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Sentry (monitoring system)
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<h2 id="sentry-risk-table">Sentry Risk Table</h2> Objects with better than a 1/500 (0.2%) cumulative chance of impact<table><tbody><tr><th>Object</th><th>Cumulativeimpactprobability</th><th>Date ofgreatest risk</th><th>Estimateddiameter(meters)</th><th><a href="/facts/Observation_arc/W7pFwuAk">Observationarc</a>(days)</th></tr><tr><td><a href="/facts/2010_RF12/yEr4LDqI">2010 RF12</a></td><td>10%</td><td>2095-09-05</td><td>7</td><td>4374</td></tr><tr><td><a href="/facts/2020_CD3/t4cqRyPu">2020 CD3</a></td><td>2.5%</td><td>2082-09-09</td><td>2</td><td>742</td></tr><tr><td><a href="/facts/2006_RH120/u20Wu4ej">2006 RH120</a></td><td>1.3%</td><td>2044-02-08</td><td>4</td><td>281</td></tr><tr><td>2017 WT28</td><td>1.2%</td><td>2104-11-24</td><td>8</td><td>19</td></tr><tr><td>2024 BY15</td><td>0.94%</td><td>2095-03-19</td><td>15</td><td>49</td></tr><tr><td>2020 VW</td><td>0.70%</td><td>2074-11-02</td><td>7</td><td>14</td></tr><tr><td><a href="/facts/2006_JY26/PlHF3Bmg">2006 JY26</a></td><td>0.50%</td><td>2074-05-03</td><td>7</td><td>3</td></tr><tr><td>2020 CQ1</td><td>0.46%</td><td>2070-02-03</td><td>6</td><td>29</td></tr><tr><td>2022 SX55</td><td>0.40%</td><td>2035-09-17</td><td>3</td><td>1</td></tr><tr><td><a href="/facts/2022_NX1/u6sS4XFD">2022 NX1</a></td><td>0.32%</td><td>2075-12-03</td><td>8</td><td>142</td></tr><tr><td><a href="/facts/2000_SG344/EmD44flP">2000 SG344</a></td><td>0.27%</td><td>2071-09-16</td><td>37</td><td>507</td></tr><tr><td><a href="/facts/2020_VV/AfKyLCdA">2020 VV</a></td><td>0.23%</td><td>2056-10-11</td><td>12</td><td>61</td></tr><tr><td>2017 LD</td><td>0.22%</td><td>2079-06-10</td><td>11</td><td>45</td></tr><tr><td>2000 LG6</td><td>0.21%</td><td>2094-05-27</td><td>5</td><td>2</td></tr></tbody></table> <p>The Impact Risk page lists a number of <a href="/facts/Lost_minor_planet/PcHePHvH">lost minor planets</a> that are, for all practical purposes, permanent residents of the risk page; their removal may depend upon a <a href="/facts/Serendipity/pvcf95kQ">serendipitous</a> rediscovery.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> Lost asteroid <a href="/facts/1979_XB/76bw4VYP">1979 XB</a> has been on the list since the list's inception.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> <a href="/facts/2007_FT3/vQadolKw">2007 FT3</a> and <a href="/facts/2014_MV67/ystDfHMX">2014 MV67</a> with their very short 1-day observation arcs have missed virtual impactor dates as they were likely quite distant from the Earth at the time. <a href="/facts/1997_XR2/Fhp3Y7TB">1997 XR2</a> was serendipitously rediscovered in 2006 after being <a href="/facts/Lost_minor_planet/PcHePHvH">lost</a> for more than 8 years. <a href="/facts/2004_BX159/PB5UJt0V">2004 BX159</a> was determined to be a harmless <a href="/facts/Main_belt/YHAq2Eh3">main belt</a> asteroid in 2014. Some objects on the Sentry Risk Table, such as <a href="/facts/2000_SG344/EmD44flP">2000 SG344</a>, might even be artificial.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p><a href="/facts/2010_RF12/yEr4LDqI">2010 RF12</a> is the asteroid with greatest probability (10%) of impacting Earth, but is only ~7 meters in diameter. The only <a href="/facts/Minor_planet_designation/le4Ro9Xj">numbered</a> objects with <a href="/facts/Observation_arc/W7pFwuAk">observation arcs</a> of several years are <a href="/facts/(29075)_1950_DA/bfDuT6qN">(29075) 1950 DA</a> and <a href="/facts/101955_Bennu/ae1ebNGR">101955 Bennu</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> Notable asteroids removed from Sentry include (most recently removed listed first): <a href="/facts/99942_Apophis/xEEpaxYe">99942 Apophis</a>, <a href="/facts/(410777)_2009_FD/owctUw00">(410777) 2009 FD</a>, <a href="/facts/2006_QV89/jvreFMel">2006 QV89</a>, <a href="/facts/2017_XO2/gQ0X0Wgm">2017 XO2</a>, <a href="/facts/1994_WR12/9bwElFB1">1994 WR12</a>, <a href="/facts/2007_VK184/A4mIp1oj">2007 VK184</a>, <a href="/facts/2013_BP73/qr4fVDsE">2013 BP73</a>, <a href="/facts/2008_CK70/34zgcbKn">2008 CK70</a>, <a href="/facts/2013_TV135/nSHjCdVc">2013 TV135</a>, <a href="/facts/2011_BT15/XITca6fg">2011 BT15</a>, <a href="/facts/367943_Duende/2gdqWxQr">367943 Duende</a>, and <a href="/facts/2011_AG5/WbXVk7xp">2011 AG5</a>. </p><p>As of February 2025<a href="https://en.wikipedia.org/w/index.php?title=Sentry_(monitoring_system)&action=edit">[update]</a>, of the 191 asteroids with better than a 1-in-10,000 chance of impacting Earth only <a href="/facts/(29075)_1950_DA/bfDuT6qN">(29075) 1950 DA</a> and <a href="/facts/101955_Bennu/ae1ebNGR">101955 Bennu</a> are larger than 50 meters in diameter. </p><p>As of March 2025<a href="https://en.wikipedia.org/w/index.php?title=Sentry_(monitoring_system)&action=edit">[update]</a>, the soonest virtual impactor of an asteroid larger than 50 meters in diameter with a better than 1:1-million chance of impact is 2022 PX1 on 11 August 2040 with a 1:310000 chance of impact.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> It is estimated to be 120-meters in diameter, has a short observation arc of 7-days, and is expected to be approximately 1.75 <a href="/facts/Astronomical_unit/gjsbu5xU">AU</a> (262 million <a href="/facts/Kilometre/hdQp79QE">km</a>) from Earth on 11 August 2040.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> The impact scenario is outside the <a href="/facts/3-sigma/IDaupJFh">3-sigma</a> uncertainty region of ± 242 million km.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p><p> The asteroid with the greatest chance of impacting Earth in 2025 is <a href="/facts/2009_VA/jojwJuk1">2009 VA</a> (6-meters in diameter) with less than a 1-day observation arc.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> It has a 1:48,000 chance of impact on 06 November 2023, but is expected to be around 0.3 <a href="/facts/Astronomical_unit/gjsbu5xU">AU</a> (45 million <a href="/facts/Kilometre/hdQp79QE">km</a>) from Earth on that date with uncertainty region of ± 900 million km.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> </p><p>With a 24-day observation arc, 2017 SA20 has the most virtual impactors with 1244 virtual impactor dates.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> </p><p>The diameter of most near-Earth asteroids that have not been studied by <a href="/facts/Radar_astronomy/AJmcEDkl">radar</a> or <a href="/facts/Infrared_astronomy/WEmAadyf">infrared</a> can generally only be estimated within about a factor of 2 based on the asteroid's <a href="/facts/Absolute_magnitude/R8RVxkLx">absolute magnitude</a> (H).<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> Their mass, consequently, is uncertain by about a factor of 10. For near-Earth asteroids without a well-determined diameter, Sentry assumes a generic <a href="/facts/Albedo/TJDRdKEB">albedo</a> of 0.15. </p><p>In August 2013, the Sentry Risk Table started using planetary <a href="/facts/Ephemeris/vjQCBG29">ephemeris</a> (<a href="/facts/Jet_Propulsion_Laboratory_Development_Ephemeris/SeCNLYkt">DE431</a>) for all NEO orbit determinations.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> DE431 (<a href="/facts/JPL_Small-Body_Database/YQQLDXng">JPL small-body</a> perturber ephemeris: SB431-BIG16) better models the gravitational <a href="/facts/Perturbation_(astronomy)/og5hPpjQ">perturbations</a> of the planets and includes the 16 most massive <a href="/facts/Main-belt_asteroid/YHAq2Eh3">main-belt asteroids</a>.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> In April 2021, Sentry transitioned to <a href="/facts/Jet_Propulsion_Laboratory_Development_Ephemeris/SeCNLYkt">DE441</a> which removed the very low impact probability of short-arc <a href="/facts/2014_MV67/ystDfHMX">2014 MV67</a> which had been less than 1:1-billion. The switch to DE441 also briefly added in the harmless Jupiter trojan <a href="/facts/2014_ES57/oyQvamb0">2014 ES57</a> with a very low impact probability of about 1:1-billion. </p><p>JPL launched major changes to the website in February 2017 and re-directed the classic page on 10 April 2017. </p><p>In 2021 JPL launched Sentry-II which handles the <a href="/facts/Yarkovsky_effect/Vo8jz4KP">Yarkovsky effect</a> that can significantly change a small asteroid's path over decades and centuries.