LTE - Observatoire de Paris - PSL - Centre de recherche en astronomie et astrophysique

The SE-OP Ephemeris is set for March

Maïder Bugnon Olano — 2026-10-15T07:29:10Z

Here we go! After years of development, the Japanese MMX (Martian Moons Exploration) mission is ready for launch. With liftoff scheduled for October 20 of this year and a backup window extending through November 7, we will soon witness the launch of this landmark mission by the Japan Aerospace Exploration Agency (JAXA). The probe will be launched by a rocket built by the Japanese manufacturer Mitsubishi, from the Tanegashima Space Center in southern Japan.

MMX Trajectory plan.Crédits JAXA

While bringing back samples from Mars isn't yet on the agenda, the MMX probe is getting close. In fact, it's set to accomplish a remarkable feat: collecting samples from Mars's moon, Phobos, and returning them to Earth. As a reminder, Mars has two moons, Phobos and Deimos, each with a radius of about 10 kilometers. While these two moons have physical characteristics similar to those of asteroids, their orbit around Mars is, however, not entirely consistent with the theory that they were captured by the planet's gravity. This has led to questions about their origins that have puzzled the scientific community for several decades.

To shed light on the origin of Phobos, an in-situ analysis of the regolith (rock dust) is not sufficient. It is therefore necessary to conduct laboratory analyses on Earth. This is precisely the primary objective of the MMX probe. In addition to remote analyses of Mars' moons, MMX will have to land on Phobos to collect samples from its surface, bring them back to Earth, with arrival scheduled for 2031. As if that weren't enough, the mission will also deploy a small Franco-German rover named Idéfix, after the beloved dog created by René Goscinny and Albert Uderzo in the Asterix comic books. The rover will attempt to explore the surface of Mars's largest moon.

The moon Phobos, as observed by the European Mars Express spacecraft. Crédits ESA/DLR/FU Berlin, CC BY-SA IGO 3.0

As you can imagine, none of this would be possible without precise knowledge of the positions of Mars's moons. And this is precisely where SE-OP comes in: JAXA has selected the ephemerides for Mars's moons developed at SE-OP to support the MMX mission. Over the past three years, we have been working closely with the Japanese space agency and the French National Centre for Space Studies (CNES) to provide the most accurate ephemerides possible, helping ensure that MMX can encounter Mars's moons under optimal conditions. Our ephemerides have also benefited from astrometric data collected by the European Space Agency's (ESA) Mars Express spacecraft. Remarkably, Mars Express has been orbiting Mars since 2004 and continues to observe the Martian system to this day. In this way, the MMX mission will carry a little piece of Europe (and of SE-OP) all the way to the Martian moons.

En savoir plus :

'The MMX Mission on the JAXA Website' https://www.mmx.jaxa.jp/en/mission/
'Mars Express on the ESA website' https://sci.esa.int/web/mars-express/
'Link to the Espace Department of the Paris Observatory' https://seop.obspm.fr/

The James Webb Space Telescope Reveals That Chariklo's Invisible Rings Are Changing

Maïder Bugnon Olano — 2026-09-10T08:00:19Z

Chariklo is a small celestial body orbiting between Saturn and Uranus, around which two dense rings have been discovered. A distinctive feature of these rings is that they are strongly perturbed by the central body through resonance phenomena. These resonances can reshape the rings' structure over time scales of decades, as data obtained with the JWST appear to show.

Artistic view of the centaur Chariklo and its ring system. The bright point in the upper-right corner represents the Sun as seen from Chariklo's distance.

L. Maquet, LTE

An international team led by the Andalusian Institute of Astrophysics (IAA-CSIC) has demonstrated for the first time that the two rings of this small Solar System body evolve on a decadal timescale.
This work is part of the ANR-funded “Roche” research project (ANR-23-CE49-0012), led by Nicolas Rambaux at the LTE, with Bruno Sicardy (co-author of the article) participating. The project aims to better understand the environment and interactions of small bodies in the Solar System.

Among the authors are also Josselin Desmars (LTE) and Damya Souami (LIRA), who are working on stellar occultations as part of the “Lucky Star” project, which brings together teams from France, Spain, and Brazil.
Until 2013, it was thought that ring systems were exclusive to the giant planets of the solar system, such as Jupiter, Saturn, Uranus, and Neptune. However, that year, a small body barely 250 kilometers in diameter, located nearly 17 times the distance between Earth and the Sun, joined this select group. This body is Chariklo.

