NASA/JPL CNEOS · MPC · IAU · Vol. III
PHA Catalogue VOL. III
Potentially Hazardous Asteroids · Sub-lunar flybys, lost objects & Aten/Atira class
Data: JPL Small-Body Database · Minor Planet Center · JPL Echo Radar Group
Data: JPL Small-Body Database · Minor Planet Center · JPL Echo Radar Group
2,400+Known PHAs
~200Sentry ever listed
4660Nereus — target
1937Oldest named PHA
Sub-lunar flyby: Any close approach within 1 Lunar Distance (384,400 km / 0.00257 au) of Earth. Roughly 5–10 such events occur annually, mostly by small undiscovered objects. PHAs reaching sub-lunar distance while large enough to cause regional damage (>~140 m) are tracked by CNEOS/Sentry and ESA NEOCC.
NEA discovery surveys — context
1973 Palomar
1994 LINEAR
2005 CSS
2009 ATLAS
2028 NEOS
Class
Torino 0 — No hazard
Torino 1 — Very low
Torino 2–3 — Attention
Torino 4+ — Concern
Designation / Name
H mag
Diam.
MOID
Period
Torino
Sub-lunar flybys & closely studied PHAs
(308635) 2005 YU55
2005 YU55 RADAR
Apollo · C-type · Spheroidal
21.9
~360 m
0.0015 au
1.22 yr
0
Discovered
2005 Dec 28
Discoverer
R. McMillan (Spacewatch, Kitt Peak)
Dimensions (radar)
360 ± 40 m (near-spherical)
Albedo
0.055–0.075 (very dark)
Rotation period
19.3 h (retrograde)
Eccentricity
0.431
Semi-major axis
1.143 au
Inclination
0.51°
2011 flyby
2011 Nov 8 — 0.85 lunar dist.
Flyby distance
324,600 km (inside lunar orbit)
Peak Torino
1 (Feb 2010 — cleared Apr 2010)
Impact prob.
None known (>100 yr)
Closest known approach by a ~300 m+ asteroid since 1976. Radar imaging by Goldstone and Arecibo during the Nov 2011 flyby revealed a near-spheroidal shape with an equatorial ridge and decameter-scale boulders comparable to Itokawa's surface. UV observations by NASA's Swift satellite captured it post-flyby. Briefly held a Torino Scale 1 rating in Feb 2010 for a potential 2103 approach — eliminated by Arecibo radar in Apr 2010. Source: Müller et al. (2013) arXiv:1307.7517 · JPL Echo radar planning · NASA Swift/UVOT · MPC
(52768) 1998 OR2
1998 OR2 RADAR
Apollo · Sq-type · Shock darkening
15.7
~1.8–2.1 km
0.0105 au
3.67 yr
0
Discovered
1998 Jul 24
Survey
NEAT (Haleakalā)
Precovery
1987 Jun 30 (Palomar DSS)
Diameter
1.8–2.1 km (CALL H=15.7, alb=0.20)
Rotation period
4.11 h
Eccentricity
0.571
Semi-major axis
2.373 au
Inclination
5.88°
2020 flyby
2020 Apr 29 — ~6.3 million km
Special property
First NEA to show shock darkening
Next approach
2079 Apr 16 — 0.0119 au
Impact prob.
None known
The first near-Earth asteroid ever identified as showing shock darkening — gradual surface darkening caused by micrometeorite bombardment and solar wind particle flux. Goldstone and Arecibo radar observations during the Apr 2020 flyby produced detailed shape models. A preliminary report suggested the surface has features resembling a face mask, generating media interest. Precovery data extends the observational arc to 1987, making the orbit very well constrained. Source: Wikipedia/MPC (CALL) · Arecibo NAIC 2020 · JPL SBDB
(7482) 1994 PC1
1994 PC1 GOLDSTONE
Apollo · V-type · Well-determined orbit
17.0
~1.1 km
0.0073 au
1.57 yr
0
Discovered
1994 Aug 9
Discoverer
R. McNaught (Siding Spring)
Diameter
~1.1 km (NEOWISE/radar)
Albedo
0.277
Rotation period
2.60 h
Eccentricity
0.329
Semi-major axis
1.348 au
Inclination
33.5°
2022 flyby
2022 Jan 18 — ~1.93 million km
Closest ever
1933 Jan 17 — ~1.07 million km
Observation arc
47+ years (precovery to present)
Impact prob.
None known
One of the best-determined PHA orbits, with a 47-year observational arc including precovery data to 1933. The Jan 2022 flyby at ~5× lunar distance was widely covered — visible in modest amateur telescopes at ~10th magnitude. Its closest historical approach was 1933 Jan 17 at ~2.78 lunar distances, found retrospectively in sky survey plates. Goldstone radar provided detailed shape constraints during the 2022 apparition. Source: Cosmoquest/CosmoVision · JPL SBDB · MPC · Goldstone DSS-14 2022
Aten class & inner-Earth objects
(163899) 2003 SD220
2003 SD220 RADAR
Aten · Sr-type · Slow rotator
17.3
~800 m
0.0192 au
0.75 yr
0
Provisional desig.
