geometry of unresolved circumstellar media through scattering, and to exoplanetary atmospheres. The ultraviolet domain is particularly valuable in this respect, as it concentrates the resonance lines of hot, highly ionised plasmas as well as the Lyman-α line; yet no broadband spectropolarimeter currently operates there. The polarised signatures of interest are weak (typically below 0.1 % of the intensity), which imposes a demanding polarimetric measurement accuracy requirement, of the order of 10⁻³.

This thesis presents the development of ultraviolet spectropolarimeters, from optical design to experimental validation, in the framework of three space missions: the CASSTOR demonstrator, the Polstar SMEX proposal, and the Pollux instrument concept for NASA's future flagship mission, the Habitable Worlds Observatory (HWO). These missions share a common polarimetric principle but split into two different technological approaches dictated by wavelength.

In the near- and mid-ultraviolet (118-380 nm), where transmissive birefringent components remain usable, a Stokes-Mueller formalism was developed to model, optimise, and tolerance polarimeters based on rotating stacks of thin MgF₂ plates. I applied it to the CASSTOR, Polstar, and Pollux polarimeters. I designed, assembled, and aligned a dedicated vacuum test bench. Its first light and the first reconstruction of polarisation states are reported here.

Below 120 nm, where no transmissive birefringent material exists, a fully reflective architecture is required. I adapted the same Stokes-Mueller formalism to enable the development, design, and tolerancing of the Pollux FUV polarimeter (a rotating K-mirror modulator followed by an analyser mirror). I adapted the test bench to this wavelength range, and a first FUV analyser (MgF₂ on B₄C) was manufactured in collaboration with a Madrid-based team.

These developments raise the maturity of UV polarimeter technologies and feed directly into the design of the Pollux UV spectropolarimeters for the future HWO space mission.

The fastest star in the Milky Way orbits so close to our supermassive black hole that it is affected by its rotation

Raphael PERALTA — 2026-08-31T15:53:00Z

Thanks to the capabilities of GRAVITY+ and new analytical methods developed in particular at LIRA, an international team has discovered S301, a star skimming past the supermassive black hole at the heart of our Galaxy at nearly 25,000 km/s, coming within a distance comparable to that between the Sun and Saturn. This record-breaking star now provides a unique laboratory for testing general relativity and paves the way for the first measurement of the rotation of Sagittarius A*.

GRAVITY+ pushes the boundaries and uncovers a record-breaking star

Figure 1 – Illustration of the positions of the stars orbiting the supermassive black hole Sagittarius A*, as measured by ESO's GRAVITY+ instrument.

These observations reveal the frenzied dance of the stars as they are subjected to the immense gravitational pull of the black hole, whose mass is estimated at 4.3 million times that of the Sun. Among them, S301 reaches a record speed of 25,000 km/s – 8 per cent of the speed of light – in a highly elliptical orbit that brings it, at its closest, to just 12 astronomical units from the black hole – roughly the distance between the Sun and Saturn.

Credit: ESO/Collaboration GRAVITY

For many years, a systematic observation programme – in which the LIRA team is involved – has been working to map, with ever-increasing precision, the vicinity of Sagittarius A* (Sgr A*), the supermassive black hole with a mass of 4.3 million solar masses located at the centre of our Galaxy. LIRA has notably contributed to the design of GRAVITY, which combines the light from the four giant telescopes of ESO's Very Large Telescope (VLT) in Chile. The instrument has enabled the frenzied dance of the stars around Sgr A* to be observed with unprecedented precision. Among them, S29 previously held the speed record, reaching nearly 8,740 km/s – 3 per cent of the speed of light – as it passed closest to the black hole. By way of comparison, the Earth orbits the Sun at just 29.8 km/s.

As observational techniques advance, astronomers are able to detect stars that are ever fainter and closer to the black hole. GRAVITY is therefore evolving into GRAVITY+, a significantly improved version to which LIRA is actively contributing. New adaptive optics systems, laser guide stars and new methods of data analysis are pushing the instrument's limits even further. It was thus in the spring of 2023 that a previously invisible star appeared: S301 (see Figure 1). By tracking its orbit, scientists discovered that it smashes the previous record set by S29, reaching 25,000 km/s – nearly three times as fast. This discovery directly illustrates how the continuous improvement of observational techniques is revealing celestial bodies that were previously beyond our reach.

