March 16, in the year 2880, was looking as though it might be a horrible day for Earth and anyone living here at that time. However, thanks to recent updates to the system used to keep track of dangerous asteroids, we can breathe a sigh of relief for our distant descendants.
Asteroid 29075 (1950 DA) is a 1.3-kilometre wide space rock first spotted on February 23, 1950. However, due to the timing of its orbit, astronomers lost track of it after that, for just over 50 years. It was only spotted again on December 31, 2000, about three months before the asteroid would make a safe flyby of Earth, at a distance of nearly 8 million kilometres.
It was fortunate that astronomers spied the asteroid when they did. It gave them the chance to aim the Goldstone and Arecibo radio telescopes at it as it flew past us. By bouncing radar beams off 1950 DA's surface, they gave us a look at its size and shape and gathered more details about how it moved through space.
Asteroid 29075 (1950 DA) is shown here in eight different radar images gathered by the Arecibo radio telescope as the asteroid tumbled past Earth on March 11, 2001. Credit: NASA CNEOS
From those observations, a new plot of 1950 DA's orbit emerged and a new assessment of its threat to Earth. As a result, 1950 DA suddenly shot up to the top of NASA's Sentry Impact Risk table, where astronomers list all of the known asteroids with any chance of impacting Earth in the future. In fact, from 2014 until now, 1950 DA was the most dangerous asteroid known!
Fortunately, it was not an immediate risk. However, for the only potential impact for 1950 DA, on March 16, 2880, it would end up being a significant worry.
Now, it wasn't a sure thing that this massive asteroid would slam into Earth on that fateful day. According to the ESA, 1950 DA's impact risk, as of 2001, was 1 in 300 (or about a one-third of one per cent chance). On the Palermo Scale, which measures the overall risk of an impact, the asteroid was ranked with a value of +0.17. According to NASA, a value between -2 and 0 indicates that the asteroid should be carefully monitored. On the other hand, a positive Palermo value indicates an actual level of concern.
A 2015 update to 1950 DA's threat level still gave a 1 in 8,000 chance of an impact. That only amounts to a 0.0125 per cent chance (or a 99.9875 per cent chance of it missing). Meanwhile, this also downgraded the Palermo scale rating to -1.4. So, it was still worth watching.
As 1950 DA orbits the Sun, it travels between the asteroid belt and a point just inside Earth's orbit. Based on this, it is an Apollo asteroid, a near-Earth object, and a potentially hazardous asteroid. Credit: ESA/NEO Coordination Office
Given the potential damage of an asteroid impact, any chance of a hit is worth keeping an eye on. In a 2003 study of 1950 DA's possible impact in 2880, the researchers examined what would happen if the asteroid crashed into the Atlantic Ocean, around 300 kilometres from the U.S. East Coast. They found that it would produce a crater nearly 20 kilometres across the sea floor, with a 100-m high tsunami that would crash into the eastern seaboard within 2 hours of the impact. In addition, Western Europe and Western Africa would see 20-metre waves arrive around 12 hours after impact.
NEW ASSESSMENT = LOWER RISK
The latest update about 1950 DA, issued on March 29, 2022, by scientists at NASA's Center for Near-Earth Object Studies (CNEOS) and the ESA's NEO Coordination Office, has significantly downgraded the threat from the asteroid.
As of now, the impact risk has been lowered from 1 in 8,000 down to 1 in 30,000. That's a nearly 4-fold decrease in the threat level posed by 1950 DA. Also, it has gone from a -1.4 to a -2.0 on the Palermo Scale. Any lower, and they would likely remove 1950 DA from their risk lists altogether.
The innovation that made this possible was NASA's new Sentry II system. As an improvement over the old Sentry system, Sentry II considers how the path of an asteroid is affected by sunlight shining on its surface. This is known as the Yarkovsky effect.
Watch below: What is the Yarkovsky effect?
According to NASA, CNEOS scientists had to make manual adjustments to asteroid orbits based on the expected influence of the Yarkovsky effect. Now, Sentry II takes care of all those calculations on its own, improving our ability to find potential impacts and rule out the danger from certain asteroids.
With the threat from 1950 DA now downgraded, the title of "most dangerous asteroid" now gets passed to 101955 Bennu, the target of NASA's OSIRIS-REx mission from Dec. 3, 2018, to May 10, 2021. The spacecraft gathered a substantial amount of data about the asteroid's composition and density and its path through space, and how that was being influenced by the Yarkovsky effect. It is also returning a sample of material from Bennu, which is expected to arrive on Sep. 24, 2023.
Based on the new information about Bennu and the calculations of the new Sentry II system, NASA actually increased the odds of Bennu hitting Earth as of last year. The changes were minor. The probability of a strike between the years 2135 and 2200 increased from 1 in 2,700 up to 1 in 1,750. The individual chance of an impact, specifically on September 24, 2182, was set at 1 in 2,700.
These impact probabilities are still tiny (a 1 in 2,700 chance of a hit = a 99.99963 per cent chance it will miss). Still, it will be close enough. Perhaps, 160 years from now, we will have the technology to harvest all the rock and minerals from Bennu, completely removing it as a potential threat to the inhabitants of Earth.