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> Sentry-II defaults to an impact pseudo-observation (IOBS) analysis technique that runs an extended orbit-determination filter that tries to converge to an impacting solution compatible with the observational data. </p> <h2 id="numbers">Numbers</h2> <p>As of February 2025<a href="https://en.wikipedia.org/w/index.php?title=Sentry_(monitoring_system)&action=edit">[update]</a>, there are over 37,000 <a href="/facts/Near-Earth_object/UwnPRnSN">near-Earth objects</a> of which roughly 1,900 near-Earth asteroids are listed on the risk table.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> Only around 21 objects on the risk table are large enough to qualify as potentially hazardous objects with a diameter greater than 140 meters (<a href="/facts/Absolute_magnitude/R8RVxkLx">absolute magnitude</a> brighter than 22). About 99% of the objects on the risk table are less than roughly 140 meters in diameter. Roughly 1400 of these risk-listed near-Earth asteroids are estimated to be about the size of the <a href="/facts/Chelyabinsk_meteor/4wpcyS0q">Chelyabinsk meteor</a> or smaller (H>26), which killed no one but had 1,491 indirect injuries. More than 3,300 asteroids have been removed from the risk table since it launched in 2002.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p><p>The only two comets that briefly appeared on the Sentry Risk Table are 197P/LINEAR (2003 KV2) and <a href="/facts/300P/Catalina/xCmzwMkK">300P/Catalina</a> (2005 JQ5).<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="jpl-sbdb-comparison">JPL SBDB comparison</h2> <p>The <a href="/facts/JPL_Small-Body_Database/YQQLDXng">JPL Small-Body Database</a> close approach table lists a <a href="/facts/Linearity/fChtg3KC">linearized</a> uncertainty. Sentry computations explore alternate orbit solutions along the line of variations and account for orbit propagation nonlinearities. </p> <h2 id="scout">Scout</h2> <p>Sentry's little brother Scout scans recently detected objects on the Minor Planet Center's <a href="/facts/Near-Earth_Object_Confirmation_Page/v8T7sdK4">Near-Earth Object Confirmation Page</a> with designations that are user-assigned and unofficial as they have not been confirmed by additional observations.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> The impact risk assessment is rated on a scale of 0–4 (negligible, small, modest, moderate, or elevated).<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> Scout is used to help identify imminent impactors. ESA's equivalent to Scout is Meerkat Asteroid Guard. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Asteroid_impact_prediction/9uTmkLQl">Asteroid impact prediction</a></li> <li><a href="/facts/Earth-grazing_fireball/btc8ecDk">Earth-grazing fireball</a></li> <li><a href="/facts/Impact_event/fbWu9Q4p">Impact event</a></li> <li><a href="/facts/List_of_asteroid_close_approaches_to_Earth/HeyI9vAI">List of asteroid close approaches to Earth</a></li> <li><a href="/facts/List_of_Earth-crossing_asteroids/E3JXnHPt">List of Earth-crossing asteroids</a></li> <li><a href="/facts/Meteoroid/5PexF2mR">Meteoroid</a></li> <li><a href="/facts/NEODyS/TakkNnsH">NEODyS</a> – Database of near earth asteroid orbits</li> <li><a href="/facts/Time-domain_astronomy/RbwWFze6">Time-domain astronomy</a></li></ul> <h2 id="notes">Notes</h2> <h2 id="external-links">External links</h2> <ul><li><a href="https://cneos.jpl.nasa.gov/sentry/intro.html">Sentry: Introduction</a></li> <li><a href="https://cneos.jpl.nasa.gov/sentry/">Sentry: Impact Risk Data table</a></li> <li>List of <a href="https://cneos.jpl.nasa.gov/sentry/removed.html">objects for which all previously detected potential impacts have been eliminated</a></li> <li>Similar lists: <a href="https://newton.spacedys.com/neodys/index.php?pc=4.1">NEODyS CLOMON2</a> / <a href="https://neo.ssa.esa.int/risk-list">ESA NEO Risk List</a> / <a href="http://www.brera.mi.astro.it/sormano/teca.html">Sormano Observatory TECA</a> / <a href="https://robertinventor.online/booklets/sentry_table_simplified.htm">Simplified List</a></li> <li><a href="https://www.youtube.com/watch?v=8M_27st1ZCI&t=142">Asteroid Hazards, Part 3: Finding the Path</a> – <a href="/facts/Minor_Planet_Center/v8T7sdK4">Minor Planet Center</a> on YouTube</li> <li><a href="https://cneos.jpl.nasa.gov/scout/intro.html">Scout: NEOCP Hazard Assessment: Introduction</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Jon Giorgini (30 July 2002). "Understanding Risk Pages". Columbine, Inc. (hohmanntransfer). Archived