CAMBRIDGE, Mass. — A NASA spacecraft has made scientific history after becoming the first probe to actually “touch” the Sun! The Parker Solar Probe successfully entered the Sun’s corona — the outermost layer of a star’s atmosphere — which maintains a scorching temperature of roughly two million degrees Fahrenheit.
Scientists and engineers, including members of the Harvard & Smithsonian Center for Astrophysics (CfA), constructed a key piece of equipment that made the achievement possible — the Solar Probe Cup. This invention collected particles from the Sun’s atmosphere, confirming that the spacecraft actually made contact with this extremely hot layer back on April 28.
“The goal of this entire mission is to learn how the Sun works. We can accomplish this by flying into the solar atmosphere,” says Michael Stevens, an astrophysicist at the CfA, in a university release. “The only way to do that is for the spacecraft to cross the outer boundary, which scientists call the Alfvén point. So, a basic part of this mission is to be able to measure whether or not we crossed this critical point.”
The corona of a star is the region where strong magnetic fields hold plasma in place and keeps solar winds from escaping and flying off into space. The Alfvén point that Stevens mentions is the threshold at which these winds reach a critical speed and are able to break away from the Sun’s gravity. Up until April, the Parker Solar Probe was circling the Sun just beyond this point.
“If you look at close-up pictures of the Sun, sometimes you’ll see these bright loops or hairs that seem to break free from the Sun but then reconnect with it,” Stevens explains. “That’s the region we’ve flown into — an area where the plasma, atmosphere and wind are magnetically stuck and interacting with the Sun.”
How did the space cup survive these temperatures?
The data coming from the Solar Probe Cup reveals that the spacecraft broke through our Sun’s corona three times during its historic mission. At one point, the probe stayed inside the corona for five hours.
So how could a man-made object survive these incredible temperatures inside the Sun’s atmosphere? Engineers used a collection of materials which have very high melting points, including tungsten, niobium, molybdenum, and sapphire.
“The amount of light hitting the Parker Solar Probe determines how hot the spacecraft will get,” adds CfA astrophysicist Anthony Case. “While much of the probe is protected by a heat shield, our cup is one of only two instruments that stick out and have no protection. It’s directly exposed to the sunlight and operating at a very high temperature while it’s making these measurements; it’s literally red-hot, with parts of the instrument at more than 1,800 degrees Fahrenheit [1,000 degrees Celsius], and glowing red-orange.”
The Sun is actually much cooler on the inside
One of the mysteries this mission is hoping to solve is why the Sun is so much hotter in this region than it is at its core.
“We don’t actually know why the outer atmosphere of the Sun is so much hotter than the Sun itself,” Stevens notes. “The Sun is 10,000 degrees Fahrenheit [5,500 degrees Celsius], but its atmosphere is about 3.6 million degrees Fahrenheit [2 million degrees Celsius].”
“We know that the energy comes from the churning magnetic fields bubbling up through the surface of the sun, but we do not know how the Sun’s atmosphere absorbs this energy,” the astrophysicist continues.
Additionally, scientists hope the Parker Solar Probe can also provide new insight into the Alfvén point and the solar flares which escape the Sun’s gravity. Solar flares and high-speed solar winds can actually have a major impact on life on Earth. When these particulars break free of the Sun, they can disrupt radio communication and power grids across the world as they interact with our planet.
“The plasma around the Sun can act as a laboratory that teaches us about processes taking place in almost every astronomical object across the entire universe,” Case concludes.
The study is published in the journal Physical Review Letters.