‘Nasa’s Parker Probe will help us solve solar mysteries’
NEWDELHI:MADHULIKA Guhathakurta, a Kolkata-born astrophysicist at the National Aeronautics and Space Administration (Nasa), has led the ‘Living With a Star’ programme at the US space agency for over 15 years and been involved in the inception and execution of a solar probe mission since 1999. As Nasa’s Parker Solar Probe prepares to embark on its journey to the sun on Saturday,
caught up with Guhathakurta, 61, to understand how the mission that will “touch” the sun could revolutionise our understanding of our favourite star. Excerpts:
Vyawahare Malavika
challenges of this harsh environment and literally slice through a bit of the sun’s corona, which is the outermost region of the sun’s atmosphere, and send back the data that scientists have sought for decades. When we look at the sun from earth, it appears pretty ordinary and featureless. But if you see pictures of the corona visible during total solar eclipses, you can see the beautifully sculpted corona shimmering and gently billowing out, escaping the gravity of the sun. The yellow orb that is the photosphere has a temperature of about 5,500 degrees Celsius, but the temperature of the corona is at least 1-3 million degrees Celsius, much hotter than the photosphere. This is a common sense-defying experience. As you move away from the source of the heat, you expect the temperature to decrease and not increase.
The other basic question is how solar wind, which is not very strong near the sun’s surface, is accelerated to a speed of 400-800km as it moves out of the corona across the Solar System. Solving these two mysteries in solar physics has been a top priority for scientists for decades. Space Weather is a relatively new term, an idea of a sunearth connection that has emerged in last 20-30 years.
Unlike terrestrial weather, where air pressure, temperature and moisture are the important factors, the magnetic field of the sun is the dominating factor in space weather, and to some extent, pressure, gravity and temperature.
Space Weather describes disturbances that occur near earth space that can disrupt modern technologies, including satellites, radio and even electricity supply.
Extreme solar storms begin with an explosion, a “solar flare” in the magnetic canopy of a sunspot.
X-rays and extreme ultraviolet radiation reach the earth at light speed, ionising the upper layers of our atmosphere; side-effects of this “solar-electromagneticpulse” include radio blackouts and GPS navigation errors.
Minutes to hours later, the electrons and protons accelerated by the blast arrive —moving slightly slower than light — and electrify satellites and damage their electronics. Then come the “coronal mass ejections” (CMES), which are billion-ton clouds of magnetised plasma that take a day or more to cross the sun-earth divide.
The resulting effect on the earth is geomagnetic storms causing widespread voltage fluctuation; complete collapse of some grid systems; or blackouts and transformer damage. As with other natural disasters, the ability to react to a solar storm depends first on the accuracy of monitoring and prediction efforts, which in turn need to be based on real-world physics. Roughly every 11 years, the sun goes through a cycle, where the peak of the cycle points to a proliferation of sunspots, potentially producing dangerous solar flares and beautiful aurora.
The solar cycle is an oscillation between two extreme states. Right now, we are going through a Solar Minimum phase, a period when solar activity is subdued, and there are fewer sunspots and solar storms.
During the extreme quiet of 2007-2009, the solar wind became slow and weak; CMES lost their punch; and cosmic rays hit a record high for the Space Age.
Normalcy was not restored by the 11-year swing of the solar cycle. Instead of a vigorous Solar Maximum, the 2010s brought us a “mini Solar Max”. There have been fewer intense flares, fewer strong geomagnetic storms, and fewer SEPS (Solar Electric Propulsion Stage) than any other Solar Max in modern times.
Indeed, there is some evidence that the sun might plunge into a Solar Minimum even deeper than the one in 2007-2009. If the sun’s magnetic field weakens and the solar wind flags, researchers anticipate a significant surge of cosmic rays penetrating the Solar System, eclipsing old records.