While standing on planet Earth, it’s easy to forget that we’re sitting on a rock hurtling through the Solar System on a path that might collide with other (smaller) space rocks, mostly because we can’t feel that motion.
If you ever feel like putting yourself completely at the mercy of random space rocks, we recommend heading over to NASA’s Eyes on Asteroids website and choosing their closest approach.
NASA and other observatories track the orbits of objects discovered in the Solar System, keeping a special eye on “near-Earth objects” (NEOs) 140 meters (460 feet) and larger in size that could cause destruction if they were to hit the Earth. By observing their orbits, astrophysicists are able to estimate the future orbits of objects and predict whether they might place them in our part of the Solar System.
These objects are given a point on the Palmero scale.
“The scale compares the likelihood of a potential impact detected with the average risk posed by objects of the same size or larger over the years up to the date of the potential impact,” explains NASA’s Center for Near-Earth Object Studies. “This average risk from random impacts is known as the background risk. For convenience, the scale is logarithmic,
so, for example, a Palermo scale value of -2 indicates that the potential impact event being detected is only 1 percent more likely event occurring in the intervening years, a value of zero indicates that the single event is as threatening as the background risk, and a value of +2 indicates an event that is 100 times more likely than a background impact from a facility at least as large as before the date of the potential impact in question.”
Objects are also given a Torino-friendly score of 0-10, with a score of 0 meaning the likelihood of impact is zero or thereabouts, and 10 meaning “a collision is certain, capable of causing global climate catastrophe that could threaten the future of civilization as we know it, whether on land or in the ocean.” These are color-coded aids in green, yellow and red to clarify the situation for the public.
Over the years of monitoring space objects, astronomers have discovered objects that have moved away from the green zone. However, there were a couple that made it to level 4; the highest level of the yellow zone.
“A close encounter that deserves the attention of astronomers,” NASA explains about the level. “Current calculations give a 1 percent or better chance of an impact capable of regional destruction. Most likely, new telescopic observations will lead to reassignment to level 0. Attention from the public and from public officials is merited if the encounter is less than a decade away.”
One of these objects was 99942 Apophis. After it was first discovered in 2004, observations placed it at level 2 on the Turin scale. However, further observations in December of that year put it at Level 4 due to a 1.6 percent chance of the asteroid hitting us in 2029. Further observations ruled out an impact in 2029, as well as 2036 and 2068. , although they will still be close encounters.
Currently, there are no known objects with a Torino score above 0. However, there are objects that require further observation, scoring -0.93 and -1.59 on the Palmero scale, which have not been assigned a Torino score since potential collisions occur more beyond. than 100 years in the future.
(29075) 1950 DA, an object 1.3 kilometers (0.81 miles) across, scores -0.93 due to a “potentially very close” approach to Earth on March 16, 2880. This is likely to change in the coming years, as have more observations made.
101955 Bennu (1999 RQ36) – more simply known as “Bennu” – currently sits at -1.59 on the Palmero scale. As far as we can tell, it will make several close approaches to the Moon and Earth. In September 2135, it is expected to pass within 0.00143 Astronomical Units (AU) of Earth, with 1 AU being the distance between Earth and the Sun. That’s 213,925 kilometers (132,927 miles)which is very close spatially.
As these asteroids orbit, more observations are made and trajectories are refined, meaning these results can go up or down. The further in time, the more likely that the objects’ orbits can be disturbed by close encounters with other objects (such as Earth).
Until now, astronomers have been able to predict the orbits of known objects up to about 100 years into the future. The good news is that “no known asteroid larger than 140 meters in size has a significant chance of hitting Earth for the next 100 years,” according to Dr Kelly Fast, manager of NASA’s NEO Observations Program. at NASA headquarters in 2018.
In better news, a team led by Oscar Fuentes-Muñoz of the University of Colorado Boulder was able to go further, predicting the paths of larger asteroids 1,000 years into the future.
“Estimating impact risk over longer time scales is a challenge as orbital uncertainties increase. To overcome this limitation we analyze the evolution of the minimum orbit intersection distance (MOID), which limits the closest possible encounters between asteroids and Earth,” the team explain in their paper. “The evolution of the MOID highlights NEOs that are in the vicinity of Earth for longer periods of time, and we propose a method to estimate the probability of a deep encounter with Earth during these periods.”
Using this method, the team was able to rule out most NEOs from hitting our planet within the next thousand years, and could estimate the probability of others hitting us like a pack of dinosaurs. The probability of being hit before the year 3000 seems pretty low according to the team, with the most likely object to hit us – 7482 (1994 PC1) – having just a 0.00151 percent chance of a close encounter, coming closest to Earth closer than the moon’s orbit.
