Source of electron acceleration and X-ray aurora of Mercury ̶ local chorus waves detected

2023-10-10

(Press-News.org) Background

Since Mercury is the closest planet to the Sun among the solar system planets, it is strongly influenced by the solar wind, a high-speed (several hundred km/s) stream of plasma blowing from the Sun. Explorations of Mercury was first carried out by the Mariner 10 spacecraft in 1974 and 1975, which revealed that Mercury has a magnetic field, and thus a magnetosphere, similar to that of Earth. In the 2000s, the MESSENGER spacecraft provided a detailed picture of the Mercury's magnetic field and magnetosphere, and revealed that Mercury's magnetic field center is shifted northward from the planet’s center by approximately 0.2 RM (RM is Mercury's radius of 2,439.7 km). The third exploration of Mercury is currently being made by the BepiColombo International Mercury Exploration Project*1) thanks to the Mio spacecraft (Project Scientist, Dr. Murakami) and the Mercury Planetary Orbiter (MPO). In particular, unlike Mariner 10 and MESSENGER, the Mio spacecraft is equipped with a full suite of plasma wave instrument (PWI, Principal Investigator Prof. Kasaba) designed specifically to investigate for the first time the electromagnetic environment around Mercury. Electromagnetic waves can efficiently accelerate plasma particles (electrons, protons, heavier ions); as such, they play an important role in the Mercury’s magnetospheric dynamics.

Results

The present study was performed by an international joint research team consisting of scientists from Kanazawa University, Tohoku University, Kyoto University, MagneDesign Corporation, Laboratoire de Physique des Plasmas, France with support from CNES (French Space Agency), and the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency (JAXA).

The Mio spacecraft, launched on October 20, 2018, is currently on its way to Mercury, with a final insertion in orbit around the planet scheduled for December 2025. Although getting Mio into Mercury's orbit is technically extremely difficult due to the strong gravity of the Sun as compared to that of Mercury, it is scheduled to enter into orbit around Mercury in 2025 after several flybys*2) of Earth, Venus, and Mercury for gravity assist maneuvers. During the Mercury flybys that occurred on October 1, 2021 and June 23, 2022, the Mio spacecraft had approached the planet at an altitude of approximately 200 km. The stowed configuration of the spacecraft during the journey to Mercury is not optimal for measuring electromagnetic waves because of the interference noise coming from the spacecraft itself. However, the Mio spacecraft was developed to lower as much as possible its electromagnetic noise level, and thus has been certified as an electromagnetically clean spacecraft through EMC tests*3). Alternating current magnetic field sensors that can cope with the scorching environment of Mercury have been developed jointly by Japan and France and have allowed the first electromagnetic wave observations around Mercury without being contaminated by the noise from the spacecraft itself. This has revealed the local generation of chorus waves, such as those that are frequently detected in the magnetosphere of Earth. The existence of chorus waves in the magnetosphere of Mercury, which is now confirmed, was predicted (frequency range, intensity, etc.) since 2000s when the plasma wave instrument (PWI) of the Mio spacecraft was designed. What most surprised the international joint research team, including Dr. Ozaki of Kanazawa University, was the ''spatial locality'' of the chorus waves, which were detected only in an extremely limited region in the dawn sector of the Mercury’s magnetosphere during the two flybys. This means that there is a physical mechanism that tends to generate chorus waves only in the dawn sector of the magnetosphere of Mercury. In order to investigate the cause of the generation of chorus waves in the dawn sector, the international joint research team used the nonlinear growth theory of chorus waves established by Prof. Omura, Kyoto University, to evaluate the effect of curvature of the magnetic field of Mercury, which is strongly distorted by the solar wind. The magnetic field lines in the night sector are stretched by the solar wind pressure, while the magnetic field lines in the dawn sector are less affected resulting in a smaller curvature. Based on the characteristics of the magnetic field lines and the nonlinear growth theory, it is revealed that in the dawn sector, energy is efficiently transferred from electrons to electromagnetic waves along magnetic field lines, creating conditions that favor chorus wave generation. The effect is also confirmed in a numerical simulation of the Mercury environment using a high-performance computer. In this study, the team has revealed the importance of the planetary magnetic field lines, which are strongly affected by the solar wind, on the locality of chorus wave generation thanks to a strong synergy between "spacecraft observation", "theory" and "simulation".

