November 25, 2019

This month, scientists at the United States National Aeronautics and Space Administration (NASA) released their latest findings from decoded transmissions sent from the space probe Voyager 2 in interstellar space (the space between the stars). About a year ago, Voyager 2 became the second spacecraft (following its twin, Voyager 1) to enter interstellar space, exiting the heliosphere, a vast, teardrop-shaped region of space containing electrically charged particles given off by the sun.

Voyager 2, seen here passing Neptune in 1989, entered interstellar space in late 2018. Credit: © Mark Garlick, Science Source

The sun and all the planets are inside the heliosphere. Scientists estimate that the nose (blunt end) of the heliosphere is about 9 billion to 15 billion miles (15 billion to 24 billion kilometers) from the sun. Voyager 1, launched in September 1977, crossed the boundary from heliosphere to interstellar space in 2012. The crossing was marked by a steady drop in temperature and an increase in the density of charged particles known as plasma. Voyager 1 also detected an abundance of cosmic rays (particles accelerated by exploding stars) in interstellar space and provided evidence that the heliosphere protects Earth and the other planets from much interstellar space radiation.

This artist’s depiction shows the approximate locations of the two Voyager spacecraft relative to the sun, the bright spot in the center, in the mid-2010′s. In 2012, Voyager 1, shown as the upper probe in the image, sailed beyond the heliopause and into interstellar space. Voyager 2, the lower probe in the image, crossed the heliopause in 2018. Credit: NASA/JPL-Caltech

Voyager 2 was launched a month before Voyager 1 in August 1977. Slightly slower than its twin craft and following a different course, Voyager 2 reached the heliopause (the edge of the heliosphere) in November 2018. Voyager 2 also detected changes in temperature and plasma and cosmic ray density, but the heliosphere at Voyager 2′s crossing point appeared to be sharper and thinner. This could be explained by Voyager 2 crossing the heliopause at a different location or at a less angled trajectory or by crossing during a period of lower solar activity than that experienced by Voyager 1 in 2012. The sun goes through a roughly 11-year cycle of high and low activity, theoretically causing the heliosphere to expand and contract or thicken and thin. Both spacecraft found that particles from the sun are trickling through the somewhat porous heliopause into interstellar space. Voyager 2 also confirmed Voyager 1′s detection of similar magnetic fields on both sides of the distant boundary.

This artist’s impression shows Voyager 1 passing through the heliopause in 2012. Credit: NASA/JPL-Caltech

Both Voyager space craft are powered by slowly decaying plutonium. In 1977, scientists did not know exactly how long the space probes would continue to operate, nor did they know if, when, or where they would reach interstellar space. Now that the probes are there, scientists hope to learn more about the distant realm before the Voyagers power down sometime in the next few years. Voyager 1 is currently more than 13.6 billion miles (22 billion kilometers) from the sun, and Voyager 2 is about 11.3 billion miles (18.2 billion kilometers) away. After they lose power, scientists expect both to continue sailing through space for billions of years.

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The path of  Voyager 2 is shown in red. Voyager 2 flew past Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. Credit: WORLD BOOK illustration by Ken Tiessen, Koralik Associates

Feb. 14, 2012

Where is the hottest place on Earth? For one brief instant it was in San Mateo, California–or to be more specific, at the Stanford Linear Accelerator Center (SLAC) at Stanford University. The staggering 3.6-million °F (2-million °C) temperature was created by scientists studying a form of plasma created in the massive heat. A plasma is a form of matter that behaves somewhat like a gas but can conduct electricity and reacts to a magnetic field. Scientists sometimes call plasmas the fourth state of matter, after solids, liquids, and gases. The scientists created the extremely intense heat by shooting a powerful beam of X rays at a piece of aluminum foil.

In the solar system, only nuclear explosions and the interior of the sun are hotter than the temperatures created in the SLAC experiment. However, the goal of the experiments was not to create the hottest temperature. Instead, the intense heat was needed to produce a form of plasma commonly called “hot dense matter.” This form of plasma is similar to the plasma that makes up the sun. Scientists believe the study of hot dense matter will help people better understand how the sun works and, possibly, how to produce the same type of matter on Earth on a much larger scale.

Lightning bolts consist of plasma. Few other forms of plasma occur naturally on Earth. © Marco Alegria, Shutterstock

The results of the experiments may help scientists trying to create a controlled fusion reaction on Earth. This reaction is the source of the sun’s enormous power. Scientists are already performing experiments to produce and control fusion. One such experiment is called the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in Livermore, California. There, scientists are using the world’s most powerful laser to create small fusion reactions. In Europe, the ITER experiment is under construction. This is the first large-scale attempt to make a controlled fusion reactor that will produce more power than it uses. Harnessing the power of fusion would revolutionize energy production. Fusion releases tremendous amounts of energy and carries a relatively small risk of environmental pollution.

Additional World Book articles:

• Ion
• Nuclear energy