Aurora on Jupiter
The Hubble Space Telescope has captured high-resolution images of auroras on Jupiter using a new instrument. Unlike previous images, this time the faint flares are not blurred by the planet's rotation during exposure. Although the Hubble Telescope has been taking pictures of the northern and southern auroras since 1990, the new Space Telescope Imaging Spectograph (STIS) is 10 times more sensitive than previous cameras. This allows for shorter exposure times, preventing Jupiter's rotation from blurring images and enabling resolutions two to five times better than conventional cameras. They are enough to show the veil of the aurora stretching several hundred kilometers above Jupiter. Images taken by the Space Shuttle of Earth's auroras look very similar.
Like Earth, Jupiter's auroras develop when electrically charged particles, trapped by the planet's magnetic field, spiral toward the magnetic north or south pole at high energy. When the particles hit the upper atmosphere, they excite atoms and molecules there, causing them to light up.
The electrons that hit the earth's atmosphere come from the sun. As a result of the solar wind, the aurora stays focused in the night sky while the Earth rotates underneath. Jupiter's auroras, on the other hand, are caused by particles ejected from volcanoes on Io, one of Jupiter's moons. These charged particles are then magnetically captured and begin to rotate with Jupiter. They produce aurorae day and night in oval areas centered on Jupiter's magnetic poles.
In addition to the northern lights, traces of light reminiscent of comets can be seen at both the north and south poles, slightly shifted towards the equator. They are caused by invisible streams of electrified particles from Io following Jupiter's magnetic field lines. The enormous current (equivalent to about a million amperes) causes a bright but spatially restricted aurora as the particles enter the planet's atmosphere. The brightest spots can be found where Io's magnetic field lines meet Jupiter.
The scientists compare Hubble's images with previous measurements by the Galileo spacecraft. They hope to use this data to better understand how the auroras form on Jupiter.
The recordings were made on September 20, 1997. The false-color images of the auroras are composed of two images from different parts of the UV spectrum, one in blue and the other in red. Because of this, the aurora emissions are white and shown in blue and red tones, while in the blended (conventional) exposure below, the sunlight reflected from the planet appears brown.
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