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"I want to know why the universe exist, why there is something greater than nothing."
Steven Hawking
Scientist, Space Lover
Like the downtown area of your favorite city and any self-respecting web site ... Io's surface is constantly under construction. This moon of Jupiter holds the distinction of being the Solar System's most volcanically active body -- its bizarre looking surface continuously formed and reformed by lava flows. Generated using 1996 data from NASA's Galileo spacecraft, this high resolution composite image is centered on the side of Io that always faces away from Jupiter. It has been enhanced to emphasize Io's surface brightness and color variations, revealing features as small as 1.5 miles across. The notable absence of impact craters suggests that the entire surface is covered with new volcanic deposits much more rapidly than craters are created. What drives this volcanic powerhouse? A likely energy source is the changing gravitational tides caused by Jupiter and the other Galilean moons as Io orbits the massive gas giant planet. Heating Io's interior, the pumping tides would generate the sulfurous volcanic activity.
Microquasars, bizarre binary star systems generating high-energy radiation and blasting out jets of particles at nearly the speed of light, live in our Milky Way galaxy. The energetic microquasar systems seem to consist of a very compact object, either a neutron star or a black hole, formed in a supernova explosion but still co-orbiting with an otherwise normal star. Using a very long array of radio telescopes, astronomers are reporting that at least one microquasar, LSI +61 303, can be traced back to its probable birthplace -- within a cluster of young stars in the constellation Cassiopeia. About 7,500 light-years from Earth, the star cluster and surrounding nebulosity, IC 1805, are shown in the deep sky image above. The cluster stars are identified by yellow boxes and circles. A yellow arrow indicates the common apparent motion of the cluster stars, the green arrow shows the deduced sky motion of the microquasar system, and the red arrow depicts the microquasar's motion relative to the star cluster itself. Seen nearly 130 light-years from the cluster it once called home, a powerful kick from the original supernova explosion likely set this microquasar in motion.
The first APOD appeared eleven years ago today, on 1995 June 16. Although garnering only 14 page views on that day, we are proud to estimate that APOD has now served over 400 million space-related images over the last eleven years. That early beginning, along with a nearly unchanging format, has allowed APOD to be a consistent and familiar site on a web frequently filled with change. Many people don't know, though, that APOD is now translated daily into many major languages. We again thank our readers and NASA for their continued support, but ask that any potentially congratulatory e-mail go to the folks who created the great pictures -- many times with considerable effort -- that APOD has been fortunate enough to feature over the past year. Many can be contacted by following links found in the credit line under the image. Some of these images are featured in the above spectacular collage of a fantasy sky above Mars submitted by an enthusiastic APOD reader skilled in digital image manipulation. How many APOD images can you identify?
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