After a journey of more than 36 years a spacecraft, Voyager 1, has for the first time crossed the heliopause into interstellar space. The heliopause is the long hypothesized boundary between the hot plasma envelope of the Sun (called the heliosphere) and the relatively cool interstellar plasma. The actual crossing is believed to have occurred at a heliospheric radial distance of 121 Astronomical Units in late August 2012, when a series of sharp increases in the cosmic ray intensities were observed, along with corresponding decreases in the solar energetic particle intensities. However, the plasma measurements needed to confirm the entry into the interstellar medium were not obtained until early the following April, as reported in the Sept. 27, 2013, issue of Science. For the first time we can now measure the unaltered intensity of galactic cosmic rays incident on the heliosphere, as well as other properties of the interstellar medium, such as the magnetic field. In this talk I will review some of the great achievements of the planetary phase of the Voyager mission, often called the “The Grand Tour of the Outer Planets,” and describe the long quest to reach the heliopause and cross into interstellar space.
Don Gurnett is the James A. Van Allen/Roy J. Carver Professor of Physics in the Department of Physics and Astronomy at the University of Iowa. He began his career in 1958 by working on the design of spacecraft electronics as an undergraduate engineer in James Van Allen’s cosmic ray research group shortly after Van Allen’s discovery of Earth’s radiation belts using Explorer 1, the first U.S. spacecraft. After receiving his B.S. in electrical engineering and his Ph.D. in physics at Iowa, he spent one year at Stanford University as a NASA trainee and then joined the Physics faculty at Iowa in 1965, where has been to the present time.
Over his career he led the development of instruments on more than 30 spacecraft projects, including many early Earth-orbiting spacecraft, and on several major planetary missions such as the famous Voyager 1 and 2 flights to the outer planets, the Galileo mission to Jupiter, and the Cassini mission to Saturn. His research primarily involves the study of radio emissions and waves that are generated in hot ionized gases, called plasmas, that occur in planetary magnetospheres and in the solar wind which is a hot ionized gas flowing outward from the Sun. These plasmas produce many different types of radio emissions and plasma waves that can provide crucial information on key properties of the plasma, such as the density and temperature, and even the rotation rate of the planet, as is the case for the outer planets. Over his career he has authored or co-authored over 600 scientific papers and has received numerous awards for his research and teaching. He has guided 62 graduate research projects and many of his students now hold prominent positions in space physics research.