The vast majority of #asteroid impacts 
are still missed 
. Based on the few successfully predicted asteroid impacts, the average time between initial detection and impact is currently around 9 hours 
https://en.wikipedia.org/wiki/Asteroid_impact_prediction#Effectiveness_of_the_current_system
Richard Moissl, head of #ESA’s #PlanetaryDefence office, 54:00 : We have a blaringly obvious blind spot. Something like #Chelyabinsk 
could happen any moment right now, we wouldn't have any prewarning https://www.youtube.com/watch?v=8njR4413hok
The warning time 
is unlikely to be more than a few months. Impacts from objects as small as 50 meters in diameter 
, which are far more common, are historically extremely destructive regionally https://en.wikipedia.org/wiki/Asteroid_impact_avoidance#Deflection_efforts
A single #HAMMER impactor (9-meter-tall, 8.8-ton) could deflect an object 90 meters in diameter by around 1.4 Earth radii with 10 years of lead time – from the time of launch to anticipated Earth impact. If limited to #telescopic 
observations, it’s possible that researchers may not be 100 percent certain of an #impact until less than a year before collision . https://www.llnl.gov/article/44186/scientists-design-conceptual-asteroid-deflector-and-evaluate-it-against-massive-potential
The 20-inch diameter #telescope will carry out a five-year baseline survey to find at least two-thirds of the unknown #NEOs larger than 140 meters . It will launch around 
September 2027 to detect and observe #asteroids and comets that could potentially pose an impact threat to Earth https://www.aerotime.aero/articles/spacex-nasa-rocket-asteroid
"The bad news is #NASA estimates that it tracks only about 40 percent 
of the #asteroids #large enough that they could cause calamity if they were to hit #Earth" https://www.washingtonpost.com/technology/2022/10/24/nasa-asteroid-telescope
#ESA : #Asteroid danger explained https://www.esa.int/ESA_Multimedia/Images/2018/06/Asteroid_danger_explained
"The YR4 episode is just the beginning for #astronomers gaining the capability to see these objects before they come calling through our neck of the woods." https://arstechnica.com/space/2025/02/asteroid-2024-yr4-may-be-a-dud-but-we-will-soon-find-many-more-threats
@ScottManleyHimself : there's a real chance we can't honestly know the answer by April when it gets too faint to observe until 2028 https://www.youtube.com/watch?v=Esk1hg2knno
#ESA : #2024YR4 is estimated to be between 40 m and 100 m wide . It is too early to determine where exactly on Earth a potential impact could occur. The #asteroid is currently moving away from Earth in almost a straight line, making it difficult to accurately determine its orbit by studying how its trajectory curves over time. It is possible it will fade from view before we are able to entirely rule out any chance of impact in 2032 https://www.esa.int/Space_Safety/Planetary_Defence/ESA_actively_monitoring_near-Earth_asteroid_2024_YR4
#ESA has determined that the #asteroid will pass the Earth on 22 December 2032 at a distance of almost 136,000 kilometers – with an #inaccuracy of 311,000 kilometers. 
https://www.heise.de/en/news/Potentially-dangerous-asteroid-2024-YR-The-risk-continues-to-rise-very-slowly-10273047.html
When discovered in 2004, #Apophis was thought to have a 2.7% chance of colliding with Earth in 2029. In 2021, #NASA ruled out these collision risks after refining its trajectory, but recent simulations have revived some concerns.
#2024YR4 will be too distant for radar observations until 2032, when it could strike Earth. #Astronomers need more data to refine its exact orbit https://www.forbes.com/sites/jamiecartereurope/2025/02/02/a-deadly-asteroid-may-strike-earth-in-2032---what-to-know
#ESA "By the time the astrometry reached the impact monitoring systems, the impact had already happened." https://www.space.com/the-universe/asteroids/asteroid-that-hit-earth-hours-after-being-detected-was-3rd-imminent-impactor-of-2024
@VRubinObs Today, #astronomers are aware of only about 40 percent of potentially hazardous #asteroids - close-flying objects that are large enough to cause continent-wide destruction if they were to impact Earth. "The idea is, if there is an object like that, we want to find it while it’s maybe 40 or 50 years out, because that gives us enough time to figure out how we’re going to deflect it.” https://www.smithsonianmag.com/science-nature/this-revolutionary-new-observatory-will-locate-threatening-asteroids-and-millions-of-galaxies-180984514/
While humankind could deflect an incoming #asteroid by nuking it, using lasers to vaporise it, sending a space “tractor” to drag it off course, or bumping it into a new direction, none of it will be of any use if we don’t first spot the threat. “It’s 100 per cent certain we’ll be hit, but we’re not 100 per cent certain when” https://www.news.com.au/technology/science/space/planetary-defenders-humanitys-greatest-challenge-to-save-the-world-from-catastrophic-asteroid-impacts/news-story/d3e2e2d71372a3d90cb02aa810f5ef60
Only eight #asteroids have ever been detected before impact with #Earth’s atmosphere. The first of these discoveries took place in 2008, and four were detected in just the last two years https://www.esa.int/Space_Safety/Planetary_Defence/Asteroid_2024_BX1_spotted_three_hours_before_impact
#Asteroid danger explained : "The main challenge stems from the population of middle-size objects, ranging from tens to hundreds of metres in diameter. There are a lot of these asteroids, and most have not been spotted yet." https://www.esa.int/ESA_Multimedia/Images/2018/06/Asteroid_danger_explained
It is impossible to know for sure how many close approaches were undetected . Of the #asteroids that were detected, the diagram shows that about half were not detected until after they had passed Earth. If they had been on course to impact Earth, they would not have been spotted before they hit , primarily because they approached from a direction close to the Sun 
https://en.wikipedia.org/wiki/Asteroid_impact_prediction#Effectiveness_of_the_current_system
