by Prasad Ganti

Flying towards the Sun

Sun, the source of energy for our planetary system, has been an object of reverence since times immemorial. The relentless quest to understand what goes on in the Sun which causes so much energy to be generated. In the last century or so, with the knowledge of nuclear reactions, it was determined that Sun is a huge nuclear reactor. Yet, the nuances of different layers and their temperatures and the solar winds which emanate from the Sun have been uncovered and much remains to be studied. Towards this end, the recently launched Parker solar probe is an exciting mission which will go closer to the Sun than any human made object has gone so far.

The core of the Sun is the hottest about 15 million degrees. This temperature is enough to cook the reserves of hydrogen into helium in a process called nuclear fusion. The temperature gradually reduces till the surface which is known as photosphere. This is the place from which we receive our light and heat. The temperature there is about 5800 degrees. Which gives the yellow color to the Sunlight. There are other stars in the night sky which are bluish or reddish in color. Blue stars are hotter and the red stars are relatively dim.

The outer layer of the Sun is the Corona, which is visible during a total solar eclipse. Like it happened in 2017. It is very hot, running into ten to twenty million degrees. It is strange that Corona which is the outer layer is hotter, compared to the inner photosphere. In addition to the light and heat, Sun also gives out charged particles, which are a mix of electrons and protons which shoot out at high speeds. This is known as the solar wind coming out from the Corona. The solar wind can be very dangerous to life on Earth. Fortunately, the Earth has a surrounding magnetic field. This field deflects the solar wind away and acts as a protective blanket. The clash of the charged particles and the magnetic field of the earth is visible as auroras closer to the poles. In the north, known as aurora borealis or the northern lights, it is visible from Alaska, Siberia, Scandinavia etc.

Sometimes, the solar wind is very intense. Called the Coronal Mass Ejection (CME), the solar flare charges outward. If the earth is in its path, the storm can cause havoc. It happened sometime in the nineteenth century when the electrical and communication infrastructure was a tiny fraction of what exists today.

The very existence of the solar wind was postulated by a scientist named Eugene Parker. The scientific community was skeptical. In fact, Parker had a tough time getting a job after he completed his Phd. Chandrasekhar Subrahmanyan, the nobel prize winning astrophysicist known as Chandra, helped him get a job. The postulation of the solar wind was rejected for publication. Chandra as the editor of the journal, overrode the objections and got the research paper published. Since then, the solar wind has established itself as more evidence came in during the ensuing decades. The space probe to study the Sun has been named in Parker’s honor, who is still alive to see his namesake galloping towards the Sun.

The space travel is not simple, like a direct point to point navigation like it is on the Earth. The probe will travel towards Venus by late September. It will use the gravity assist of Venus to slow down and move closer to Sun. The probe will then begin its first of the twenty four orbits around the sun. It will be an elongated orbit. The closest approach to sun, called perihelion will happen on Nov 1. With each orbit, the spacecraft will move closer and closer to the sun, eventually coming to less than 4 million miles above the photosphere, taking measurements in its environment. Along the way, it will get six more gravity assists from Venus during the next seven years.

Given below is the picture of the trajectory of the Parker probe as it ventures into the sun’s neighborhood.

Parker probe trajectory, courtesy planetary.org

A carbon disk protects the probe and its electronics from getting fried. Going to so hot a neighborhood, yet keeping its cool ! That is the miracle of modern day technology, being used to probe the mysteries of the nature.