Near Earth Objects: Twenty years of studies on asteroids

Near Earth Objects: Twenty years of studies on asteroids
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The NASA department for the study of potentially dangerous Earth-like asteroids at the turning point of twenty years.

The study of the potentially dangerous objects for the Earth has extended to those of 140 meters per kilometer, which would not be “armageddon” if they were impacted, but could still cause serious damage.

The NASA research center for the study of “objects” passing close to the Earth enters its third decade of life. It was March 11, 1998 when astronomers studying the asteroids received an alarming message: data concerning the observation of an asteroid discovered a few months earlier, called 1997 XF11 , suggested that there was the possibility that the object – almost a kilometer in diameter! – could have hit the Earth in 2028.

The alarm was issued by the Minor Planet Center, which collects data from observations and the determination of asteroid orbits. Although it was intended to alert only the small astronomical community that studies the asteroids, the news spread rapidly.

Near Earth Objects


The tam tam following the spread of the news led many to conclude that the Earth had its days counted. Fortunately, a few more observations were needed to find out that no, our planet was not in danger, and that 1997 XF11 would have passed so relatively close, but without risk of impact.

Don Yeomans, then coordinator of NASA’s Solar System Dynamics, and his colleague Paul Chodas stated that on the basis of verified data “the impact of 2028 was impossible”. Chodas, who is now director of CNEOS (Center for Near Earth Object Studies), said: “We are more certain that there is no possibility that XF11 will impact with the Earth, not for the next 200 years at least.” The “200 years” is the interval for which the orbital data are considered reliable with a low margin of uncertainty.

The number of asteroids and other mapped objects increases day by day: here an animation of our crowded Solar System (click on the image to start the animation).


The data published by CNEOS are the result of the calculations elaborated by the Minor Planet Center on the basis of data coming from satellites and, above all, from observers from all over the world – which, day after day, detect the movement of asteroids and comets.

Near Earth Objects

In the last two decades, the CNEOS data have allowed NASA to establish itself in this sector of information, with the result that there is an effective, excellent coordination for the surveillance of known objects, in particular those that can cross the Earth’s orbit. “We calculate high precision orbits for all asteroids and comets, and map their position in the Solar System, both forward in time to detect potential impacts, and back to see where they came from,” Chodas says today: “We have compiled the best orbit map for all the small bodies known in the Solar System.”

18,000 and INCREASING

These small objects, asteroids and comets that pass near the Earth, called NEO (Near Earth Objects), revolve around the Sun on orbits that lead them into the inner Solar System, within 195 million kilometers from the Sun, and also within 50 million kilometers compared to Earth’s orbit.

The frenzy born around the 1997 affair XF11 demonstrated the need for clarity and precision in communicating to the scientific community and to the public when a new object potentially dangerous for the Earth is discovered.

So for 20 years CNEOS has been the nerve center for mapping the NEOs and for predicting close crossings and reliably assessing the level of danger for the planet. About 18,000 potentially dangerous objects are known to date, and about forty new ones are added every week.

The work is far from being concluded, also because since 2005 we are searching and studying objects with a diameter of 140 meters per kilometer (before we were looking only for objects above a kilometer in diameter): bolides whose numbers seem infinite, which would not have a catastrophic impact but which could still cause far-reaching damage.

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