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Draft:2025 UC11

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2025 UC11
2025 UC11 at 12:00 UTC on 30 October 2025
(Courtesy NASA/JPL-Caltech)
Discovery
Discovered byJPL SynTrack Robotic Telescope: SRO #1 (awaiting Minor Planet Center confirmation)[1]
Discovery siteSierra Remote Observatories, Auberry, California (awaiting Minor Planet Center confirmation)[2]
Discovery date30 October 2025
Designations
NEO • Aten meteoroid
Orbital characteristics
Uncertainty parameter 4
0.94585 AU
Eccentricity0.051987
336 days (0.92 years)
186.48°
1.0715°/day
Inclination5.11432°
Earth MOID0.000275535 AU[3]
Mercury MOID0.43308 AU[4]
Venus MOID0.17688 AU[5]
Physical characteristics
0.41 m - 0.93 m
34.037

2025 UC11 is an Aten meteoroid[6] and near-Earth object[7] that is the closest and smallest flyby to date to have been tracked with modern telescopes. It was listed by NASA[8]/CalTech[9] Jet Propulsion Laboratory's[10] Close Approach Database[11] as having reached its closest point to earth on October 30, 2025 at 12:11 UTC, having descended to an altitude 4,101 miles from Earth's center (approximately 142 to 152 miles from the Earth's surface)[12] The near-Earth object was officially announced at 20:57 UTC in Minor Planet Center Electronic Circular #2025-U298.[13]

2025 UC11 is a near-Earth object flyby, in a well-understood orbit, with up-to-date ephemerides,[14] whose range of diameters falls entirely within the range defining a meteoroid;[6] that is, the minimum and maximum of its diameter (0.41 m - 0.93 m) are both less than 1 meter. 2025 UC11 has the smallest diameter of any near-Earth object that can currently be queried in NASA's NEO Earth Close Approaches database.[15]

The fact that 2025 UC11 approached Earth 90 miles more closely than 2020 VT4,[16] which passed within 4,191 miles from Earth's center on November 13, 2020, differentiates this near-Earth object as having the closest approach to Earth that was simultaneously tracked with modern telescopes, and did not burn up in the atmosphere or impact the Earth's surface.

The Minor Planet Center circular[17] and an associated update[18] list 11 separate observatories that tracked this near-Earth object, including Farpoint Observatory,[19] Cerro Tololo Inter-American Observatory in Chile,[20] Palomar Mountain Observatory,[21] and Tenerife Observatory.[22]

2025 UC11 approached Earth from a distance of between 80 and 90 miles above the Kármán Line,[23] which defines the lower part of the Earth's thermosphere,[24] 100 kilometers (62 miles) above mean sea level.

If 2025 UC11 had not survived its encounter with Earth, it most likely would have vaporized after burning up in the atmosphere due to its small size.[25]

The observation and tracking of the object at such a near distance from Earth signal astronomers' improving ability to monitor increasingly small near-Earth objects. While it is still exceedingly difficult to provide advance warning of objects of this size before they approach Earth very closely, in previous years it would have been difficult to track them at all.[26]

Initial Discovery Observation

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Michael Shao, [27] Navtej Singh,[28] and Russell Trahan,[29] while operating the JPL SynTrack Robotic Telescope[30] at the Sierra Remote Observatories, Auberry, California,[31] made the first discovery observation of 2025 UC11 on October 30, 2025, at 05:13 UTC (9:13 pm local Pacific time), some seven hours before it would reach its closest point to Earth (perigee).[32][33][34] The astronomers assigned it the local designation K25U11C.[35]

On October 30, 2025 at 20:57 UTC, after nine more observatories[36] contributed additional measurements, and roughly 16 hours after astronomers at the Sierra Remote Observatories provided the earliest discovery observation, the Minor Planet Center confirmed the object as a new minor planet on its website in Electronic Circular #2025-U298.[37] and gave the object the provisional designation 2025 UC11, thus informing the public of the discovery.[38]

An animation of how the Earth appeared from the vantage of 2025 UC11 as it made its approach is shown below. Observatories that contributed measurements of the near-Earth object show up as brief points of light at the times that those measurements were reported.

close approach time lapse animation of 2025 UC11 (1 second = ~1 hour)

Dunn, Tony (animator/director) (October 30, 2025). Close Approach of 2025 UC11 (motion picture). United States: Dunn, Tony [used with permission].

Notable Characteristics

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2025 UC11 is the closest near-Earth flyby on record to have been tracked with modern telescopes, approaching more closely to Earth than 2020 VT4,[39] which passed within 4,191 miles from Earth's center on November 13, 2020.

However, it should be noted that data from modern telescopes do not encompass the Earth's complete astronomical record.

