A new view of lunar magnetism

One of the enduring mysteries about the Moon is whether it ever had an internal-generated magnetic field, and if so, when the core dynamo ceased. New research by Tinghong Zhou, John Tarduno, Rory Cottrell, and Eric Blackman at the University of Rochester and collaborators from the University of Notre Dame, UC Santa Cruz, and the University of Arizona, in a study supported by NSF and NASA, have provided new insights into this lunar puzzle, narrowing down the potential lifespan of the Moon’s dynamo to its first ~140 million years. The new study focused on analyzing magnetic field intensity (called paleointensity) recorded in Apollo samples that are between 4.36 to 3.7 billion years old. Using an advanced technique known as single-crystal paleointensity analysis, the researchers were able to obtain accurate measurements of the Moon’s ancient ambient surface magnetic field environment – which indicated negligible field strengths. This evidence for the absence of a dynamo resolves the long-lasting paradox between the previously hypothesized long-lived lunar dynamo and energy considerations, namely that the tiny lunar core would have been unable to power a strong, sustained magnetic field.

Figure 1: Astronaut John Young stands on the rim of the Plum Crater on the Moon. Image source: NASA, Apollo Lunar Surface Journal, Apollo Image Library Hasselblad Magazine, 109/G (B&W), AS16-109-17804.

A key part of this new understanding of lunar magnetic history comes from a focus on magnetic carriers meeting the demanding requirements of paleointensity theory. Single-domain magnetic grains, which are very small, some 20 to 200 nm in size, are required. In contrast, larger magnetic grains are far less reliable because their internal domain walls can move with time and during laboratory treatments, corrupting any original magnetic signal. Magnetic minerals in lunar rocks are dominated by these problematic multidomain grains, making paleointensity analysis very challenging. The single-crystal paleointensity technique used in the study by Zhou and others builds on an earlier study led by the University of Rochester and focuses on silicate crystals that contain single-domain magnetic grain inclusions to meet the paleointensity recording requirement. The authors tested the fidelity of their records by CO2 laser heating in different fields and in the presence or absence of an applied field. These tests exclude thermal alteration and provide a measure of recording efficiency. The authors found high recording efficiencies, indicating that if surface fields had been present, they would have been recorded. Hence, the absence of a paleointensity indicates absence of a surface field.

In addition to the single crystal paleointensity, the study also employed whole rock paleointensity on 3.7-billion-year-old Apollo basalts using a non-thermal technique. Unlike thermal methods that measure magnetization acquired from natural cooling, non-thermal methods rely on additional assumptions and empirical calibrations. The results from the non-thermal technique showed abnormally high and inconsistent paleointensities. These anomalies could indicate shock magnetization from lunar impacts or issues with the multidomain grains and/or the applied non-thermal method. Because non-thermal analysis of whole rocks is the basis for some calls for an episodic lunar dynamo, the researchers conclude there is no robust evidence for such a phenomenon from Apollo samples.

Figure 2: Lunar magnetic history indicated by paleointensity data. Single crystals suggest a null lunar magnetic field since 4.36 Ga, while some whole rock data obtained by non-thermal methods yield abnormally high values that might be related to large multidomain magnetic grains and/or impact induced magnetic field. Figure modified from Tarduno et al., 2021 and Zhou et al., 2024.

If the Moon did not have a dynamo for most of its history, the early Earth’s (for example, during the Archean and Hadean eons) atmosphere can be transferred to the Moon, which would be unshielded by an intrinsic field, and preserved in its regolith. With a smaller Earth-Moon distance and the stronger solar wind in the Archean and Hadean, this transfer would have been enhanced. By studying the volatiles trapped in the lunar regolith, we might have opportunities to better understand the composition of the early Earth’s atmosphere and the conditions that influenced the evolution of life.

Tinghong Zhou is a postdoctoral researcher at the University of Rochester mentored by Professor John A. Tarduno. Her research focuses on the long-term evolution of the geomagnetic field and its correlation with the Earth’s deep interior, and the origin of the lunar magnetism. Email address: tzhou16@ur.rochester.edu

Exploration of the Jovian system #2

There are two icy moon missions of this decade that will reach their respective bodies of interest beginning of next decade- JUpiter ICy moons Explorer (JUICE) and Europa Clipper. The main focus of JUICE is Ganymede and for Clipper is Europa. Both these planetary bodies are moons of our Solar System's largest planet Jupiter. Scientists are particularly interested in the Jovian moons because these bodies contain large oceans under their surface making them a suitable place to study for potential habitability. They are called 'icy moons' because their surface is made up of ice! If you are interested to learn more about these moons, head to our previous blogs about them!

