Asteroid Apophis — one of the scariest rocks in the solar system — won’t pose a threat to Earth for at least another century, according to updated NASA calculations.
Every 80,000 years or so, an object measuring around three football fields in length smashes into Earth, unleashing the equivalent of over 1,000 megatons of TNT. The discovery of Apophis in 2004 fit the description of one of these once-in-80,000-year events, understandably freaking a lot of people out. A hit from Apophis wouldn’t be Chicxulub bad — the 16 km-wide asteroid that wiped out most life on the planet some 66 million years ago — but it’d inflict catastrophic levels of local damage and trigger a global-scale impact winter.
In 2004, astronomers detected asteroid 99942 Apophis, a near Earth object measuring around 340 metres long. Its status as a potentially hazardous object has been continually refined over the years, but 2068 continued to represent a particularly worrisome year for the asteroid to hit us.
We can now breathe a sigh of relief, however, as the latest calculations suggest the asteroid won’t pose a threat to Earth for the time being, according to a NASA statement. A recent flyby of Apophis, in which the asteroid came to within 44 times the distance of Earth to the Moon, allowed NASA to refine its measurements, resulting in the new assessment.
“A 2068 impact is not in the realm of possibility anymore, and our calculations don’t show any impact risk for at least the next 100 years,” Davide Farnocchia of NASA’s Centre for Near-Earth Object Studies explained in the space agency’s announcement.
As a consequence, NASA has now removed Apophis from its naughty list, otherwise known as the Sentry Impact Risk Table. This table, maintained by CNEOS, had ranked Apophis as the third most dangerous known object, assessing an impact probability at around 1 in 150,000. The odds were slim but undeniably nonzero. The new calculations have allowed CNEOS to remove Apophis from the risk table altogether.
“With the support of recent optical observations and additional radar observations, the uncertainty in Apophis’ orbit has collapsed from hundreds of kilometers to just a handful of kilometers when projected to 2029,” said Farnocchia. “This greatly improved knowledge of its position in 2029 provides more certainty of its future motion, so we can now remove Apophis from the risk list.”
The year 2029 is notable because that’s the next time Apophis will fly past Earth, during which time it’ll seriously invade our personal space. It will come to within 32,000 km of our planet, which is a tenth the distance of Earth to the Moon and within the reach of some satellites. Apophis will be so close that it’ll be visible to small telescopes and binoculars.
When Apophis flew past Earth in early March this year, it was just 17 million km away. NASA took the opportunity to study and refine the asteroid’s position, which the space agency did using the radio antenna at Deep Space Network’s Goldstone Deep Space Communications Complex in California. This instrument allowed the team to calculate Apophis’s position to an accuracy of roughly 150 metres.
Marina Brozovic, the JPL scientist who led the radar campaign, said if “we had binoculars as powerful as this radar, we would be able to sit in Los Angeles and read a dinner menu at a restaurant in New York,” as she explained in the statement.
Using the Green Bank Telescope in West Virginia, the team was able to double the strength of the incoming radio signal, resulting in an imaging resolution of 38.75 metres per pixel.
Analysis of the data is still incomplete, and the team is hoping to better characterise the shape of Apophis (it’s suspected to have a bilobed appearance, in which two asteroids fused together to create a peanut-like shape), along with improved estimates of its rotation rate and spin state along its axis. These numbers will help to predict the object’s behaviour for the 2029 flyby, which scientists say is a once-in-a-thousand-year opportunity to study an object of this size from such close proximity.
With Apophis officially booted from the Sentry Impact Risk Table, the top rated NEOs in terms of risk are the 2 km-wide asteroid 29075 (1950 DA), which has a 1 in 8,300 risk of hitting Earth in 2880; the 490 metre-wide asteroid 101955 Bennu (1999 RQ36), which has a 1 in 2,700 chance of impact from 2175 to 2199; and the 37 metre-wide asteroid 2009 JF1, which has a 1 in 3,800 chance of hitting Earth next year (May 6, to be exact, so mark your calendars).
These rankings are based on the Palermo Technical Impact Scale, which takes other variables into account aside from impact probability, such as an object’s potential to inflict wide-scale damage.
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