Photographs of near-Earth objects that approached at lower altitudes[40] than 2025 UC11 (but were not tracked with the same precision as those today, and were not formally named)[41] suggest that near-Earth objects have sporadically approached Earth more closely in the past than the data from modern instruments would imply.

2025 UC11 is very small and very dim. The object's absolute magnitude[42] (H) was measured at 34.037. A typical formula using absolute magnitude and an assumed range of albedos[43] (0.05 < A < 0.25) estimates the diameter of 2025 UC11 to be between 1 and 3 feet (1 meter or less).[44]

Additionally, available data from the JPL Center for Near Earth Object Studies indicate that 2025 UC11 is the smallest near-Earth object to have been both observed and tracked and currently in orbit about the sun, measuring 0.41 meters to 0.93 meters in diameter.[45] The measurements are supported by observations and predictions over three separate dates spanning an 81-year period (2004-2085), combined with all of the database's historical observations.

A near-Earth object this small is difficult for astronomers to detect until it is very close to Earth.[46]

Orbit and Classification

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2025 UC11 is currently on an Earth-crossing Aten-type[47][48] orbit with an orbital semi-major axis of 0.945847 AU (141 million km; 87.9 million mi) and an orbital period of 0.92 years or 336 days. With a nominal perihelion distance of 0.897 AU and an aphelion distance of 0.9950 AU, 2025 UC11's orbit can cross the orbital path of Earth, resulting in occasional close passes with our planet. The nominal minimum orbit intersection distances (MOID) with Jupiter and Earth are approximately 3.9695 AU (593,830,000 km; 368,990,000 mi) and .0003 AU (45,000 km; 28,000 mi), respectively. 2025 UC11 has an orbital eccentricity of 0.052 and an inclination of 5.1 degrees to the ecliptic.[49]

Synodic orbital path of 2025 UC11 following the motion of Earth about the Sun with the object's relative trajectory moving around it in 3D from 14 Oct 2025 to 5 Nov 2025. Courtesy: European Space Agency - ESA

Before the Earth encounter on October 30, 2020, 2025 UC11 had an Apollo-type orbit, also crossing the path of Earth. It had a perihelion distance of 0.920 AU and a semi-major axis of 1.079 AU (161 million km; 100 million mi), with an orbital period of 1.12 years or 409 days. The orbit had an orbital eccentricity of 0.147 and an inclination of 1.24 degrees to the ecliptic.[50]

Orbital simulations from the JPL Horizons application show that since the year 1600 A.D., 2025 UC11 has not appeared to cross the orbital path of any other planet in the solar system, except Earth, nor is it expected to encounter the orbital path of any other planet, except Earth, by 2200 A.D., notwithstanding the changes in its orbital characteristics since encountering near-Earth orbit, as shown in the comparative table below, and in the animation at left.

Orbital Elements
Parameter Epoch Period
(p) 		Aphelion
(Q) 		Perihelion
(q) 		Semi-major axis
(a) 		Eccentricity
(e) 		Inclination
(i)
Units (days) AU Unitless 0<=e<=1 (°)
Pre-flyby 2025-Mar-31[51] 409.1 1.238 0.920 1.079 0.147 1.24°
Post-flyby 2025-Nov-21[52] 335.99 0.995 0.897 0.946 0.052 5.11°

While 2025 UC11's orbit would meet the criteria of a potentially hazardous object, its size would need to be many multiple times larger in volume than what it is to qualify as potentially hazardous. 2025 UC11 is not a threat to Earth.[53]

Formal Assignment of Discoverer of 2025 UC11

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It is important to note parenthetically that the formal notice of the official discoverer of 2025 UC11, or any minor planet, occurs when the Minor Planet Center (MPC) provides formal numbering of that minor planet, signaling a catalogued and credited "discoverer."[54]

The number, once assigned by the MPC, may be found in the MPCORB (Minor Planet Center Orbital) database.[55]

For near-Earth objects such as 2025 UC11, the MPC often expedites the process of issuing a formal number, reducing the requirement of observing four or more oppositions[56] to three or even two.[57] Even so, the process can take years. Some minor planets never receive official numbering, because their orbits are not understood with sufficient precision for the MPC to credit their discovery with a discoverer.

Synthetic Tracking of Near-Earth Objects

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Orbit of 2025 UC11 from above at 0.015 AU from Earth. (Courtesy NASA/JPL-Caltech)

The JPL Syntrack Robotic Telescope used "synthetic tracking" to plot the orbit of 2025 UC11.[58] The Sierra Remote Observatories' astronomers, who used this telescope to provide the initial discovery observation of 2025 UC11, describe synthetic tracking in an academic paper as "a potent technique for observing fast-moving near-Earth objects (NEOs), offering enhanced detection sensitivity and astrometric accuracy" (the precision with which an object's position in the sky can be measured) "by avoiding trailing loss."