While JUICE launched on April 14th 2023, Clipper is all set to launch this month! If you are a space enthusiast and are interested in watching the launch: in person- head to Kennedy Space Center in Florida, USA, or online: head to NASA's website. The launch window starts within a week on October 10th and goes up till the end of the month. It will take Clipper five and a half years to reach Jupiter in 2030.

Image Credit: NASA

Where is the magnetized material located on the lunar surface?

Magnetometers onboard spacecraft have detected magnetic field signals originating from the lunar crust. These signals are known as magnetic anomalies and are generated by rocks that are permanently magnetized. Lunar magnetic anomalies are distributed heterogeneously over the lunar surface and the geological processes that gave rise to them is under debate. Thus, the Moon's geological history can be further assessed by inferring the shape of the underlying magnetized material. Up to now, these sources were not fully described for such geological assessment studies.

Joana Oliveira and her colleagues, in a recently published work, evaluated the ability of a methodology up to now used to infer the direction of the magnetization, called the method of Parker, to recover the location and shape of the magnetized material by using orbital magnetic field data only.

Lunar magnetic field map at 30 km altitude using Tsunakawa et al. 2015 model.

Through a series of tests, the authors of this study have shown that the Parker’s method can constrain the shape of the source of a magnetic anomaly, provided that the respective part of the crust is magnetized along a common direction.

"We tried to take it a step further to crack the unidirectional assumption by testing complex bodies with different directions, and we were surprised by how this method was still able to recover most of the magnetized structure”, Joana said.

The authors also applied the method to two lunar magnetic anomalies related to two visible geological features an impact crater and an albedo anomaly, also know by swirls. Results show that the inferred shape and location of the magnetized material are in good agreement with the associated geological features and suggest that one originated by an impact event and the other by volcanic activity.

Parker inversion results for the Mendal-Rydberg basin. The magnetized material (related to the dipole moments) is correlated with the inner depression in blue color of the topography map, despite the magnetic field signal being shifted to the southwest from the center of the basin. Figure adapted from Oliveira et al. 2024.

Future applications can focus on constraining the origin of the many lunar magnetic anomalies that are not associated with visible geological features.

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Joana S. Oliveira is an archive scientist working for the European Space Agency (ESA) JUICE and Heliophysics missions, with a background in planetary sciences. She is interested in learning about the history of rocky planets through their magnetic field signals.

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Lets meet Titan again!

Titan is the second largest moon of the Solar System (after Jupiter's Ganymede) and the largest moon of Saturn. It has icy and rocky materials in its interior and is the only moon that has a denser atmosphere than the Earth. Its surface has been characterised to have a combination of features- lakes, craters, volcanoes, mountains! The surface is ideal for understanding the chemical processes that took place before life emerged.

Titan was discovered by Dutch astronomer Christiaan Huygens, after whom ESA's Huygens probe of NASA's Cassini mission was named. On 14 January 2005, the probe touched down at the surface and provided us with measurements before its lifetime of 72 minutes after a 2 hours descent. 

Dragonfly is a NASA rotorcraft lander mission that will visit the moon in 2034 with launch in July 2028. The plan is to fly to different locations on Titan and collect data to understand the progression of prebiotic chemistry and characterise habitability of its environment. The mission will be a first of its kind with many technical feats such as operating in temperatures of -180°C in an atmosphere that is four times denser. 

Good luck to Dragonfly! Lets meet Titan again!

Image credits: NASA/John Hopkins APL/Steve Gribben

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Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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Europa: Candidate for habitability

Continuing our series on the upcoming missions to the Jupiter system and talking about the Jovian moons, here is a brief overview of Europa and why it is the best suited candidate for habitability in our Solar System. 

The size of Europa is quite similar to that of our own moon but their interior structures are a little different. Europa, like Ganymede, is considered to be an icy moon. It consists of an ice shell followed by a layer of liquid water ocean. The final two layers consist of a rocky mantle and a metallic core. An interesting fact about its ocean is that it is believed to hold twice as much water as we find on the oceans on Earth! Even pictures of the surface of Europa show signs of water being present in its interior.

