Two small instruments designed by MIT scientists are orbiting Earth aboard a satellite whose mission is to study the solar wind, or the charged particles emitted by the sun that are responsible for phenomena such as the Northern Lights and occasional power blackouts.
The MIT instruments, known as Faraday Cups, were fully activated November 17 when they began collecting samples of these particles to measure their speed, density and other properties.
Such measurements will aid scientists' understanding of the solar wind, with "the overall goal of understanding how changes in the wind affect the environment around Earth," said Dr. Alan J. Lazarus, a senior research scientist in physics and head of the MIT team.
Because the satellite these instruments are aboard has an orbit that places it a significant distance between Earth and the sun, it could also provide an early warning of especially powerful gusts of solar wind that could affect Earth-orbiting spacecraft and national power grids. With such a warning, scientists could turn off the sensitive electronics on spacecraft that might otherwise be damaged, and power companies could prepare for possible disruptions of their systems.
The Faraday Cups are part of the Solar Wind Experiment (SWE) aboard the Wind satellite, which began orbiting November 1. The MIT team also developed some of the data-analysis software for SWE, while scientists from NASA, the University of New Hampshire and Boston University developed other significant parts of the experiment. Six additional experiments on the satellite are focusing on other phenomena associated with the solar wind.
The solar wind hurtles toward Earth at about a million miles an hour. Its speed and other properties, however, are affected by solar activity (outbursts from the sun can cause strong gusts of wind, for example). Eventually the wind reaches the magnetic field that surrounds Earth-the magnetosphere-and like water rushing around a rock in a stream, it is forced to flow around the field. As it moves past, the wind pulls the magnetosphere out into a long tail.
Some of the solar wind particles, however, leak through the barrier between outer space and the magnetosphere and become trapped in the magnetosphere; others are carried into other parts of Earth's atmosphere. In either case they affect their surrounding environment. For example, they can interact with atoms and molecules to cause the Northern and Southern Lights, or damage the electronics aboard Earth-orbiting spacecraft.
Changes in the solar wind can also cause magnetic "storms" on Earth, during which Earth's magnetic field fluctuates. "And that varying magnetic field affects power grids, which can cause massive power outages," said Dr. Lazarus. (One such outage occurred in Canada in 1989.)
Currently, however, scientists can't predict these phenomena well or give reliable warnings to those who might be affected (for example, power companies that could shift their loads to prevent outages). So in addition to learning more about how the solar wind interacts with the magnetosphere and transfers energy from the sun to Earth, scientists working with the Wind satellite hope to give people on Earth up to an hour's warning of changes in the solar wind that could cause such storms.
That's because the Wind mission is designed to measure properties of the solar wind before it reaches the Earth. Currently the satellite is flying in an orbit that allows it to study the turbulent area just outside of the magnetosphere. But around Christmas, it will swing into a wider orbit that will allow it to take measurements of the wind up to an hour before it reaches the magnetosphere. Ultimately the satellite will go into yet another orbit between the Earth and the sun that will allow it to make continuous readings of the solar wind an hour before it reaches Earth.
"There are efforts to return data in real time from this spacecraft, so we can report solar wind conditions to people who could be affected," said Dr. John T. Steinberg, a research scientist at the Center for Space Research and a member of the MIT team.
The Wind satellite is one of several in an international program to study the solar wind known as ISTP (International Solar Terrestrial Physics). Each satellite will explore key areas of geospace, or "the region around Earth where the dynamics are controlled by Earth's magnetic field and its interaction with the solar wind," said Dr. Steinberg. For example, while the Wind satellite's orbit places it in the solar wind slightly upstream from Earth, a Japanese satellite (Geotail) is currently in the tail of the magnetosphere.
The SWE experiment is funded by NASA; the MIT portion of the data analysis is funded for 18 months. Dr. Lazarus noted that originally the mission was to be funded for 30 months, but was reduced because of recent NASA budget cuts. "It's frustrating to have worked for so long on an experiment only to have it significantly cut just as it's ready to produce exciting data," he said.
In addition to Drs. Lazarus and Steinberg, other members of the MIT SWE team include David Breslau, project mechanical technician at the Center for Space Research (CSR); Michael Enright, electronic technician at the CSR's Lab for Space Experiments, and John Tappan, a member of the sponsored research technical staff also at the Lab for Space Experiments.
UROP students involved in the work are Albert Dvornik and Frank V. Marcoline, seniors in physics, and Robert P. Wagner, a sophomore in physics. UROP alumni are Ken Dinndorf (MIT PhD '93), Mark Rubin '90, Terry Alkasab '92, Kai Pok Chan '94, Craig West '94 and Jim Reiner '94.
A version of this article appeared in the November 30, 1994 issue of MIT Tech Talk (Volume 39, Number 13).