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That's where the science is |
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-Bruce Springsteen Indeed, Mom probably did tell you never to stare directly at the Sun. However, scientists led by a team at NASA/Marshall have proposed a new scientific instrument called JASMIN that would do just that - and reveal scientific details never before seen on our nearest stellar neighbor. JASMIN - the Japanese American Solar Magnetograph INstrument - is a collaboration between scientists across the nation, from Hawaii to the East Coast. If selected for flight, JASMIN will be built by a consortium of midwest industries, and will ride to orbit on board Japan's Solar-B satellite scheduled to launch in the year 2004. "The Sun still holds many mysteries," said Dr. John Davis, JASMIN's Principal Investigator at NASA/Marshall's Space Sciences Laboratory, "especially how its atmosphere and magnetic field work together as a single system. JASMIN would be one of three instruments on Solar-B, which together can give us a better understanding of the detailed physics, in order to learn how, why, where, and when things happen on the Sun." Above, right: A portion of a three-image picture that goes to the heart of a solar mystery JASMIN will help try to solve. The complete picture (58KB) shows a clear relationship between the hottest areas of the outer solar atmosphere (left picture), the observed magnetic field on the Sun's surface (middle picture), and changes forced upon the magnetic field by roilings on the solar surface. Scientists don't yet know the exact relationship. credits |
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The Sun-Earth Connection Nearly all of the phenomena we observe on the Sun are controlled by magnetic fields, from the heating of the outer solar atmosphere (the corona), to sunspots, solar flares, and huge eruptions of material called coronal mass ejections. These events are more than just scientific curiosities because they can - and do - disrupt communications and navigation in space and on the Earth. Even small variations in heating in the outer layers of the Sun can change the amount of light and heat the Earth receives by enough to change our climate. "Solar flares are explosive events," Davis explained. "They release huge amounts of energy in a very short time. Exactly how they do this is not clear." Since the flares are always associated with strong magnetic fields, it is thought that the flares' energy is stored in the form of magnetic energy. JASMIN will help unravel these mysteries with the first measurements of the direction and strength of these magnetic fields taken from space." "Solar flares always happen at night or on cloudy days," is a common lament for solar scientists. Ground-based telescopes can see the Sun only during clear days. And even then, Earth's turbulent atmosphere distorts the view most of the time. |
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Solar-B and JASMIN The solution is to put the telescope above the sky in an orbit that shifts a little each day so the Sun never sets on the satellite. This is the plan for the Japanese Solar-B mission. Its 50 cm (20 in.) telescope, the largest solar telescope ever orbited, would feed images to JASMIN, which can operate in three distinct scientific modes. |
 Inside JASMIN - about the size of two large suitcases
- will be a complex arrangement of filters and other optics that
will resolve the strength and direction of the magnetic field
more than ten times better than anything done before. |
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Above: An artist's concept of the Solar-B satellite ready for launch in 2004. Links to larger image. "We'll be able to map the magnetic field over large areas of the Sun with a resolution corresponding to a box with 100 km (60 miles) sides. This might sound like a rather large area, but it's nearly 20 times better than anything we can do from the ground," Davis said. "Currently our ability to resolve details of the Sun's magnetic field is like trying to watch a football game from a mile up. You can see the field, but all the interesting action is taking place on scales smaller than you can see." "Solar-B will be the first mission to 'break the resolution barrier' and observe the Sun on the spatial scales where the physics is happening." The Science of Solar-B/JASMIN JASMIN will study several fundamental questions of Solar Science critical to developing an accurate and quantitative understanding of the Sun's dynamics. For example, Heat waves When we go upward from the surface into the Earth's atmosphere, the air generally gets cooler. The Sun works in reverse. Its outermost layer, the corona, is hotter than 1,000,000 ºC (1.8 million degrees F) while the visible surface, or photosphere - where the atmosphere originates - has a temperature of only about 6,000 ºC (11,000 ºF) . How the corona is heated is one of the great mysteries of solar physics. "It should be possible to heat the corona with waves," Davis said. "All kinds of waves are generated in the photosphere - such as acoustic waves, from mechanical motions, or Alfven waves, from shaking magnetic fields. These waves spread upward into the corona which absorbs energy from the waves. "The trouble with this idea is that none of the waves likes to be absorbed by the corona. They either go right through, or are reflected back to their starting point. This is a long-standing problem and nobody has a good solution for it. Alternatively, Marshall scientists have suggested that energy is pumped into the corona through a series of little explosive effects - microflares - that occur all over the place." Microflares, if they are real, are small-scale versions of well-known solar flares. The question is: Are there enough of them to do the job? They are too small to understand with current telescopes, but will be within Solar-B's grasp. Living with stress Virtually all of the dynamic phenomena we observe on the Sun can be traced back to magnetic fields which form deep in the Sun's interior. These fields can emerge in large active regions that would swallow the entire Earth many times over, or on scales smaller than we can currently see - about 100 km across. As these fields rise, they are twisted and stretched, and store energy much like a rubber band stores energy when it is twisted or stretched.
Right, above: A Naval Research Laboratory model depicts coronal magnetic flux tubes. JASMIN will allow us to understand, in detail, what happens to magnetic structures like this in active regions. Links to larger image.
Left: This red-orange X-ray image from Yohkoh, showing very hot coronal loops, is overlaid with markers derived from highly-processed data (the green lines) from Marshall's solar vector magnetograph. The green lines show where strong magnetic fields at the solar surface are highly stressed. These markers are good predictors of especially hot regions in the solar corona. This view spans about one solar radius (700,000 km or about 54 Earths laid end-to-end). Links to a larger image (28KB). |
| Measuring the Magnetic Field | |||
| Determining the strength and direction of the magnetic field on Earth is not difficult. A compass can tell us the direction, and other simple devices can measure its strength. We can't put a compass on the Sun, but since the structure of the magnetic field is encoded in the light we collect from the Sun; we can try to decipher it. |
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"This is an area that Marshall solar scientists pioneered," Davis said. "It is not an easy measurement, and the theoretical interpretation is difficult." Like much of what happens in physics, it comes down to understanding how individual atoms behave. When atoms are heated, they collide and knock electrons into higher energy orbits. The electrons can then return to a lower energy level by releasing energy in the form of light. The color of the light emitted depends on the amount of energy released. Each element has its own unique color set, because of its unique set of energy levels. If light from heated atoms is studied with a spectrometer - an instrument that analyzes light in its different colors - these very narrow lines of color, called spectral lines, are observed.
Certain crystals have properties that allow them to transmit light only when its oscillations are lined up in a certain way. These crystals are known as polarizers. When polarized light is passed through a polarizer the light can be transmitted or blocked by rotating the polarizer, so the degree of polarization can be measured. Above, right: JASMIN's polarization maps will be similar to these maps produced at NASA/Marshall's pioneering Solar Vector Magnetograph. Links to larger image. Solar Vector Magnetographs do just this. They contain optical systems that spread the light enough to show spectral lines, and then measure how much the lines are polarized. This allows scientists to then calculate the strength and direction of the magnetic fields at the point on the Sun from which the light originated.
"One of the unexpected and most important results from this instrument was that flares almost always occurred in the regions where the magnetic field was stressed," Davis said. "When scientists saw that, it made perfect sense. Those observations were the ground truth of what we were doing, and it reinvigorated solar physics in this area." "JASMIN, on board Solar-B, will show how the three dimensional field patterns change with time on very fine spatial scales. With this, we will be in a good position to solve many of the puzzles of solar physics," Davis said. |
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Marshall's Solar Physics Web Site More Space Science Headlines - NASA research on the web NASA's Office of Space Science press releases and other news related to NASA and astrophysics |
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top picture: The solar coronal image is from the Japanese Yohkoh satellite (Soft X-ray telescope), the magnetic field image is a Mees/Hawaii Fabry-Perot vector magnetogram, and the image of the granules on the solar surface is from the National Solar Observatory. Links to 548x345 pixel, 58KB image.  Join
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