Schematic representation of the stellar occultation by Chariklo's rings observed with the James Webb Space Telescope (JWST) on 18 October 2022. Comparison with previous occultations reveals opposite changes in the two rings: C1R shows a stronger signal, while C2R appears much weaker.

Yücel Kılıç, Pablo Santos-Sanz and Celia Navas (IAA-CSIC)

On October 18, 2022, the Andalusian Institute of Astrophysics (IAA-CSIC) led an observation using the James Webb Space Telescope (JWST) to study Chariklo's rings via a stellar occultation—a technique that measures the decrease in a star's brightness when an object passes in front of it. The results show that Chariklo's rings have undergone changes on timescales of just a few years, with the inner ring gaining material and the outer ring losing it.

A SCIENTIFIC AND TECHNOLOGICAL ADVANCEMENT

Animated GIF of the occultation by Chariklo, captured by the JWST.

NASA, ESA, CSA, Pablo Santos-Sanz and Nicolás Morales (IAA-CSIC).

This study also represents a major technological breakthrough: the occultation by Chariklo was the first stellar occultation specifically predicted and planned to be observed with the James Webb Space Telescope.
“To achieve this, we needed to know with extraordinary precision the orbit of Chariklo, the position of the star—thanks to ESA's Gaia mission—and the trajectory of the JWST itself around the L2 Lagrange point, a region of space located about 1.5 million kilometers from Earth. The JWST orbits this region along a trajectory that must be periodically corrected through maintenance maneuvers,” explains Yücel Kilic, a postdoctoral researcher at the IAA-CSIC and co-author of the study.

Chariklo's rings are so narrow and the body is so distant that it is impossible to photograph them directly even with the largest telescopes available today. Stellar occultations allow us to study them indirectly by measuring the brief drops in a star's brightness as each ring passes in front of it. This observation has thus yielded an unprecedented spatial resolution (on the order of a kilometer) of Chariklo's rings.

The detected changes suggest that Chariklo's rings are dynamically active. “Our results force us to rethink how they form, how they evolve, and what mechanisms ensure their stability. The ability to detect these changes opens a new avenue for understanding the evolution of these systems and, eventually, that of other ring systems in the Solar System,” emphasizes Santos-Sanz. The physical origin of the detected changes, however, remains an open question: they could reflect temporal evolution of the rings, differences related to the use of different observation filters, or a combination of these two effects.

Learn more :

REFERENCES

‘JWST stellar occultation reveals unexpected changes in Chariklo's ring system'
https://doi.org/10.1126/sciadv.aeh4794

'Link to the IAA CSIC website'
https://www.iaa.csic.es/noticia/jwst-descubre-invisibles-anillos-chariklo-cambiando/

Press Release :

CONTACTS:

Bruno Sicardy bruno.sicardy@obspm.fr (LTE)
Josselin Desmars josselin.desmars@obspm.fr (LTE)
Damya Souami damya.souami@obspm.fr (LIRA)

View online : ‘JWST stellar occultation reveals unexpected changes in Chariklo's ring system'

Cluster's encore for reentry science a success

Maïder Bugnon Olano — 2026-09-04T08:54:31Z

The LTE participated in an airborne observation mission of the atmospheric reentry of the two ESA satellites, “Cluster 3 – Samba” and “Cluster 4 – Tango,” on September 1 and 2, 2026. Although complex, the observations were conducted under nominal conditions, and all 30 onboard instruments recorded scientific data useful for understanding the disintegration of artificial satellites in our atmosphere. This topic is becoming increasingly important every day due to the growing number of launches. Using the collected data, ESA aims to improve its understanding of atmospheric re-entry and better predict the distribution and disintegration of debris.

“The image shows Cluster 4's reentry into the atmosphere in black-and-white or in blue false color to indicate that this was a daytime observation. That said, the infrared camera detects colors that the human eye cannot see. Several fragments of the satellite can be seen disintegrating in the image.”

J. Vaubaillon, LTE - Observatoire de Paris, ESA.

The mission required the joint efforts of researchers, industry partners, and space agencies: ESA (space agency), Astros Solution, Zafiro Systems, Falcon Air (industry partners), IRS/Hefdig (Germany), Comenius University (Slovakia), the University of Southern Queensland (Australia), and the Paris Observatory.

