Archive of Astronomy Questions and Answers

What was the NASA Solar Maximum Mission all about?

The Solar Maximum Mission ( SMM) was a solar observatory launched by NASA in 1980 to study the Sun during its peak years of activity. It operated for 9.5 months before its attitude control system failed. It was later repaired on-orbit by astronauts aboard the Space Shuttle in the spring of 1984. It eventually fell out of orbit in 1989, but not before returning a tremendous amount of data about the Sun, its variability, and other serendipitous discoveries. Curiously, when the peak of the next solar cycle occurred in 1990, the atmosphere expanded by about a few kilometers which was enough to increase the drag on the spacecraft and cause it to steadily loose altitude in a year-long death spiral.

The SMM carried a gamma ray telescope to study the composition of solar and interstellar gamma ray emission; A visible light coronagraph to study the faint solar corona by blocking out the disk of the Sun; a high-precision photometer to measure the total energy of the Sun.

Among its discoveries:

     The confirmation of previous observations of an interstellar 
            isotope of aluminum.

     Discovery of 10 comets which either fell into the Sun, or grazed it

     Monitored Halley's Comet during its perihelion passage using its
            coronagraph

     Observed coronal mass ejections from the Sun into interplanetary 
            space.

     Monitored the output of the Sun and discovered that the luminosity
            of the Sun varied by 0.2 percent on short time scales. The
            dips were correlated with the appearance of large sunspots.

At the distance of the Earth, the Sun provides 2 calories per square centimeter per minute of heat and light energy. But a change of only a percent over a long period of time is enough to cause a 1-2 degree dip in the Earth's mean temperature, or a heating by the same amount. A 1 degree dip was all it took to bring-on the so- called 'Little Ice Age' in Europe 300 years ago.

Prior to SMM, scientists had suspected that the output of energy from the Sun varied, but could not agree by just how much based on a variety of different kinds of data. Because the Sun's energy drives the Earth's weather, any amount of variation could have big impacts on the long-term behavior of our Earth's atmosphere. Based on the first five month's of data, Dr. Richard Willson at the Jet Propulsion Laboratory (JPL) in California reported that, according to the very precise measurements made by SMM, the Sun's output changed almost on a daily basis by as much as 0.2 percent. The larger dips occurred just as a group of sunspots were crossing the center of the Sun. Later on, a particularly large sunspot group caused a brief 0.23 percent lowering of the solar output. SMM had proved convincingly that the output of the Sun does change, and pointed to sunspots as a possible culprit.

For more information on this mission, visit the NASA Marshall Space Flight Center information page on SMM.