Sentry (monitoring system)

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Asteroid 2020 VV risk corridor for the obsolete virtual impactor of 12 October 2033. 2020VV risk corridor.png
Asteroid 2020 VV risk corridor for the obsolete virtual impactor of 12 October 2033.

Sentry is a highly automated impact prediction system operated by the JPL Center for NEO Studies (CNEOS) since 2002. It continually monitors the most up-to-date asteroid catalog for possibilities of future impact with Earth over the next 100+ years. [1] Whenever a potential impact is detected it will be analyzed and the results immediately published by the Center for Near-Earth Object Studies. [1] However, several weeks of optical data are not enough to conclusively identify an impact years in the future. [2] By contrast, eliminating an entry on the risk page is a negative prediction (a prediction of where it will not be). [2]

Contents

Scientists warn against worrying about the possibility of impact with an object based on only a few weeks of optical data that show a possible Earth encounter years from now. [2] Sometimes, it cannot even be said for certain what side of the Sun such an object will be at the time of the listed virtual impactor date. [2] For example, even though 2005 ED224 had a 1-in-500,000 chance of impacting Earth on 11 March 2023, it was expected to be farther than the Sun at the time. [3] Most objects on the Sentry Risk Table have an observation arc of less than 14 days and have not been observed for years.

There are 1620 near-Earth asteroids listed on the risk table with 37,736 virtual impactor dates. For each asteroid listed on the risk table there are on average about 23 virtual impactors. Only about 19 objects on the risk list are large enough to be considered potentially hazardous objects with a diameter greater than about 140 meters. The average size of an object on the default page of Sentry is 120 meters with an average impact probability of 1:500. More eccentric orbits (such as 2015 RD36) that extend to nearly the orbit of Jupiter can make atmospheric entry at velocities of ~40 km/s (25 mi/s). [4]

Sentry Risk Table

Objects with better than a 1/500 (0.2%) cumulative chance of impact
ObjectCumulative
Impact
Probability		Date of
Greatest Risk		Estimated
Diameter
(meters)		 Observation
arc
(days)
2010 RF12 10%2095-09-0574374
2020 CD3 2.5%2082-09-092742
2006 RH120 1.3%2044-02-084281
2017 WT281.2%2104-11-24819
2020 VW0.70%2074-11-02714
2006 JY26 0.50%2074-05-0373
2020 CQ10.46%2070-02-03629
2022 SX550.40%2035-09-1731
2022 NX1 0.32%2075-12-038142
2000 SG344 0.27%2071-09-1637507
2022 YO1 0.23%2024-12-1731
2020 VV 0.23%2056-10-111261
2017 LD0.22%2079-06-101145
2000 LG60.21%2094-05-2752

The Impact Risk page lists a number of lost minor planets that are, for all practical purposes, permanent residents of the risk page; their removal may depend upon a serendipitous rediscovery. [5] Lost asteroid 1979 XB has been on the list since the list's inception. [6] 2007 FT3 and 2014 MV67 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. 1997 XR2 was serendipitously rediscovered in 2006 after being lost for more than 8 years. 2004 BX159 was determined to be a harmless main belt asteroid in 2014. Some objects on the Sentry Risk Table, such as 2000 SG344 , might even be artificial. [7]

2010 RF12 is the asteroid with greatest probability (10%) of impacting Earth, but is only ~7 meters in diameter. The only numbered objects with observation arcs of several years are (29075) 1950 DA and 101955 Bennu. [1] Notable asteroids removed from Sentry include (most recently removed listed first): 99942 Apophis, (410777) 2009 FD, 2006 QV89 , 2017 XO2 , 1994 WR12 , 2007 VK184 , 2013 BP73 , 2008 CK70 , 2013 TV135 , 2011 BT15 , 367943 Duende, and 2011 AG5 .

Of the 160 asteroids with better than a 1-in-10,000 chance of impacting Earth only 101955 Bennu is larger than 50 meters in diameter.

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 1:330000 chance of impact. [8] It is estimated to be 120-meters in diameter, has a short observation arc of 3.1-days, and is expected to be 1.78  AU (266 million  km ) from Earth on 11 August 2040. [9] The impact scenario is outside the 3-sigma uncertainty region of ± 240 million km.

The asteroid with the greatest chance of impacting Earth in 2023 is 2016 LP10 (4-meters in diameter) with less than a 1-day observation arc. [8] It had a 1:53,000 chance of impact on 10 June 2023, but was expected to be around 0.6  AU (90 million  km ) from Earth on that date. [10] Such an impact would be similar to 2008 TC3 .