Thirty scientific instruments were installed aboard a Dassault Falcon 900 (Falcon Air). The controlled atmospheric re-entries of artificial satellites took place in the South Pacific. The team prepared in Sydney and deployed to the main island of the Kingdom of Tonga. The observations took place around noon local time.

In partnership with ONERA, the Paris Observatory (LTE/LIRA/UFE) deployed a cooled infrared camera specifically for this event. The LTE has extensive experience in atmospheric observations of natural and artificial meteors. The LIRA and UFE provided the camera and the acquisition software.

Learn More :

Press Release : https://www.esa.int/Space_Safety/Space_Debris/Cluster_s_encore_for_reentry_science_a_success

Blog : https://blogs.esa.int/rocketscience/2026/08/30/final-cluster-reentries-live-blog/

Operations : https://x.com/esaoperations/status/2093315827462226336?s=48

View online : Press Release

“The Earth is round”

Maïder Bugnon Olano — 2026-08-26T11:45:44Z

We know that many philosophers of antiquity were convinced that the Earth was round. How could they have been so sure without all the technology we have today? Through deductive reasoning based on their observations.

Take a journey back to antiquity with them and discover how they conducted their experiments by letting yourself be guided by the interactive virtual reality headset app developed by the LTE's SE-OP.

Once the app is launched, you'll enter an ethereal world where three workshops await you. You can recreate their experiments: measure shadows the way Eratosthenes did, simulate a lunar eclipse with Aristotle, and discover what the horizon reveals.

Grasp their insights, reenact their methods, and experience the power of simple observations that have changed our view of the world.

The app is free, and we hope you'll have the chance to try it out at home, in a museum, or at an event!

https://www.meta.com/fr-fr/experien...

View online : Link to the app on the Meta Store

Solar eclipse on Wednesday 12 August: what to look for and where?

Sylvie Lemaître — 2026-08-07T08:33:35Z

Everyone's talking about it, yet you're still not quite sure what it's all about?!
What will you be able to see from home? Where should you look? At what time? How can you observe it safely?
We've put together a brief summary for you!

Total or partial eclipse ?

In France, the eclipse will be visible as a partial eclipse, whilst it will be total in northern Spain. However, as the path of totality (where the eclipse is total) runs very close to France, the percentage of the Sun that is eclipsed will be high, guaranteeing a spectacular sight!

Path of the eclipse: the central path, shown in dark grey, passes through northern Spain.

What will we see?

The eclipse will be visible across the whole of France. The percentage of the Sun that is eclipsed will depend on where you are observing it from. In the south of France, it will be close to 99 per cent. It will decrease as you move northwards from the south, where it will be 90 per cent.

Depending on your location, only 1 to 10 per cent of the Sun's surface will therefore remain visible in the form of a thin crescent!
An unusual and rare spectacle!

Percentage of the Sun eclipsed over French territory.

What time is the eclipse taking place?

Be ready from 7 pm! The eclipse will begin at approximately 7.15 pm to 7.30 pm, depending on where you are in France. The Moon will then gradually begin to obscure the Sun.

The eclipse will reach its peak between 8.14 pm and 8.27 pm, depending on your location.

The Moon will then gradually move away from the Sun, and the eclipse will end between 9.05 pm and 9.20 pm. However, for much of central and eastern France, the very end of the eclipse will not be visible as the Sun will have set just before then.

From start to finish, the eclipse lasts almost two hours: plenty of time to enjoy the spectacle and share it with others!

Start, peak and end times of the eclipse, and the percentage of the Sun obscured for selected towns in France, in French standard time.

For accurate, up-to-date local information about your viewing location, visit our website eclipseop.obspm.fr or scan this QR code.

Where can I watch it?

The eclipse will take place in the late afternoon, before sunset: you will therefore need to look towards the west.

Also, as the Sun will be low on the horizon, you'll need to make sure you find a spot where the western horizon is completely unobstructed, with no trees or buildings in the way, so you can enjoy the spectacle. Finding a higher vantage point is also a good option!

How can you observe safely?

The only way to ensure you can view the eclipse safely is to get hold of special eclipse glasses that meet European standards. These glasses are available from a wide range of outlets for between 1 and 7 euros each (pharmacies, opticians, etc.), or are included with certain magazines and books currently on sale. Make sure you plan ahead!