from the original on 8 December 2002. Retrieved 21 November 2011. <a href="https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm" target="_blank">https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Jon Giorgini (30 July 2002). "Understanding Risk Pages". Columbine, Inc. (hohmanntransfer). Archived from the original on 8 December 2002. Retrieved 21 November 2011. <a href="https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm" target="_blank">https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Jon Giorgini (30 July 2002). "Understanding Risk Pages". Columbine, Inc. (hohmanntransfer). Archived from the original on 8 December 2002. Retrieved 21 November 2011. <a href="https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm" target="_blank">https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Jon Giorgini (30 July 2002). "Understanding Risk Pages". Columbine, Inc. (hohmanntransfer). Archived from the original on 8 December 2002. Retrieved 21 November 2011. <a href="https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm" target="_blank">https://web.archive.org/web/20021208202559/http://www.hohmanntransfer.com/by/giorgjon.htm</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"2005ED224 Ephemerides for March 2023". NEODyS (Near Earth Objects – Dynamic Site). Retrieved 26 March 2021. (Having not been observed since 2005 with an orbital period of 2.6±0.3 years, we do not know where on its orbit 2005 ED224 is.) <a href="https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=2005ED224&oc=500&y0=2023&m0=3&d0=10&h0=0&mi0=0&y1=2023&m1=3&d1=12&h1=0&mi1=0&ti=1.0&tiu=days" target="_blank">https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=2005ED224&oc=500&y0=2023&m0=3&d0=10&h0=0&mi0=0&y1=2023&m1=3&d1=12&h1=0&mi1=0&ti=1.0&tiu=days</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Sentry Risk Table: 2015 RD36" (using 2022-Sep-13 solution). NASA JPL CNEOS. Retrieved 2 October 2022. <a href="https://cneos.jpl.nasa.gov/sentry/details.html#?des=2015%20RD36" target="_blank">https://cneos.jpl.nasa.gov/sentry/details.html#?des=2015%20RD36</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"IMPACT RISK ASSESSMENT: AN INTRODUCTION". NASA/JPL Near-Earth Object Program Office. 31 August 2005. Archived from the original on 19 April 2002. Retrieved 14 October 2011. <a href="https://web.archive.org/web/20020419174057/http://neo.jpl.nasa.gov/risk/doc/sentry.html" target="_blank">https://web.archive.org/web/20020419174057/http://neo.jpl.nasa.gov/risk/doc/sentry.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"2002 Archive of Sentry Risk Table". Archived from the original on 21 March 2002. <a href="https://web.archive.org/web/20020321092735/http://neo.jpl.nasa.gov/risk/" target="_blank">https://web.archive.org/web/20020321092735/http://neo.jpl.nasa.gov/risk/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Much Ado about 2000 SG344". NASA Science. NASA. Retrieved 27 September 2023. <a href="https://science.nasa.gov/science-news/science-at-nasa/2000/ast06nov_2" target="_blank">https://science.nasa.gov/science-news/science-at-nasa/2000/ast06nov_2</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"VI (Virtual Impactor) Data". NASA/JPL Near-Earth Object Program Office. Retrieved 9 November 2022. Unconstrained Settings, Sort by Date. For objects larger than 50 meters and odds of impact better than 1:1 million also include Impact Probability ≥ 1e-6 and H≤24. <a href="https://cneos.jpl.nasa.gov/sentry/vi.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/vi.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"JPL Horizons: 2022 PX1 geocentric distance and uncertainty on 11 August 2040". JPL Horizons. Retrieved 13 March 2025. <a href="https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272022+PX1%27&START_TIME=%272040-Aug-11%27&STOP_TIME=%272040-Aug-12%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27" target="_blank">https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272022+PX1%27&START_TIME=%272040-Aug-11%27&STOP_TIME=%272040-Aug-12%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>"JPL Horizons: 2022 PX1 geocentric distance and uncertainty on 11 August 2040". JPL Horizons. Retrieved 13 March 2025. <a href="https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272022+PX1%27&START_TIME=%272040-Aug-11%27&STOP_TIME=%272040-Aug-12%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27" target="_blank">https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272022+PX1%27&START_TIME=%272040-Aug-11%27&STOP_TIME=%272040-Aug-12%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>"VI (Virtual Impactor) Data". NASA/JPL Near-Earth Object Program Office. Retrieved 9 November 2022. Unconstrained Settings, Sort by Date. For objects larger than 50 meters and odds of impact better than 1:1 million also include Impact Probability ≥ 1e-6 and H≤24. <a href="https://cneos.jpl.nasa.gov/sentry/vi.