With a 24-day observation arc, 2017 SA20 has the most virtual impactors with 1244 virtual impactor dates. [1] [11]

The diameter of most near-Earth asteroids that have not been studied by radar or infrared can generally only be estimated within about a factor of 2 based on the asteroid's absolute magnitude (H). [1] Their mass, consequently, is uncertain by about a factor of 10. For near-Earth asteroids without a well-determined diameter, Sentry assumes a generic albedo of 0.15.

In August 2013, the Sentry Risk Table started using planetary ephemeris (DE431) for all NEO orbit determinations. [12] DE431 (JPL small-body perturber ephemeris: SB431-BIG16) better models the gravitational perturbations of the planets and includes the 16 most massive main-belt asteroids. [12] In April 2021, Sentry transitioned to DE441 which removed the very low impact probability of short-arc 2014 MV67 which had been less than 1:1-billion. The switch to DE441 also briefly added in the harmless Jupiter trojan 2014 ES57 with a very low impact probability of about 1:1-billion.

JPL launched major changes to the website in February 2017 and re-directed the classic page on 10 April 2017.

In 2021 JPL launched Sentry-II which handles the Yarkovsky effect that can significantly change a small asteroids path over decades and centuries. [13] 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.

Numbers

Plot of orbits of known potentially hazardous asteroids Potentially Hazardous Asteroids 2013.png
Plot of orbits of known potentially hazardous asteroids

As of September 2023, there are over 32,955 near-Earth objects of which roughly 1,620 near-Earth asteroids are listed on the risk table. [1] Only around 19 objects on the risk table are large enough to qualify as potentially hazardous objects with a diameter greater than 140 meters (absolute magnitude brighter than 22). About 99% of the objects on the risk table are less than roughly 140 meters in diameter. Roughly 1,200 of these risk-listed near-Earth asteroids are estimated to be about the size of the Chelyabinsk meteor (H>26), which killed no one but had 1,491 non-direct injuries; or smaller. More than 3,140 asteroids have been removed from the risk table since it launched in 2002. [14]

The only two comets that briefly appeared on the Sentry Risk Table are 197P/LINEAR (2003 KV2) and 300P/Catalina (2005 JQ5). [14]

JPL SBDB comparison

The JPL Small-Body Database close approach table lists a linearized uncertainty. Sentry computations explore alternate orbit solutions along the line of variations and account for orbit propagation nonlinearities.

Scout

Sentry's little brother Scout scans recently detected objects on the Minor Planet Center's Near-Earth Object Confirmation Page with designations that are user-assigned and unofficial as they have not been confirmed by additional observations. [15] The impact risk assessment is rated on a scale of 0–4 (negligible, small, modest, moderate, or elevated). [note 1] Scout is used to help identify imminent impactors.

See also

Notes

  1. ↑ "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.

Related Research Articles

The Torino scale is a method for categorizing the impact hazard associated with near-Earth objects (NEOs) such as asteroids and comets. It is intended as a communication tool for astronomers and the public to assess the seriousness of collision predictions, by combining probability statistics and known kinetic damage potentials into a single threat value. The Palermo Technical Impact Hazard Scale is a similar, but more complex scale. Near-Earth objects with a Torino scale of 1 are discovered several times a year, and may last a few weeks until they have a longer observation arc that eliminates any possibility of a collision. The highest rating ever assigned on the Torino Scale was given to the asteroid 99942 Apophis, which had a rating of 4 for four days in late 2004.

<span class="nowrap">2000 SG<sub>344</sub></span> Small risk–listed near-Earth asteroid

2000 SG344 is a small Aten asteroid first observed in 2000. It is assumed to have a diameter of approximately 37 meters (120 feet) – or roughly twice that of the Chelyabinsk meteor – and an assumed mass of 7.1×107 kg (71,000 tonnes), but the size is only known within about a factor 2. It is the largest object known to have a better than 1/1000 chance (0.1%) of impacting Earth and has the fourth highest cumulative Palermo rating at −2.79. The next good chance to observe the object will be in May 2028 when it passes 0.02 AU (3,000,000 km; 1,900,000 mi) from Earth.

2010 RF12 is a very small asteroid, classified as near-Earth object of the Apollo group, that passed between Earth and the Moon on 8 September 2010, at 21:12 UTC, approaching Earth within 79,000 kilometres (49,000 mi) above Antarctica. The asteroid was discovered by the Mount Lemmon Survey near Tucson, Arizona on 5 September 2010 along with 2010 RX30. Based on a short 7-day observation arc from that apparation, it was listed for 12 years on the Sentry Risk Table as the asteroid with the greatest known probability (5%) of impacting Earth. 2010 RF12 was recovered in August 2022, and now has a 12 year observation arc and a much better known orbit. As of the December 2022 solution which accounts for nongravitational forces, there is a 1-in-10 chance of an Earth impact on 5 September 2095.