And S301 is breaking record after record. It completes one revolution around the black hole in just 8.7 years, in a highly elliptical orbit that brings it, at its closest, to within just 12 astronomical units of Sgr A* — roughly the distance between the Sun and Saturn. It thus becomes the star known to have the shortest orbital period and the tightest orbit around the galactic centre, passing ten times closer to the black hole than the closest star known until then. This feat is all the more remarkable given that S301 shines two billion times fainter than Betelgeuse, in the midst of a region where light sources are almost indistinguishable. Picking out its signal is like hearing the buzz of a fly amidst a symphony orchestra! Yet it was possible to distinguish it from its neighbours by a mere few milliseconds of arc: a level of precision that, from Earth, would allow one to distinguish an object on the Moon the size of the Apollo lunar module.

“The discovery of S301 is no coincidence. It is the result of a long-term endeavour,” says Thibaut Paumard, co-investigator on the GRAVITY+ project and deputy director of LIRA, “with the development of several adaptive optics systems from the 1990s onwards, the GRAVITY instrument, which was commissioned in 2017 after more than ten years of development, followed by its upgrade, GRAVITY+, in 2024, and soon MICADO, which has also been under development for several years. At the same time, we are also developing the digital tools that enable us to compare observational data with theoretical predictions, such as the Gyoto software for calculating trajectories and gravitational lensing effects.”

S301 paves the way for the first measurement of a black hole's rotation

Figure 2 – Diagram illustrating the two effects of general relativity associated with the immense mass of the Sagittarius A* black hole.

Schwarzschild precession occurs in any black hole, whilst Lense–Thirring precession occurs only in a rotating black hole. The angles are greatly exaggerated in the diagram. If Sagittarius A* is rotating rapidly, the Lense–Thirring precession of the new star S301 could be of the same order as the Schwarzschild precession of the star S2, measured in 2018 by GRAVITY, thereby paving the way for the direct measurement of the black hole's rotation.

Credit: Karim Abd El Dayem (former PhD student at LIRA, co-author of the article).

Tracking a star so close to Sagittarius A* presents a real technical challenge, but also a unique opportunity to test general relativity in one of the most extreme gravitational environments in our Galaxy. To determine the orbit of S301, scientists analysed several years' worth of observations in order to track its position precisely. Its proximity to the black hole changes the situation considerably:

“Without this star, we would have to measure the orbits of the other stars for several more decades in the hope of detecting an effect caused by the rotation of Sagittarius A*,” explains Juan Osorno, a postdoctoral researcher at LIRA.

For around a black hole, Newton's laws no longer apply. The orbit of S301 gradually deviates from the ellipse predicted by these laws, revealing the effects of general relativity (see Figure 2). The first, Schwarzschild precession, is caused by the curvature of space-time due to the black hole's mass: with each orbit, the point at which the star passes closest to Sgr A* shifts slightly, gradually tracing a sort of rosette pattern. This effect has already been observed with the star S2. But by venturing much closer to the black hole, S301 becomes susceptible to a second, far more subtle phenomenon: Lense–Thirring precession, caused this time by the black hole's rotation — or spin — (see Figure 3).

“What I find particularly fascinating about S301 is that it finally gives us a chance to directly observe an effect linked to the rotation of a black hole. A rotating black hole does not merely warp space and time around it: it literally drags them along in its rotation. This effect, known as Lense-Thirring precession, is extremely weak and has never before been measured around a black hole. S301 passes close enough to Sagittarius A* for this minute distortion of space-time to leave a measurable trace in its orbit. By continuing to track this star over the coming years, we could therefore use its motion as a tool to measure the rotation of the black hole at the centre of our Galaxy, explains Abd El Dayem Karim, a former PhD student at LIRA.”

S301, a new laboratory for general relativity

Figure 3 – Illustration of the Lense–Thirring effect, resulting from the rotation of a black hole, on the orbit of S301.

S301's exceptional proximity to the black hole could reveal the Lense-Thirring effect: as it rotates, the black hole drags the space-time around it and very slightly alters the star's orbit. This minute deviation, on the scale of the Earth's orbit around the Sun, would nevertheless be significant enough to be measured using the VLTI and ESO's Extremely Large Telescope (ELT), currently under construction. Ultimately, this measurement would make it possible to determine the rotation of Sagittarius A*.

Credit: ESO/Collaboration GRAVITY/M. Kornmesser/L. Calçada

Unlike the hot gas observed around other black holes, such as that in M87 imaged by the Event Horizon Telescope, S301 offers a valuable advantage: its motion can be tracked directly. By combining the extremely precise measurements of its position obtained with GRAVITY+ and those of its radial velocity taken with MICADO, a future instrument on ESO's Extremely Large Telescope (ELT), scientists will be able to reconstruct its three-dimensional motion and thus directly measure the rotation of Sgr A*.

But to achieve this, it will be necessary to disentangle several effects that could perturb its orbit.

