Weekly Notes from the Yohkoh Soft X-Ray Telescope

(Week 43, 2002)

Science Nugget: October 25, 2002


The final Yohkoh SXT science nugget

Introduction and farewell

It is a sad moment, but Yohkoh is gone and the nugget-writers have been turning their attention towards new things; and we are bringing these pages to an end. There has been a new Yohkoh science nugget each week since October 1997. Of course we have continued to find new things in the archived Yohkoh data as well, and expect that to continue into the Galileo archive era, which we anticipate will continue to bring interesting discoveries forward.

We are going to summarize our nugget experience in a poster paper at the Winter 2002 AGU meeting in San Francisco, and make that an opportunity to discuss future plans with whomever. A new nugget series will almost certainly ensue, probably based on this model but with new players involved.

Yohkoh SXT Chronology

  • 1984: Active informal discussion about a 3-axis Japanese solar satellite
  • 1985: Concept Report, "A US-Japan Joint Program for High-Energy Solar Physics"
  • 1985: HESP Working Group report (ISAS; in Japanese) with the first publication of the actual project schedule, faithfully followed until the edge of the paper in 1995
  • 1985: Letter from Doschek (NRL) to Ogawara (ISAS) proposing a Bent Crystal Spectrometer for SOLAR-A
  • 1986: NASA AO for a soft X-ray telescope to go on SOLAR-A
  • 1987: First SOLAR-A science planning meeting
  • 1991: SOLAR-A launch on the schedule dictated in 1985
  • 1995: Smiles all around as Yohkoh, the renamed SOLAR-A, exceeds all lifetime expectations
  • 1997: The first Yohkoh SXT science nugget tackles "dimming"
  • 2001: An unpredictable series of problems brings Yohkoh science operations to an end
  • 2002: The Yohkoh 10th anniversary science meeting
  • 2002: This (the final) science nugget

    And how was reconnection viewed?

    It is interesting to note, since so many of the Yohkoh scientific discoveries relate to coronal magnetism (perhaps all of them), that the pioneers were already keen on magnetic reconnection in 1984-1985.

    The frontispiece of the brief Concept Report, dated April 1985. It shows "magnetic islands" thought theoretically (and with some justification from the Earth's magnetosphere) to show how plasmoids might form accompanying magnetic reconnection. As the report said, "[Yohkoh] would be the first opportunity in any astrophysical context to form images of reconnecting magnetic fields." Brave words!
    A cartoon from the winning U.S. proposal, presciently showing what we now think of as the "three-legged loop" model of loop interaction (Machado-Nishio-Hanaoka). It still makes sense but we still don't know the most important parts of the story.

    Conclusion

    Why single out magnetic reconnection in this final nugget? The reason is that, in spite of a great deal of observational and theoretical progress, we remain stumped by the simplest of questions: Can the cause of one of our events be attributed to something called "magnetic reconnection"? How are our abundant accelerated particles related to "magnetic reconnection"? When will "magnetic reconnection" occur? Some hints are in the nuggets, many facts are in papers published during the Yohkoh era, but we really cannot yet answer these questions convincingly.

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    October 25, 2002

    Hugh Hudson hudson@hhudson@ssl.berkeley.edu