CCNet 62/2003 - 2 September 2003 -------------------------------- Today both risk monitors downgraded their overall risk assessments for this object, with NEODyS dropping its impact solution count by one and no longer having any solutions rated above Torino Scale 0 (TS-0). JPL, however, added and removed impact solutions for a net gain of two (31 total in the years 2014-2099), and still rates its solution for 21 March 2014 at TS-1 ("merits special monitoring"). --Asteroid/Comet Connection, 1 September 2003 As far as the public is concerned, it just isn't worth getting worried about an object with a couple weeks of optical data showing a possible Earth encounter years from now. Sometimes, it can't even be said for certain what side of the Sun such an object will be on at the time of the listed possible impact. A few days later, additional measurements will shrink the orbit uncertainty region by a relatively large amount and the Earth will fall out of the risk zone. --Jon Giorgini, Jet Propulsion Laboratory, CCNet - 26 July 2002 (1) ASTEROID IMPACT RISK DOWNGRADED (2) POTENTIALLY HAZARDOUS ASTEROID GIVEN TORINO 1 RATING (3) ASTEROID WARNING FOR 2014 (4) THE MEANING OF ASTEROID RISK LISTINGS ================ (1) ASTEROID IMPACT RISK DOWNGRADED Asteroid/Comet Connection, 1 September 2003 http://www.hohmanntransfer.com/news.htm The Sunday DOU carries observations of 2003 QQ47 overnight by Sormano and Great Shefford observatories. Today both risk monitors downgraded their overall risk assessments for this object, with NEODyS (http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:2003QQ47;risk) dropping its impact solution count by one and no longer having any solutions rated above Torino Scale 0 (TS-0). JPL (http://neo.jpl.nasa.gov/risk/2003qq47.html), however, added and removed impact solutions for a net gain of two (31 total in the years 2014-2099), and still rates its solution for 21 March 2014 at TS-1 ("merits special monitoring"). NEODyS continues to show two impact solutions in 2076 and JPL one, but both have now significantly lowered their risk ratings for that year, which at different times they had independently rated at TS-1. Such assessments are ephemeral and of no importance once superceded with newer data and analysis, but they do help demonstrate the routine cycle of observation and calculation used to discover and eliminate risk concerns. Copyright 2003, Asteroid/Comet Connection =============== (2) "POTENTIALLY HAZARDOUS ASTEROID GIVEN TORINO 1 RATING" NEO Information Centre, 2 September 2003 http://www.nearearthobjects.co.uk/news_display.cfm?code=news_intro&itemID=196 A potential asteroid impact on 21 March 2014 has been given a Torino hazard rating of 1, defined as 'an event meriting careful monitoring'. The newly discovered 1.2 km wide asteroid, known to scientists as 2003 QQ47, has a mass of around 2 600 billion kg, and would deliver around 350 000 MT of energy in an impact with Earth. Currently, the overall probability of this asteroid impacting Earth is 1 in 909 000. However, the orbit calculations are based on just 51 observations during a 7-day period. Dr Alan Fitzsimmons of Queen's University, Belfast, one of the expert team advising the UK NEO information Centre said "The NEO will be observable from Earth for the next 2 months, and astronomers will continue to track it over this period." Lincoln Near Earth Asteroid Research Program (LINEAR), operating out of Socorro, New Mexico, first observed the giant rock on 24 August and reported their observations to the Minor Planet Centre in Massachusetts. The Minor Planet Centre plays a crucial role as the clearinghouse for all new discoveries of asteroids and comets. "As additional observations are made over the coming months, and the uncertainties decrease, asteroid 2003 QQ47 is likely to drop down the Torino scale," said Kevin Yates, project manager for the UK NEO Information Centre, based at the National Space Centre in Leicester. "The NEO Information Centre will continue to monitor the latest results of observations and publish regular updates on our website." Asteroids such as 2003 QQ47 are chunks of rock left over from the formation of our Solar System 4.5 billion years ago. Most are kept at a safe distance from Earth in the asteroid belt between the orbits of Mars and Jupiter. However, the gravitational influence of giant planets such as Jupiter can nudge asteroids out of these safe orbits and send them plunging into the Earth's neighbourhood. =============== (3) "ASTEROID WARNING FOR 2014" BBC News Online, 2 September 2003 http://news.bbc.co.uk/1/hi/uk/3200019.stm The British agency responsible for identifying potentially hazardous asteroids says US astronomers are warning of a possible collision in 2014. The UK Government's Near Earth Object Centre says American astronomers have discovered a large, fast-approaching asteroid that could hit the Earth on 21 March, 2014. But they add the chances of it doing so are just one in 909,000. What is more, any risk of an impact is likely to decrease as further data is gathered, they