“The effect produced by spin on the motion of the star S301 is similar to that caused by the presence of a disc — that is, a flattened distribution — of non-luminous matter that may lie around the supermassive black hole Sgr A*. We will therefore need to determine both effects simultaneously, which opens up the possibility of gaining a better understanding of the environment surrounding Sgr A* by measuring the non-luminous mass around it,” explains Arianna Foschi, a postdoctoral researcher at LIRA. ”

The challenge thus becomes an opportunity: S301 could both reveal the black hole's rotation and probe the invisible matter surrounding it.

In the longer term, the aim is to go even further by testing the Kerr metric, which describes the space-time around a rotating black hole.

“General relativity predicts that a black hole is fully described by just two parameters: its mass and its spin,” explains Frédéric Vincent, a research fellow at LIRA. “This fundamental result is known as the no-hair theorem (the ‘hair' symbolising the lack of complexity in the black hole object). The star S301 will enable us to determine whether the black hole is distorted by its rotation, in the same way that the Earth is flattened by its rotation. This deformation, if it exists, must depend on the two parameters of mass and spin, according to the no-hair theorem. Verifying this prediction of general relativity would constitute a major test of our understanding of gravity in its most extreme regime.”

And the prospects already extend beyond S301 and the centre of our Galaxy.

“This new result obtained with GRAVITY on our galactic centre demonstrates the power of long-baseline interferometry, which has reached full maturity with the instrument on the VLTI,” emphasises Guy Perrin, an astronomer at the Paris Observatory and co-investigator on the GRAVITY project. “In its GRAVITY+ version, GRAVITY will be able to broaden the scope of possibilities and focus on a very large number of supermassive black holes. It also opens up new horizons for future instruments with much longer baselines, whose resolving power will be even greater, with the potential to reach scales that are currently inaccessible – just as GRAVITY did more than twenty years ago.”

Mathias Nowak has been awarded a ‘PSL Young Researcher Starting Grant' for 2026

Raphael PERALTA — 2026-08-28T13:51:38Z

Mathias Nowak has been selected for the 2026 edition of the PSL Young Researcher Starting Grants, a scheme designed to support early-career researchers at a key stage in their careers: the launch of their own research programme. Thanks to this funding, they will be able to recruit talented young researchers, develop innovative scientific approaches and strengthen their independence within the university's laboratories.

For these early-career researchers, this grant often acts as a real catalyst: it gives them the means to build a team, explore ambitious lines of research and lay the foundations for a long-term scientific project.

Mathias Nowak

Mathias Nowak, a CNRS research fellow at the Laboratory for Space Studies and Astrophysical Instrumentation (LIRA) at the Paris Observatory – PSL, is developing new techniques for observing exoplanets. His project aims to push the limits of the GRAVITY instrument, installed on the Very Large Telescope (VLT), in order to observe planets orbiting ever closer to their stars and to measure their properties more accurately. These advances will enable the characterisation of a new generation of exoplanets detected by the Gaia space mission and will provide new insights into the formation and evolution of giant planets.

Even if you realise your calling a bit late in life, all is not lost: you should give it a go.

First observation of the rotation of a protoplanetary disc

Raphael PERALTA — 2026-07-27T10:32:35Z

How can we observe the birth of a planet? Around the young star AB Aurigae, located some 530 light-years from Earth, a vast disc of gas and dust features spiral arms, several compact structures and other signs suggesting that planets are forming there. Thanks to its brightness and the size of its disc, AB Aurigae provides an exceptional laboratory for studying the early stages of planet formation. By combining three observation campaigns carried out between 2019 and 2023 using the SPHERE instrument on ESO's Very Large Telescope, an international team led by LIRA has, for the first time, managed to track the rotation of a protoplanetary disc over a period of nearly four years. The study provides new evidence for active and particularly complex planetary formation, with several protoplanet candidates likely to be shaping the disc simultaneously.

Searching for protoplanets at the heart of the AB Aurigae disc

Figure 1. Image of the disc of gas and dust surrounding the young star AB Aurigae, taken in the near-infrared (H-band) using the SPHERE instrument fitted to ESO's Very Large Telescope (VLT).

The image has been processed to highlight the main structures of the disc: the four protoplanetary candidates (f1, f2, f3 and AB Aur b), the spiral arms and the inner disc. The star's light has been blocked out by a coronagraph in order to reveal the faintest structures in the disc. Its position is indicated by a yellow cross.

Credit: ESO / A. Boccaletti et al. (2026)

Although thousands of exoplanets are now known, their formation remains difficult to observe, as young planets emit little light and remain hidden within their surroundings. They are thought to form during the first few million years of a planetary system's life, within vast protoplanetary discs composed of gas and dust. AB Aurigae is a very young star surrounded by such a disc, in which there are numerous indications that a process of planetary formation is underway. Thanks to its brightness and the extent of its disc, AB Aurigae provides an ideal laboratory for studying the conditions under which planets begin to form around intermediate-mass stars.