2010 AU118 (also written 2010 AU118) is a potential Amor near-Earth asteroid with an observation arc of only 1.4 days and thus a poorly determined orbit. It was announced on 27 May 2010 based on images taken by the Wide-field Infrared Survey Explorer (WISE) on 13–15 January 2010. It was removed from the Sentry Risk Table on 14 June 2014 as a result of an update to the Sentry software. Another software update restored it to the Sentry Risk Table in 2017. It was again removed from the sentry list on 3 October 2018.

2012 KP24 (also written 2012 KP24) is a Chelyabinsk-sized near-Earth asteroid with an observation arc of only 5 days and has a modestly determined orbit for an object of its size. Around 31 May 2023 ±3 days it will pass between 0.19–24 lunar distances (73,000–9,200,000 km) from Earth. Nominally the asteroid is expected to pass 0.026 AU (3,900,000 km; 10 LD) from Earth and brighten to around apparent magnitude 21.6.

2008 CK70 (also written 2008 CK70) is an Apollo near-Earth asteroid. In 2013 it had the 7th highest impact threat on the Palermo Technical Impact Hazard Scale. It was discovered on 9 February 2008 by Lincoln Near-Earth Asteroid Research (LINEAR) at an apparent magnitude of 19 using a 1.0-meter (39 in) reflecting telescope. It has an estimated diameter of 31 meters (102 ft) and is not large enough to qualify as a potentially hazardous object. Ten precovery images from January 2008 have been located. It was removed from the Sentry Risk Table on 21 December 2013. It may be possible to recover the asteroid in late September 2017, but it will have an apparent magnitude of about 22.

2013 TV135 is an Apollo near-Earth asteroid estimated to have a diameter of 450 meters (1,480 ft). On 16 September 2013, it passed about 0.0448 AU (6,700,000 km; 4,160,000 mi) from Earth. On 20 September 2013, it came to perihelion (closest approach to the Sun). The asteroid was discovered on 12 October 2013 by Ukrainian amateur astronomer Gennadiy Borisov with a custom 0.2-meter (7.9 in) telescope using images dating back to 8 October 2013. It was rated level 1 on the Torino Scale from 16 October 2013 until JPL solution 26 on 3 November 2013. It reached a Palermo Technical Impact Hazard Scale rating of -0.73. It was removed from the JPL Sentry Risk Table on 8 November 2013 using JPL solution 32 with an observation arc of 27 days.

2014 DX110 is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group, approximately 30 meters in diameter. It passed less than 1 lunar distance from Earth on 5 March 2014. With an absolute magnitude of 25.7, this asteroid is potentially the largest asteroid to come inside the orbit of the Moon since 2013 PJ10 on 4 August 2013. The close approach was webcast live by Slooh and Virtual Telescope.

2012 FN is an Apollo asteroid and a near-Earth object that has a 1 in 4 billion chance of impacting Earth on 7 March 2113. It is estimated to be 5 meters in diameter, which means that it poses no threat if it impacts Earth. An impact would have the kinetic energy of about 3 kt of TNT, and would probably result in an air burst in the upper atmosphere. It is the least threatening asteroid listed on the Sentry Risk Table. The very short observation arc of only 3 hours results in a very poorly constrained orbit, and it could just as easily be 2 AU from Earth on 7 March 2113.

2007 VE191 is a sub-kilometer asteroid, classified as near-Earth asteroid of the Apollo group that was listed on the Sentry Risk Table.

2013 TX68 is an Apollo asteroid and near-Earth object discovered on 6 October 2013 by the Catalina Sky Survey, during which it was near a close approach of 5.4 Lunar distances (LD) from the Earth. The asteroid only has a 10-day observation arc which makes long-term predictions of its position less certain. It was observed for three days as it approached Earth in the night sky starting with the sixth of October, 2013. Then it became unobservable by being between the Earth and the Sun, then not recovered due to its small size and dimness. Precovery images by Pan-STARRS from 29 September 2013 were announced on 11 February 2016 that extended the observation arc to 10 days. It was removed from the Sentry Risk Table on 11 February 2016, so there is no risk of impact from this object for the next hundred years or more. The asteroid was last observed on 9 October 2013.

