{"682899":{"#nid":"682899","#data":{"type":"news","title":"How Do Scientists Calculate the Probability That an Asteroid Could Hit\u00a0Earth?","body":[{"value":"\u003Cdiv class=\u0022theconversation-article-body\u0022\u003E\u003Cp\u003EI was preparing for my early morning class back in January 2025 when I received \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/01\/29\/nasa-shares-observations-of-recently-identified-near-earth-asteroid\/\u0022\u003Ea notice regarding an asteroid called 2024 YR4\u003C\/a\u003E. It said the probability it could hit Earth was unusually high.\u003C\/p\u003E\u003Cp\u003EAs defending Earth from unexpected intruders such as asteroids is \u003Ca href=\u0022https:\/\/scholar.google.com\/citations?user=8_qb8h8AAAAJ\u0026amp;hl=en\u0022\u003Epart of my expertise\u003C\/a\u003E, I immediately started receiving questions from my students and colleagues about what was happening.\u003C\/p\u003E\u003Cp\u003EWhen scientists spot an asteroid whose trajectory might \u003Ca href=\u0022https:\/\/theconversation.com\/neowise-the-nasa-mission-that-cataloged-objects-around-earth-for-over-a-decade-has-come-to-an-end-237921\u0022\u003Etake it close to Earth\u003C\/a\u003E, they monitor it frequently and calculate the probability that it might collide with our planet. As they receive more observational data, they get a better picture of what could happen.\u003C\/p\u003E\u003Cp\u003EJust having more data points early doesn\u2019t make scientists\u2019 predictions better. They need to keep following the asteroid as it moves through space to better understand its trajectory.\u003C\/p\u003E\u003Cp\u003EReflecting on the incident a few months later, I wondered whether there might have been a better way for scientists to communicate about the risk with the public. We got accurate information, but as the questions I heard indicated, it wasn\u2019t always enough to understand what it actually means.\u003C\/p\u003E\u003Ch2\u003ENumbers Change Every Day\u003C\/h2\u003E\u003Cp\u003EThe 2024 YR24 asteroid has a \u003Ca href=\u0022https:\/\/blogs.nasa.gov\/webb\/2025\/04\/02\/nasas-webb-finds-asteroid-2024-yr4-is-building-sized\/\u0022\u003Ediameter of about 196 feet (60 meters)\u003C\/a\u003E \u2013 equivalent to approximately a 15-story building in length.\u003C\/p\u003E\u003Cp\u003EAt the time of the announcement in January, the asteroid\u2019s impact probability was reported to \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/01\/29\/nasa-shares-observations-of-recently-identified-near-earth-asteroid\/\u0022\u003Eexceed 1%\u003C\/a\u003E. The impact probability describes how likely a hazardous asteroid is to hit Earth. For example, if the impact probability is 1%, it means that in 1 of 100 cases, it hits Earth. One in 100 is kind of rare, but still too close for comfort if you\u2019re talking about the odds of a collision that could devastate Earth.\u003C\/p\u003E\u003Cp\u003EOver time, though, further observations and analyses revealed an almost-zero chance of this asteroid colliding with Earth.\u003C\/p\u003E\u003Cp\u003EAfter the initial notice in January, the impact probability continuously increased up to 3.1% on \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/02\/19\/dark-skies-bring-new-observations-of-asteroid-2024-yr4-lower-impact-probability\/\u0022\u003EFeb. 18\u003C\/a\u003E, but dropped to 1.5% on \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/02\/19\/dark-skies-bring-new-observations-of-asteroid-2024-yr4-lower-impact-probability\/\u0022\u003EFeb. 19\u003C\/a\u003E. Then, the impact probability continuously went down, until it hit 0.004% on \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/02\/24\/latest-calculations-conclude-asteroid-2024-yr4-now-poses-no-significant-threat-to-earth-in-2032-and-beyond\/\u0022\u003EFeb. 24\u003C\/a\u003E. \u003Ca href=\u0022https:\/\/cneos.jpl.nasa.gov\/sentry\/details.html#?des=2024%20YR4\u0022\u003EAs of June 15\u003C\/a\u003E, it now has an impact probability of less than 0.0000081%.