Periodic Reporting for period 1 - PETRA (Deciphering the magnetic record of planetary rocks using spacecraft and laboratory measurements)
Berichtszeitraum: 2019-09-01 bis 2021-08-31
The project PETRA – “Deciphering the magnetic record of planetary rocks using spacecraft and laboratory measurements” aims at increasing our understanding of how planets form and evolve. For this, it focuses on deciphering the information carried by the magnetic record of billion years old extraterrestrial rocks.
The movement of the electrically conducting, fluid portion of a planetary core generates a magnetic field of planetary scale through a process known as dynamo. The dynamo magnetic field magnetizes the crust of terrestrial planetary bodies. The property of rocks to retain this magnetization over time periods that can extend up to billions of years provides us with a record of the past dynamo magnetic field, known as the paleomagnetic field. Moreover, crustal magnetization gives rise to a secondary magnetic field, known as the crustal magnetic field. The strength, geometry and evolution over time of planetary paleomagnetic and crustal magnetic fields are directly related to the structure, composition, and thermal state of the planetary bodies’ deep interiors, to surface processes such as hydrothermal activity and meteor impacts, and to atmospheric and climate evolution. Therefore, studying the paleomagnetic and crustal magnetic fields as these are recorded by planetary rocks opens a window into the deep interior and the geological past of a planetary body.
Ongoing and upcoming spacecraft missions that are either led by the European Space Agency, ESA, (e.g. the mission to planet Mercury, BepiColombo) or involve collaboration with ESA (e.g. the program to send humans to the Moon, Artemis, and the sample return phase of the Mars 2020 mission) create an unprecedented opportunity to use crustal magnetism and paleomagnetism to drastically expand our understanding of planetary formation and evolution. Maximizing the outcome of these missions relies on optimizing the synergy between studies based on spacecraft magnetic field measurements and laboratory studies of magnetized samples. This project lies precisely at this intersection.
It focuses on studying the geological history and deep interior of planet Mars and of the Moon by studying meteorites, lunar return samples and spacecraft magnetic field measurements. In particular, it addresses the questions of how the Martian dynamo evolved with time and what is the origin of lunar magnetism. The methodologies developed in the framework of this project can be applied to any terrestrial body, whether a planet, a moon or an asteroid.
The movement of the electrically conducting, fluid portion of a planetary core generates a magnetic field of planetary scale through a process known as dynamo. The dynamo magnetic field magnetizes the crust of terrestrial planetary bodies. The property of rocks to retain this magnetization over time periods that can extend up to billions of years provides us with a record of the past dynamo magnetic field, known as the paleomagnetic field. Moreover, crustal magnetization gives rise to a secondary magnetic field, known as the crustal magnetic field. The strength, geometry and evolution over time of planetary paleomagnetic and crustal magnetic fields are directly related to the structure, composition, and thermal state of the planetary bodies’ deep interiors, to surface processes such as hydrothermal activity and meteor impacts, and to atmospheric and climate evolution. Therefore, studying the paleomagnetic and crustal magnetic fields as these are recorded by planetary rocks opens a window into the deep interior and the geological past of a planetary body.
Ongoing and upcoming spacecraft missions that are either led by the European Space Agency, ESA, (e.g. the mission to planet Mercury, BepiColombo) or involve collaboration with ESA (e.g. the program to send humans to the Moon, Artemis, and the sample return phase of the Mars 2020 mission) create an unprecedented opportunity to use crustal magnetism and paleomagnetism to drastically expand our understanding of planetary formation and evolution. Maximizing the outcome of these missions relies on optimizing the synergy between studies based on spacecraft magnetic field measurements and laboratory studies of magnetized samples. This project lies precisely at this intersection.
It focuses on studying the geological history and deep interior of planet Mars and of the Moon by studying meteorites, lunar return samples and spacecraft magnetic field measurements. In particular, it addresses the questions of how the Martian dynamo evolved with time and what is the origin of lunar magnetism. The methodologies developed in the framework of this project can be applied to any terrestrial body, whether a planet, a moon or an asteroid.
We collected samples from ten different paired stones of the oldest Martian meteorite available on Earth, NWA 7034. This meteorite has grains that are dated to be 4.4 billion years old, which makes it the only meteorite available on Earth that dates from the early epoch of the Martian dynamo and could therefore give us valuable information about the deep interior of Mars at its early history. Unfortunately, after conducting laboratory measurements, we concluded that all samples except one have been remagnetized on Earth. The one sample that has not had its magnetic record completely overwritten allowed us to calculate an estimate of the intensity of the magnetic field that magnetized it on Mars. The fact thought that we only have one sample does not allow us to proceed with a comprehensive study of this magnetic record.
The study of lunar magnetism presents less challenges because astronauts of the Apollo missions have returned to Earth lunar rocks that are safely kept at the NASA's Johnson Space Center. In the framework of this project, we are conducting measurements on two different types of rocks, returned by the Apollo 16 and Apollo 17 missions. These rocks are 3.7 billion years old and can therefore give us information about the magnetic field of the Moon at its early history. The origin of lunar magnetism is still under debate and therefore these measurements allow us to provide much needed constraints on the nature and strength of the lunar magnetic field.
Another aspect of this study has been to develop a new methodology that will allow us to infer the direction of the magnetization from spacecraft magnetic field measurements. While rocks provide a very sparse sampling of the surface of a planetary body, spacecrafts measurements provide global coverage. We showed that our methodology works on synthetic data set, and we are now working further on applying it to real spacecraft measurements. This methodology can be applied to magnetic field data sets obtained by spacecrafts that have orbited Mars, the Moon and Mercury. Being able to infer the direction of the crustal magnetization at a global scale will give us an unprecedented view of the evolution of the deep interiors of these planetary bodies over geological times.