<span class="nowrap">2017 XO<sub>2</sub></span>

2017 XO2, also written 2017 XO2, is a sub-kilometer asteroid and near-Earth object of the Apollo group approximately 110 meters (360 feet) in diameter. The asteroid was discovered by Pan-STARRS in December 2017, after it already had approached Earth at 0.051 AU (7,600,000 km) or 20 lunar distances (LD) on 6 November 2017. On 26 April 2057, it will pass Earth at a similar distance of 21 LD again.

<span class="nowrap">2018 XB<sub>4</sub></span>

2018 XB4 (also written 2018 XB4) is an Apollo near-Earth asteroid roughly 53 meters (170 feet) in diameter. It was discovered on 13 December 2018 when the asteroid was about 0.125 AU (18,700,000 km; 11,600,000 mi) from Earth and had a solar elongation of 146°. It passed closest approach to Earth on 1 January 2019. Of the asteroids discovered in 2018, it had the highest Palermo scale rating at –3.6. In mid-2019 it was recovered which extended the observation arc to 177 days and was removed from the Sentry Risk Table on 12 June 2019. It is now known that on 22 June 2092 the asteroid will pass about 0.033±0.015 AU from Earth.

2011 ES4 (also written 2011 ES4) is an Apollo near-Earth asteroid roughly 22–49 meters (72–160 feet) in diameter. It was first observed on 2 March 2011 when the asteroid was about 0.054 AU (8,100,000 km; 5,000,000 mi) from Earth and had a solar elongation of 159 degrees. It passed closest approach to Earth on 13 March 2011. Before the 2020 approach, the asteroid had a short observation arc of 4 days and had not been observed since March 2011. The asteroid was expected to pass within 1 lunar distance of Earth in early September 2020, but did not. There was no risk of a 2020 impact because the line of variation (LOV) did not pass through where Earth would be, and the closest possible 2020 Earth approach was about 0.00047 AU (70,000 km; 44,000 mi). One line of variation showed the asteroid passing closest to Earth on 5 September 2020 at 0.06 AU (9,000,000 km; 5,600,000 mi) with a magnitude of 23, which would place it near the limiting magnitude of even the best automated astronomical surveys.

2018 VP1 is an Apollo near-Earth asteroid roughly 2 meters (7 feet) in diameter. The asteroid had a 0.41% chance (1 in 240) of impacting Earth on 2 November 2020 01:12 UT. It was discovered on 3 November 2018 when it was about 0.003 AU (450,000 km; 280,000 mi) from Earth and had a solar elongation of 165 degrees. The asteroid has a short 12.9 day observation arc. It was last observed on 16 November 2018 by the European Southern Observatory Very Large Telescope at apparent magnitude 26 pushing the telescope close to the limiting magnitude.

2007 FT3 (also written 2007 FT3) is a lost asteroid with a short observation arc of 1.2 days that can not be recovered with targeted observations and awaits serendipitous survey observations. It has a poorly constrained orbit and has not been seen since 2007. It was first observed on 20 March 2007 when the asteroid was estimated to be 0.19 ± 0.01 AU (28.4 ± 1.5 million km) from Earth and had a solar elongation of 107 degrees. 2007 FT3 is the fourth largest asteroid with better than a 1-in-2 million cumulative chance of impacting Earth after (29075) 1950 DA, 1979 XB, and 101955 Bennu. With a cumulative Palermo Technical Impact Hazard Scale of -2.93, the poorly known orbit and assumed size place 2007 FT3 fifth on an unconstrained listing of the Sentry Risk Table.

1979 XB is a lost asteroid with a short observation arc of 3.9 days that cannot be recovered with targeted observations and awaits serendipitous survey observations. It is classified as a near-Earth object and potentially hazardous asteroid of the Apollo group and is estimated to be 660 meters in diameter. The unnumbered minor planet has a poorly constrained orbit and has not been observed in 40 years. It has been listed on the Sentry Risk Table since the list started in 2002. With a cumulative Palermo Technical Impact Hazard Scale of −2.72, the poorly known orbit and assumed size place 1979 XB third on an unconstrained listing of the Sentry Risk Table.

<span class="mw-page-title-main">2020 VV</span> Small risk–listed near-Earth asteroid

2020 VV is an Apollo near-Earth asteroid roughly 12 meters in diameter. On 20 November 2020, the asteroid had a 4.4% chance of impacting Earth on 12 October 2033 11:43 UT. As of mid-December 2020, the asteroid has a modest 61 day observation arc. The nominal Earth approach is on 17 October 2033 at a distance of 0.009 AU, but the line of variations (LOV) is only known with an accuracy of ±22 hours. The line of variations allows the asteroid to come as close as 0.006 AU or pass as far away as 0.01 AU. With a diameter range of 10–22 meters the asteroid could be as large as the Chelyabinsk meteor.