\u003C\/p\u003E\u003Cfigure class=\u0022align-center zoomable\u0022\u003E\u003Cp\u003E\u003Ca href=\u0022https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=1000\u0026amp;fit=clip\u0022\u003E\u003Cimg alt=\u0022A diagram showing the orbit paths of Earth, 2024 YR4 and some other planets in the solar system. 2024 YR4\u0026apos;s orbit intersects with Earth\u0026apos;s.\u0022 src=\u0022https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=754\u0026amp;fit=clip\u0022 srcset=\u0022https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=391\u0026amp;fit=crop\u0026amp;dpr=1 600w, https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=30\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=391\u0026amp;fit=crop\u0026amp;dpr=2 1200w, https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=15\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=391\u0026amp;fit=crop\u0026amp;dpr=3 1800w, https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=492\u0026amp;fit=crop\u0026amp;dpr=1 754w, https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=30\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=492\u0026amp;fit=crop\u0026amp;dpr=2 1508w, https:\/\/images.theconversation.com\/files\/668464\/original\/file-20250516-56-eggnpx.jpg?ixlib=rb-4.1.0\u0026amp;q=15\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=492\u0026amp;fit=crop\u0026amp;dpr=3 2262w\u0022 sizes=\u0022(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px\u0022\u003E\u003C\/a\u003E\u003C\/p\u003E\u003Cfigcaption\u003E\u003Cspan class=\u0022caption\u0022\u003EThe orbit of 2024 YR4 will take it close to Earth, but scientists have found the chance of a collision to be exceedingly low.\u003C\/span\u003E \u003Ca class=\u0022source\u0022 href=\u0022https:\/\/ssd.jpl.nasa.gov\/tools\/sbdb_lookup.html#\/?sstr=2024%20YR4\u0026amp;view=VOP\u0022\u003E\u003Cspan class=\u0022attribution\u0022\u003ENASA\/JPL\u003C\/span\u003E\u003C\/a\u003E\u003C\/figcaption\u003E\u003C\/figure\u003E\u003Cp\u003EBut while the probability of hitting Earth went down, the probability of the asteroid hitting the Moon started increasing. It went up to 1.7% on \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/02\/24\/latest-calculations-conclude-asteroid-2024-yr4-now-poses-no-significant-threat-to-earth-in-2032-and-beyond\/\u0022\u003EFeb. 24\u003C\/a\u003E. As of April 2, it is \u003Ca href=\u0022https:\/\/science.nasa.gov\/blogs\/planetary-defense\/2025\/04\/02\/nasa-update-on-the-size-estimate-and-lunar-impact-probability-of-asteroid-2024-yr4\/\u0022\u003E3.8%\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003EIf it hits the Moon, some ejected materials from this collision could reach the Earth. However, these materials would burn away when they enter the Earth\u2019s thick atmosphere.\u003C\/p\u003E\u003Ch2\u003EImpact Probability\u003C\/h2\u003E\u003Cp\u003ETo see whether an approaching object could hit Earth, researchers find out what an asteroid\u2019s orbit looks like using a technique called astrometry. This technique can accurately determine an object\u2019s orbit, down to only a few kilometers of uncertainty. But astrometry needs accurate observational data taken for a long time.\u003C\/p\u003E\u003Cfigure\u003E\u003Cp\u003E\u003Ciframe width=\u0022440\u0022 height=\u0022260\u0022 src=\u0022https:\/\/www.youtube.com\/embed\/53Js-_vo3mo?wmode=transparent\u0026amp;start=0\u0022 frameborder=\u00220\u0022 allowfullscreen=\u0022\u0022\u003E\u003C\/iframe\u003E\u003C\/p\u003E\u003Cfigcaption\u003E\u003Cspan class=\u0022caption\u0022\u003EIf an asteroid might get close to Earth, astronomers take observational data to better track the object\u2019s path and eliminate uncertainty.\u003C\/span\u003E\u003C\/figcaption\u003E\u003C\/figure\u003E\u003Cp\u003EAny uncertainty in the calculation of the object\u2019s orbit causes variations in the predicted solution. Instead of one precise orbit, the calculation usually gives scientists a cloud of its possible orbits. The ellipse enclosing these locations is called an error ellipse.