Don't take any risks: neither for yourself nor for those around you. Eye damage caused by the sun is painless, and some of it is irreversible!

Another alternative is to observe using a projection. Place two sheets of paper facing the Sun, about 50 cm apart, with a small hole punched in the first one. The image of the Sun passes through the hole in the first sheet and is projected onto the second. You can use this principle with a shoebox, the edges of which will block out the light inside to produce a sharper image. This activity is suitable for children, and also allows you to take a break during observation to rest your eyes and neck!

The principle of observing an eclipse by projection.

Also remember to protect your equipment (smartphone, camera, binoculars) with suitable filters. If you do not have filters on your binoculars, camera or telescope, do not under any circumstances look through the eyepiece: it concentrates sunlight even more than the eye does and thus exposes you to the risk of even more serious damage.

Learn more

Find:
– our specially produced educational guide, complete with glasses : Trois éclipses en lumière
– a previous article on the subject: https://lte.observatoiredeparis.psl.eu/Two-summers-and-one-winter-three-rare-events-the-Iberian-trilogy-of-eclipses?lang=en
– our newsletter which this month – as in previous issues – includes a dedicated section entitled "Des éclipses en lumières"

Jean-Luc Margot's welcome at the LTE

Sylvie Lemaître — 2026-07-03T13:26:33Z

In September 2026, the Temps Espace Laboratory will welcome Professor Jean-Luc Margot, holder of the Tocqueville-Fulbright Chair of Excellence at the Paris Observatory-PSL. The aim of this chair is to establish, develop and strengthen Franco-American cooperation.

Jean-Luc Margot, a professor at the University of California, Los Angeles (UCLA), is an astronomer of international renown for his work in planetary radar astronomy, high-precision measurements of the rotations of planetary bodies, and the search for technosignatures. He is set to become a member of the Royal Academy of Sciences, Letters and Fine Arts of Belgium before the end of the year. He also heads the UCLA SETI initiative and has worked with over 200 students and 40,000 volunteers in the search for life in the universe.

From September, he will be working within the Astronomy and Dynamical Systems (ASD) team, alongside N. Rambaux (Sorbonne University) and J. Laskar (CNRS), on the study of Venus – the target of the forthcoming Envision mission – as well as on the study of icy moons and small bodies in the Solar System.

He will be giving public talks on the search for technosignatures and on high-precision radar measurements of planetary rotation, which you will be able to find in the newsletter and on our LinkedIn page shortly.

Jean-Luc Margot will finally be giving a lecture as part of the series of lectures at PSL Week on 23 November.

Learn more

Related projects by the ASD team : Envision (ESA), ANR ROCHE
https://psl-week.psl.eu/
https://seti.ucla.edu/jlm/
https://fulbright-france.org/fr/bourses/institutions/chaire-tocqueville-fulbright

A system comprising at least six exoplanets has been discovered following ten years of observations

Sylvie Lemaître — 2026-07-03T12:31:55Z

An international team led by Salomé Grouffal (Aix-Marseille University and Grenoble Alpes University), including members of the LTE, has spent ten years studying an exceptional planetary system comprising at least six planets with long orbital periods. The orbital period of the outermost planet (around one and a half years) is of the same order of orbital period of Mars. Such a rare system offers a new insight into the diversity of planetary systems.

The planets in the HIP 41378 system pass in front of their star (the transit method), resulting in an almost perfect alignment with Earth. However, only one in every 200 systems like HIP 41378 has this configuration. The HIP 41378 system is therefore a rare gem, enabling the study of planets with orbits comparable to those of the planets in the Solar System.

Five planets in the system were first discovered in 2015 by the Kepler telescope, but little was known about their nature and orbits. Understanding this system required a decade of observations using instruments mainly based in Chile, which measured variations in the star's velocity caused by the planets (the radial velocity method).

HIP 41378 is thus one of the first multiple-planet systems in which long-period planets have been well characterised. It consists of three inner planets smaller than Neptune and three outer planets, which are low in density and may be as large as Saturn. A seventh, more distant planet has yet to be confirmed.

Among the exoplanets, HIP 41378 f is particularly intriguing: its extremely large radius, given its mass, defies planetary formation models. One hypothesis, currently being investigated at the LTE as part of the WRAPS project (“Where do Rings Appear in Planetary Systems?”), suggests that this planet is in fact surrounded by highly inclined, opaque rings, giving it the appearance of a larger planet (see Figure). The formation of such a ring could be the natural result of a moon's evolution around this planet.

