ISRO’s Aditya-L1 Solar Mission: Its First Accomplishment …

India’s Aditya-L1 solar mission, launched on September 2, 2023, has notched up its first major achievement: Its cutting-edge equipment—–the Visible Emission Line Coronagraph (Velc)—–has precisely estimated the onset time of a Coronal Mass Ejection (CME) on the Sun on July 16.

Prof Ramesh of the Indian Institute of Astrophysics, Bengaluru, Velc’s designer and its principal investigator, who has published a paper in Astrophysical Journal Letters on the coronal ejection that his Velc captured at 13.08 GMT on 16 July, said the CME originated on the side of the earth, but “within half an hour of its journey, it got deflected and went in a different direction, going behind the Sun. As it was too far away, it did not impact earth’s weather.”

CME is an explosive burst of charged particles from the Sun. They “could weigh up to a trillion kilograms and can attain a speed of up to 3000 Km per second while traveling. It can head out in any direction, including towards the earth”, said Prof  Ramesh.

Solar storms—–a sudden explosion of particles, energy, magnetic fields and material blasted into the solar system by the Sun when its magnetic fields explosively realign—in the form of solar flares and CMEs routinely impact Earth’s weather. They also impact the space weather in which about 7800 satellites are stationed. The charged particles of a CME can make all the electronics on a satellite malfunction. Thus, CMEs can seriously affect weather and communication satellites. According to Space.com, they rarely pose a direct threat to human life. But they can cause mayhem on Earth by interfering with the Earth’s magnetic field. They can knock down power grids.

Sometimes solar flares and CMEs happen at the same time. It is observed that the strongest solar flares are almost always correlated with CMEs. A solar flare is a brilliant flash of light. On the other hand, a CME is an immense cloud of magnetized particles hurled into space in a particular direction, sometimes toward Earth.

The most powerful solar storm in recorded history called the ‘Carrington Event’, occurred in 1859. It triggered intense auroral lights and knocked out telegraph lines across the globe. NASA scientists say that a powerful CME tore through Earth’s orbit on 23 July but that we were “incredibly fortunate” that instead of hitting our planet, it hit NASA's solar observatory STEREO-A in space. In 1989, a CME knocked out part of Quebec’s power grid for nine hours leaving six million people without power. On 4 November 2015, solar storms disrupted air traffic control at Sweden and some other European airports, leading to travel chaos for hours.

Today, as Prof Ramesh said, “our lives fully depend on communication satellites and CMEs can trip the internet, phone lines, and radio communication that can lead to absolute chaos”. It is in this context that ISRO’s breakthrough finding is considered crucial for the world. For, it will enable scientists to watch the happenings on the Sun and spot a CME in real time, watch its trajectory, and issue accurate early warnings for solar storms. This forewarning, in turn, shall help to switch off power grids and satellites to keep them out of harm’s way.

Of course, ISRO is not the only agency that is examining the Sun to understand its magnetic activity. Indeed, US space agency NASA, the European Space Agency (ESA), Japan and China have been watching the Sun through their space-based solar missions for decades. A question may now arise: How then has ISRO’s discovery turned important for the world?

To get an answer to this question, we need to understand Velc’s design specificities and the eclipse-like advantage thereof. As we all know, when we look at the Sun from Earth, we see the photosphere—–the Sun’s surface or the brightest part of the star. But, during a total eclipse when the Moon passes between Earth and the Sun covering the photosphere, we can see the solar corona—– the Sun’s outermost layer.

According to Prof Ramesh, India’s coronograph has a slight advantage over the coronagraph in NASA’s joint Solar and Heliospheric Observatory. India’s coronograph is of that size which enables it to mimic the role of the moon in eclipse formation and therefore artificially hide the Sun’s photosphere affording “Aditya-L1 an uninterrupted view of the corona 24 hours a day 365 days a year”. And this feature enabled Velc to “precisely estimate the time a CME begins and in which direction it’s headed”, said Prof Ramesh.

As against this, NASA’s coronograph, being bigger in size, hides not only the photosphere but also parts of the corona, and hence it cannot see the genesis of a CME if it originates in the hidden region.

That aside, India also looks at the Sun from three ground-based observatories located in Kodaikanal, Gauribidanur in the south and Udaipur in the northwest. According to Prof Ramesh, adding up the findings of these observatories with that of Aditya-L1's, India can greatly improve its understanding of the Sun.

With the Sun approaching a solar maximum in its 11-year activity cycle, the frequency of CMEs is expected to increase significantly. In such a scenario, the data collected by Aditya-L1 will play a vital role in developing future predictive models that will help protect Earth’s infrastructure, including satellites, power grids, and communication systems, from potential disruptions caused by CMEs.

So, yes, a big congratulations to ISRO for their remarkable achievement!

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