\u003C\/p\u003E\u003Cp\u003EThe \u003Ca href=\u0022https:\/\/doi.org\/10.1016\/j.icarus.2015.05.032\u0022\u003Eimpact probability\u003C\/a\u003E describes how many orbital predictions in this ellipse hit the Earth.\u003C\/p\u003E\u003Cp\u003EWithout enough observational data, the orbital uncertainty is high, so the ellipse tends to be large. In a large ellipse, there\u2019s a higher chance that the ellipse \u201caccidentally\u201d includes Earth \u2013 even if the center is off the planet. So, even if an asteroid ultimately won\u2019t hit Earth, its error ellipse might \u003Ca href=\u0022https:\/\/doi.org\/10.1016\/j.icarus.2015.05.032\u0022\u003Estill include the planet\u003C\/a\u003E before scientists collect enough data to narrow down the uncertainty.\u003C\/p\u003E\u003Cp\u003EAs the level of uncertainty goes down, the ellipse shrinks. So, when Earth is inside a small error ellipse, the impact probability may become higher than when it\u2019s inside a large error ellipse. Once the error ellipse shrinks enough that it no longer includes Earth, the impact probability goes down significantly. That\u2019s what happened to 2024 YR4.\u003C\/p\u003E\u003Cfigure class=\u0022align-center zoomable\u0022\u003E\u003Cp\u003E\u003Ca href=\u0022https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=1000\u0026amp;fit=clip\u0022\u003E\u003Cimg alt=\u0022A diagram showing impact probability on the y axis and time on the x axis, with three drawings of the Earth and an error ellipse. As time goes on, the ellipse shrinks and in the third drawing it isn\u0026apos;t overlapping with the Earth.\u0022 src=\u0022https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=754\u0026amp;fit=clip\u0022 srcset=\u0022https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=310\u0026amp;fit=crop\u0026amp;dpr=1 600w, https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=30\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=310\u0026amp;fit=crop\u0026amp;dpr=2 1200w, https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=15\u0026amp;auto=format\u0026amp;w=600\u0026amp;h=310\u0026amp;fit=crop\u0026amp;dpr=3 1800w, https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=45\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=390\u0026amp;fit=crop\u0026amp;dpr=1 754w, https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=30\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=390\u0026amp;fit=crop\u0026amp;dpr=2 1508w, https:\/\/images.theconversation.com\/files\/668495\/original\/file-20250516-62-591osa.png?ixlib=rb-4.1.0\u0026amp;q=15\u0026amp;auto=format\u0026amp;w=754\u0026amp;h=390\u0026amp;fit=crop\u0026amp;dpr=3 2262w\u0022 sizes=\u0022(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px\u0022\u003E\u003C\/a\u003E\u003C\/p\u003E\u003Cfigcaption\u003E\u003Cspan class=\u0022caption\u0022\u003EAs the error ellipse shrinks, the chance of the asteroid hitting Earth either goes down or goes way up, if it ends up overlapping with the Earth.\u003C\/span\u003E \u003Cspan class=\u0022attribution source\u0022\u003EToshi Hirabayashi\u003C\/span\u003E\u003C\/figcaption\u003E\u003C\/figure\u003E\u003Cp\u003EThe impact probability is a single, practical value offering meaningful insight into an impact threat. However, just using the impact probability without any context may not provide meaningful guidelines to the public, as we saw with 2024 YR4.\u003C\/p\u003E\u003Cp\u003EHolding on and waiting for more data to refine a collision prediction, or introducing new metrics for assessing impacts on Earth, are alternative courses of action to provide people with better guidelines for future threats before adding confusion and fear.\u003C!-- Below is The Conversation\u0027s page counter tag. Please DO NOT REMOVE. --\u003E\u003Cimg style=\u0022border-color:!important;border-style:none;box-shadow:none !important;margin:0 !important;max-height:1px !important;max-width:1px !important;min-height:1px !important;min-width:1px !important;opacity:0 !important;outline:none !important;padding:0 !important;\u0022 src=\u0022https:\/\/counter.theconversation.com\/content\/249834\/count.gif?distributor=republish-lightbox-basic\u0022 alt=\u0022The Conversation\u0022 width=\u00221\u0022 height=\u00221\u0022 referrerpolicy=\u0022no-referrer-when-downgrade\u0022\u003E\u003C!