New Breakthrough on Solar Wind Unveiled by India’s Mars Orbiter Mission (MOM)!

You may wonder that, based on their limited observations, in the early days, people thought the Sun had an atmosphere,  like Earth, experiencing seasons and even forming clouds. These clouds were thought to be responsible for the dark spots observed on the Sun’s surface  (now these are known as sunspots, dark regions on the Sun’s surface that appear due to locally lower temperatures compared to their surroundings).

However,  with the advancement in fundamental physics and deeper understanding of the physical processes, scientists realise that in the amount of energy coming out from the Sun, particles can not exist in the neutral form and will get ionized. This meant that the Sun’s atmosphere was not as initially imagined but instead existed in a charged state, later named the “Solar Corona”, that extends across our entire solar system. The speed at which the solar corona expands and moves through space is known as solar wind velocity. That makes it crucial to understand the Sun’s atmosphere and its impact on life on Earth and beyond.

The challenge, however, lies in measuring the behavior of the Sun’s atmosphere close to its surface. To address this, scientists from various centers of ISRO came up with an innovative idea and measured the solar corona close to the Sun using radio signals from India’s first interplanetary mission, Mangalyaan Mission (Mars Orbiter Mission; MOM). It was launched in November 2013 and inserted into Mars orbit in September 2014. The mission concluded its life in September 2022, more than the planned duration (6 months), with remarkable scientific outcomes. 

The recorded data was analyzed by Keshav Aggrawal, a PhD student at IIT Indore, as part of his Ph.D. thesis research. His findings revealed that the dense solar atmosphere (plasma density ~10^{10} particles per cubic meter) in the region 5 to 8 solar radii from the Sun’s surface (1 solar radius ≈ 700,000 km) is expanding outward at a velocity of 100 to 150 km/s. For context, the distance between Earth and the Sun is approximately 215 times the Sun’s radius.   

What’s the Idea?

Another highlight of this experiment is that it was not initially planned, and scientists came up with an innovative idea and utilized the existing setup of the MOM orbiter to probe the Solar Corona during a suitable solar conjunction (shown in the figure). In the planned experiment, the radio signal from the MOM spacecraft passes very close to the Sun, hence the solar corona. As these signals travel through the hot, bubbly corona, they get “stretched out” or broadened due to tiny changes in the plasma density (the mix of charged particles in the Sun’s atmosphere). This broadening in signal was recorded by a large ground-based antenna at the Indian Deep Space Network (IDSN), Bengaluru, India. By calculating how much the signal broadens, researchers can estimate the speed of the solar wind. In this study, researchers measured speeds between 100 and 150 km/s in a region roughly 5 to 8 Solar radii from the Sun’s center.

Figure: The geometry of the experiment conducted using the Indian Mars Orbiter Mission

Why Does It Matter?

The solar wind is a stream of high-energy particles traveling at tremendous speeds from the Sun, significantly influencing the environment around Earth and beyond. It interacts with Earth’s intrinsic magnetic field, which serves as a protective shield against these energetic particles from space.

During intense space weather events, these particles can disrupt satellites and power grids. A recent example is the deorbiting of several Starlink satellites, emphasizing the need for continuous and frequent monitoring of the Sun’s atmosphere to ensure space safety.

By analyzing the speed of the solar wind and its variations across different regions of the solar atmosphere, researchers can enhance existing models and improve space weather forecasts, ultimately helping to mitigate its potential impacts on life and technology on Earth.

Key feature of the study

Quiet Sun Observations: The study measured the solar wind when the Sun was least active and highlighted how the differences in electron density, especially in areas where the density is lower in the solar corona ( also defined as coronal holes), can affect the speed estimates.

Aggarwal, Keshav, R. K. Choudhary, Abhirup Datta, Roopa MV, and Bijoy K. Dai. “Insights into Solar Wind Flow Speeds from the Coronal Radio Occultation Experiment: Findings from the Indian Mars Orbiter Mission.” The Astrophysical Journal 982, no. 2 (2025): 152.

Future aspects

This research not only brings us closer to understanding the complex behavior of the solar wind but also provides a foundation for future studies. Its findings are crucial for improving models that predict the behavior of the solar corona and solar wind, ultimately helping to mitigate their impact on life on Earth.    

Stay tuned to New Wave Particle for more exciting updates!