This NASA Hubble Space Telescope pair of images of Jupiter's volcanic moon Io shows the surprising emergence of a 200-mile diameter large yellowish-white feature near the center of the moon's disk (photo on the right). This is a more dramatic change in 16 months than any seen over the previous 15 years, say researchers. They suggest the spot may be a new class of transient feature on the moon. For comparison the photo on the left was taken in March 1994 – before the spot emerged – and shows that Io's surface had undergone only subtle changes since it was last seen close-up by the Voyager 2 probe in 1979. The new spot seen in the July 1995 Hubble image replaces a smaller whitish spot seen in about the same place in the March 1994 image. Note the much more subtle changes seen elsewhere on this face of Io over the 16 months between the images. Each image is a composite of frames taken at near-ultraviolet, violet, and yellow wavelengths, with Hubble's Wide Field and Planetary Camera 2. "The new spot surrounds the volcano Ra Patera, which was photographed by Voyager, and is probably composed of material, probably frozen gas, ejected from Ra Patera by a large volcanic explosion or fresh lava flows...," according to John Spencer of Lowell Observatory in Flagstaff, Arizona. The new bright spot is also unusual because it is much yellower than other bright regions of Io, which are whitish in color. The unusual color may result from the freshness of the deposit and will probably provide clues as to the composition of new volcanic materials on Io. The temperature on Io's surface is about -150 degrees Celsius (-238 degrees Fahrenheit); however, "hot spots" associated with volcanic activity may be as warm as 1,000 degrees Celsius (1,800 degrees Fahrenheit). Follow-up observations by Hubble, in coordination with the Galileo spacecraft, scheduled to arrive at Jupiter and fly by Io in December 1995, will reveal the evolution and lifetime of the new feature. Galileo will be able to see much greater detail on Io in visible light, but will still rely on information gleaned from Hubble UV observations and Hubble observations taken at times when Galileo cannot observe Io. These further observations should also tell whether astronomers have witnessed, for the first time, one of the processes which creates the bright regions on Io.
Credits
J. Spencer (Lowell Observatory), and NASA| About The Object | |
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| Object Name | Io |
| About The Object | |
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| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
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| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