2003 SD220 / 2000 AD229
Discovered
2003 Sep 29 (LONEOS)
Diameter (NEOWISE)
0.80 ± 0.02 km
Albedo (NEOWISE)
0.30 ± 0.04
Rotation period
~12 days (NPA rotation)
Eccentricity
0.210
Semi-major axis
0.828 au
Inclination
8.5°
Shape
Highly elongated (radar)
2021 flyby
2021 Dec 17 — 0.036 au (14.1 LD)
Spectral type
S/Sr — ordinary chondrite analog
Impact prob.
None known
One of the most slowly rotating PHAs: a rotation period of ~12 days combined with radar imaging from Goldstone (2015, 2018) and Arecibo (2015) revealed a highly elongated shape and non-principal-axis (tumbling) rotation. The linked provisional designation 2000 AD229 extended the observational arc. Independently classified as a Sr-type (S-subtype with reddish spectral slope) by IOP/Perna et al. 2015. Source: JPL Echo radar planning 2021 · Nugent et al. (2016) NEOWISE · Perna et al. (2015) AJ
(33342) 1998 WT24
1998 WT24 RADAR
Aten · E-type · High albedo
17.9
~415 m
0.0039 au
0.72 yr
0
Discovered
1998 Nov 30 (LINEAR)
Diameter (radar)
415 ± 40 m
Spectral type
E-type (enstatite; very rare)
Optical albedo
~0.42–0.73 (among brightest known)
Rotation period
3.697 h
Eccentricity
0.418
Semi-major axis
0.719 au
Inclination
7.3°
2001 flyby
2001 Dec 11 — 10.9 LD (0.028 au)
Radar model
3-D shape (Benner et al. 2002)
Bistatic radar
Goldstone–Parkes DSN bistatic 2015
Impact prob.
None known
Rare E-type (enstatite achondrite) PHA — only a handful of E-type NEAs are known. Its extraordinarily high optical albedo of 0.42–0.73 makes it one of the brightest known minor planets relative to its size; published albedo values vary because enstatite-rich surfaces are poorly modelled by standard thermal models. Full 3-D shape model published by Benner et al. (2002) from Goldstone observations. A Goldstone–DSS-13 / Parkes bistatic campaign was conducted in Dec 2015. Source: Benner et al. (2002) · JPL Echo planning 2015 · Johnston Archive radar table
(163693) Atira
Atira BINARY
Atira (IEO) · binary · Class namesake
16.3
~4.8 km
0.0261 au
0.53 yr
0
Provisional desig.
2003 CP20
Discovered
2003 Feb 12 (LINEAR)
Orbit class
Interior Earth Object (IEO/Atira)
Primary diameter (radar)
4.92 ± 0.95 km
Secondary diameter
~0.80 km
Optical albedo
0.022 (extremely dark)
Rotation period
~3.4 h (primary)
Eccentricity
0.322
Semi-major axis
0.741 au
Aphelion
0.977 au (never reaches 1 au)
Inclination
25.6°
Impact prob.
None known
Class namesake of all Atira-type (Interior Earth Object) asteroids — a rare subclass whose entire orbit lies within Earth's orbit (aphelion < 1.0 au). Fewer than ~30 Atiras are known. Goldstone radar revealed it is a binary system with a ~0.8 km secondary (Rivkin et al. 2017, Johnston Archive BIN-55). Primary diameter of ~4.9 km makes it the largest known Atira by a large margin. Spectral type consistent with a primitive dark C/D-type object. Source: Rivkin et al. (2017) AJ · Johnston Archive BIN-55 · JPL SBDB
Historic close approaches & lost asteroids
(69230) Hermes
Hermes LOST 1937–2003
Apollo · Sq-type · Binary · Last named lost ast.
17.5
~810 m
0.0041 au
2.13 yr
0
Provisional desig.
1937 UB
Discovered
1937 Oct 28 (K. Reinmuth, Heidelberg)
Recovered
2003 Oct 15 (B. Skiff, LONEOS)
Years lost
66 years
Primary diameter
600 ± 120 m
Secondary diameter
540 ± 120 m
Binary separation
~1.1 km
Eccentricity
0.624
Semi-major axis
1.655 au
Inclination
6.1°
1937 flyby
1937 Oct 30 — 0.00494 au (1.9 LD)
1942 flyby
1942 Apr 26 — 0.00424 au (1.6 LD) unobserved
Impact prob.
None known (<100 yr)
The last remaining named lost asteroid, recovered after 66 years by Brian Skiff at LONEOS on 2003 Oct 15. Originally seen for just 4 days in 1937, giving too short an arc to compute a reliable orbit. Its 1937 flyby held the record for closest known asteroid approach until (4581) Asclepius in 1989. The unobserved 1942 flyby — at wartime — was even closer at 1.6 lunar distances. Near-IR spectroscopy (Rivkin & Binzel, IRTF) confirmed an Sq-type spectrum consistent with LL-chondrite surface composition. Radar confirmed binary system in 2003. Source: Wikipedia/MPC (2003 recovery) · Rivkin & Binzel (2004) Icarus · JPL SBDB
(4581) Asclepius
Asclepius 1989 MISS
Apollo · S-type · 1989 record flyby
20.0
200–420 m
0.0025 au
0.99 yr
0
Provisional desig.
