January 17, 2014
Two spacecraft (Mariner-Jupiter–Saturn, MJS-77) were launched in 1977 on a four-year mission to encounter the planets Jupiter and Saturn. Renamed Voyager 1 and 2 after commissioning, the Science Steering Group began to plan for a much longer-lasting mission that envisioned flybys of Uranus and Neptune, executing the so-called Grand Tour of the outer planets that took advantage of a particular planetary alignment occurring once every 176 years. Following the Neptune encounter in 1989 a new mission was established-the Voyager Interstellar Mission-with the principal objective of investigating the interaction of the solar system with nearby interstellar space. Much has been accomplished so far, including crossing of the heliospheric termination shock where the solar wind becomes subsonic, investigating the source of anomalous cosmic rays, discovering a region where the solar wind no longer expands radially, and entering a new region on August 25, 2012 at a distance of 121.6 AU (1 AU = 150x106 km, the Sun-Earth distance) where solar particles have disappeared and galactic cosmic rays have increased to apparent interstellar intensities. Thus Voyager 1 has now left the heliopause (the border between our solar system and the local interstellar medium) behind and is poised to explore the Galaxy. Voyager 2 on the other hand, being slower than Voyager 1, is exploring the southern ecliptic at a distance of 103.8 AU and is still sampling normal solar material. The JHU/APL-built Low Energy Charged Particle (LECP) experiment has provided critical measurements in identifying this boundary and has performed exceptionally well over the entire mission.
References
Krimigis, S. M., E. C. Roelof, R. B. Decker, and M. E. Hill, Zero Outward Flow Velocity for Plasma in a Heliosheath Transition Layer, Nature, 474, 359-361, doi: 10.1038/nature10115, 2011.
Decker, R.B., S.M. Krimigis, E.C. Roelof, and M.E. Hill, No Meridional Plasma Flow in the Heliosheath Transition Region, Nature, 489, 124-127, doi: 10.1038/nature11441, 2012.
Krimigis, S. M. et al., Search for the Exit: Voyager 1 at Heliosphere's Border with the Galaxy, Science, 341, 144, doi: 10.1126/science.1235721, 2013.
Burlaga, L.F. et al., Magnetic Field Observations as Voyager 1 Entered the Heliosheath Depletion Region, Science, 341, 147, doi: 10.1126/science.1235451, 2013.
Stone, E.C. et al., Voyager 1 Observes Low-Energy Galactic Cosmic Rays in a Region Depleted of Heliospheric Ions, Science, 341, 150, doi: 10.1126/science.1236408, 2013.
Gurnett, D.A. et al., In Situ Observations of Interstellar Plasma with Voyager 1, Science, 341, 1489, doi: 10.1126/science.1241681, 2013.
Dr. Stamatios Krimigis received his B.S. Physics from the University of Minnesota (1961), his M.S (1963) and Ph.D. (1965) in Physics from the University of Iowa, and served on the faculty there. In 1968 he moved to the Applied Physics Laboratory of Johns Hopkins University, became Chief Scientist in 1980, Space Department Head in 1991, and Emeritus Head in 2004. The Space Department has designed, built and operated more than 65 spacecraft, and expanded its activities to planetary missions during his tenure. He is Principal Investigator on several NASA spacecraft, including Voyagers 1 and 2 to the Outer Planets and the Voyager Interstellar Mission, and the Cassini-Huygens mission to Saturn and Titan. He and colleagues proposed and implemented the Near Earth Asteroid Rendezvous (NEAR) mission and oversaw its landing on the asteroid Eros on February 12, 2000, the first ever landing on an asteroid. He has designed and built instruments that have flown to all eight planets, and also the New Horizons mission currently headed to Pluto. He has published more than 530 papers in peer-reviewed journals and books on the physics of the sun, interplanetary medium, planetary magnetospheres, and the heliosphere, with over 10,700 citations. He is recipient of NASA’s Exceptional Scientific Achievement Medal twice, is a Fellow of the American Physical Society, American Geophysical Union, American Association for the Advancement of Science, and American Institute of Aeronautics and Astronautics, recipient of COSPAR’s Space Science Award in 2002, a recipient of the Basic Sciences Award of the International Academy of Astronautics where he chairs the Board of Trustees for Basic Sciences, awardee of the Council of European Aerospace Societies CEAS Gold Medal for 2011, recipient of the Jean Dominique Cassini Medal of the European Geophysical Union for 2014, a member of the Academy of Athens since 2005 occupying the Chair of “Science of Space”, and chairman of Greece’s National Council of Research and Technology.