In 2017, ALMA (Atacama Large Millimetre/submillimetre Array) observed AB Aurigae in the submillimetre wavelength range in order to map the large dust particles and cold gas in the disc. The observations revealed two vast spiral arms of gas less than 100 astronomical units from the star, as well as a cavity at the centre of the disc. Models suggest that these spiral arms could be caused by an invisible companion located between 60 and 80 AU, whose gravitational influence disturbs the gas and produces waves comparable to a boat's wake. They also suggest that the large cavity observed at the centre of the disc could be explained by a second companion located at around 30 AU, which is approximately the distance from Neptune to the Sun.

In 2019 and 2020, an international team led by LIRA observed these spirals using the SPHERE instrument on the Very Large Telescope (ESO), a project in which the laboratory is heavily involved. By imaging, in the near-infrared, the starlight scattered by dust, SPHERE confirms the existence of the two spiral arms and, crucially, reveals a twist at their junction, at the position corresponding to the f1 structure (see Figure 1). This structure, which connects an inward-pointing spiral arm to an outward-pointing one, is consistent with models of planetary formation and provides further strong evidence for the existence of a protoplanet. However, the protoplanet remains invisible and its mass is still difficult to determine.

In 2021, an American team used the Hubble Space Telescope and the Subaru Telescope (Hawaii) to observe the disc in the visible spectrum and to image the hydrogen (Hα) emission line, characteristic of the very hot gas surrounding a forming planet. The observations revealed a bright spot consistent with a Jupiter-like protoplanet located approximately 93 astronomical units from the star. Named AB Aur b, this source is difficult to detect in the SPHERE images (see Figure 1). However, this interpretation is disputed by other teams, who believe that this signal may simply be a reflection of stellar emission.

Finally, astrometric data from the Gaia satellite could also suggest the presence of a stellar companion rather than a protoplanet. However, this hypothesis remains highly uncertain, as the measurements are significantly disrupted by the gas- and dust-rich environment that still surrounds this young star, some of whose material is accreting onto its surface, creating areas of overbrightness.

The net is closing in on the protoplanet trail

Figure 2. The first time-lapse sequence of the rotation of a protoplanetary disc, captured using the SPHERE instrument on ESO's Very Large Telescope (VLT) over a period of nearly four years.

SPHERE's exceptional resolution makes it possible to track changes in numerous structures within the disc, particularly twists that may indicate the presence of forming planets. These structures are most clearly visible on the right-hand side of the video, where image processing enhances their contrast. The images also reveal faint radial shadows cast by opaque structures located in the inner regions of the disc (see Figure 3).

Credit: ESO / A. Boccaletti et al. (2026)

To gain a better understanding of the origin of these structures, the international team led by LIRA is continuing to image AB Aurigae using the SPHERE instrument on the Very Large Telescope. These new observations complement the previous ones, bringing the total number of observations carried out between 2019 and 2023 to three. This consistent series of observations makes it possible, for the first time, to track the rotation of a protoplanetary disc over nearly four years and to observe the evolution of its various structures with unprecedented precision (see Figure 2). This long-term monitoring has revealed several new findings.

Firstly, the scientists studied the disc's rotation around the star and found that the inner region does not rotate as predicted by current models. The authors suggest that this behaviour could be explained by the interaction of several protoplanets orbiting in elliptical paths inclined relative to the disc's plane.

The second finding concerns the three bright, compact structures (f1, f2 and f3), which are candidates for protoplanets (see Figure 1). The study shows that their orbits are inclined by several tens of degrees relative to the plane of the disc, a behaviour consistent with forming objects. However, the observations do not yet allow us to determine whether these are genuine protoplanets or simply concentrations of gas and dust. As for the candidate AB Aur b, the observation in the Hα line does not confirm the expected emission, calling its initial interpretation into question.

Finally, the images revealed seven faint radial shadows sweeping rapidly across the surface of the disc (see Figures 2 and 3). Like the shadows cast by clouds at sunset, they indicate the presence of opaque structures that are too small to be imaged directly. By tracking their movement from one observation to the next, it is, however, possible to estimate their position, with some being consistent with structures such as f1 (see Figure 3). These shadows could be produced by protoplanets, but also by opaque dust clumps; it is not yet possible to determine which is the case.

The quest continues

Figure 3. Images obtained using SPHERE showing the evolution of radial shadows (indicated by the arrows), cast by opaque structures located in the inner regions of the disc. These structures could correspond to protoplanets in the process of formation or to particularly dense concentrations of gas and dust.

