On Tuesday 14 December, scientists announced that NASA’s spacecraft had successfully flown through the corona, the outermost part of the Sun’s atmosphere. The achievement means that scientists can explore some of the world’s biggest unanswered questions about the star.
The mission took place on 28 April, but it has taken several months to receive and confirm the data.
"Parker Solar Probe ‘touching the Sun’ is a monumental moment for solar science and a truly remarkable feat," said Thomas Zurbuchen, the Associate Administrator for the Science Mission Directorate at NASA Headquarters in Washington.
"Not only does this milestone provide us with deeper insights into our Sun's evolution and its impacts on our solar system, but everything we learn about our own star also teaches us more about stars in the rest of the universe.”
This historic milestone will also help scientists to predict and understand extreme space weather events, that can damage satellites and communications.
Shining a light on new discoveries
The probe was first launched in 2018, with the goal of making humanity’s first visit to a star.
Travelling at over 320,000 mph, Parker Solar Probe is the fastest known object built by humans. It has made many new discoveries since its launch, measuring phenomena previously only estimated. These include critical information on explosions that create space weather and the dangers of super-speedy dust.
The Sun’s outer edge begins at the Alfvén critical surface: the point between the Sun’s atmosphere and an outer region of space directly controlled by the solar wind. Many scientists think that sudden reverses in the Sun’s magnetic field, called switchbacks, emerge from this area.
This past April, the probe spent five hours below the Alfvén critical surface in direct contact with the Sun’s plasma. Below that surface, the pressure and energy of the Sun’s magnetic field was stronger than the pressure and energy of the particles. The spacecraft passed above and below the surface three separate times during its encounter. This is the first time a spacecraft has entered the solar corona and touched the atmosphere of the Sun.
“We have been observing the Sun and its corona for decades, and we know there is interesting physics going on there to heat and accelerate the solar wind plasma. Still, we cannot tell precisely what that physics is,” said Nour E. Raouafi, the Parker Solar Probe Project Scientist at JHU/APL. “With Parker Solar Probe now flying into the magnetically dominated corona, we will get the long-awaited insights into the inner workings of this mysterious region.”
The new findings suggest that direct observations by spacecraft have much to illuminate about the physics of coronal heating and solar wind formation. Having achieved its goal of touching the Sun, Parker Solar Probe will now descend even deeper into the Sun’s atmosphere and linger for longer periods of time.
According to Gary Zank, a Co-investigator on the probe’s Solar Wind Electrons Alphas and Protons (SWEAP) instrument and a member of the National Academy of Sciences, “It is hard to overstate the significance of both the event and the observations made by Parker Solar Probe. For over 50 years, since the dawn of the space age, the heliospheric community has grappled with the unanswered problem of how the solar corona is heated to well over a million degrees to drive the solar wind. The first measurements of the sub-Alfvénic solar wind may represent the most major step forward in understanding the physics behind the acceleration of the solar wind since the formative model by Parker.”
Looking to the future
The mission will continue until the Parker’s final orbit in 2025, during which it is set to fly only 6.2 million kilometres (3.86 million miles) from the solar surface, well within the orbit of Mercury.
“I’m excited to see what Parker finds as it repeatedly passes through the corona in the years to come,” said Nicola Fox, Division Director for the Heliophysics Division at NASA Headquarters. “The opportunity for new discoveries is boundless.”