What are Plasma Waves?
Plasma waves are short-time scale fluctuations in the electric and magnetic fields observed in plasmas, which are ionized gases consisting of positively charged ions and free electrons. Plasma waves play an important role in the energization and transport of the charged particles in the plasma environment of planets. However, not much is known about the existence and characteristics of plasma waves in the vicinity of unmagnetized planets like Mars, which do not have any intrinsic magnetic field and interact directly with the high-speed solar wind coming from the Sun.
How were they Detected?
Scientists, including researchers from the Indian Institute of Geomagnetism (IIG), an autonomous institute of Department of Science and Technology, have detected high-frequency plasma waves in the Martian upper atmosphere using data from the Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft of NASA. The study was carried out in collaboration with scientists from Japan, USA, and UAE and it has been published in Astronomy & Astrophysics Journal.
The researchers have examined the existence of high-frequency plasma waves in the Martian plasma environment by making use of the high-resolution electric field data from the MAVEN spacecraft. These waves could be either electron oscillations that propagate parallel to the background magnetic field (Langmuir waves) or electron oscillations that propagate perpendicular to the background magnetic field (upper-hybrid type waves) in the magnetosheath region of Mars. The magnetosheath is a region where the solar wind is slowed down by the planet’s obstacle effect.
The scientists observed two distinct wave modes with frequency below and above the electron plasma frequency in the Martian magnetosphere. These waves were observed around 5 LT (local time) on February 9, 2015, when the MAVEN spacecraft crossed the magnetopause boundary and entered the magnetosheath region. These waves are either broadband- or narrowband-type with distinguishable features in the frequency domain. The broadband waves were consistently found to have periodic patchy structures with a periodicity of 8–14 milliseconds.
Why are they Important?
Observations of such high-frequency plasma waves provide a tool to explore how electrons gain or dissipate energy in the Martian plasma environment. The physical mechanism responsible for the generation of broadband-type waves and its modulation remains unexplained and further investigation is required. The study also suggests that these waves could be used as a diagnostic tool to estimate the electron density and temperature in the Martian upper atmosphere.
Understanding the presence and characteristics of plasma waves in the context of planetary atmospheres, such as Mars, helps scientists gain insights into the interactions between the solar wind and the planet’s atmosphere, especially in the absence of an intrinsic magnetic field. This can also shed light on the history of Mars’ atmosphere, climate, liquid water, and planetary habitability by examining the role of volatiles loss to space over time.
What is Next?
The detection of high-frequency plasma waves in the Martian upper atmosphere is a novel discovery that can help understand plasma processes over Mars. The study demonstrates the use of MAVEN spacecraft data to explore the Martian plasma environment and its implications for planetary science. The researchers hope to further investigate the generation mechanism and modulation of these waves and their effects on the charged particles in the Martian atmosphere.
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