The image on the right has been processed to highlight the main structures of the disc, in particular the spiral arms, twists and radial shadows.

Credit: ESO / A. Boccaletti et al. (2026)

Taken together, the results from this latest study paint a more complex picture than previously envisaged: rather than a single planet shaping the disc, several objects in the process of formation may be interacting simultaneously with the gas and dust.

The search for protoplanets around AB Aurigae continues. To take this research further, the scientific team has already secured two nights of observation on each of the two largest optical telescopes in the northern hemisphere: the Keck Telescope and the Subaru Telescope, both located in Hawaii. These new observations, carried out in the near-infrared with Keck (L-band) and in the visible and near-infrared with Subaru, should help to better test the various hypotheses and, perhaps, finally shed light on the mysterious structures surrounding AB Aurigae.

A tribute to Annie Baglin

Raphael PERALTA — 2026-06-30T10:30:42Z

It is with great sadness that we learn of the death of Annie Baglin.

Annie began her career in astrophysics with a thesis on the evolution of hot degenerate stars, supervised by Evry Schatzman and defended in 1967 at the Paris Institute of Astrophysics (IAP).
She joined the CNRS in 1968 and moved from the IAP to the Nice Observatory the following year. There, for nearly twenty years, she continued her theoretical work exploring the internal structure of stars.
During this period, she took an interest in the development of stellar evolution codes, an interest which led her in the 1980s to champion the development of the French CESAM code within the GdR 131 Internal Structure research group. It was also during this time that she launched the internal structure schools – autumn schools which have continued in their current form as the Evry Schatzman Schools of the PNPS.
She very quickly recognised stellar pulsations as a promising source of information for studying the internal structure of stars. She subsequently supervised several PhD theses in this field and collaborated on ground-based stellar pulsation observation projects. She also forged links with the DESPA team at the Paris Observatory, which advocated the need for space-based observations.

In the 1980s, she also became enthusiastic about ESA's Hipparcos space mission, the world's first space-based astrometry mission, and helped to compile its initial catalogue under the guidance of Catherine Turon.
In 1988, she joined the Paris Observatory as head of the DASGAL in-house team, replacing Françoise Praderie to lead the EVRIS project – a stellar seismology experiment scheduled to observe during the journey aboard the Russian MARS96 probe, intended for the exploration of Mars.

In 1996, EVRIS was launched… and immediately lost, but Annie rallied the community behind CoRoT, a new space-based stellar seismology project. Under her leadership, and after overcoming numerous obstacles, CoRoT's programme was expanded to become the first space mission to search for exoplanets via the transit method, now involving not only the Paris Observatory, but also the LAM in Marseille, the Toulouse Observatory, the Nice Observatory and more than twenty institutes across Europe and Brazil. CoRoT was finally approved and launched in 2006, with the success we are all familiar with.

Annie was thus a key figure in the development of stellar seismology at the Paris Observatory, at DASGAL, and subsequently at DESPA and LESIA. The CoRoT mission, which she championed on the international stage, was a major achievement for CNES and its international partner agencies. It was CoRoT, launched in 2006 and led by Annie Baglin, that truly marked the starting point for space-based stellar seismology and the search for exoplanets via transits from space. By championing (with all her might!) and then leading the CoRoT project, Annie helped to develop and shape a large and dynamic community with strong roots in Europe.

Until 2018, following her retirement and appointment as professor emeritus, Annie worked to promote the legacy of CoRoT and to prepare for the future.
Annie's legacy lives on today in the PLATO mission, in which the French community and LIRA are key drivers, particularly through the major contribution that the open-source Cesam2k20 code for stellar internal structure and evolution now makes to the mission.
Beyond her own research, Annie also played a major role in the management and leadership of astrophysics in France: as director of the DASGAL laboratory at the Paris Observatory, a member of Section 14 of the CNRS, and vice-chair of the Scientific Council of the Paris Observatory. And throughout all her activities, Annie was always committed to supporting and encouraging young women to pursue a career in research.

All those who worked alongside her in her many and varied activities, both professional and personal, will remember with fondness her enthusiasm, her energy and her immense human qualities. Many of us feel privileged to have had her as a colleague and friend, and to have benefited, at one time or another in our careers, from her support and her example.

We wish to express our condolences to her family, to her son Jérôme, to her grandchildren, and to her brother Gérard.

The International Astronomical Union has recognised Antonin Wargnier's doctoral thesis, carried out at LIRA

Raphael PERALTA — 2026-06-26T09:36:08Z

Antonin Wargnier, a PhD holder from the Paris Observatory – PSL and Sorbonne University, has received an honourable mention in the International Astronomical Union's (IAU) 2025 Doctoral Prizes. This distinction recognises his work on the Martian moons Phobos and Deimos and highlights the excellence of the research carried out at LIRA, where he completed his PhD.