1989 FC
Discovered
1989 Mar 31
Discoverers
H. Holt & N. Thomas (Palomar)
Diameter estimate
189–423 m (brightness-based)
Eccentricity
0.360
Semi-major axis
0.989 au
Inclination
4.9°
1989 flyby
1989 Mar 22 — 0.00457 au (1.8 LD)
Record at time
Closest known flyby since Hermes 1937
Quote (Dr. H. Holt)
"On the cosmic scale, a close call"
Impact prob.
None known
Discovered 9 days after its closest approach — a demonstration of survey incompleteness in 1989. Its flyby at 1.8 lunar distances was the closest asteroid approach known since Hermes in 1937, and it passed through the point where Earth had been 6 hours earlier. The event directly motivated increased congressional funding for NEO surveys and laid groundwork for the Spaceguard programme. Named after the Greek god of medicine. Source: Wikipedia 4581 Asclepius · Holt/Thomas Palomar discovery report · David Darling Encyclopedia · JPL SBDB
Well-surveyed modern PHAs
(138971) 2001 CB21
2001 CB21
Apollo · S-type · 2022 passage
18.0
0.56–1.2 km
0.0263 au
1.05 yr
0
Discovered
2001 Feb 8
Survey
LINEAR
Diameter estimate
560 m – 1.2 km (CNEOS range)
Rotation period
3.305 ± 0.002 h (Pulkovo 2022)
Eccentricity
0.491
Semi-major axis
1.049 au
Inclination
3.6°
2022 flyby
2022 Mar 4 — ~4.9 million km (12.7 LD)
Next approach
2043 Mar 6 — ~4.8 million km
Orbital period
384 days (near 1:1 resonance)
Impact prob.
None known (>100 yr)
Photographed by the Virtual Telescope Project (G. Masi) on Jan 30, 2022 at 34.6 million km, then again on Feb 23 at 10 million km. Lightcurve analysis at the Pulkovo Astronomical Observatory (Main Astronomical Observatory RAS, 2022) confirmed a rotation period of 3.305 h. Devyatkin et al. (2025) published improved orbital elements and Yarkovsky effect assessment based on the 2022 apparition. Source: Devyatkin et al. (2025) Solar System Research · Virtual Telescope Project · CNEOS
(4660) Nereus
Nereus NHATS target
Apollo · Xe-type · Human mission target
18.3
~330 m
0.0033 au
1.82 yr
0
div
Provisional desig.
1982 DB
Discovered
1982 Feb 28 (E. Helin, Palomar)
Diameter (radar)
0.33 km (Goldstone 2021)
Albedo
0.54 (high, Xe-type)
Rotation period
15.1 h
Eccentricity
0.360
Semi-major axis
1.489 au
Inclination
1.4°
2021 flyby
2021 Dec 11 — 0.0263 au (10.2 LD)
NHATS rank
Top-rated human mission target (ΔV)
Spectral type
Xe (enstatite/aubrite-like)
Impact prob.
None known
Consistently ranked among the top human-accessible asteroid targets by NASA's NHATS (Near-Earth Object Human Space Flight Accessible Targets Study) due to its low ΔV requirements (~4.5 km/s). It has been the subject of multiple mission concepts. Goldstone radar observations during Dec 2021 gave a definitive diameter of 0.33 km. High albedo of 0.54 is consistent with its Xe spectral type. Named after the Greek sea deity Nereus. Source: JPL Echo planning 2021 · NHATS database · JPL SBDB · Johnston Archive
(2101) Adonis
Adonis LOST 1936–1977
Apollo · C-type · Second numbered NEA
18.7
~600–900 m
0.0434 au
2.54 yr
0
Provisional desig.
1936 CA
Discovered
1936 Feb 12 (E. Delporte, Uccle)
Recovered
1977 Feb 12 (C. Kowal, Palomar)
Years lost
41 years
Eccentricity
0.765
Semi-major axis
1.874 au
Inclination
1.35°
Perihelion
0.441 au (Venus-crosser)
1936 flyby
1936 Feb — ~2 million km
Historical significance
2nd asteroid known to cross Earth orbit
Impact prob.
None known
The second asteroid ever found to cross Earth's orbit (after Apollo in 1932), discovered by Eugène Delporte at the Royal Observatory of Belgium, Uccle. Lost after 1936 due to an insufficient observational arc, recovered 41 years later by Charles Kowal at Palomar. Along with Apollo (1932) and Hermes (1937), it was one of only three unnumbered but named asteroids before being assigned number 2101 in 1977. Its very low inclination (1.35°) makes it a frequent conjunction target. Source: JPL SBDB · MPC MPEC 1977-C02 · Wikipedia/IAU