Trailing Loss

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Trailing loss occurs in traditional long-exposure astrophotography when fast-moving near-Earth objects (NEOs) appear as faint streaks rather than bright points, making them difficult to detect against background noise.

orbital flyby diagram of 2025 UC11 (image provided by the International Astronomical Union's Minor Planet Center)

Background Noise

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In general, synthetic tracking alleviates many problems of background noise by taking multiple short exposures and computationally stacking them to align the image of the moving object, concentrating its light and improving the ability to discover fainter, smaller NEOs. The accuracy of the results are, according to the study authors, comparable with the results obtained from stellar astrometry.[59]

The main causes of background noise in astrophotography are low signal-to-noise ratio due to faint light, thermal noise from long exposures, and high ISO or gain settings that amplify both signal and noise. Other factors include light pollution, which adds unwanted background light, and inherent camera noise such as electronic "grain" and shot noise, the graininess or fuzziness seen in images caused by the random nature of cosmic rays, high-energy particles (like protons or atomic nuclei) from outer space, directly hitting the image sensor. Also, differential chromatic refraction (DCR) can cause light of different colors from a distant object to be bent by slightly different amounts as it passes through Earth's atmosphere.[60][61]

Star Confusion

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Background noise is particularly noticeable in astrometry when it involves a phenomenon known as "star confusion." When the track of a near-Earth object overlaps a star in a discrete set of images taken over time, the brightness of the star will, as the images are viewed sequentially as in a motion picture, overwhelm and mask the track of the near-Earth object.[62]

Synthetic tracking addresses star confusion by isolating the images that have exceeded a threshold of confusion, where the star and the near-Earth object coincide in the frames. The threshold is calculated using a formula dividing the level of brightness gradient of the star by the brightness gradient of the targeted near-Earth object, further divided by an index of image sharpness. In so doing, the threshold value may be used to exclude any frames from the stack that exceed the threshold. What emerges from the sequence of output images is a gap that had previously depicted the star through which the fainter point of light from the near-Earth object can be much more easily observed.[63]

Characterizing 2025 UC11 with Synthetic Tracking

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The study specifically mentions JPL’s Syntrack Robotic Telescope, SRO1 (U68), which was credited in MPC Circular #2025-U298 with the discovery observation. This telescope, in tests of the efficacy of synthetic tracking, proved to be a capable instrument, outperforming the Table Mountain Observatory on a key metric, the ability to detect and identify fast-moving near-Earth objects that are also faint (high apparent magnitude or H).[64]

The study authors have helped to advance the techniques used in synthetic tracking, and they have recommended that other observatories use them. They cite several observatories that have, Haleakala Observatory among them, and which have adopted synthetic tracking in their astrometric methodologies. Haleakala Observatory also contributed measurements toward the discovery of 2025 UC11, subsequent to its discovery observation by SRO1.[65]

While data acquisition and much of the processing involved in synthetic tracking are automated, astronomers remain crucial for setting up the system, fine-tuning photographic parameters, such as the ideal frame exposure time to balance trailing loss and noise[66], handling the detection of challenging objects, and reviewing final images.

