365daysDate: September 2, 2009

Title: STEREO/IMPACT: Our Un-Quiet Sun


Podcaster: Dr. Janet Luhmann interviewed by Ms. Priya Desai

Organization: Center for Science Education at UC Berkeley’s Space Sciences Laboratory cse.ssl.berkeley.edu/impact

Description: STEREO (Solar TErrestrial RElations Observatory) is a two-spacecraft NASA mission orbiting the Sun near Earth’s orbit to study the dynamic eruptions of mass from the outermost atmosphere of the Sun, the Corona. The STEREO spacecraft are very large and have suites of instruments on-board studying specific types of solar science questions. We will feature the science and data being gathered from the IMPACT (In-situ Measurements of Particles and CME Transients) instrument suite. In this podcast we will talk with Dr Janet Luhmann, the principal investigator of IMPACT, about the origin and consequences of Coronal Mass Ejections (CME’s,) which are the most energetic eruptions on the Sun. Dr. Luhmann shares why we should care about what happens on the Sun. We will also discuss with IMPACT’s Education and Public Outreach Lead, Dr. Laura Peticolas, about whether we can hear the Sun. Can we hear the violent flares and wind that it spits out? Not really in the sense of sound – because there are no sounds in space; but we CAN use the particles, magnetic and electric field and the image data and convert the data into sound to demonstrate what the data tell us. We will explore how images can be “sonified” and how we can musically “play” the Sun.

Bio: Dr. Janet Luhmann is Senior Fellow at the Space Sciences Laboratory, University of California in Berkeley and the principal investigators on the STEREO-IMPACT mission launched in 2006. She was responsible for a lot of the Pioneer Venus magnetometer data analysis, and has been a Co-Investigator on two POLAR experiments. She is currently a member of the Cassini Saturn Orbiter Ion-Neutral Mass Spectrometer Team, Co-director of an NSF Science and Technology Center for Space Weather Modeling. A major focus of her work has been the comparison of spacecraft observations with models of the solar wind interaction with the planets.

Dr. Laura Peticolas is an educator and scientist with many years of experience in studying the aurora and in teaching physics to undergraduates, teachers, and the public. She creates high school and junior college lessons, in collaboration with teachers and the E/PO team. She also organizes and teaches at professional development workshops. As the lead E/PO personnel of the THEMIS, STEREO-IMPACT, and Wind E/PO efforts, she leverages efforts from multiple NASA missions that are studying everything from the Sun to auroras.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Earl Wilson.



Dr. Janet Luhmann interviewed by Ms. Priya Desai, both of UC Berkeley’s Space Sciences Lab.
[background sounds – see end note.]

Priya: Hello and welcome to the 365 Days of the Astronomy podcast. I am Priya Desai and today we will be talking with Dr. Janet Luhmann, the Principle Investigator for the STEREO mission about the Sun’s unusual behavior these days and its impact on the STEREO mission. Hello to you, Dr. Luhmann, and thank you so much for coming.

Dr. Janet Luhmann: Hello, Priya, it’s good to be here.

Priya: Dr. Luhmann we have so many questions about the Sun and this mission, but let me start by asking you why did the scientist feel the need for a mission like STEREO? I mean, what would you say are some of the highlights of this mission?

Janet: Well, I think that the science community and NASA have always been responsible for understanding what’s happening to us in space, and part of that is the Sun, and what the Sun is giving off. And so we know that the Sun goes through activity cycles, approximately every eleven years — plus or minus several years — and these activity cycles were once viewed in terms of the number of dark spots on the solar disk, which are called Sunspots, but as the Space Age developed, we’ve come to appreciate more and more that this so-called solar activity involves a lot more than Sunspots, that we in fact live in the atmosphere of our star, the Sun. And that that atmosphere is constantly giving off gases and magnetic fields, and undergoes periods of massive eruptions that are called Coronal Mass Ejections. So STEREO is going out there to better understand the solar activity cycle and in particular the Coronal Mass Ejections.

Priya: So, from what I understand, STEREO was launched to study the coronal mass ejections, which are most frequent when the solar activity is at its peak. But now this is so much in the news lately about how the next solar cycle, which is Cycle 24, is not showing any signs of starting, that the Sunspots, which you said are the sign of the solar activity, have been the fewest in the past year that have been recorded in the past eighty years, so the fewest since about 80 years. Now, is that true?

Janet: Well, it is among the lowest annual Sunspot numbers on record in the past year. The cycle actually caught STEREO scientists a bit by surprise. We had thought that, by this time, the Sunspot cycle would have turned up its increasing Sunspot number trend for the next solar maximum.

