NASA has just confirmed that asteroid 99942 Apophis has no risk of hitting Earth for at least the next hundred years. These are the conclusions of the analysis of the latest radar data that have allowed us to better describe the orbit of this colossus, baptized as the ‘god of chaos’ (Apophis) and which, after its discovery in 2004, was thought to have many possibilities of impact. against the Earth.
The asteroid in question has an estimated diameter of 340 meters, and at first three probable shock dates had been estimated: 2029, 2036 and 2068. Later, the successive observations allowed a more precise estimation of the orbit of Apophis, and had been ruled out all possible crashes except for the one in 2068.
A unique opportunity for science
The orbit of Apophis around the Sun lasts just over 323 days, and its trajectory takes it through the orbit of the Earth from time to time. In early March, the asteroid passed relatively close to our planet, not close enough to pose an impact hazard, but close enough that scientists could study Apophis’s features more precisely. The new observations have made it possible to safely reject not only the risk of impact in 2068, but any other probability of collision in the next hundred years.
The astronomers turned to a 70-meter radio antenna at the Goldstone Deep Space Communications Complex (California), to accurately track the movement of Apophis. ” Although it was 17 million kilometers away, we were able to acquire incredibly precise information about its location with an accuracy of approximately 150 meters,” explains Marina Brozovic, a JPL scientist who led the radar campaign. “This campaign not only helped us to rule out any risk of impact, it provided us with a wonderful scientific opportunity.”
The Goldstone team also worked in collaboration with the Green Bank 100-meter Telescope in West Virginia to enable imaging of Apophis: Goldstone was transmitting while Green Bank was receiving, a “bistatic” experiment that doubled the strength of the received signal.
Although the Apophis radar images appear pixelated, they have a resolution of 38.75 meters per pixel, “something remarkable, considering that the asteroid was 17 million kilometers away, or about 44 times the Earth-Moon distance,” he adds. Brozovic: ” If we had binoculars as powerful as this radar, we could sit in Los Angeles and read the dinner menu at a restaurant in New York.”
Peanut shape
As the radar team further analyzes their data, they also hope to learn more about the asteroid’s shape. Previous radar observations have suggested that Apophis has a “bilobed” or peanut-like appearance. This is a relatively common shape among near-Earth asteroids over 200 meters in diameter; at least one in six has two lobes. Astronomers are also working to develop a better understanding of the asteroid’s rotational speed and the axis on which it spins. This knowledge will allow them to determine the orientation that the asteroid will have with the Earth when it meets the gravitational field of our planet in 2029, which could change that state of spin and even cause “asteroid tremors”.
