It has been 124 days since Parker Solar Probe was launched, and several weeks ago it did the closest approach, any spacecraft has ever made a star. Now scientists get their hands on data from close range. Four scientists at the last meeting of the United States Geophysical Union in Washington, D.C. shared what they hope they can learn from the probe. They hope that data from Parker Solar Probe will help them answer the decades of the sun, its corona and solar wind.
Researchers studying the sun have been waiting for this for a long time, and the wait has been worth it.
"Heliophysicists have been waiting for more than 60 years for an assignment like this to be possible. The sun mysteries we want to solve are waiting in the corona." – Nicola Fox, Head of the Heliophysics Division at NASA's headquarters.
The thrill lies around the PSP's first sunrise phase. From October 31 to November 11, 2018, Parker Solar Probe completed the first solar phase, running through the sun's outer atmosphere – the corona – collecting unmatched data with four suites of advanced instruments. The PSP will circulate the sun 24 times, for 24 sunrise phases. During the mission, the probe will use 7 Venus gravity-assist airfields to incrementally reduce its circulation around the sun.
Each solar phase occurs when the probe is within .25 AU from the sun, and during these times the science instrument collects data. The probe is exposed to extreme heat and radiation during that time and can not communicate. Only once it goes out of every phase can it send its data back to earth for helio physicists to contemplate.
"Parker Solar Probe gives us the measurements that are necessary to understand the solar phenomena that have puzzled us for decades." – Nour Raouafi, PSP Project Researcher, JHU / APL.
The first sunrise phase is complete, and although the mission has a lot of work to do, Parker's researchers shared some of what they hoped to learn from the mission at the American Geophysical Union in Washington DC.
When the PSP mission was designed, researchers wanted to address three key questions about helio physics:
- How is the outer atmosphere of the sun, the corona, heated to temperatures about 300 times higher than the visible surface below?
- How does the sun wind accelerate so fast at the high speeds we observe?
- How do some of the sun's most energetic particles shed away from the sun in more than half of light's speed?
"Parker Solar Probe gives us the measurements necessary to understand the solar phenomena that have puzzled us for decades," said Nour Raouafi, Project Manager for Parker Solar Probe at Johns Hopkins University Applied Physics Lab in Laurel, Maryland. "To close the link requires local sampling of the sunshine and the young solar wind, and Parker Solar Probe does exactly that."
No spacecraft has ever been as close to the sun as the PSP has, so researchers do not know exactly what to expect from data. They know what they hope to learn, but can not be safe.
"We do not know what to expect as close to the sun until we get the data, and we will see some new phenomena," said Raouafi. "Parker is a prospecting mission – the potential for new discoveries is huge."
Reports from PSP suggest that the first science phase captured quality data. This is due in part to Venus, when the probe could take some measurements of the planet and verify that the instruments worked. Some data from science phase one have been downloaded, but heliophysicists have to wait to get hands on everything. Due to the challenges in the mission profile, some of the scientific data from this meeting will not link until after the mission's second solar experience in April 2019.
Parker Solar Probe is not the only spacecraft studying the sun. Other crafts include SOHO (Solar Heliospheric Observatory), SDO (Observatory for Sol Dynamics) and STEREO-A (Space and Terrestrial Relations Observatory Ahead) spacecraft. But none of these three have come close to the sun like the PSP, even though they make their own important science.
"Parker Solar Probe goes to a region we have never visited before," said Terry Kucera, a sun physicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Meanwhile, we can observe the sun's corona, which drives the complex environment around Parker Solar Probe."
The gifts below show current data from NASA's spacecraft for the Solar and Terrestrial Relations Observatory (STEREO-A) along with the location of Parker Solar Probe as it flies through the sun's outer atmosphere during its first solar phase in November 2018. These images provide an important context for understanding Parker Solar Probes observations. (Image credits: NASA / STEREO)
Each of the spacecraft studying the sun gives a different context and point of view for what the others see. The PSP will travel to within .25 AU, while STEREO circuits the sun at about 1 AU. The SDO is in a geosynchronous terrain, and SOHO is in a halo round the Sun-Earth LaGrange 1-point.
"The STEREO mission is about observing the heliosphere from different locations, and Parker is part of what makes measurements from a perspective we've never had before," said Kucera.
Science is incremental, and PSP researchers want to point out that incremental improvement of models of how the sun works is part of PSP's work, even though we can not answer our questions.
Models are a great way to test theories of the underlying physics of the sun. By creating a simulation based on a certain mechanism for explaining coronal heating – for example, a certain type of plasma wave called an Alfvén wave scientist can check the model's prediction on current data from Parker Solar Probe to see if they are correct agreed. If they do, it means that the underlying theory can be what really happens. If they do not, it's back to the drawing board.
"We have had great success predicting the structure of the sun coron under total sun eclipses," said Riley. "Parker Solar Probe will provide unparalleled measurements that will further limit the models and theories embedded within them."
PSP's record speed is crucial to its work.
The sun rotates approximately once every 27 days as we see it from the earth, and the sun's structures that carry much of its activity go on with it. It creates a problem for researchers because they can not be sure that the variability they see is driven by actual changes in the region that produce the activity – temporal variation – or caused by only receiving solar material from a new source region – space variation. PSP speed means that it can solve the problem.
The gifts below are from a model showing how the sun wind flows out of the sun, with the perspective of Parker Solar Probes WISPR instrument superimposed.
Credits: Predictive Science Inc.
At some points, Parker Solar Probe is fast enough to accurately match Sun's rotation speed, meaning Parker "hangs" over a zone in the sun for a short while. Researchers can be sure that changes in data during this period are caused by actual changes to the sun, rather than solar rotation.
Parker Solar Probe is part of NASA's Living with a Star program to explore aspects of the Sun-Earth system that directly affect life and society.