Priya: So how is this, in fact, a serious science objective?

Janet: So STEREO has continued to watch the Sun as it was designed to do. And because we have this unusual behavior, at least unusual from the perspective of the cycles that have been observed since the Space Age began, and since we began having pretty good observations of the Sun. It has given us a new appreciation of the fact that not all solar cycles are created equal. It’s also given us appreciation of the fact that solar minimum is not entirely a quiet time. And, in fact, there have been quite a few coronal mass ejections, CME’s, during the few years that STEREO has been up during this solar minimum. It was known that there were some CME’s during solar minimum, but now we’ve has a chance to really watch those in great detail and get a better feeling for where they’re coming from, what their shape is, and perhaps what’s controlling their generation.

Priya: So what can we learn about the quiet Sun from STEREO?

Janet: Well , we’ve learned already that the quiet Sun isn’t quiet. In addition to continuing to generate coronal mass ejections, a few of which have caused disturbance in the space around the earth — not enough to cause a geomagnetic storm or auroral storm — but still to cause a disturbance, we’ve also been able to observe the fact that the solar wind itself is not very uniform coming out from the Sun between the coronal mass ejections… that in fact there are lots of blobs and globs in it of all sizes, and it’s a highly structured outflow that’s always there, even in the quietest times. So the Sun is not just expanding its atmosphere in a quiet and laminar (smooth) way, it’s embedding us in a constantly evolving and disturbed medium. And the fact is, it will only get more disturbed as solar activity cranks up.

Priya: I was going through some old NASA press releases, and I was reading where they were saying the Sun’s “conveyor belt” is slowing down, and they predicted in this particular press release that Cycle 25, which would be probably the next one and peak in 2022, would be the weakest in centuries. Could you comment on that and explain to us what they are talking about?

Janet: Well, the thinking is that all of this stuff that we see going on in the solar atmosphere is driven from way inside the Sun. The Sun is a very hot ball of gas like any star under very high pressures, and it’s got a nuclear furnace in its center. It’s got a layer of convecting hot gases as part of the “envelope” that surrounds that hot core, and they’re very turbulent and they have a circulation pattern just like the earth’s atmosphere has a circulation pattern. And that circulation pattern is what is determining what pops out of the surface of the Sun that we see, which is called the photosphere, and it determines how many Sunspots pop out, among other things, by cycling, creating, and cycling magnetic fields through the solar interior. We think of it sometimes as twisted up rubber bands, that the magnetic fields inside the Sun are like rubber bands that are always being stretched and pulled by the circulation of the solar convection zone, and once in a while they will become twisted and pop out like a…hernia hahaha, so I think of sunspots as “solar hernias” in a way, and they pop out with greater frequency in a cyclical way for reasons that a whole bunch of solar scientists who work on nothing but the solar dynamo, the so called internal dynamo, are trying to understand. But the conveyor belt is thought to be one of the larger scale circulation patterns inside the Sun. It is thought that the speed in which this conveyor belt carries magnetic fields throughout that interior of the convection zone, throughout that subsurface, somehow determines the amount of stuff that pops out in these active regions where Sunspots, or solar magnetic field hernias that I’m referring to. And so the conveyor belt is not constant in time. It’s thought that it probably had different states and different speeds. And the circulation pattern for each cycle can be quite unique.

So I think what we’ve seen in the past two cycles has been a situation where the internal circulation was quite similar, but now all of a sudden we’re seeing one with modern instruments where that internal circulation is actually quite different.

Priya: And its slowing down?

Janet: It looks like its slowing down and it’s not vigorous enough to cause as many hernias. (smile)

Priya: Wow. This is fascinating stuff… but, before we close, there is one thing I wanted to ask you, on a personal note. What made you get into the business of studying the Sun?

Janet: Well, I had always been fascinated by the fact that we are in this solar system, part of that original cloud that became the Sun, and everything we do, our very existence, depends on the fact that the Sun exists. So it’s central to everything from the planets to how we live and something that’s so all encompassing is just a fascinating thing to work on.

Priya: That is so true, and that is so inspiring. That you so much for coming in Dr. Luhmann, it was a pleasure talking to you.

Janet: Thank you, I’m glad you enjoyed it.

Dr. Laura Peticolas: The background sounds were created using data from the solar wind collected by the STEREO mission. For more information, visit our website at cse.ssl.berkeley.edu/impact.

End of podcast:

365 Days of Astronomy
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