Figure: Artist's impression of the system around the star HIP 41378. The rings around HIP 41378 f have not been confirmed. Credit : Salomé Grouffal

Learn more

Read the CNRS press release.

Read the original article : A decade of monitoring the HIP 41378 planetary system: Masses and orbital periods of six planets and a planet candidate, Astronomy & Astrophysics n°710, A275, 2026.

New release : Trois éclipses en lumière

Sylvie Lemaître — 2026-06-19T12:48:56Z

The Space Service (SE-OP) of LTE is publishing this illustrated book to observe and understand everything about next solar eclipses partially visible in France.

And to ensure you can view the eclipse safely, special eclipse glasses are included.

View The table of contents.

See some page extracts.

The book is available from the publisher via this link, or in bookshops.

Format 14 × 21 cm – 88 pages
Editor : EDP Sciences
ISBN : 978-2-7598-4018-2
Publication date : 9 juillet 2026
Prix : 12,90€

ÉclipSEOP: a web app to observe the summer eclipse

Sylvie Lemaître — 2026-04-17T13:34:06Z

To mark the astronomical event of 2026, the Service espace of Paris Observatory (SE-OP) is expanding its range of services for the general public and launching a web application, ÉclipSEOP, dedicated to observing the solar eclipse on 12 August 2026.

The ÉclipSEOP app provides access to all the information you need to observe the eclipse from anywhere on Earth. It is very easy to use, and its intuitive interface allows you to view the timings of the eclipse's various phases and a graphical representation of the phenomenon as it will appear at a specific location, all with just a few clicks.

Once you have selected a location on the interactive map showing the eclipse's path of totality, you will be able to see the type of eclipse (partial or total) visible from that location, the time of maximum eclipse along with the magnitude and degree of obscuration, its duration, and the duration of the totality phase if it is visible.

The local conditions of the eclipse and the times of sunrise and sunset at the chosen location are presented in chronological order, making it easy to understand the visibility of the eclipse's various phases. The Sun's altitude and azimuth at key moments during the eclipse are also provided.

Times shown in the app are in Universal Coordinated Time (UTC). To find out the time in mainland France, add 2 hours.

All data is provided by the Service Espace of the Paris Observatory (SE-OP), which compiles and publishes ephemerides for the bodies of the Solar System.

Learn more
• Link to ÉclipSEOP app
• Link to the SE-OP calculation forms portal

Numerical simulations of rings around irregular bodies: the unexpected role of resonance 1/3

Sylvie Lemaître — 2026-04-10T13:41:01Z

An international team, comprising a researcher from the Paris Observatory – PSL, Sorbonne University and the CNRS, and a researcher from the University of Oulu in Finland, has studied ring dynamics using N-body collision simulations. These simulations show that the 1/3 spin-orbit resonance can effectively confine rings around irregular bodies such as Chariklo by transferring the energy provided by this resonance to free Lindblad modes, a process never previously observed. This work is the subject of a paper published in the journal Astronomy & Astrophysics on 26 March 2026.

In recent years, rings have been discovered around small bodies in the solar system, such as Centaur-type objects like Chariklo and Chiron, or trans-Neptunian objects like Haumea and Quaoar. Unlike the giant planets, which are practically axisymmetric, these small bodies are irregular, creating strong spin-orbit resonances between the central object and its rings. In fact, several of the rings discovered are close to a 1/3 spin-orbit resonance with the body, in which the body completes three rotations whilst a particle in the rings completes one orbital revolution.

This is not the first time that resonances have been linked to the presence of confined rings. In fact, several of the rings of Saturn, Uranus and Neptune are confined by first-order m/m-1 resonances with a satellite, whereby the satellite completes m-1 revolutions whilst the particle completes m. These resonances, known as Lindblad resonances, were studied in the 1960s in the context of galactic dynamics. They force the formation of spiral arms in the disc, and in the case of rings, they can lead to the confinement of narrow rings.

