The year 2021 was marked by a slew of firsts. One of them was when NASA’s Parker solar probe penetrated the Sun’s corona or outer atmosphere.
This project was announced by NASA in 2009 to study solar storms and the behavior of the star’s magnetic field. It was first released in 2018. It initially reached the solar corona on April 28, 2021, getting within 13.08 million kilometers of the sun’s surface. In December, it came even closer, approaching 7.86 million kilometers from Earth’s surface. By 2025, the probe will have traveled up to 6.16 million kilometers to make its closest approach.
The temperature of the sun’s surface is roughly 5,500 oC. For unknown reasons, the solar corona is substantially hotter than usual over a million degrees. One of the Parker probe’s study goals is to investigate the coronal heating problem. So why hasn’t the probe melted yet?
Temperature, as defined by the definition, is a measurement of how fast particles move. In other words, the average kinetic energy of the particles that make up a body is its heat. Heat, on the other hand, is a measurement of the amount of energy transferred by fast-moving particles.
This is why a body might have a high temperature but produce little heat. That is, the body’s particles may have a lot of kinetic energy, but there aren’t enough of them to transfer it. Space, for example, has a constant baseline temperature but, due to its vastness, has a very low density and hence transfers essentially no heat to the objects within it.
Another method to appreciate this is to put a spoon in a pot of boiling water and then measure the temperature of the spoon in both the pot and the oven. Because it interacts with more particles in boiling water than it does in cold water, it will have a greater temperature.
The solar corona is the outermost layer of the sun. Although it has a low density, it has a high temperature. As a result, the Parker probe comes into contact with fewer particles.