Officially we haven’t declared a specific point in our solar system defined as the “edge”, however, Voyager 2 reached its final frontier last August, which resulted in some surprising news. The data revealed that at a distance of 83.7 astronomical units (1 AU is the average distance between the Earth and Sun), Voyager 2 had at least five encounters with a turbulent region known as the termination shock, according to the July 3 edition of Nature. This area is where solar wind reaches cold interstellar space and abruptly slows. Solar wind froms what is known as the heliosphere, a large bubble that extends well beyond the orbit of Pluto.
This encounter has prompted scientists to carefully study how this bubble interacts with surrounding space, and how the similar bubbles formed by other stars affect their surroundings. Interestingly, researchers only expected Voyager to have one encounter with this mysterious region of space. It is like a wave approaching a beach, that grows, breaks, dissipates, and then re-forms closer to shore.”
Voyager lead investigator Ed Stone of the California Institute of Technology in Pasadena, California suggests, “gusts in the solar wind may cause the shock to “come and go, re-forming itself and decaying.”
Voyager 2 (launched in 1977) followed in its sister craft’s footsteps, heading for the outer regions of the solar system in the opposite direction. Voyager 1 reached termination shock in 2004, but interestingly, Voyager 2 reached termination shock some 1.6 billion kilometers closer to the sun than the Voyager 1 shock. This has lead scientists to think that the universe may be lopsided-the bubble carved by the solar wind is pushed in on the southern side.
Researchers as considering the possibility that pressure from the Milky Way’s magnetic field could result in this dent. Stone suggests that, though the field is generally uniform, it may be “tilted in such a way that it’s pushing more on the south than the north.” He goes on to suggest that a series of super nova explosions billions of years ago could have tilted the field.
Even with this astounding information, it is not the only surprise researches encountered. Scientists studying the flow of energy at the solar systems edge discovered that at the termination shock, the solar wind slows and dumps a large amount of energy into space. The energy must obviously then exist in some form; most likely heat. But John Richardson of the Massachusetts Institute of Technology and his colleagues found that the temperature of protons — a main constituent of the solar wind — in the slowed-down region is five to 10 times cooler than expected.*
Using a spacecraft known as STEREO, researches at the University of California, Berkeley traced the missing energy to a large group of “pickup protons”, which are particles that started out as neutral hydrogen atoms from interstellar space and then infiltrated the solar system. These atoms were ionized as a result of the solar wind, turning them into protons. These protons were carried by the solar wind to the termination shock. About 80 percent of the energy released when the solar wind slows goes into accelerating the pickup protons, the researchers report.
The STEREO findings were a surprise because detectors on the twin craft are designed to detect energetic charged particles coming from the sun, which fluctuate in intensity due to variations in the solar magnetic field that pushes them around. But Wang’s team found that the sensors had detected a group of particles from the termination shock region that didn’t fluctuate in intensity and therefore must be neutral. These particles started out as pick-up protons.
The Berkeley-led team concluded that these particles came from the interstellar medium, providing the first map of particles from just beyond the solar system. This new map is especially important because material at the solar system’s edge is too tenuous and faint to be imaged by a visible-light telescope.
“Over the past few years, the stream of in situ and remote data from the outer reaches of the heliosphere has revolutionized our view of how the sun interacts with the galaxy,” comments J.R. Jokipii of the University of Arizona in Tucson. More is to come, he adds, as the two Voyager craft continue their journeys past the termination shock, to the very edge of the solar system during the coming decade.
*Quoted from article on ScienceNews.org
Tags: Atoms, Cosmology, particle physics, Physics, solar system, solar wind, Space, STEREO, sun, termination point, Voyager 1, Voyager 2