In principle, the effect of a second-order m/m+2 resonance (i.e. 1/3 for m=1) is destructive. Indeed, unlike Lindblad resonances, the 1/3 resonance causes the current lines forced by this resonance to cross, a highly dangerous situation for a collisional ring. It is as if motorways were being built that cross without traffic lights! This is illustrated in the figure opposite, where we see the central body with a mass anomaly (small circle attached to the central body), surrounded on the left by the periodic orbit of a particle in a 1/2 spin-orbit resonance with the central body. This orbit does not intersect itself, unlike the periodic orbit corresponding to the 1/3 resonance on the right, which has a self-intersection point (blue dot).

The authors of the paper used N-body simulations, in which tens of thousands of particles with radii of a few tens of metres undergo inelastic collisions, whilst being perturbed by an irregular central body. This irregularity is modelled by a mass anomaly representing, for example, a mountain or a crater on the surface of Chariklo; see the figure above. This mass anomaly is quantified by a dimensionless parameter µ, which measures its mass relative to that of the central body.

Following an excitation phase that leads to the self-crossing of the current line excited by the 1/3 resonance, a surprising phenomenon occurs: the ring transfers the energy it receives to free Lindblad modes, thereby eliminating the self-crossing of the orbits. Even more surprisingly, these free modes ultimately lead to the radial confinement of the ring.

This process is illustrated in the figure above. It is the result of an N-body simulation involving 40,000 particles with a radius of 25 metres undergoing inelastic collisions and perturbed by the 1/3 resonance. The positions of the particles are shown in a longitude-radius diagram, with the dotted line indicating the radius of the 1/3 resonance. In the case of Chariklo, the radius range covered here (from 2.03 to 2.12) corresponds to a radial distance of approximately 18 km centred on the orbital radius of the resonance towards a radius of 2.08, corresponding to 400 km for Chariklo. The time shown is in units of Chariklo's rotation period (approximately 7 hours), i.e. approximately 130, 136 and 205 years for the left, centre and right panels, respectively. On the left, we see the current line forced by the 1/3 resonance, with self-crossing, followed by a transition period in the centre panel, which leads on the right to a strongly confined ring, which now avoids any self-crossing. Fourier analysis of this ring shows that it results from the superposition of Lindblad free modes.

By varying the mass anomaly µ and the particle radius, and using dimensional analysis, the authors show that Chariklo's main ring can be confined with mass anomalies of the order of µ≈10⁻³, assuming particles of the order of one metre in size. This value corresponds to a mountain (or crater) approximately 10 km high (or deep) on the surface of Chariklo, which is physically plausible for a small body with a diameter of approximately 250 km.

Votre navigateur ne supporte pas la vidéo HTML5.

This animation shows the confinement of a ring around the 1/3 resonance with Chariklo. It is the result of an N-body simulation involving 40,000 particles with a radius of 25 metres undergoing inelastic collisions and perturbed by the 1/3 resonance with Chariklo, with Chariklo completing three rotations whilst the particles complete one orbital revolution. The ring's arc is shown in perspective, with the distance on the x-axis (2 to 2.12) corresponding to approximately 24 km. The elapsed time in years since the start of the simulation is shown at the bottom right of the image.

This mechanism could also apply to the rings of Haumea and Quaoar, given that the latter also has a ring that is close to a 5/7 resonance with the central body. Like the 1/3 resonance, it is of order two, and therefore has the same topological structure, with self-crossings of the periodic orbits, and possibly the same behaviour as Chariklo's ring.

Reference

The article is published under the title : "Rings around irregular bodies II. Numerical simulations of the 1/3 spin-orbit resonance confinement and applications to Chariklo" dated 26 March 2026, https://doi.org/10.1051/0004-6361/202556946.
Another article setting out the theoretical aspects of resonances, by Sicardy, Salo, El Moutamid, Renner and Souami, was published on 25 November 2025, https://doi.org/10.1051/0004-6361/202556950.
This research was partly funded by the "Roche" project of the French National Research Agency ANR-23-CE49-0012. It is the result of scientific research carried out in France, at the Paris Observatory – PSL in Laboratoire Temps et Espace (Paris Observatory – PSL / CNRS / Sorbonne University / University of Lille) and at the University of Oulu in Finland.

Contacts

Bruno Sicardy, Professor Emeritus SU, LTE
+33 (0) 1 40 51 23 34
bruno.sicardy@observatoiredeparis.psl.eu

Heikki Salo, Space Physics & Astronomy Research unit, University of Oulu
90014 Oulu, Finland
Heikki.salo@oulu.fi