say. Credible threat The BBC's science correspondent Christine McGourty says that, although the chances this asteroid will hit the Earth are slim, it is considered worth monitoring due to its sheer size and velocity. The rock is said to measure approximately two thirds of a mile across - only one tenth of the size of the meteor thought to have wiped out the dinosaurs 65 million years ago. It is travelling at a speed of about 20 miles per second. "In theory such an asteroid could cause devastation across an entire continent," Christine McGourty says. It has been labelled "2003 QQ 47" and astronomers will be monitoring it closely for the next two months. Copyright 2003, BBC ================ (4) THE MEANING OF ASTEROID RISK LISTINGS CCNet, 26 July 2002 http://abob.libs.uga.edu/bobk/ccc/cc072602.html Jon Giorgini
Dear Benny, Based on discussions with the press and others in the wake of 2002 NT7, it seems NONE of the people I have talked to (no one outside the "impact community") understands the meaning of a listing on a risk page. That is, the difference between the "potential impacts" and "predicted impacts". Two or three weeks of optical data is not enough to conclusively identify an impact years in the future. POSSIBLE hazards can be flagged, but these are actually due to the lack of orbit knowledge; the asteroid could be so many places the Earth can't help but be in some of them. These listings are POSSIBLE impacts, not PREDICTED impacts. To PREDICT an asteroid's orbit reliably you need radar measurements or at least optical observations spanning 1 (preferably two) orbit periods of the asteroid. With an orbit period of 2.29 years, that means we should be able to usefully predict 2002 NT7's orbit in a positive way for a few decades after 2-4 more years of tracking it. By contrast, eliminating an entry on the risk page is a negative prediction; a prediction of where it will NOT be. Results with less data -- 2 or 3 weeks or even months -- are simply astronomer's doing their routine, daily chore of eliminating obscure possibilities. The listings are not really PREDICTIONS of impact, but a statement that one is POSSIBLE, primarily because it is not known for sure where the asteroid will be. Of course lots, of things are possible, most of which will not happen. It's possible I will be on top of Mount Everest next month but I am not predicting it. And there will come a point when my being on Mount Everest at some instant can be positively excluded ("that's impossible!"). The purpose behind the risk web page JPL produces is to communicate possibilities to other astronomers so they know which objects require more observations. A listing is not a declaration that an object is predicted to impact, or even come close to the Earth at that time, only that the possibility has not been ruled out. As far as the public is concerned, it just isn't worth getting worked up over an object with a couple weeks of optical data showing a possible Earth encounter years from now. SOMETIMES, IT CAN'T EVEN BE SAID FOR CERTAIN WHAT SIDE OF THE SUN SUCH AN OBJECT WILL BE ON AT THE TIME OF THE LISTED POSSIBLE IMPACT. A few days later, additional measurements will shrink the orbit uncertainty region by a relatively large amount and the Earth will fall out of the risk zone. A pointer to such objects is valuable to astronomers however, so they can organize their limited resources to continuing tracking objects with POSSIBLE (but by no means PREDICTED) impact potential. In general, it is very difficult for fuzzy optical measurements to narrow the uncertainties for newly discovered objects. A conclusive impact detection will almost certainly have to come from radar which can measure the position of an object to within a few meters. Optical measurements are typically good only at the 10's-100's of km level which fuzzes out knowledge quickly in a few years. The only substantive hazard prediction out there is 1950 DA; 51 years of optical data and recent radar data together indicate a possible impact event with odds between 0 and 1-in-300 on March 16, 2880. Ground-based observers could track 1950 DA for the next few decades without substantially changing the possibilities since the orbit uncertainties are so small they are dominated by the way the asteroid spins in space. Regards, Jon Giorgini |Navigation & Mission Design Section Senior Engineer | Solar System Dynamics Group Jon.Giorgini@jpl.nasa.gov | Jet Propulsion Laboratory ----------- CCNet is a scholarly electronic network. To subscribe/unsubscribe, please contact the moderator Benny Peiser (email@example.com). Information circulated on this network is for scholarly and educational use only. The attached information may not be copied or reproduced for any other purposes without prior permission of the copyright holders. DISCLAIMER: The opinions, beliefs and viewpoints expressed in the articles and texts and in other CCNet contributions do not necessarily reflect the opinions, beliefs and viewpoints of the moderator of this network.
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