References

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  1. ^ "map for JPL SynTrack Robotic Telescope".
  2. ^ "website of Sierra Remote Observatories".
  3. ^ "MPC update on 2025 UC11". Note that initial Atira designation of orbital type was in error.
  4. ^ "MPC update on 2025 UC11".
  5. ^ "MPC update on 2025 UC11".
  6. ^ a b Rubin, Alan E. (14 September 2009). "Meteorite and meteoroid: New comprehensive definitions". Meteoritics & Planetary Science. 45 (1): 114. doi:10.1111/j.1945-5100.2009.01009.x. Retrieved 9 November 2025.
  7. ^ "United Nations statement on near-Earth objects".
  8. ^ "NASA website".
  9. ^ "California Institute of Technology JPL research website".
  10. ^ "JPL website".
  11. ^ "JPL CAD website".
  12. ^ "Small Body Database Lookup".Closest approach time is visible by expanding the section titled "Close Approach Data"
  13. ^ "Minor Planet Center Electronic Circular #2025-U298".
  14. ^ "NASA Horizons Web Application". NASA. Retrieved 9 November 2025.
  15. ^ "Center for near-Earth Object Studies". NEO Earth Close Approaches database. NASA / JPL. Retrieved 8 November 2025.
  16. ^ "2020 VT4 at spacereference.org".
  17. ^ "Minor Planet Center Electronic Circular #2025-U298".
  18. ^ "MPC update on 2025 UC11". Note this MPC update added two additional observatories to the end of the observation log for this object.
  19. ^ "website of Farpoint Observatory".
  20. ^ "website of Cerro Tololo Inter-American Observatory".
  21. ^ "website of Palomar Mountain Observatory".
  22. ^ "website of Tenerife Observatory".
  23. ^ "the Kármán Line". 27 November 2023.
  24. ^ "the thermosphere".
  25. ^ "Meteors and Meteorites". NASA. 26 October 2017. Retrieved 6 November 2025.
  26. ^ "lead time of asteroid impacts by size".
  27. ^ "JPL Principal Research Scientist Michael Shao".
  28. ^ "Data Scientist Navtej Singh (Saini)".
  29. ^ "Optical Engineer Dr. Russell Trahan". Jet Propulsion Laboratory.
  30. ^ "MPEC Watch report on the JPL SynTrack Robotic Telescope".
  31. ^ "About the Sierra Remote Observatories".
  32. ^ "Merriam-Webster definition of perigee". Merriam Webster. 8 October 2025. Retrieved 4 November 2025.
  33. ^ "Minor Planet Circular #2025-U298". Note the last three characters of each observation line constitute the code for a specific observatory.
  34. ^ "Lookup table of observatory codes".
  35. ^ "MPEC Watch - Object K25U11C".
  36. ^ "MPC update on 2025 UC11". Note an MPC update added two additional observatories to the end of the observation log for this object.
  37. ^ "Minor Planet Center Electronic Circular #2025-U298".
  38. ^ The meteoroid was also detected in earlier observations by astronomers at the Palomar Mountain Observatory less than three minutes before its observation by the Sierra Remote Observatories. The first observation to name a minor planet as a new and uncatalogued object, and to provide supporting orbital data, is considered the "discovery observation," regardless of the number of observations that preceded it.
  39. ^ "spacereference.org listing for 2020 VT4".
  40. ^ "web archive photo of the 1972 Great Daylight Fireball". Archived from the original on 19 October 2016.
  41. ^ Ceplecha, Z. (18 August 1993). "Earth-grazing daylight fireball of August 10, 1972". Astronomy and Astrophysics. 283 (1): 287. Bibcode:1994A&A...283..287C. Retrieved 6 November 2025.
  42. ^ "absolute magnitude".
  43. ^ "Merriam-Webster definition of albedo".
  44. ^ "convenient asteroidal diameter calculator with the formula explained in simple English".
  45. ^ "Center for near-Earth Object Studies". NEO Earth Close Approaches database. NASA / JPL. Retrieved 8 November 2025.
  46. ^ Horner, Jonti (22 March 2019). Lund, Michael; Keenihan, Sarah (eds.). "Why dangerous asteroids heading to Earth are so hard to detect". theconversation.com. doi:10.64628/AA.yffjeuy3x. Retrieved 7 November 2025.
  47. ^ "JPL Small-Body Database Lookup". verifying the orbital type as Aten rather than Atira.
  48. ^ "Minor Planet Center orbital diagram". MPC orbital diagram shows 2025 UC11 crosses Earth orbit; therefore, its orbital type is not Atira.
  49. ^ "JPL Small-Body Database Lookup". Retrieved 4 November 2025.
  50. ^ "JPL Horizons application". Retrieved 4 November 2025.
  51. ^ "JPL Horizons application".
  52. ^ "JPL Small-Body Database Lookup".
  53. ^ "Center for near-Earth Object Studies - Glossary". NEO Earth Close Approaches. NASA / JPL. Retrieved 8 November 2025.
  54. ^ "Editorial notice regarding rules of assignment of discovery of a minor planet".
  55. ^ "MPCORB website". Minor Planet Center. Retrieved 6 November 2025.
  56. ^ "opposition of asteroids explained". earthsky.org. 15 January 2022. Retrieved 6 November 2025.
  57. ^ "How Asteroids are Numbered". Minor Planet Center. Retrieved 6 November 2025.
  58. ^ Zhai, Chengxing; Shao, Michael; Saini, Navtej; Choi, Philip; Evans, Nez; Trahan, Russell; Nazli, Kutay; Zhan, Max (October 2021). "Near-Earth Object Observations using Synthetic Tracking". Bulletin of the American Astronomical Society. 53 (7). arXiv:2401.03255.
  59. ^ Zhai, Shao, et al., 2021, p. 10.
  60. ^ "Reducing Noise for Astrophotography and the Night Sky". 17 February 2021.
  61. ^ Zhai, Shao, et al., 2021, pp. 6–7.
  62. ^ Zhai, Shao, et al., 2021, p. 12.
  63. ^ Zhai, Shao, et al., 2021, pp. 14–15.
  64. ^ Zhai, Shao, et al., 2021, pp. 12, 16.
  65. ^ Zhai, Shao, et al., 2021, p. 17.
  66. ^ Zhai, Shao, et al., 2021, p. 2.
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