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From: TerryMoselaol.com Date: Fri, 3 Mar 2006 18:55:49 EST Subject: Jupiter's new Red Spot, Asteroid impact threat Hi all, 1. Jupiter has developed a new Red Spot! Only about half the size of the one we know and love so well, but nevertheless, a really fascinating development! "Christopher Go of the Philippines photographed it on February 27th using an 11-inch telescope and a CCD camera: Above: Red spots on Jupiter, photographed by amateur astronomer Christopher Go on Feb. 27, 2006. The official name of this storm is "Oval BA," but "Red Jr." might be better. It's about half the size of the famous Great Red Spot and almost exactly the same color. Oval BA first appeared in the year 2000 when three smaller spots collided and merged. Using Hubble and other telescopes, astronomers watched with great interest. A similar merger centuries ago may have created the original Great Red Spot, a storm twice as wide as our planet and at least 300 years old. At first, Oval BA remained white - the same color as the storms that combined to create it. But in recent months, things began to change: "The oval was white in November 2005, it slowly turned brown in December 2005, and red a few weeks ago," reports Go. "Now it is the same color as the Great Red Spot!" "Wow!" says Dr. Glenn Orton, an astronomer at JPL who specializes in studies of storms on Jupiter and other giant planets. "This is convincing. We've been monitoring Jupiter for years to see if Oval BA would turn red - and it finally seems to be happening." (Red Jr? Orton prefers "the not-so-Great Red Spot.") Why red? Curiously, no one knows precisely why the Great Red Spot itself is red. A favorite idea is that the storm dredges material from deep beneath Jupiter's cloudtops and lifts it to high altitudes where solar ultraviolet radiation - via some unknown chemical reaction - produces the familiar brick color. "The Great Red Spot is the most powerful storm on Jupiter, indeed, in the whole solar system," says Orton. The top of the storm rises 8 km above surrounding clouds. "It takes a powerful storm to lift material so high," he adds. Above: Hubble images detail the birth of oval BA in 1997-2000. Oval BA may have strengthened enough to do the same. Like the Great Red Spot, Red Jr. may be lifting material above the clouds where solar ultraviolet rays turn "chromophores" (color-changing compounds) red. If so, the deepening red is a sign that the storm is intensifying. "Some of Jupiter's white ovals have appeared slightly reddish before, for example in late 1999, but not often and not for long," says Dr. John Rogers, author of the book "Jupiter: The Giant Planet," which recounts telescopic observations of Jupiter for the last 100+ years. "It will indeed be interesting to see if Oval BA becomes permanently red." See for yourself: Jupiter is easy to find in the dawn sky. Step outside before sunrise, look south and up. Jupiter outshines everything around it. Small telescopes have no trouble making out Jupiter's cloudbelts and its four largest moons. Telescopes 10-inches or larger with CCD cameras should be able to track Red Jr. with ease. What's next? Will Red Jr. remain red? Will it grow or subside?" - Definitely worth a look! 2. "Asteroid 2004 VD17 Classed as Torino Scale 2 STATUS REPORT Date Released: Wednesday, March 1, 2006 Source: Jet Propulsion Laboratory At the end of February, orbital calculations for near-earth-asteroid (NEA) 2004 VD17 indicated that the risk of an impact within the next century (specifically on May 4, 2102) was higher than that of any other known asteroid. The probability, based on 687 telescopic observations spanning 475 days, is listed on the NASA/JPL NEO Program webpage as a bit less than 1 in 1000. This probability, while small, raises the possible 2102 impact to a Torino scale value of 2 (meriting attention from astronomers), which is higher than any other asteroid. (Note: the impact probability for 1950 DA is larger, but since this hazard is not realized until 2080, it falls outside the one-century range of the Torino scale). Judging from its brightness, NEA 2004 VD17 has a nominal diameter near 500 m and a mass of nearly a billion tons. While below the threshold for a global catastrophe, the nominal impact energy of more than 10,000 megatons is comparable to all the world's nuclear arsenals. There are no radar observations available, and the asteroid has not been characterized in any detail, so all these numbers should be taken as approximate. For comparison, NEA Apophis (formerly 2004 MN4) is currently listed on the NEO webpage as Torino scale 1, with an impact probability on April 13, 2036, of about 1 part in 5000. Apophis is also smaller, with a nominal diameter of 300 m and mass of less than 100 million tons. These are the only two asteroids currently with a Torino Scale listing of greater than 0. Fortunately, it is nearly a century before the close pass from VD17. This should provide ample time to refine the orbit and, most probably, determine that the asteroid will miss the Earth. On the other hand, there are no near-term opportunities for additional observations, so VD17 will probably remain at Torino scale 2 for quite some time. All the above information is taken from the NASA/JPL NEO Program Office webpage at http://neo.jpl.nasa.gov. T. M.'s Comment: This may well be headlined by the media, as they love a good scary headline! But don't be too alarmed! Due to a statistical anomaly, the calculated risk of an impact often increases from a very low level, to a higher level, before further observations refining the orbit then reveal the risk to be actually zero. This is very hard to explain without a diagram, but in very simple terms the predicted position of the asteroid as it crosses the Earth's orbit on a certain date is an 'uncertainty ellipse', because we don't know the asteroid's orbit really well yet. If the Earth's position on that date, which is known very accurately, lies within that ellipse, then the relative cross-sectional area of the Earth to the size of the ellipse gives the probability of an impact - say 1:5,000. Further observations then refine the orbit of the asteroid, so the new calculated uncertainty ellipse is smaller. But if the Earth still lies within that ellipse, then the probability of an impact goes up, because the ratio of Earth size to ellipse size has got smaller - say 1:2,000. But what usually happens then is that the next refinement of the orbit reduces the size of the ellipse even further, to the point where the Earth now lies outside the ellipse, so the probability of collision goes to zero. Obviously this is not certain at this stage, but don't be worrying about your children or grandchildren just yet! Clear skies, Terry Moseley
Last Revised: 2006 March 6th
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