These four images are combined radio-optical images of a large solar flare that occurred on 17 June 1989. The red-orange background images are optical images (H-Alpha) and the superimposed contours show radio emission as seen with the VLA at a wavelength of 4.9 GHz. The four images are from four different times during the event, showing the progression toward maximum radio emission (bottom right). This soft X-ray flare was accompanied by a coronal mass ejection.
The two H alpha ribbons correspond to the "footpoints" of an arcade of magnetic loops which arch NE/SW. The magnetic field is strongest toward the NW, where prominent sunspots appear dark in H alpha. Early in the event, the magnetically stronger footpoint emits radio waves first (a), followed by magnetically conjugate footpoints to the SW (b). The entire magnetic arch connecting the two footpoints then emits (c,d).
This pair of images shows the planet Jupiter before (left) and after (right) fragments of the comet Shoemaker-Levy 9 struck the planet in 1994. The disk of the planet is in the center of the images. The bright red spots are regions high above Jupiter's "surface" where electrons interacting with the planet's intense magnetic field are producing strong radio emission. These "radiation belts" are similar to the Van Allen Radiation Belts discovered above the Earth in 1958. The pair of images shows the effect of the comet impacts on this pattern of radio emission.
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The VLA-Goldstone Radar SystemWhile the VLA has no transmitters on its dish antennas, which are equipped only for receiving, the VLA works in conjunction with the NASA Solar System Radar transmitter at Goldstone, California. At Goldstone, a half-million-watt transmitter sends a beam of radio waves out into the Solar System, aimed at some planet, moon or other object. The beam strikes that object, bounces off it, and some of the radio waves return to Earth. Here, the VLA receives those reflected signals and processes them to make a radar map of the planet or other object. Below you will see some of those radar maps. |
In this Goldstone-VLA radar image made in 1991, red areas are areas of high radar reflectivity, which can be a result of either the surface and near-surface composition or of surface roughness. The area of highest radar reflectivity is at the planet's north pole (top of image). This is believed to be due to significant amounts of water ice residing in permanently-shaded areas within craters in the polar region. The other two large regions of high reflectivity are in areas that never have been imaged by spacecraft, so the cause of the high reflectivity remains a mystery.
This is a radar image of Mars, made with the Goldstone-VLA radar system in 1988. Red areas are areas of high radar reflectivity. The south polar ice cap, at the bottom of the image, is the area of highest reflectivity. The other areas of high reflectivity are associated with the giant shield volcanoes of the Tharsis ridge. The dark area to the West of the Tharsis ridge showed no detectable radar echoes, and thus was dubbed the "Stealth" region.