NASA - Top Story - Spacecraft Fleet Tracks Blast Wave Through Solar System

This animation is an artist's concept of the path of a coronal mass ejection (CME) as it blasts through the solar system, past solar sentinels like SOHO, past Earth, Mars Odyssey at Mars, Ulysses at Jupiter, Cassini at Saturn and then onto Voyager 2 and Voyager 1 at the farthest point. Fast moving solar wind carves out a local cavity in the galaxy called the heliosphere that extends beyond the orbit of Pluto, the most distant planet. The orbits of the planets are represented as white elliptical lines. The yellow areas represent the CMEs -- billions of tons of electrified gas (plasma) -- launched by the solar storms of October-November 2003, which were the most severe on record. This plasma formed a blast wave as it raced as fast as 5 million miles per hour (eight million km/hr) through the solar system, traversing the 93 million miles (148 million km) from the Sun to the Earth in less than a day. Slowing to an average speed of 1.5 million miles per hour (2.4 million km/hr) as it plowed into the outer heliosphere, the blast wave reached Voyager 2 at 7 billion miles (11 billion kilometers) from the Sun on April 28 and continued outward toward Voyager 1 at almost 9 billion miles (14.5 billion km) from the Sun. In the months ahead, the blast wave will crash into the heliopause - the tangible edge of the heliosphere where the material ejected by the Sun piles up against the interstellar wind from explosions of nearby stars. The collision may generate extremely low-frequency radio signals that will give us a much more accurate understanding of the size of the Sun's domain. The energy carried by the material will push the interstellar gas outward by as much as 400 million miles (640 million km), about 4 times the distance from the Sun to the Earth.

Credit: NASA/Walt Feimer

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Caption:

This is a multi-instrument movie of the October - November 2003 solar storms. The movie combines false-color views from three instruments on board the Solar and Heliospheric Observatory (SOHO) spacecraft. The Sun is the center object, in green. This view, from the Extreme ultraviolet Imaging Telescope (EIT) instrument on board SOHO, shows a series of powerful solar explosions called solar flares in ultraviolet light. (Flares appear as bright sparks on the green disk). The middle image, in red, is a close up view of the solar atmosphere made with SOHO's Large Angle and Spectrometric Coronagraph (LASCO) C2 instrument. This instrument makes an artificial eclipse of the Sun so the faint outer atmosphere (corona) can be seen. Massive eruptions of electrified gas (plasma) called coronal mass ejections (CMEs) can be seen as white areas moving rapidly away from the Sun. The outer image, in blue, is a wide-angle view of the corona made with SOHO's LASCO C3 instrument. As the CMEs travel further from the Sun, they are seen as bright areas in this view. White dots that periodically obscure the image are electrically charged particles (electrons and atomic nuclei) that have been accelerated to high speeds by the flares and CMEs. They create spots on the image when they hit detectors in the instruments. This is one type of space radiation that can be hazardous to unprotected spacecraft and astronauts. The bright object moving to the left in part of the movie is the planet Mercury.

Credit: NASA/Tom Bridgman and the European Space Agency

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Caption:

This movie is an artist's concept of the blast wave passing the Voyager spacecraft. Electrically charged gas (plasma) comprising the blast wave is represented by yellowish areas.

Credit: NASA/Walt Feimer

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Caption:

This movie is an artist's concept showing the blast wave (CME) as it travels to the edge of the heliosphere. The heliosphere is the region where solar wind, i.e. the influence of the Sun, reigns supreme. In the movie, the Sun is the bright yellow dot in the center of the image, and the blast wave is represented by a yellow-orange blob that moves out away from the Sun. The orbits of the outer planets, in order of increasing distance from the Sun -- Jupiter, Saturn, Uranus, Neptune, and Pluto -- are represented by white elliptical lines around the Sun. The solar wind (a thin stream of plasma that blows continuously from the Sun, represented in the movie by light streamers coming from the Sun) creates a bubble that envelops our solar system. A boundary, called the heliopause, exists separating our solar system from the vastness of interstellar space. The heliosphere is represented as the dark blue area enclosing the Sun and the planets, and the heliopause is the blue line where the heliosphere meets the black area, which represents interstellar space. This boundary is fluid and changes with the cycles of the Sun; in this case, the "Halloween" storms were so intense that they also affected the boundaries of this region. Scientists predict that in a matter of months the shock wave will reach the heliopause and expand the region by as much as 400 million miles, much like an inflated balloon with more air pumped into it.

Credit: NASA/Walt Feimer

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July 08, 2004 - (date of web publication)

SPACECRAFT FLEET TRACKS BLAST WAVE THROUGH SOLAR SYSTEM

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A fleet of spacecraft dispersed throughout the solar system gave the most comprehensive picture to date of how blast waves from solar storms propagate through the solar system and the radiation generated in their wake.

