This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Hannah Schunker is a Lecturer in Physics at the University of Newcastle
David Pontin, Associate Professor of Physics at the University of Newcastle
Why is the sun's surface hotter than its atmosphere? Olivia, age 9, Canberra
(Image credit: The Conversation).
That's an excellent question, Olivia! It's a question that many scientists are trying to answer.
We don't know the truth! We do know that we don't know where the heat from the sun's surface comes from. However, we do have some ideas. This has a lot do with the suns magnetic field. Let me tell you what this means.
The temperature of the sun
The sun's core is where heat is created. It is at this temperature that the sun radiates 27 million degrees Celsius. The temperature drops further from the core, just as if you walk away from a campfire.
The surface temperature of the sun is approximately 6,000 degrees C. This means that it's cooler than its core. It cools down only a little bit above the surface.
Higher up, in the atmosphere, temperatures suddenly rise to over a million degrees. There must be something heating the sun's atmosphere. We can't find it easily.
Similar: What's in the Sun? Star tour from the inside-out
The sun's magnetic field is the key to unlocking its secrets
Experts agree that the sun's magnetic fields is actually bringing energy up through the sun's surface and into the atmosphere.
The sun also has a magnetic field, just like Earth. A magnetic field can be described as invisible lines that connect the north and south poles on a star or planet.
Magnetic fields are invisible to us, but they can be seen by objects that react to them. A compass needle placed on Earth, for example, will always point towards the North Pole due to Earth's magnetic field.
This diagram shows how Earth's magnet field loops back and forth between space and the Earth. The north pole is represented by the red end, while the south pole is represented by the white end. (Image credit: Shutterstock)
Although the sun has a north-south pole, its magnetic field behaves differently than Earth's. It also has a center and a south pole. However, it looks much messier. The magnetic field lines at the surface of the sun look like many loops rising out of the surface into space. These loops are constantly changing.
The loops can touch one another and cause huge explosions of energy, which heats up the atmosphere. We also know that waves travel along the magnetic fields lines, bringing up energy. Could they be responsible to heating the atmosphere?
Are the waves and explosions causing this phenomenon? Or is it something else entirely? Understanding the magnetic field of the sun would be a great help.
This is how we imagine the sun's magnetic fields lines would look if they were visible rising from its surface. NASA image credit
Measurement of the magnetic field
Although magnetic fields are invisible, we can still measure them as they cause small changes in the sunlight that reaches the earth. Because the sun's surface is bright, it is easy to detect changes in light and measure the magnetic fields.
The sun's heat makes it impossible to see the light. Instead, it produces X-rays which is a type we cannot see. Even if we have special Xray telescopes, the Xrays from the sun's atmospheric are too dim to be able to see the magnetic field.
NASA's Parker Solar Probe is a new satellite that orbits close to the sun, but not too close, and is actually flying through the magnetic fields to measure it. Over the next five-years, we should receive a lot more exciting information from it.
This magnetic field measurement will help us understand what makes the atmosphere of the sun and other stars hotter than their surfaces.
The size of NASA's Solar Parker Probe measures about the same as a car. NASA image credit
Continue reading: Curious kids: How does the Sun create such beautiful colours at sunrises and sunsets?
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