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HPL Research

The Heliospheric Physics Laboratory develops instruments and models to investigate the origin and evolution of the solar wind, low-energy cosmic rays, and the interaction of the Sun's heliosphere with the local interstellar medium. The Laboratory designs and implements unique multimission and multidisciplinary data services to advance NASA's solar-terrestrial program and our understanding of the Sun-Earth system.

Strategic Priorities

• Solar wind acceleration and heating
• Wave-particle interaction and turbulence in the solar wind
• Solar energetic particle acceleration and diffusion
• Coronal Mass Ejection propagation and evolution
• Interplanetary shock and discontinuity physics
• Global MHD heliospheric models
• The interaction of the heliosphere with the interstellar medium
• Miniaturization of energetic particle instruments for CubeSat missions
• Develop new mission concepts for heliospheric applications.

Development Areas

• Energetic particle instrumentation
• Neutron and Gamma ray instrumentation
• CubeSat missions
• Global heliospheric modeling
• Data systems

Current Flight Missions

• ACE
• Wind
• STEREO
• IBEX
• Voyagers
• Cluster

Flight Missions in Development

• SPP
• DSCOVR
• CeREs (CubeSat)

Core Activities

• R&A
• Modeling efforts
• SPDF
• Virtual Observatories (VHO, VMO, VEPO, VITMO)
• SPP EPI-Hi instrument
• CeREs
• CubeSat proposals

The IBEX Ribbon

The Interstellar Boundary Explorer (IBEX), launched in October 2008, was designed to measure Energetic Neutral Atoms (ENAs) from the edge of the solar system in the energy range of 10 eV to 6 keV. A full sky map is obtained every 6-month of operations. The most striking result has been the observation of a “ribbon” structure at three times the background intensities. The source of this ENA ribbon is still a puzzle. At least eleven different theories have been put forward to explain it. Five place the source region between the solar wind termination shock and the heliopasuse, two right at the helipause, four in the region where the interstellar plasma is modified by the heliosphere, and one from the undisturbed distant interstellar medium.

E. Christian (672), T. Moore (670) and E. J. Summerlin (672) used astronomical parallax techniques to distinguish between these theories in a model independent way. Changes in the ribbon shape and apparent position make determining parallax very difficult. Using the first six IBEX full sky maps (3 years of observations) a lower boundary of the distance to the ribbon was determined to be 142 AU at a one-sigma level or 57 AU at a three-sigma level. The observed motion of the ribbon of 0.05 +/- 0.10 degrees/year is consistent with a stationary source. This parallax results definitively ruled out one theory at the 5.5 sigma level, and five others are very unlikely at the 2 sigma level. Adding new maps will further reduce the uncertainties of these results.

The Composition of Solar Energetic Particles

The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) was the first to determine the composition of SEPs at the highest of energies (electrons, H, 3He, 4He, up through C). PAMELA observed the first GLE of solar cycle 24 on 17 May 2012. This event was also observed by neutron monitors in the world-wide network. Using particle tracing techniques, PAMELA measured the incident direction of each individual particle. Black crosses in the figure (over the Indian Ocean) show the location of the center of the interplanetary magnetic field measured by ACE and Wind with contours representing equal angles from the IMF direction. Color dots show the incident direction of each observed particle with the colors representing different energies. The black line over North America represents the orbit of the spacecraft during this event. The results of this observation indicate that the high energy component of this GLE is highly beamed. Moreover, the team was able to quantify the transition from the high-energy SEP component that is beamed to the more isotropic galactic cosmic ray component for the first time. G. De Nolfo (672) is a member of the PAMELA team.