Why parker probe has not melted?

fig  (Illustration: NASA)

The year 2021 is an astonishing year for the science community! Apart from the pandemic thing, it is a great year! There is a number of breakthroughs that have been taken place this year. From the first-ever breathtaking picture of a black hole (by EHT), the Discovery of four new subatomic particles at the CERN supercollider to the Launching of a gigantic successor of the Hubble Space Telescope i.e James Webb Space Telescope (JWST). This year will be taken as the year of a great leap in the history of humankind.

In addition to one of such breakthroughs, there is another one, which also happened for the first time in the history of humankind. One of our space probes has actually entered the outer atmosphere of the sun i.e Corona. This probe is named after a living genius DR. EUGENE NEWMAN PARKER. He is an astrophysicist at the UNIVERSITY OF CHICAGO, in the honor of this legend the probe has been named by NASA as Parker Solar Probe.

This mission has been announced by NASA in 2009. Mainly to study Solar Storms and the behavior of the magnetic field of the sun. Probe was launched by Delta IV-Heavy rocket from Cape Canaveral, Aug. 12, 2018. Since then, this probe is heading towards the sun so that it could go closer and closer to the sun. It has touched the outer atmosphere on 28 April and after 7 and half months, it has finally entered the outer atmosphere. In its closest approach on Dec. 14, it has reached up to a distance of 8 million miles i.e 18.8 solar radii, and it will plunge further up to 3.83 million miles which will be its final closest approach expected in 2024.

After all this information there must be a question going on in your mind. Why it hasn't melted yet?

Well to understand this part we need to know a few basics of thermal physics that is the difference between temperature and heat. Obviously, the first answer will be that it is designed in such a way to withstand extreme and adverse conditions. But this is not the entire story.

As the definition goes temperature is a unit that defines how fast particles are moving while heat is something which tells that how much energy that fast-moving particles are transferring. There can be a high-temperature range with low heat means that particles can be fast-moving but if they are in less number that is low density this means they won't transfer that much energy to heat up to a certain level for melting. As space is extremely empty so there are significantly fewer particles to transfer that much amount of heat.

Corona is the outermost layer of the sun's atmosphere which has low density but has a high temperature. If I tell you in a more trouble-free manner. You can think of putting your hand in boiling water {please do not try this at home} and putting it in a hot oven. Where do you think you can withstand more? Obviously, oven! Why? Because in the case of water your hand is interacting with a larger number of particles than in an oven. Similarly, Parker Probe is interacting with a smaller number of particles even though the temperature is quite high.

But still, the temperature is in million degrees Celsius which is tremendously high, so to overcome this issue there is a heat shield in front of it, known as the TPS (Thermal Protection system). Which is 115 mm thick and 2.4 m in diameter. It is made up of a composite foam sandwiched between two carbon plates. This technology is named as Carbon-Carbon Advanced Technology. Interesting name, right? The sun-facing plate is polished with white ceramic paint to reflect the maximum amount of heat (as white color is a great reflector). With all this TPS can withstand up to a temperature of 1,650 C. 

But as the final descent has already begun thus spacecraft circuits and all instruments will need more protection, thus for that case engineers have installed a simple cooling system. It consists of a heated tank fill of 3.7 liters of deionized water as a coolant, two radiators, and aluminum fins. Heated tanks and radiators keep the coolant from freezing and aluminum fins will pump the coolant to circulate to maintain the temperature.

Entire Spacecraft is designed in such a way to work autonomously to keep it self-safe also keep itself on the right track plus keep communicating with the communication room. It will autonomously change its position according to the instruction given to it’s by the central computer which has been programmed in such a way that it will make sure everything will be on right track and without any human intervention.