-- End of code. If you don\u0027t see any code above, please get new code from the Advanced tab after you click the republish button. The page counter does not collect any personal data. More info: https:\/\/theconversation.com\/republishing-guidelines --\u003E\u003C\/p\u003E\u003Cp\u003E\u0026nbsp;\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis article is republished from \u003C\/em\u003E\u003Ca href=\u0022https:\/\/theconversation.com\u0022\u003E\u003Cem\u003EThe Conversation\u003C\/em\u003E\u003C\/a\u003E\u003Cem\u003E under a Creative Commons license. Read the \u003C\/em\u003E\u003Ca href=\u0022https:\/\/theconversation.com\/how-do-scientists-calculate-the-probability-that-an-asteroid-could-hit-earth-249834\u0022\u003E\u003Cem\u003Eoriginal article\u003C\/em\u003E\u003C\/a\u003E\u003Cem\u003E.\u003C\/em\u003E\u003C\/p\u003E\u003C\/div\u003E","summary":"","format":"full_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EWhen scientists spot an asteroid whose trajectory might take it close to Earth, they monitor it frequently and calculate the probability that it might collide with our planet. As they receive more observational data, they get a better picture of what coul\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"When scientists spot an asteroid whose trajectory might take it close to Earth, they monitor it frequently and calculate the probability that it might collide with our planet. "}],"uid":"27469","created_gmt":"2025-06-25 13:40:47","changed_gmt":"2025-07-01 11:49:27","author":"Kristen Bailey","boilerplate_text":"","field_publication":"","field_article_url":"","location":"Atlanta, GA","dateline":{"date":"2025-06-25T00:00:00-04:00","iso_date":"2025-06-25T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"677287":{"id":"677287","type":"image","title":"Asteroid 2024 YR4","body":"\u003Cp\u003ENASA\u2019s Webb telescope captured a photo of the asteroid 2024 YR4 from afar. \u003Ca href=\u0022https:\/\/newsroom.ap.org\/detail\/NewlyDiscoveredAsteroid\/eecb6be6ddc3406caaa5cdd2c4a9be8f\/photo?Query=2024%20yr4\u0026amp;mediaType=photo\u0026amp;sortBy=\u0026amp;dateRange=Anytime\u0026amp;totalCount=9\u0026amp;currentItemNo=1\u0022\u003EEuropean Space Agency via AP\u003C\/a\u003E\u003C\/p\u003E","created":"1750945488","gmt_created":"2025-06-26 13:44:48","changed":"1750945488","gmt_changed":"2025-06-26 13:44:48","alt":"Asteroid 2024 YR4","file":{"fid":"261171","name":"file-20250516-62-wffqck.jpg","image_path":"\/sites\/default\/files\/2025\/06\/26\/file-20250516-62-wffqck.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/2025\/06\/26\/file-20250516-62-wffqck.jpg","mime":"image\/jpeg","size":75693,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/2025\/06\/26\/file-20250516-62-wffqck.jpg?itok=QDb13wwf"}}},"media_ids":["677287"],"related_links":[{"url":"https:\/\/theconversation.com\/how-do-scientists-calculate-the-probability-that-an-asteroid-could-hit-earth-249834","title":"Read This Article on The Conversation"}],"groups":[{"id":"1188","name":"Research Horizons"},{"id":"660370","name":"Space"}],"categories":[],"keywords":[{"id":"187915","name":"go-researchnews"}],"core_research_areas":[{"id":"193657","name":"Space Research Initiative"}],"news_room_topics":[{"id":"71911","name":"Earth and Environment"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Ch5\u003EAuthor:\u003C\/h5\u003E\u003Cp\u003E\u003Ca href=\u0022https:\/\/theconversation.com\/profiles\/toshi-hirabayashi-1647682\u0022\u003EToshi Hirabayashi\u003C\/a\u003E, associate professor of Aerospace Engineering, Georgia Institute of Technology\u003C\/p\u003E\u003Ch5\u003EMedia Contact:\u003C\/h5\u003E\u003Cp\u003EShelley Wunder-Smith\u003Cbr\u003E\u003Ca href=\u0022mailto:shelley.wunder-smith@research.gatech.edu\u0022\u003E\u003Cstrong\u003Eshelley.wunder-smith@research.gatech.edu\u003C\/strong\u003E\u003C\/a\u003E\u003C\/p\u003E","format":"limited_html"}],"email":[],"slides":[],"orientation":[],"userdata":""}}}