Future Prospects

In the Mercury flyby observations, the team prepared for the comprehensive electromagnetic environment survey using the planned Mio spacecraft probe in orbit around Mercury. Chorus waves, which were expected to be detected at the time of planning, are observed in a quite local manner, i.e. in the dawn sector of Mercury, which was not expected, and the results show various fluctuations in the magnetosphere of Mercury. The data demonstrate the existence of energetic electrons on Mercury that can generate chorus waves, the possibility of generating active electrons efficiently accelerated by chorus waves, and the generation of X-ray auroras by electrons forcibly precipitating from Mercury's magnetosphere to the surface of Mercury driven by chorus waves. These observations will have a wide impact on the scientific understanding of Mercury's environment. The Mio spacecraft is on its way to carry out a comprehensive exploration of Mercury. Based on flyby observations we have found that magnetic field distortion is responsible for the local (i.e. dawn sector) generation of the chorus waves. The comprehensive exploration of the electromagnetic environment by the Mio spacecraft in Mercury's orbit will contribute not only to understanding the plasma environment of the entire Mercury’s magnetosphere but also to a deep understanding of the magnetospheric dynamics in general. The magnetosphere acts as a barrier preventing life-threatening cosmic radiations on the planets of the solar system. Comparison of data from Mercury and Earth will strengthen our understanding of this important natural shielding of our home planet.

Glossary

*1) BepiColombo International Mercury Exploration Project

Comprehensive exploration project for Mercury using two spacecraft probes (Mio and MPO) by Japan-Europe cooperation. In particular, Japan is in charge of the Mercury magnetosphere probe Mio, equipped with electromagnetic wave observation instruments, etc.

*2) Flyby

With a spacecraft probe passing in proximity to a planet. The orbit of the spacecraft probe is to be changed in a desired manner by using the gravity of the planet.

*3) EMC (electromagnetic compatibility) test

Evaluation test to check whether unnecessary electromagnetic noise is emitted and whether the equipment is designed and manufactured in such a way that it will not malfunction even if it receives unwanted electromagnetic noise.

Reference

Authors: Mitsunori OZAKI, Satoshi YAGITANI, Yasumasa KASABA, Yoshiya KASAHARA, Shoya MATSUDA, Yoshiharu OMURA, Mitsuru HIKISHIMA, Fouad SAHRAOUI, Laurent MIRIONI, Gérard CHANTEUR, Satoshi KURITA, Satoru NAKAZAWA, Go MURAKAMI.
Title: Whistler-mode waves in Mercury’s magnetosphere observed by BepiColombo/Mio
Journal: Nature Astronomy
Published online on Sept. 14, 2023
DOI: 10.1038/s41550-023-02055-0
URL: https://doi.org/10.1038/s41550-023-02055-0

Funders

This work was supported by JSPS KAKENHI (No. JP20H02162), the Mitani Foundation for Research and Development.

END

[Attachments] See images for this press release:

ELSE PRESS RELEASES FROM THIS DATE:

NIH provides $1.2 million for ambitious effort to battle antibiotic resistance

2023-10-10

University of Virginia researchers are working to outrace two dangerous germs known for quickly developing resistance to new antibiotics – and the scientists’ efforts could help us better combat antibiotic resistance more broadly. A team led by Jason Papin, PhD, is developing sophisticated computer models of Staphylococcus aureus and Pseudomonas aeruginosa, two multi-drug resistant bacteria that infect thousands of Americans every year. The researchers will use their models to better understand the cellular processes and gene activity that make the bacteria ...

Researchers test large language model that preserves patient privacy

2023-10-10

OAK BROOK, Ill. – Locally run large language models (LLMs) may be a feasible option for extracting data from text-based radiology reports while preserving patient privacy, according to a new study from the National Institutes of Health Clinical Center (NIH CC) published in Radiology, a journal of the Radiological Society of North America (RSNA). LLMs are deep-learning models trained to understand and generate text in a human-like way. Recently released LLM models such as ChatGPT and GPT-4 have garnered attention. However, they are not compatible with healthcare data due to privacy constraints. “ChatGPT and GPT-4 are proprietary models that require the user ...