The study of lunar magnetism presents less challenges because astronauts of the Apollo missions have returned to Earth lunar rocks that are safely kept at the NASA's Johnson Space Center. In the framework of this project, we are conducting measurements on two different types of rocks, returned by the Apollo 16 and Apollo 17 missions. These rocks are 3.7 billion years old and can therefore give us information about the magnetic field of the Moon at its early history. The origin of lunar magnetism is still under debate and therefore these measurements allow us to provide much needed constraints on the nature and strength of the lunar magnetic field.
Another aspect of this study has been to develop a new methodology that will allow us to infer the direction of the magnetization from spacecraft magnetic field measurements. While rocks provide a very sparse sampling of the surface of a planetary body, spacecrafts measurements provide global coverage. We showed that our methodology works on synthetic data set, and we are now working further on applying it to real spacecraft measurements. This methodology can be applied to magnetic field data sets obtained by spacecrafts that have orbited Mars, the Moon and Mercury. Being able to infer the direction of the crustal magnetization at a global scale will give us an unprecedented view of the evolution of the deep interiors of these planetary bodies over geological times.
Progress beyond the state of the art:
- We have obtained the first paleointensity estimate (estimate of the strength of the magnetic field that magnetized a rock) of the oldest Martian meteorite available on Earth. Due to the fact that we could only acquire one data point we do not have enough evidence to make sufficient progress beyond the state of the art.
- We have studied the magnetic record of lunar mare basalts from the Apollo 17 mission. We found them to carry evidence of being magnetized by a uniform magnetic field. Moreover, we found one of the subsamples to carry two distinct magnetic signatures, one from the time the rock formed and one from a much younger impact event. These results combined offer strong evidence that the Moon had a lunar dynamo during the early phase of its geological history, an hypothesis still under debate in the scientific community.
- We have developed a new methodology that allows to infer the magnetization direction of small-scale sources from magnetic field spacecraft measurements.
For the remaining of the project, we expect the following outcomes:
- Finalize the studies on the Apollo 17 mare basalts. We are now working on assessing their magnetic recording properties.
- Study two Apollo 16 regolith breccias. I am currently preparing the subsamples and getting trained in the measurement technique, which is different than the one used for the mare basalts. This technique offers even more accurate paleointensity estimates than the one used for the Apollo 17 rocks and therefore will provide us with very valuable additional constraints on the debated origin of lunar magnetism.
- Apply our new methodology to infer magnetization direction from spacecraft magnetic field measurements on Mars or the Moon and showcase its potential for upcoming space missions.
- Study the feasibility of the 4.4 billion years old grains of the Martian meteorite NWA 7034 to preserve their primary magnetization. This will inform the ongoing selection process of rock samples by the Perseverance rover of the Mars 2020 mission and will train me in magnetic microscopy.
- If there is enough time, study the magnetic record of terrestrial rocks that date from the Archean (4 Gy-2.5 Gy) and Paleoproterozoic (2.5 Gy-1.5 Gy) eons in order to constrain Earth’s primitive magnetic field.
The expected socio-economic impact and the wider societal implications of the project:
- Improve our understanding of how planets form and evolve.
- Increase European expertise in space missions, including spacecrafts orbiting planetary bodies, helicopters or drones flying on other planets, and sample return missions.
- We have obtained the first paleointensity estimate (estimate of the strength of the magnetic field that magnetized a rock) of the oldest Martian meteorite available on Earth. Due to the fact that we could only acquire one data point we do not have enough evidence to make sufficient progress beyond the state of the art.
- We have studied the magnetic record of lunar mare basalts from the Apollo 17 mission. We found them to carry evidence of being magnetized by a uniform magnetic field. Moreover, we found one of the subsamples to carry two distinct magnetic signatures, one from the time the rock formed and one from a much younger impact event. These results combined offer strong evidence that the Moon had a lunar dynamo during the early phase of its geological history, an hypothesis still under debate in the scientific community.
- We have developed a new methodology that allows to infer the magnetization direction of small-scale sources from magnetic field spacecraft measurements.
For the remaining of the project, we expect the following outcomes:
- Finalize the studies on the Apollo 17 mare basalts. We are now working on assessing their magnetic recording properties.
- Study two Apollo 16 regolith breccias. I am currently preparing the subsamples and getting trained in the measurement technique, which is different than the one used for the mare basalts. This technique offers even more accurate paleointensity estimates than the one used for the Apollo 17 rocks and therefore will provide us with very valuable additional constraints on the debated origin of lunar magnetism.
- Apply our new methodology to infer magnetization direction from spacecraft magnetic field measurements on Mars or the Moon and showcase its potential for upcoming space missions.
- Study the feasibility of the 4.4 billion years old grains of the Martian meteorite NWA 7034 to preserve their primary magnetization. This will inform the ongoing selection process of rock samples by the Perseverance rover of the Mars 2020 mission and will train me in magnetic microscopy.
- If there is enough time, study the magnetic record of terrestrial rocks that date from the Archean (4 Gy-2.5 Gy) and Paleoproterozoic (2.5 Gy-1.5 Gy) eons in order to constrain Earth’s primitive magnetic field.
The expected socio-economic impact and the wider societal implications of the project:
- Improve our understanding of how planets form and evolve.
- Increase European expertise in space missions, including spacecrafts orbiting planetary bodies, helicopters or drones flying on other planets, and sample return missions.