2005 ED224 was the soonest virtual impactor of an asteroid larger than 50 meters in diameter with a better than 1:1-million chance of impacting Earth. On 11 March 2023 the line of variations (LOV) showed a 1-in-500,000 chance of impact. It is estimated to be 54-meters in diameter and has a short observation arc of 3-days. On 11 March 2023 it was nominally expected to be 2.7 AU (400 million km) from Earth but had an uncertainty region billions of kilometers long. Since it has not been observed since 2005 and has an orbital period of 2.6±0.3 years, we do not know where on its orbit 2005 ED224 is. Between 2005 and 2023 it could have orbited the Sun 6.2 to 7.8 times. On 11 March 2030 it has a 1-in-6,300,000 chance of impact but is expected to be 3.5 AU (520 million km) from Earth (near the asteroid's farthest distance from the Sun). On 10 March 2064 it has a 1-in-2,600,000 chance of impact but is expected to be 3.2 AU (480 million km) from Earth.

2022 AE1 is a Tunguska event-sized asteroid, classified as a near-Earth object of the Apollo group, approximately 70 meters (230 feet) in diameter. It was discovered by the Mount Lemmon Survey on 6 January 2022, when it was 0.09 AU (13 million km) from Earth. On 9 January 2022 with an observation arc of 3 days, it was rated with a Torino scale of 1 for a virtual impactor on 4 July 2023 16:28 UTC. Nominal approach is expected to occur 1 July 2023 01:13 ± 1 day. With a Palermo scale rating of as high as –0.66 at the European Space Agency on 11 January 2022, the odds of impact peaked at about 4.6 times less than the background hazard level. NEODyS was the first risk-page to drop to Torino scale 0 on 12 January 2022 followed by ESA on 13 January 2022, but by January 14 both returned to Torino scale 1. On 14 January 2022 the waxing gibbous moon was as little as 3 degrees from the asteroid delaying observations of the asteroid from January 12–19. On 20 January 2022 with a 16-day observation arc, using JPL #11 the Sentry Risk Table dropped the asteroid to Torino scale 0 and then later that day JPL #12 resulted in it being removed from the risk table.

References

  1. 1 2 3 4 5 6 "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)
  2. 1 2 3 4 Jon Giorgini (30 July 2002). "Understanding Risk Pages". Columbine, Inc. (hohmanntransfer). Archived from the original on 8 December 2002. Retrieved 21 November 2011.
  3. ↑ "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.)
  4. ↑ "Sentry Risk Table: 2015 RD36" (using 2022-Sep-13 solution). NASA JPL CNEOS . Retrieved 2 October 2022.
  5. ↑ "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.
  6. ↑ "2002 Archive of Sentry Risk Table". Archived from the original on 21 March 2002.
  7. ↑ "Much Ado about 2000 SG344". NASA Science. NASA. Retrieved 27 September 2023.
  8. 1 2 "VI (Virtual Impactor) Data". NASA/JPL Near-Earth Object Program Office. Retrieved 9 November 2022. Unconstrained Settings, Sort by Date. For objects larger than the Chelyabinsk meteor and better than 1:1 million also include Impact Probability ≥ 1e-6 and H≤26 (17–38 meters).
  9. ↑ "JPL Horizons: 2022 PX1 geocentric distance and uncertainty on 11 August 2040". JPL Horizons. Retrieved 15 March 2023.
  10. ↑ "Horizons Batch for 2023-06-10 Virtual Impactor". JPL Horizons. Archived from the original on 9 November 2022. Retrieved 9 November 2021. RNG_3sigma = uncertainty range in km. (JPL#4/Soln.date: 2021-Apr-15 generates RNG_3sigma = 134116335 km for 2023-Jun-10.)
  11. ↑ Sentry: 2017 SA20 (1244 VIs) using 2022-Aug-30 solution
  12. 1 2 "Sentry Notes". NASA/JPL Near-Earth Object Program Office. 12 August 2013. Retrieved 13 April 2017.
  13. ↑ "NASA's Next-Generation Asteroid Impact Monitoring System Goes Online". NASA/JPL Near-Earth Object Program Office. 6 December 2021.
  14. 1 2 "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.)
  15. ↑ "Scout: NEOCP Hazard Assessment". NASA/JPL Near-Earth Object Program Office. Retrieved 26 June 2019.
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