DNA aptamer finds novel application in regulating cell differentiation

2023-10-10

Generating specific cell lineages from induced pluripotent stem cells and embryonic stem cells is the holy grail of regenerative medicine. Guiding iPSCs toward a target cell line has garnered much attention, but the process remains challenging. Now, researchers from Japan have discovered that an anti-nucleolin DNA aptamer, iSN04, can determine a cell’s lineage during differentiation. By demonstrating the generation of cardiomyocytes from murine pluripotent stem cells, their concept shows promise as a regenerative therapy. Self-renewal ...

Monitoring African copper and cobalt mining emissions from space

2023-10-10

Emissions associated with mining operations in Africa’s Copperbelt can be quantified from space, according to new research led by the National Center for Atmospheric Research (NCAR). Mining for copper and cobalt in Africa has rapidly increased, the latter in response to growing global demand for electric vehicles, laptops, smartphones, and other devices that rely on lithium-ion batteries, the vast majority of which contain cobalt. The new study is published in Geophysical Research Letters, ...

Study compares health information exchange data versus patient self-reports to measure cancer screening uptake

2023-10-10

INDIANAPOLIS – Knowing which populations are following cancer screening guidelines is important to public health officials and policy makers as well as researchers developing strategies to improve adherence. A recent study is one of the first to compare using health information exchange (HIE) data with patient self-reported data as a means of gathering this intelligence. The researchers found that completeness of information differed by data source and screening test. HIE data provided more information than patient self-reports about ...

Seamlessly multiplexing memory storage and recall

2023-10-10

Every day we store memories, some of which we are able to recall later. But while we do so, do we keep on storing? Yes! We cannot afford to stop memory formation while we are retrieving prior ones. Imagine, for instance, that you are navigating the city while recalling last night’s events to a friend tagging along. Your brain must memorize aspects of the route even while you are in the story, so that you can find your way back later or reach your next destination. We seem to perform this task without much conscious effort. Big deal, one could say, as we know that the brain has trillions of synaptic connections, so parallel processing ...

UNIST recognized for design excellence at IDEA 2023!

2023-10-10

The design concept of a disaster alert balloon, capable of changing its color like a chameleon, has been honored for its design excellence at the internationally renowned International Design Excellence Award (IDEA) 2023. The awarded concept, named SAFEUP, serves as a hazard indicator, providing visual information about the condition of accident sites from a safe distance. Developed by Professor Chajoong Kim and his team in the Department of Design at UNIST, SAFEUP has received the ‘IDEA 2023’ Bronze Award in the category of Concepts & Speculative Design. The ...

The ribosome–depression link

2023-10-10

A group of ribosomal protein genes connect animal models of depression to human patients with major depressive disorder. In order to research depression treatments, scientists use a mouse model, inducing a state with similarities to depression though exposure to variable, unpredictable, and uncontrolled stressors over days or weeks. But is this state molecularly akin to what humans with major depressive disorder experience? To find out, Xiaolu Zhang, Mahmoud Ali Eladawi, and colleagues examine transcriptomics data from postmortem human brain tissue and from several mouse models of stress, seeking to pinpoint conserved ...

Ionic crystal generates molecular ions upon positron irradiation, finds new study

2023-10-10

Positron, the antiparticle of electron, has the same mass and charge as that of an electron but with the sign flipped for the charge. It is an attractive particle for scientists because the use of positrons has led to important insights and developments in the fields of elementary particle physics, atomic physics, materials science, astrophysics, and medicine. For instance, positrons are known to be components of antimatter. They are also powerful in detecting lattice defects in solids and semiconductors and in structural analysis of the topmost surface of crystals. Positronic compounds, namely ...

Maternal obesity predicts heart disease risk better than pregnancy complications

2023-10-10

First study to determine the role pre-pregnancy obesity plays in future poor heart health Those with overweight or obese BMI in early pregnancy had a higher risk of developing hypertensive disorders of pregnancy ‘If pre-pregnancy obesity is the culprit or cause of risk, we should be targeting this with interventions’ Pregnancy complications such as preeclampsia and gestational diabetes have recently been associated with a higher risk of developing heart disease later in life. But a new Northwestern Medicine study has found obesity before or during ...

Source of electron acceleration and X-ray aurora of Mercury ̶ local chorus waves detected

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: