The
so-called northern and southern lights
glow and shimmer colorfully in what 19th
century Scottish poet W.E. Aytoun
described as streamers shooting all
night long across the trembling sky.
Despite their visual appeal, these
brilliant light shows are storms -
geomagnetic storms. Scientists call them
substorms, a part of larger storms of
energy propelled from the sun at
supersonic speeds toward Earth and
elsewhere in the solar system.
This energy involves tons of charged
particles, hurled our way in the
so-called solar wind. Earth's magnetic
field repels most of this onslaught, but
some occasionally leaks through as a
result of a sudden, explosive release of
these particles from the solar wind.
The outcome is the light shows over the
poles and sometimes the undesirable
disruption of electrical power systems
and telecommunications on Earth and
spacecraft in orbit.
Solar physicist Vassilis Angelopoulos of
the University of California at Berkeley
says the precise point in Earth's
magnetic field where this explosive
particle release occurs and the sequence
of events leading to it have puzzled
scientists for three decades. "Knowing
the trigger location identifies the
correct physics at play. The problem has
been that the substorms start at a
single point in space, somewhere near
Earth, and, within minutes, it
progresses past the moon's orbit, so a
single satellite alone cannot identify
the substorm time and point of origin,"
he said.
To seek the answer to this mystery, NASA
has launched five satellites aboard a
Delta rocket from Florida to train their
instruments on the northern and southern
lights. The project is called THEMIS.
Once in orbit, two of the THEMIS
spacecraft will circle Earth about
one-sixth the distance to the moon while
the other two circle half way to the
moon. A fifth will be a reserve, if one
of the others fails during the two-year
mission.
Angelopoulos says a finding will help
scientists know more about the
threatening solar storms and how our
planet's magnetic field works.
"Understanding and predicting space
storms is important for protecting our
satellites and astronauts in space.
Meteorologists study tornadoes to
understand the most severe
thunderstorms, and we, too, want to
study substorms to gain insight into the
most intense space storms," he said.
Cramming five miniature satellites into
the nose of one launch rocket has had a
collateral engineering benefit. Each is
a cube, less than one meter wide and
high. The THEMIS project manager at the
University of California, Peter Harvey,
says it has taught technicians how to
make small satellites with little
computers and other instruments. "It has
been a challenging project to pack so
much into five small spacecraft. We
learned a lot about how to build a
constellation of spacecraft. We look
forward to some terrific scientific
discoveries," he said. |
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光彩夺目的北极光和南极光曾经被19世纪的诗人艾顿形容为“在夜空不断流动的光束”。
极光虽然看起来很灿烂，实际上却是一种风暴，也就是科学家所称的“亚暴”，是由太阳射出的能量所造成的大风暴的一部份。太阳能以超音速的速度射向地球和太阳系的其他地方。
这种能量包括有数以吨计的附电荷粒子，随着太阳风冲向地球，其中大部份被地球磁场遮挡，但是也有一些由太阳风突然爆发出来的粒子会穿过地球磁场，结果产生极光，有些时候也会使地面上和宇宙飞船的电力和通讯系统受到干扰。
美国柏克莱加州大学的太阳物理学家安吉罗波洛斯说，30年来，科学家对于这些粒子在地球磁场当中爆发的确切位置以及之后的情况一直无法理解。他说，了解爆发的位置就可以辨认出正确的物理作用。
“亚暴”在接近地球的太空当中某一个点掀起，几分钟之内就会穿过月球的轨道，所以单独一个卫星无法测出“亚暴”发生的时间和起源。为了解开这个迷团，美国宇航局从佛罗里达州发射了一枚带有5颗人造卫星的火箭，这5颗卫星上的仪器对准北极和南极瞄准。这个探测计划被命名为“特弥斯”。
在进入轨道之后，两颗“特弥斯”卫星在相当于地球和月球之间的距离大约六分之一的地方绕地球飞行，另外两个卫星的轨道在相当地球和月球距离一半的地方。第5颗卫星是后备，可以用来代替在为期两年的探测计划中任何一颗失灵的卫星。安吉罗波洛斯说，这项探测工作可以帮助科学家对具有威胁性的太阳风暴和地球磁场的作用有进一步的了解。
安吉罗波洛斯说：“为了保护我们的卫星和在太空中的宇航员，了解并且预测太空风暴是很重要的，气象学家为了要了解猛烈的雷暴雨而对龙卷风加以研究，我们为了解最猛烈的太空风暴而对“亚暴”进行研究。”
把五颗袖珍卫星装进一枚火箭也在工程学方面有所贡献。每颗卫星一个宽度和高度都不到一米的立方体。加州大学的专家哈维是“特弥斯”计划的管理人。他说，技术人员从这项计划学习到怎么样利用小型电脑和其他仪器来制造袖珍卫星。哈维说，把这么多仪器装入5颗很小的卫星是一种挑战。
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