Unveiling the sun’s mysteries
Six decades ago in 1958, Eugene Parker predicted the existence of solar wind. Like a garden sprinkler spewing water droplets, the sun is blowing out a stream of charged particles nonstop.
This is the solar wind which impacts human activity both on earth and in space. Parker’s theory suggested that the interplanetary space is not a vacuum. Instead, it is filled with the solar wind.
Not everyone accepted his hotly debated hypothesis. His theoretical prediction was confirmed only in 1962 by the Mariner 2 spacecraft on its way to Venus.
Parker submitted his paper to Astrophysical Journal for its publication but reviewers rejected it outright. However, Nobel Laureate S. Chandrashekhar used his discretion to accept it as the then chief editor of the journal. A living legend, and an eminent astrophysicist at the university of Chicago, Parker turned 91 in June this year. He must be wondering what would have happened if Chandrashekhar too had rejected his path-breaking hypothesis.
The visible surface of the sun is about 6000 degrees hot. So, it was against common sense or thermodynamics that its outer atmosphere (corona) could be much hotter. Doesn’t it defy the laws of nature? Isn’t it like water flowing uphill? In the early 1940s, theoretical works of Nobel Laureate Hannes Alfvén and an eminent physicist Bengt Edlén resulted in the discovery of the million-degree-hot solar corona.
Rocket-borne experiments in 1946 and 1949 confirmed the sun to have ultraviolet and x-ray eyes too. This simply meant that the corona must be million-degree-hot. Thus began the space-era.
Since then, these two discoveries continue to be outstanding problems in astrophysics. Why corona exists and how is it heated to millions of degrees popularly known as ‘coronal heating problem’? And why is the sun compelled to propel the solar wind and how is it accelerated to supersonic speeds?
On August 12, 2018, NASA launched a satellite named Parker Solar Probe, which will go closer to the sun than any before. This probe is the fastest-moving man-made spacecraft in history. It is also the first spacecraft, which is
THE SCIENTIFIC OBJECTIVE IS TO FIGURE OUT THE MYSTERY OF WHAT MAKES THE SOLAR CORONA 200TIMES HOTTER THAN ITS VISIBLE SURFACE
named after a living legend Parker. It will travel around the sun at speeds of up to 690,000 km/hr. This is like travelling from New York to Tokyo in less than a minute.
Parker probe, during its seven-year presence in space, will make 24 loops around the sun. It will dip inside the solar atmosphere, and will explore physical conditions there from about 6.16 million km from the sun’s broiling surface. If you imagine the sun-earth to be one meter apart, then this probe will be just about four centimetres away from the sun.
The scientific objective of this mission is two-fold. First is to figure out the profound mystery of what makes the solar corona 200-times hotter than its visible surface. And the second is to figure out what accelerates charged particles to supersonic speeds.
Many spacecraft, especially beginning from Skylab in 1970s to date, have been exploring the answers to these questions. But they remain unanswered satisfactorily. What motivated scientists to go for this ambitious mission is the fact that ‘unless you go there and touch the sun, you cannot answer these questions’.
In today’s tech-dependent society, we want to know the space weather. It has direct influence on our technology in space, our spacecraft, our communications, hazardous environment for astronauts, disruption of our power grids etc.
Naming this mission after Eugene Parker, a living legend in space science, is a befitting recognition. When I approached him in 2003 to write a preface to my book ‘Dynamic Sun’ published by the Cambridge Unversity Press, he happily agreed to do so. He is not only a scientist par excellence but also a great human being.
PROF BN DWIVEDI