Philippe LOGNONNÉ

Professor in Geophysics, University Paris Cité
Planetary Seismologist, Institut de physique du globe de Paris

Philippe Lognonné, 61years, is Professor in Geophysics at University Paris Cité and Planetary Seismologist at the Institut de physique du globe de Paris. He performs his research in the Planetary and Space Science team he founded in 1996 and is director of the French National Observation Services responsible for InSight SEIS and Far Side data distribution (and analysis). He is also director of the Pole Spatial of Université Paris Cité.

His researches are related to long period seismology, to the seismic coupling of telluric planets with their atmosphere and ionosphere, including for tsunami mitigation on Earth and to Planetary Geophysics and seismology, including lunar and Mars seismology.

He started Mars seismology just after his PhD in 1989 and was from 1991 to 1996 co-Principal Investigator of the seismometer onboard the Russian Mars96 Small stations, lost after mission launch in November 1996… He then succeeded, together with Dr. Bruce Banerdt, from the Jet Propulsion Laboratory and an international team, to get the NASA InSight mission selected by NASA.

He was the principal investigator of the SEIS experiment of that mission, which landed on Mars by the end of 11/2018, operated until December 2022 and provided the first seismic survey of the red planet. He is also the lead co-investigator of the VBB seismometer in the JPL lead Farside Seismic Suite experiment to the Moon (to land on the Moon in summer 2025 in the Schrödinger basin) and international co-investigator of the Chang’E-7 seismometer. He is author or co-author of more than 260 peer review papers, including 20 highly cited papers, is fellow of AGU, recipient of the 2020 Astrophysic and Space Science prize of the French Academy of Science, of the 2021 International Astronautic Prize of the French Association of Astronomy and was AGU 2022 Beno Gutenberg lecturer.

Planetary Seismology on Mars, The Moon and Beyond

Despite making its debut in space exploration less than five years after Spoutnik-1 with the lunar seismometer onboard Ranger 3 in January 1962, and despite the success of the Apollo Passive Seismic experiment, which deployed a network of four seismometers on the Moon in the 1970s, planetary seismology experienced a hiatus of more than 40 years between the last seismic data from the Mars Viking lander 2 and the inaugural data from the SEIS experiment, acquired shortly after the end of 2018. It is now back in planetary sciences…

SEIS, the French led international seismometer of Nasa's insight mission, operated on Mars until mid-December 2022. Through meticulous robotic installation and wind shielding, the very-broad-band sensors of SEIS achieved ultra-low noise levels (down to 2x10^-10 ms^-2 Hz^-1/2 between 0.1-1Hz) during the first half of the night. The magnitude detection threshold was m<3 in the InSight hemisphere and approximately m~4 in the antipodal one. Although noise levels were higher during the rest of each day, they exceeded the noise recorded on the Moon, they remained always 10 times or more less than the quietest sites on Earth in the 0.1-1hz bandwidth.

SEIS detected 1319 events, including a marsquake with a magnitude of 4.7 that excited surface waves and likely normal modes, along with 90 teleseismic events down to magnitude 2.5. Eight impacts were also confirmed by orbital crater imaging, two of which associated to very large craters. Nearly half of the events were located near Cerberus fossae, suggesting either recent or possibly ongoing volcanic seismo-tectonics.

Through these seismic events, SEIS provided the first interior seismic models of Mars, from the 40 km thick crust beneath insight down to the core. These models revealed the stratigraphy of the crust, including through surface wave anisotropy, the structure and thickness of the thermal lithosphere, and the presence of a molten silicate layer at the bottom of the core beneath a partially molten layer. Comparisons of these martian interior and seismic properties with those of the Moon and Earth, obtained from Apollo data and international seismic networks, respectively, are now possible, opening a new research field: the comparative planetary seismology

Last but not least, SEIS not only achieved the first seismic exploration of the Martian interior but also played a role in the revival of planetary seismology. In 2024, a series of seismic sensors either landed on the moon (with Chandrayaan-3 in 2023) or are scheduled for lunar landing in 2026 (with the JPL/CNES/IPGP Farside Seismic Suite in 2026 and the Chang'E-7 seismometer in 2026-2027). Other projects toward the Moon, Europa, Venus, and even Enceladus are incorporating seismic experiments in their core payloads and concepts for gravitational wave detectors on the moon with ultra-sensitive seismic sensors are also emerging, promising exciting prospects for the next decades.