Cosmic Paparazzi – Saturn and Tethys

Saturn and moon Tethys

Saturn and moon Tethys


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This view of Saturn, its rings and the moon Tethys represents “Target 1” in the fall 2009 edition of the Cassini Scientist for a Day contest. (See http://saturn.jpl.nasa.gov/education/scientistforaday8thedition/.) The contest is designed to give students a taste of life as a scientist by challenging them to write an essay describing the value of one target choice among three for Cassini to image.

A bonus feature in the image is the presence of bright spokes on and just above the ansa, or curved edge of the darkened ringplane. The spokes are made visible here by sunlight scattering through the dust-sized icy particles and toward Cassini’s cameras.

Images taken using red, blue and green spectral filters were combined to create this color view. The images were acquired with the Cassini wide-angle camera on Oct. 11, 2009 at a distance of 1.7 million kilometers (1 million miles) from Saturn. – NASA

Cosmic Paparazzi – Pismis 24

Pismis 24
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The small open star cluster Pismis 24 lies in the core of the NGC 6357 nebula in Scorpius, about 8,000 light-years away from Earth. The brightest object in the center of this image is designated Pismis 24-1 and was once thought to weigh as much as 200 to 300 solar masses. This would not only have made it by far the most massive known star in the galaxy, but would have put it considerably above the currently believed upper mass limit of about 150 solar masses for individual stars.

However, Hubble Space Telescope high-resolution images of the star show that it is really two stars orbiting one another that are each estimated to be 100 solar masses.

In addition, spectroscopic observations with ground-based telescopes further reveal that one of the stars is actually a tight binary that is too compact to be resolved even by Hubble. This divides the estimated mass for Pismis 24-1 among the three stars. Although the stars are still among the heaviest known, the mass limit has not been broken due to the multiplicity of the system.

The images of NGC 6357 were taken with Hubble’s Wide Field and Planetary Camera 2 in April 2002.

ImageCredit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)

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