The "Halloween" solar storms in October-November 2003 launched billions of tons of electrified gas (plasma) that blasted by Earth within a day and past Mars hours later. The most recent reports come from



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the twin Voyager spacecraft at the fringe of the solar system near an unexplored region where the solar wind becomes turbulent as it crashes into the thin gas between stars. (Item 3 is an artist's concept of the blast wave passing Voyager.)

Fast moving solar wind carves out a local cavity in the galaxy called the heliosphere. The material launched by the huge solar storms last fall blasted by Earth at five million miles per hour (eight million km/hr) and raced past spacecraft near Earth, Mars, Jupiter, and Saturn on its way to Voyager. (Refer to Item 1 for an artist's



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concept of the blast wave moving through the solar system.) Slowing to an average speed of 1.5 million miles per hour (2.4 million km/hr) as it plowed into the outer heliosphere, the blast wave reached Voyager 2 at 7 billion miles (11 billion kilometers) from the Sun on April 28 and continued outward toward Voyager 1 at almost 9 billion miles (14.5 billion km) from the Sun.

The Halloween storms were the most powerful ever measured. The storms broke all-time records for X-ray intensity and for speed and temperature of the solar wind observed near Earth. About a third of the total particle radiation emitted by the Sun in the last decade in the deadly 30-50 MeV energy range came from these storms, even though the solar activity cycle was well past its maximum. (Refer to Item 2 for a movie of these solar storms.)

There are at least two kinds of solar storm effects: prompt radiation and shocks that accelerate electrically charged (ionized) atomic particles. The prompt radiation travels at nearly the speed of light, causes the most severe electrical effects on satellites, and has the greatest impact on the Earth's electrically charged upper atmosphere (ionosphere) and long-distance radio communications. The prompt radiation was detected in radio waves throughout the solar system in the moments (hours in the case of



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Cassini out near Saturn) after each storm. The shocks that accelerate particles to millions of miles per hour take a little longer to develop, but they pack the biggest wallop when it comes to the aurora, power grids, and energetic particles that become trapped in the Earth's Van Allen radiation belts. These storms created a new radiation belt near Earth that lasted for several weeks.

The storms' effects on Earth were severe enough to cause the rerouting of aircraft, affect satellite operations, and precipitate a power failure in Malmoe, Sweden. Long-distance radio communications were disrupted because of the effects on the ionosphere, and northern lights (aurora borealis) were seen as far south as Florida. Fortunately no NASA satellites near Earth were severely damaged by the storms a tribute to advance planning and engineering. The International Space Station astronauts curtailed some of their activities and took shelter in the Russian-supplied Service Module several times during the storm.

The Earth wasn't alone in feeling the effects -- the storms rocked the inner solar system from Mars to Saturn. The Mars Radiation Environment Experiment (MARIE) instrument on the Mars Odyssey spacecraft was disabled by radiation in Mars' orbit. The MARIE instrument successfully monitored space radiation to evaluate the risks to future Mars-bound astronauts before it stopped working during the period of intense solar activity on Oct. 28, 2003. The Ulysses spacecraft near Jupiter and the Cassini spacecraft near Saturn both detected radio waves from magnetic storms generated as the blast wave slammed into the vast magnetic fields around these giant planets.

"It's striking



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that this blast wave was powerful enough to generate a magnetic storm all the way out to Saturn, almost ten times farther from the Sun than Earth is," said Dr. Edward Stone of Caltech/JPL.

The shocks created by the storms in the inner solar system not only accelerated electrons and protons to high energy, they also trapped the particles in the inner heliosphere. This resulted in elevated radiation levels everywhere between Venus and Mars that decayed only gradually over a period of weeks. This kind of event will have significant implications for radiation protection requirements for explorers who venture outside of the Earth's protective magnetosphere (magnetic field).

"Over many decades, improvements in weather forecasting have saved lives and property. Space weather forecasting is still in development, but is needed to better protect our space infrastructure and future human and robotic explorers," said Carl Walz, Astronaut and Program Executive for Advanced Concepts and Project Prometheus at NASA Headquarters, Washington.

The widely dispersed fleet of "space buoys" are helping scientists piece together a more comprehensive picture of how disturbances propagate through the solar system. What determines the evolving shape and variable speed with which the shocks travel in different directions is not well understood. The differences in the speeds and arrival times at Mars and Earth suggest that the process is not simple. The Sun's magnetic field also affects how well connected different places in the solar system are. Understanding how particle-accelerating shocks travel through the solar system will help us understand and predict how radiation levels will change in different locations in space. These widely scattered spacecraft provide some of the first information about the tracks of storms in the interplanetary "ocean."

In the months ahead, the blast wave will crash into the heliopause - the tangible edge of the heliosphere where the material ejected by the Sun piles up against the interstellar wind from explosions of nearby stars. The collision may generate extremely low-frequency radio signals that will give us a much more accurate understanding of the size of the Sun's domain. The energy carried by the material will push the interstellar gas outward by as much as 400 million miles (640 million km), about 4 times the distance from the Sun to the Earth. (Refer to Item 4 for an artist's concept of the collision.)

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