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The introduction of the sophisticated JPL Sentry and NEODyS impact monitoring systems over the last several years mean non-zero Torino Scale ratings are now a regular occurrence. The assessment of the impact hazard of NEOs and the complex task of assigning a Torino Scale rating for each object is performed by two independent systems, Sentry at NASA's Jet Propulsion Laboratory in Pasadena, and the NEODyS system at the University of Pisa in Italy.
These two monitoring systems perform complex calculations that search for possible impact scenarios for over a hundred years into the future. These calculations take several hours for each asteroid, despite being run on very fast computers. The results of these calculations allow impact probabilities and Torino Scale ratings to be assigned.
The dramatic increase in detection rates for near earth asteroids (NEAs) over the last five years means there is no shortage of newly discovered asteroids for the systems to monitor. Between January and July 2003, an average of 30 new NEAs were detected each month worldwide, this compares with only 12 per month for the same period in 1998. The increase is largely due to the introduction of dedicated search programs such as the Lincoln Near Earth Asteroid Research Project (LINEAR) and the Near Earth Asteroid Tracking Project (NEAT).
As of 7 September this year, the Minor Planet Centre in Massachusetts reports a total of 2412 known NEAs. The Minor Planet Centre is the clearinghouse for newly discovered asteroids and comets and is responsible for collection, computation, checking and dissemination of observations and orbits for minor planets and comets.
The most recent case of an asteroid with an initial Torino Scale rating '1' is 2003 QO104, a 2.6 km wide asteroid discovered on 31 August. Astronomers are keen to point out that such ratings should not be interpreted as �warnings� or �alarms�. Brian Marsden of the MPC told the NEO Information Centre in Leicester, �Given this situation, the Torino scale may not be the best tool for communicating potential risk.�
When asteroids have only been observed for only a few days or weeks, there is a high level of uncertainty in the computed orbit, because only a small part of the orbit has been observed. It is like watching a tennis serve, one frame at a time, and trying to predict whether the serve will be in or out, when the ball is just a few inches in its journey off the racquet. Experience has shown that, whilst it is not a forgone conclusion, more observations lead to a downgrading of the initial risk as potential impacts can often be ruled out.
More info: Asteroid and Comet Impact Hazard - Torino Scale
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