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/vi.html</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"Horizons Batch for 2025-11-06 Virtual Impactor". JPL Horizons. Retrieved 3 February 2025. RNG_3sigma = uncertainty range in km. (JPL#7/Soln.date: 2021-Apr-15 generates RNG_3sigma = 934114563 km for 2025-Nov-06.) <a href="https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272009+VA%27&START_TIME=%272025-11-06%27&STOP_TIME=%272025-11-07%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27" target="_blank">https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272009+VA%27&START_TIME=%272025-11-06%27&STOP_TIME=%272025-11-07%27&STEP_SIZE=%272%20day%27&QUANTITIES=%2720,39%27</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Sentry: 2017 SA20 (1244 VIs) using 2022-Aug-30 solution <a href="https://cneos.jpl.nasa.gov/sentry/details.html#?des=2017%20SA20" target="_blank">https://cneos.jpl.nasa.gov/sentry/details.html#?des=2017%20SA20</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>"Sentry Notes". NASA/JPL Near-Earth Object Program Office. 12 August 2013. Retrieved 13 April 2017. <a href="https://cneos.jpl.nasa.gov/sentry/notes.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/notes.html</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>"Sentry Notes". NASA/JPL Near-Earth Object Program Office. 12 August 2013. Retrieved 13 April 2017. <a href="https://cneos.jpl.nasa.gov/sentry/notes.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/notes.html</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>"NASA's Next-Generation Asteroid Impact Monitoring System Goes Online". NASA/JPL Near-Earth Object Program Office. 6 December 2021. <a href="https://www.jpl.nasa.gov/news/nasas-next-generation-asteroid-impact-monitoring-system-goes-online" target="_blank">https://www.jpl.nasa.gov/news/nasas-next-generation-asteroid-impact-monitoring-system-goes-online</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>"Sentry Risk Table". NASA/JPL Near-Earth Object Program Office. Retrieved 13 April 2017. (Click "Use Unconstrained Settings" to see how many objects are on the list; H<=22 for list of PHAs) <a href="https://cneos.jpl.nasa.gov/sentry/" target="_blank">https://cneos.jpl.nasa.gov/sentry/</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>"Removed Objects". NASA/JPL Near-Earth Object Program Office. Archived from the original on 25 February 2017. Retrieved 16 February 2017.(Search for "P/" to list comets removed.) <a href="https://cneos.jpl.nasa.gov/sentry/removed.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/removed.html</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></p></li> <li id="fn:26"><p>"Removed Objects". NASA/JPL Near-Earth Object Program Office. Archived from the original on 25 February 2017. Retrieved 16 February 2017.(Search for "P/" to list comets removed.) <a href="https://cneos.jpl.nasa.gov/sentry/removed.html" target="_blank">https://cneos.jpl.nasa.gov/sentry/removed.html</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></p></li> <li id="fn:27"><p>"Scout: NEOCP Hazard Assessment". NASA/JPL Near-Earth Object Program Office. Retrieved 26 June 2019. <a href="https://cneos.jpl.nasa.gov/scout/intro.html" target="_blank">https://cneos.jpl.nasa.gov/scout/intro.html</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></p></li> <li id="fn:28"><p>"Negligible" (0) is for objects where no impacting solution was identified. "Small" (1) is for objects with a <0.1% chance of impact. "Modest" (2) is for a 0.1-1% chance. "Moderate" (3) is for a 1-10% chance, and "Elevated" (4) is for a >10% chance of impact. <a href="#fnref:28" class="footnote-back-ref">↩</a></p></li> </ol>