What makes Europa different from the other icy moons in our Solar System is its interaction between the ocean and rocky mantle layer. There is possibility of hydrothermal vents where the two layers meet which indicates a sign of chemistry that can sustain life. We see similar vents on Earth that are home to microbial lifeforms. It will be interesting to see the results we get from the Europa Clipper and JUICE missions in the next decade. In the meantime, drop your questions about Europa below and let us know what you are curious to find about the moon!

Image: Europa. Credit: NASA/ JPL-Caltech/ DLR.

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Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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Ganymede: The largest icy moon of Jupiter

Following up on our last blog about the icy moons of Jupiter, in this blog we start off with understanding the largest moon of the planet and our Solar System, Ganymede! Although we have only a few measurements from the moon through the Galileo and Juno missions orbiting Jupiter, we have quite a lot of information from them.

Ganymede is a very unique moon. It is the only moon we know of that is capable of generating its own magnetic field, possibly through a dynamo. This means that there is some conducting liquid in which convection is taking place that is producing a magnetic field of the order of ~103 nT. This dynamo is expected to be an iron and iron sulphide alloy.

While the most important and interesting insight about Ganymede is the dynamo, another fascinating feature is the presence of a subsurface ocean. However, we are still unsure if the field we observed was from an ocean or just part of the dynamo signal. When we model magnetic field data of the moon, both these possibilities arise and hence to confirm which of them are true, we would require more data from around the moon.

Once we have a wealth of measurements from future missions, we would be able to better model the magnetic field as well as other observations like the gravity field which will help us better understand its interior structure. In the meantime, drop your questions about Ganymede below and let us know what you are curious to find about the moon!

Image: Ganymede from Galileo. Credit: NASA.

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Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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The icy moons of Jupiter

Jupiter is a giant ball of gas which is 10 times larger than the planet we live on. Naturally, the magnetic field it produces is also stronger, more than 20 times Earth's magnetic field!

While we need to understand Earth's field for our day to day tasks like navigation, we study Jupiter's field to understand the evolution of the Solar System. One major consequence of the strong field of Jupiter is its effect on the Galilean moons.

The Galilean moons, namely Io, Europa, Ganymede and Callisto are the biggest four moons that orbit Jupiter. Making use of the limited data we have from them, we believe that the moons have a conducting liquid near the surface. This liquid is most likely an ocean of water and salts except in Io where we think its a magma ocean. The evidence for this primarily comes from magnetic field measurements of the moons. 

Magnetic field provides a unique way to study the interior of the object that produces it. Thanks to it and the satellites that take the instrument to measure it, we can study the electromagnetic induction in the moons of Jupiter sitting in our offices on Earth. When there is a periodically varying field near a body which has conducting material, induction takes places inside the body which produces a magnetic field. In this case, the time varying field is the large magnetic field of Jupiter and the conducting material is the subsurface ocean of the moons. If we study the induced field from the satellite measurements, we can find properties like the depth, conductivity and thickness of these oceans. All we need are magnetic observations from near the moons. While it seems easy, we do have to wait a few years before ESA's JUpiter ICy Moons Explorer (JUICE) and NASA's Europa Clipper missions can reach and transmit their observations from the Jovian system!

Image credits: ESA

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Shivangi Sharan is a postdoctoral research associate at Imperial College London, working on prioritising the research that will be carried out using the JUICE magnetometer data. Previously, she has worked on the interior of Mars and Jupiter using their magnetic observations. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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Space News

Let's have a glance at the upcoming Space missions' news!

In 2024, there are some milestones to be achieved for different Space missions. 

Find a sneak peak below.

1) Intuitive Machines 1 - NASA lunar lander launch in mid-February

2) Chang'e 6 - Chinese lunar sample return mission launch in May

3) Bepi Colombo - ESA mission fourth and fifth Mercury flyby on September 5 and December 2

4) Martian Moon eXploration - JAXA Phobos sample return launch in September

5) Europa Clipper - NASA Jupiter orbiter launch in October

6) Hera - ESA asteroids mission launch in October

7) VIPER - NASA lunar lander launch in November

Source: NASA

Image Credit: ESA- D. Ducros 

Exploration of the Jovian system

In a month's time, the European Space Agency's (ESA) JUICE mission would be launched. JUICE is the
Jupiter Icy Moons Explorer which aims to study 3 Galilean moons in an attempt to understand their internal structure.

The first measurements around Jupiter's moons were received from the Galileo mission. Galileo was launched by NASA in October 1989 and provided data from 1996 to 2003. Based on the data from the spacecraft, scientists believe that Europa, Callisto and Ganymede might have a subsurface ocean. Ganymede even has its own magnetic field while Io has active volcanoes. The data from the upcoming JUICE mission will provide further evidences to better constrain the interior of these natural satellites.