International recognition

The International Astronomical Union (IAU) has announced the recipients of its 2025 PhD Prizes, which each year recognize the most outstanding doctoral research carried out worldwide. Through these awards, the IAU highlights the importance of supporting early-career researchers and celebrates the scientific excellence, commitment, and perseverance required to advance our understanding of the Universe.

Among the 22 researchers honoured this year, Antonin Wargnier received an Honourable Mention from Division F, "Planetary Systems and Bioastronomy", for his PhD thesis carried out at LIRA and Sorbonne University. The selection committee praised the comprehensive nature of his research, which successfully combines instrumental expertise, laboratory experiments and modelling, while establishing a strong connection between laboratory measurements and space-based observations.

All awardees will be invited to present their work during the "Division Days" of the XXXIII IAU General Assembly, to be held in Rome, Italy, from 10 to 19 August 2027.

Antonin Wargnier's research

Entitled "Spectrophotometric Properties of the Surfaces of Phobos and Deimos: Preparation for the Exploration Mission to the Martian Moons", Antonin Wargnier's PhD thesis has made a major contribution to our understanding of Mars' two natural satellites. In particular, his work demonstrated the common origin of Phobos and Deimos through the analysis of data from the SRC instrument aboard the Mars Express mission (orbiting Mars since December 2003), for which he carried out the first complete recalibration in more than twenty years.

He also developed a regolith simulator, named OPPS, designed to prepare the interpretation of future observations from JAXA's MMX (Martian Moons eXploration) mission, where he is now a postdoctoral researcher.

"This international distinction highlights the excellence of the planetary exploration research conducted at Observatoire de Paris – PSL. It comes at a particularly exciting time, as the MMX mission, to which our scientists from the Laboratory for Instrumentation and Research in Astrophysics (LIRA) contribute, is entering its decisive phase, with a launch scheduled for the end of the year from the Tanegashima Space Center. I warmly congratulate Antonin Wargnier on this recognition, which crowns exemplary work serving the space science of tomorrow," said Philippe Stée, President of Observatoire de Paris – PSL.

First Light for the French AIRS Instrument of the ARIEL Mission.

Sylvestre Taburet — 2026-06-19T16:03:47Z

Currently under development, the French AIRS spectrometer for the future ARIEL telescope has just reached a major milestone.

ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is the fourth medium-class mission (M4) of the European Space Agency's Cosmic Vision programme, with launch planned for 2032. The mission is entirely dedicated to the study of exoplanet atmospheres: around one thousand exoplanets will be observed over a four-year period.

A successful test campaign for the AIRS instrument

The development of space hardware requires several intermediate models to progressively validate the mechanical, thermal, electrical, and software design. Structural and Thermal Models (STM), for example, are used to validate the mechanical and thermal design, while Avionics Models (AVM) and Engineering Models (EM) are used to perform complete electrical and functional validation. The flight model is then produced based on these results, or alternatively on a qualification model that incorporates all the equipment's functions.

As part of the development of the AIRS instrument, and particularly of the cold section of the spectrometer, the engineering model was designed as a qualification model with the objective of fully validating its design, especially with respect to the ARIEL mission's space-environment requirements, both mechanical and thermal. Alongside these tests, an extensive calibration campaign has been underway since March 2026 to measure the instrument's performance, including the acquisition of the spectrometer's first image.

The AIRS instrument consists of an electronic unit, the ADCU (AIRS Detector Control Unit), and the spectrometer's cold section, the CU (Cold Unit), which includes two optical benches coupled to two focal planes in order to cover the wavelength range from 1.95 to 7.8 microns. CEA develops the detector readout chains, from the detectors mounted on the focal plane through to the complete ADCU control unit. IAS is responsible for the two optical benches, their integration and alignment, as well as the measurement of their physical properties and vibration testing.

The optical benches are composed of several subsystems (lenses, prisms) mounted in mechanical supports. These subsystems are assembled and tested at IAS, where their optical characteristics are verified and their ability to withstand launch loads is assessed.

Figure 1: Assembly of the Optical Benches and Verification of Prism Alignment

Crédit IAS

Once the optical benches have been assembled and aligned, the focal planes are mounted onto them. All assembly operations are performed in a clean room to ensure that no dust or contamination is deposited on the optics, which could otherwise degrade the instrument's performance.

