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University of Delaware plasma physicist Bill Matthaeus helped to lay the groundwork for NASA’s Parker Solar Probe, which is closer to the sun than any previous mission.
University of Delaware plasma physicist Bill Matthaeus helped to lay the groundwork for NASA’s Parker Solar Probe, which is closer to the sun than any previous mission.

NASA Parker Solar Probe

Photo by Evan Krape | Photo illustration and video by Jeffrey C. Chase

UD’s Bill Matthaeus offers early perspectives on data from mission to the sun

Researchers are providing their first analyses on data coming back from the Parker Solar Probe, NASA’s most ambitious sun-related mission ever. The  spacecraft is the first to enter the sun’s corona.

An article released on Wednesday, Dec. 4 in Nature, with the University of Delaware’s William Matthaeus, Unidel Professor of Physics and Astronomy, as a co-author, describes early analysis of data drawn from the probe’s first two orbits.

NASA already has released data collected from the four instrument suites onboard — FIELDS, ISʘIS, SWEAP, and WISPR — which are capturing  characteristics of the solar wind (fields, waves, flows and particles) in the corona. It will host a Reddit AMA (Ask Me Anything) on Thursday, Dec. 5, starting at 2 p.m. EST.

UDaily offers this question-and-answer interview with Matthaeus, who recently was awarded the American Physical Society’s 2019 James C. Maxwell Prize for plasma physics.

Q: Any surprises so far from the Parker Solar Probe (PSP)?

Matthaeus: The biggest surprise for me has been the very large fluctuations in the plasma velocity and magnetic field as the PSP spacecraft made its closest approaches in each orbit. The spacecraft is not so far outside the region in which the magnetic field becomes too weak to constrain the flows, but we don't know exactly where that critical region is. Evidently that region is full of these large fluctuations, that some scientists are calling "switchbacks." If we were below that critical region, the entire solar atmosphere should be co-rotating along with the sun itself. Above that region, this co-rotation does not need to happen, but the PSP is already seeing sporadic bursts of rotational motion that could be hints that the plasma is still remembering that not so far below it was rigidly rotating while expanding. It's useful to think of jumping off a merry-go-round while it is operating.

Q: What has been your primary role in this mission?

Matthaeus: I've been involved formally since the early 2000's. First, on a Heliophysics Survey Committee report that made the probe mission the highest priority for the decade, and then on two National Academy sponsored Science and Technology Definition Team reports that defined the purpose and requirements for the mission. Since NASA selected the instrument teams, I have been a co-investigator on the ISOIS energetic particle instruments. I am working on data interpretation and theoretical analysis. After launch, the FIELDS magnetic and electric fields team and the SWEAP plasma team made me an affiliate on their respective instruments.

Q: From what you know, is all of the instrumentation working as hoped?

Matthaeus: So far everything has gone as expected according to what I have heard. There's a lot of radiation and high-speed dust out there, and I believe there have been some likely impacts that have caused some minor issues on a few instruments. I recall that ISOIS, which has many channels that record data, is having some anomalies in some of the high-energy channels, but those on that team believe it can be fixed. Of course, during the first few orbits there has constantly been work done on calibration of all the instruments, and we have seen a great improvement in data quality leading to the public release of the first few orbits' data.

Q: Do you get data continually from the PSP? Or do you get chunks now and then?

Matthaeus: The data are stored on a digital recorder onboard the spacecraft and beamed to Earth when conditions permit. This is very important since there are some encounters, including the first two, during which the Earth and PSP are on opposite sides of the sun. So far this plan for getting data is working extremely well, and we have actually gotten significantly more data than the original plan called for. This is a great credit to the project people at Johns Hopkins Applied Physics lab. One of my former Ph.D. students — Doug Rodgers — works on these data transmission plans.

Q: What will you do with the data that has reached you so far?

Matthaeus: We have been looking at data and analyzing it for certain science problems we have selected to look at. This has been going on for basically a year, since the first fragments of data came down from PSP. On our "PSP festival" team we have a FIELDS Co-Investigator and long-time UD collaborator Mel Goldstein; a SWEAP core member, Prof. Bennett Maruca; and myself, an ISOIS Co-Investigator. So we have immediate access to almost all the PSP data (except the imager WISPR).

Going back to November 2018, we planned several projects in coordination with the PSP teams at Berkeley, Michigan and Princeton, and we have actually collected five of these projects. All have junior UD team members — doctoral students and postdocs — as first authors and we anticipate papers will be published soon.

Q: What will you be looking for in data from future orbits?

Matthaeus: From the point of view of the ISOIS instruments, we would like to see the sun "wake up" from what has been a very deep and quiet solar minimum period. There have been very few energetic particle events, and not very big ones. As the sun approaches solar maximum, it is likely there will be more activity in the form of flares and coronal mass ejections. It is very likely that there will be a lot more energetic particle events and they will be bigger. But of course this cannot be guaranteed. As PSP moves closer and inside the corona in later orbits, we hope to have a pristine look at the acceleration processes that produce these particles. This is essential information to understand space weather.

From the perspective of the PSP mission as a whole, as the mission acquires more data close to the sun, and ever closer in later orbits, the teams will be able to better investigate the heating of the corona and the origins of the solar wind itself. These are fundamental to understanding why there is a heliosphere at all.

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