Changes in Saturn Rings Puzzle ScientistsChanges in Saturn Rings Puzzle Scientists
New observations by the international Cassini spacecraft reveal that Saturn's trademark shimmering rings, which have dazzled astronomers since Galileo's time, have dramatically changed over just the past 25 years. Among the most surprising findings is that parts of Saturn's innermost ring - the D ring - have grown dimmer since the Voyager spacecraft flew by the planet in 1981, and a piece of the D ring has moved 125 miles inward toward Saturn. While scientists puzzle over what caused the changes, their observations could reveal something about the age and lifetime of the rings. Cassini-related discoveries were discussed Monday at a meeting of the American Astronomical Society's division of planetary sciences in Cambridge, England. "I don't think Saturn's rings will disappear anytime soon, but this tells us how the rings are evolving and how long they might last, " deputy project scientist Linda Spilker said in a telephone interview from England. Scientists are interested in Saturn's rings because they are a model of the disk of gas and dust that initially surrounded the sun. Studying them could yield important clues about how the planets formed from that disc 4.5 billion years ago. The ring observations were made this summer. The $3.3 billion Cassini mission, funded by NASA and the European and Italian space agencies, was launched in 1997.
Deep Impact space collision reveals comets to be fluffy balls of powder
Out is the long-held view of hardened, dirty snowballs hurtling through space. In is the comet as a fluffy ball of powder, blowing puffs of dust whenever sunlight falls on it. The insight came yesterday when researchers announced the first detailed results of Deep Impact, an elaborate experiment played out in space on July 4. Under the gaze of cameras on nearby spacecraft and more than 70 ground-based telescopes, the Deep Impact probe fired a metre-long copper bullet on a collision course with a 4-mile-wide block of dust and ice known as Comet 9P/Tempel 1. The 23,000mph collision produced a huge crater and gave scientists their first ever look inside a speeding comet. Most striking is that the comet is not made up of very much at all. "It's mostly empty," said Prof A'Hearn. The fine particles of dust and ice are held together extremely loosely, with pores thought to run throughout. "We have deduced that around 75% to 80% of the nucleus is empty and that tells me there is probably no solid nucleus. That is a significant advance in our understanding," said Prof A'Hearn. The finding overturns the view held by some scientists that comets were hard balls of solid dust and ice. Among the material were a host of organic molecules. Some scientists believe that comets carried these compounds to other planets, releasing them on impact, and seeding them with the building blocks of life. "I'd argue that's more likely now, because we saw this big enhancement of organic material coming out on impact," said Prof A'Hearn.