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MIT devices shed light on solar bursts

Two small instruments built at MIT are helping scientists understand the impact of solar bursts on the near-Earth space environment.

This year, the instruments, called Faraday Cups, have allowed scientists to verify for the first time whether particular solar clouds seen leaving the sun actually arrive at Earth. The instruments eventually may help scientists predict the changing space environment about 100 miles above the planet's surface.

The Faraday Cups are part of the Solar Wind Experiment aboard the Wind satellite, which went into orbit in November 1994 and has made valuable measurements continuously since then.

Scientists have for some time recognized that coronal mass ejections, or "burps" of clouds of particles from the solar atmosphere, drive "weather" in space. Racing toward Earth at one million miles per hour, they can cause disturbances in the near- Earth space environment which could disrupt communications and/or damage satellite hardware.

Such disturbances occur a few times a year at the minimum of the 11-year solar cycle, which is occurring now, to as often as a few times a month near the maximum of the solar cycle. The very largest of these disturbances--occurring about once every 11 years--can damage electric power systems on Earth. The clouds also cause the Northern and Southern Lights to change color and become brighter.

The first solar burst seen at the sun and then followed to its arrival at Earth took place in January. It was followed by bursts in February and April.

"In January, for the first time scientists identified a cloud of material from the solar corona leaving the sun four days before that cloud impacted the Earth's magnetic field," said John T. Steinberg, a research scientist in the Center for Space Research and a member of the MIT team that built the Faraday Cups.

"Before this time, scientists were not certain they could detect the Earthward-moving coronal mass ejections," said Dr. Steinberg. "It is much easier to see those moving out sideways to the sun [from Earth's view]."

Alan J. Lazarus, a senior research scientist in physics, is head of the MIT team which built the Faraday Cups. The cups, which are each 7.5 inches in diameter and 4 inches deep, measure the speed, density and other properties of charged particles emitted by the sun. The electronics which detect the signal from this solar wind were built at Boston University in a collaborative effort with NASA's Goddard Space Flight Center.

The three solar clouds this year were seen at the sun using cameras on the Solar and Heliospheric Observatory (SOHO) satellite. The clouds were seen several days later near Earth with the Wind satellite (using the Faraday Cups). The disturbance in the space environment near Earth was studied with various instruments on the satellite which passes over Earth's north and south poles.

"These events have greatly increased our confidence that we will eventually be able to predict the near-Earth space environment with up to several days notice for solar-induced disturbances," Dr. Steinberg said.

"This is a great step forward toward predicting activity at Earth," Dr. Lazarus said. "And that can help designers of satellites better understand the environment into which they are putting their

MIT's involvement and all the new scientific results are highly collaborative, the MIT scientists said. Measurements from the MIT detector in Wind are used to verify whether the coronal mass ejections detected with the cameras on SOHO arrive at Earth.

The intensity of the disturbance in the near-Earth space environment measured with the polar satellite is directly related to the cloud material measured by the MIT Wind detector just before it impacts Earth's magnetic field. The Wind measurements are needed to help understand the Polar measurements.

Funding from NASA for the project runs through 1998. Dr. Lazarus said the scientists are trying to get an extension of the project through the year 2001 so they can take measurements at the peak of the 11-year solar cycle.

"If we get more occurrences, we might be able to learn to predict how large, small, strong or weak the disturbance will be at Earth," Dr. Steinberg said.

A version of this article appeared in MIT Tech Talk on May 7, 1997.

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