The JUICE mission is scheduled to launch on 13th April from French Guiana. It will carry 10 scientific instruments focused on understanding the Jovian magnetosphere and its interaction with the satellites. The spacecraft will revolve around Jupiter and is expected to make a total of 35 flybys providing data near the moons. During the final phase of the mission, JUICE will also orbit around Ganymede, which will give a clearer picture about its internal magnetic field.

Image Credit: ESA (Jupiter with its 4 Galilean moons- Io, Europa, Ganymede, Callisto).

If you are interested to know more, ask us in the comments or on our social media platforms (top left of page). You can also visit ESA's website about the JUICE mission here.

Space News

Our last space news blog was about the Artemis launch which is the first step to get humans back on the Moon. In this blog, we update you with the mission....

Orion spacecraft from the Artemis 1 mission has successfully come back to Earth! Artemis 1 launched from Earth on November 16th, 2022 for a 25 days mission with the aim of a test run before a crewed flyby mission to the Moon in Artemis 2 and a crewed landing in Artemis 3. 

Orion splashed down in the Pacific after which tests were performed on it. It has now been shifted to a ship which will deliver it back to the NASA centre for further tests to be carried out. Science standing on the moon again is not long now!

Orion after it splashed down in the Pacific Ocean. Credit: NASA

Space News

The new Artemis 1 launch attempt is in 2 days!

Artemis I is an uncrewed mission that will orbit the moon for 25 days. It is a test mission before NASA sends the Artemis 2 for a crewed flyby around the moon, followed by a landing by Artemis 3.

It would be the first attempt for a lunar landing after the Apollo Missions. The Apollo 11 to 17 missions landed a total of 12 people on the surface. With Artemis 3, scientists including a woman and a person of colour will set foot on the moon for the first time.

The launch for Artemis 1 was originally planned for 29th August. However, it got delayed due to technical reasons. The next attempt was planned for 3rd September which also got postponed due to technical issues. After some weather delays, the new launch window is for 16th November followed by a back-up window on 19th November. We hope this time Artemis flies. Keep your eyes on the sky or on the live updates!

Artemis 1 Map. Credits: NASA

The Naming Game : Moon Edition

What are moons? Moons are satellites that orbit around a planet. So, technically they'd be 'natural satellites of the planets' because "Moon" is just one, but, practically, don't we all just call them "moons"?! Currently, there are over 200 moons in our Solar System, and that's excluding the ones orbiting the dwarf or minor planets. 

Some moons have atmospheres, some have volcanic activities going on them and some even have oceans. Some moons orbit in direction of the rotation of planet and some orbit in opposite direction. But do you know how or what they are named?

The official names of celestial bodies are taken care of by the International Astronomical Union. Most of them are named after Greek and Roman mythology characters, but some are also named after literary characters.

While Mercury and Venus don't have any moons, our moon has many different names in different languages. The word "Moon" was named after two Latin words meaning 'to measure' and 'month'.

Mars, named after the Greek mythological God of war, Ares, has two moons -  Phobos and Deimos - named after the sons of Ares meaning 'fear' and 'dread'.

Jupiter has a plethora - 53 named moons and 26 unnamed ones. The planet is named after the Greek God, Zeus, and its moons are named after his lovers or descendants. Galileo first discovered the moons of Jupiter and hence the four biggest moons - Ganymede, Callisto, Io and Europa - are called the Galilean moons.

Saturn has such a large family of moons - around 82 which we know of - that there was a shortage for names. They were named after the Titans (children of Greek Gods Uranus and Gaia) and their descendants, but are now named also after the giants of the Norse, Gallic and Inuit mythology.

Uranus has 27 moons and they are named after Shakespeare's characters. A few are named after Alexander Pope's characters. Look them up to know if your favorite character made the cut; the maximum number coming from 'The Tempest'.

And finally, Neptune has 14 moons. Neptune, named after the Roman God of sea has its moons named after other Roman and Greek sea gods and nymphs.

Moons that are yet to be confirmed are named with a letter and year. 

Images : (1) Kevin Gill on Flickr. (2) Hubble. (3) Adobe Stock.

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Shivangi Sharan is a second year PhD student at the Laboratory of Planetology and Geodynamics in France. Her research focusses on the study of the magnetic field of Mars and to infer its internal structure from it. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.

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