Figure 2: Assembly of the Focal Planes onto the Optical Benches

crédit IAS/CEA

Figure 2.1: Focal Planes Integrated onto the Optical Benches

crédit IAS/CEA

Once the entire assembly—optical benches plus focal planes—is complete, vibration tests are carried out using the IAS shaker facility. The integrity of the instrument is then verified, along with the relative alignment of the two optical benches, to ensure that no deformation has occurred during testing.

Figure 3: AIRS CU Engineering Model in the Clean Room for Physical Property Measurements and Preparation for Qualification-Level Vibration Testing

Crédit CNRS/L. Godart

The cold section is then shipped to LIRA for thermal testing and instrument calibration.

Since March 2026, the engineering model of the AIRS infrared spectrometer has been installed at LIRA in the SimEnOm cryogenic vacuum chamber of the MESPAL facility. This chamber reproduces conditions close to those encountered in space and allows verification of the instrument's proper operation.

LIRA is responsible for the entire test campaign: it provides the test equipment, including an optical bench that simulates the telescope, and performs all measurements required to assess the instrument's performance.

Figure 4: Integration of the AIRS CU Engineering Model at LIRA

Crédit LIRA, Observatoire de Paris

These tests will continue until November 2026, with the participation of scientific teams from CEA, IAS, and IAP. Once this phase is complete, the instrument will be delivered to the Rutherford Appleton Laboratory (RAL) in the United Kingdom for additional testing together with all systems integrated into the ARIEL payload.

A new milestone for AIRS

Recently, in order to verify the performance of the AIRS instrument, a measurement was carried out using a cell containing gaseous methane. Methane is an organic compound present in Earth's atmosphere and one that may also be found in the atmospheres of exoplanets observed by ARIEL.

The positions of methane's spectral lines are known with great accuracy, making them an ideal reference for verifying that the instrument responds nominally when detecting them.

The measurement procedure is straightforward. Two acquisitions are performed with AIRS: the first with methane in the optical path, and the second without methane, serving as a reference. By taking the ratio of the two measurements, the methane spectrum obtained with AIRS can be compared with a theoretical model.

The figure below shows, on the left, the raw spectra from the reference measurement and the methane-cell measurement, and on the right, the comparison between the measured spectrum and the theoretical model. The excellent agreement between the two suggests that the instrument is performing nominally.

Figure 5: First Methane Spectrum Measured by AIRS

French contribution to the ARIEL mission

France is making a major contribution through the provision of the AIRS (ARIEL Infra-Red Spectrometer) infrared spectrometer. The instrument is being developed under the leadership of CEA-Irfu (Department of Astrophysics, AIM Joint Research Unit), with major contributions from IAS (Institut d'Astrophysique Spatiale), LIRA (Laboratory for Instrumentation Research in Astrophysics), and LAB (Laboratoire d'Astrophysique de Bordeaux). CNES serves as the contracting authority. IAP (Institut d'Astrophysique de Paris) and LISA (Laboratoire Interuniversitaire des Systèmes Atmosphériques) will also contribute to the scientific preparation of the mission through simulations and data-processing pipelines.

Selection of the Plasma Observatory mission by ESA

Raphael PERALTA — 2026-06-17T08:02:26Z

The Paris Observatory – PSL welcomes the recommendation made on 11 June 2026 by the ESA Science Programme Committee in favour of the Plasma Observatory mission, a future mission dedicated to the study of plasmas in the Earth's environment, in which LIRA teams are closely involved.

At its meeting on June 10 and 11, 2026, at the Instituto Astrofísico de Canarias in Tenerife, the ESA Science Program Committee recommended the selection of Plasma Observatory as the agency's next medium-class (M7) mission under its science program.

Plasma Observatory was among three finalists—along with THESEUS and M-MATISSE—selected by ESA in 2023. It would thus be the first medium-class mission to join Voyage 2050, ESA's future science program, with a launch scheduled for the mid-2030s.

An ambitious mission to understand the physics of natural plasmas

Plasma Observatory will be an observatory dedicated, as its name suggests, to a state of matter that is very rare on Earth in its natural state but constitutes the bulk of observable matter in the Universe: plasma, which consists of charged particles. The physics of space plasmas thus lies at the intersection of fundamental physics and astrophysics, shining a spotlight on the direct study of physical phenomena observed in space through space probes.

Plasma Observatory builds on the legacy of Cluster, a pioneering ESA mission consisting of four spacecraft, which has shaped research on space plasmas in Europe and around the world over the past 25 years, alongside multi-point missions such as Themis and MMS. With seven identical probes forming two interlocking tetrahedrons that will operate in a coordinated manner, Plasma Observatory will mark a new milestone in the exploration of Earth's magnetosphere, the closest and most accessible natural plasma laboratory for observation.

This mission will simultaneously observe several characteristic scales, ranging from collective plasma motions to processes involving ions and, in certain regions, electrons.

Its objectives are to:

understand how particles are accelerated and gain energy in the magnetosphere;
identify the physical mechanisms that transport energy and govern interactions between the different regions of Earth's magnetosphere.

Plasma Observatory will thus make it possible, for the first time, to link the observed microscopic phenomena to the global dynamics of the magnetosphere, in order to better understand the fundamental mechanisms at work in the plasmas of the Universe.

Plasma Observatory sera la première mission capable de mettre en évidence les couplages d'échelle au sein du système magnétosphérique terrestre grâce à des mesures effectuées en sept points de l'espace.

Credit: INAF/LPP

Recognized Expertise from the Paris Observatory

Researchers and engineers at the Paris Observatory bring world-class expertise in the in situ measurement of space plasmas to this European mission.

Their contribution draws on a long tradition of instrumentation, which takes on a new dimension here: historically specialized in radio wave measurements and the study of electromagnetic fields (Solar Orbiter, BepiColombo, Parker Solar Probe), Laboratory for Instrumentation and Research in Astrophysics - LIRA's contribution to the Plasma Observatory is based on the design of the flight software (derived from Plato) for the suite of instruments dedicated to particle measurements.

One of the LIRA team's objectives is therefore to reconcile the measurements taken by three particle analyzers with local magnetic field measurements.

One of the sub-instruments is a 3DCAM camera, named iEPC and developed at the Plasma Physics Laboratory, which operates under the secondary supervision of the Observatory. LIRA is a partner in the development of a flight model of the 3DCAM camera that could fly aboard a low-Earth orbit spacecraft for validation as early as 2028, before being deployed on constellations dedicated to acquiring data for space weather monitoring.

Philippe Stee, President of the Paris Observatory – PSL, welcomes this major milestone: I am delighted to see the expertise of the Paris Observatory – PSL teams put to use in this new European space venture dedicated to a better understanding of our planet; alongside our partners, we will continue our commitment toward the final approval of the mission, which is expected to yield numerous scientific benefits.

The official decision regarding the final approval of the Plasma Observatory mission by ESA is expected in November 2026.

Defence of Léa GRITON's doctoral thesis on Wednesday 1 July 2026

Raphael PERALTA — 2026-06-17T06:52:10Z

Léa GRITON will defend her HDR (Habilitation à Diriger des Recherches), entitled "Interaction of the solar wind with Mercury and Uranus", on Wednesday 1 July 2026 at 2 pm. The defence will take place in the Evry Shatzmann lecture theatre at the Meudon site of the Paris Observatory-PSL.

It can be watched live on the LIRA YouTube channel

Title of the HDR

Interaction of the solar wind with Mercury and Uranus.

Composition of the jury

Mathieu Barthelemy, Professor at the University of Grenoble Alpes (IPAG), Rapporteur
Aurélie Marchaudon, Senior Research Fellow at the CNRS (IRAP), Rapporteur
Petr Hellinger, Senior Researcher at the Institute of Atmospheric Physics in Prague, Rapporteur
Laurence Rezeau, Professor Emerita at Sorbonne University, Chair of the jury
Dimitra Koutroumpa (CNRS, LATMOS), Examinatrice
Eric Buchlin (CNRS, IAS), Examinateur

Abstract

Léa Griton's (LIRA) research focuses on the role of space plasmas in star-planet interactions, with expertise in magnetohydrodynamic (MHD) modelling of the interaction between the solar wind and the magnetospheres of Mercury and Uranus, having co-developed the AMRVAC-PLANET code with Filippo Pantellini (LIRA). She has expanded her expertise to include kinetic numerical simulations, contributing to the development of the Winterfell centre-guide code to study energetic particles, whilst co-supervising Ahmed Houeibib's PhD thesis (to be defended in 2025). She has also developed instrumental expertise, notably through the operation of the SORBET receiver (BepiColombo) and the analysis of FIELDS data (Parker Solar Probe), co-supervising with Karine Issautier (LIRA) the PhD thesis of Baptiste Verkampt (defence scheduled for 2027). Since 2022, she has been responsible for LIRA's contribution to the Plasma Observatory mission (in the M7 competition at ESA).

Her work has yielded three major results: the analysis of the properties of the slow solar wind using the Parker Solar Probe; the study of the boundaries of Mercury's magnetosphere using BepiColombo and magnetohydrodynamic simulations; and the preparation for the Uranus Orbiter & Probe mission through simulations of rotating magnetospheres. She is currently supervising Inès Mertz's PhD thesis (defence scheduled for 2028, co-supervised with Filippo Pantellini) on the magnetospheric dynamics of Mercury, in collaboration with national and international experts.