2012 TC₄

Radar movie of2012 TC4[1]
Discovery[2][3]
Discovered by	Pan-STARRS 1
Discovery site	Haleakala Obs.
Discovery date	4 October 2012
Designations
MPC designation	2012 TC4
Minor planet category	NEO Apollo[2][4]
Orbital characteristics[2]
Epoch 1 October 2017 (JD 2458027.5)
Uncertainty parameter 1
Observation arc	5.19 yr (1,897 d)
Aphelion	1.8786 AU
Perihelion	0.9335 AU
Semi-major axis	1.4061 AU
Eccentricity	0.3361
Orbital period (sidereal)	1.67 yr (609 d)
Mean anomaly	332.79°
Mean motion	0° 35m 27.96s / day
Inclination	0.8572°
Longitude of ascending node	198.23°
Argument of perihelion	222.58°
Earth MOID	0.000149 AU (0.0580 LD)
Mars MOID	0.03 AU[4]
Physical characteristics
Dimensions	15 m × 8 m[5][6]
Mean diameter	7–13 m[7][8] 15 m[8]
Synodic rotation period	0.2038 h[9][a] 0.142 h[8] NPAR[8][9]
Geometric albedo	0.35±0.1[7] 0.30±0.01(radiometric)
Spectral type	E/Xe[7][6] S(assumed)[9] V–R =0.41±0.02[7]
Apparent magnitude	12.9–31[10]
Absolute magnitude (H)	26.7[2] 26.8[4][10]

2012 TC₄ is a tumbling micro-asteroid classified as a brightnear-Earth object of theApollo group, approximately 10 meters (30 feet) in diameter.^[6][7][8] It was first observed byPan-STARRS atHaleakala Observatory on the Hawaiian island ofMaui, in the United States. As of 1 October 2017, it had a small Earthminimum orbital intersection distance of 0.000149 AU (22,300 km).^[2] On 12 October 2017, it passed Earth at 0.00033524 AU (50,151 km).^[2] The asteroid was removed from theSentry Risk Table on 16 October 2017^[11] and with a 5-yearobservation arc has a well-known orbit.^[2] For example, on the previously risk-listed date of 12 October 2022,^[12] it is now known that the asteroid will be more than 3 AU (450 million km) from Earth.^[13]

Orbital modeling shows the asteroid nominally passed about 1 million km from Earth in October 1986, but the uncertainty region suggests it could have passed as close as 20 km.^[2]

Data from JPL 60 solution date 3 November 2017^[2]

2012 TC₄ was discovered on 4 October 2012 at apparent i-band magnitude 20.1 while the asteroid was 0.03 AU (4,500,000 km; 2,800,000 mi) from Earth.^[3] It came within 0.000634 AU (0.247 LD, 94,800 km, 58,900 mi) from Earth on 12 October 2012.^[2]

During the 2012 close approach, the asteroid only had anobservation arc of 7 days, between 4 and 11 October 2012, so the exact distance of the 2017 closest approach was poorly constrained. With the 7 day observation arc, the asteroid had a3-sigma chance of passing between 0.00008818 and 0.002896 AU (0.034 to 1.127 LD, 13,200–433,200 km, 8,200–269,200 mi) from Earth on 12 October 2017.^[15] Astronomers were certain that it would not pass closer than 6,800 km from the surface of Earth, ruling out any possibility that it could hit the Earth in 2017.^[16]

Orbit in yellow among inner solar system planets before 2017 flyby

Orbit of2012 TC₄ deflected by Earth's gravity. Earth is blue. For reference, a geosynchronous satellite and the Moon are included in this animation. The green path of2012 TC₄ turns darker as it dips below the ecliptic plane (click for animation).

Orbits from pre-2012 to post-2017 encounters. The orbit of2012 TC₄ has changed twice since 2012.

On 12 October 2017 at 5:42 UT, the asteroid passed 0.00033524 AU (50,151 km; 31,163 mi) from Earth.^[2] Observations between July and October reduced the uncertainty region from several hundred thousand kilometers^[15] to about ±140 meters.^[17][2] The asteroid was removed from theSentry Risk Table on 16 October 2017 using JPL solution #56.^[11] Prior to the encounter, it was rated −4.11 on thePalermo scale, with a 1 in 1,000 chance of impact over the next hundred years.^[12]

Paul Chodas ofNASA's Center for near-Earth Object Studies, andVishnu Reddy of the University of Arizona'sLunar and Planetary Laboratory, viewed the 2017 flyby (inside of the orbit of the Moon) as a way to test and refine the global asteroid detection and tracking network designed to give warning of objects heading toward Earth.^[16] Reddy coordinated the effort, involving over a dozen institutions worldwide.^[16][18][19] In addition to the observation campaign, NASA used this exercise to test communications between the many observers and also to test internal U.S. government messaging and communications up through the executive branch and across government agencies, as it would during an actual predicted impact emergency. Results of the campaign were published on 3 November 2017.^[5]

The asteroid remained too faint to be recovered with automatedastronomical surveys until early September,^[20] but a more targeted observation with theVery Large Telescope recovered it on 27 July 2017 atapparent magnitude 26.8, while the asteroid was 0.4 AU (60,000,000 km; 37,000,000 mi) from Earth, making it one of the dimmest asteroid recoveries ever. As such,2012 TC₄ has become the first known asteroid ever to be observed passing less than 1Lunar distance from Earth twice in a row.^[21] At the time of recovery the asteroid was about 100 million times fainter than what can be seen with thenaked eye^[22] and 500 times fainter than when it was discovered in 2012. As a result of the 2017 recovery observations, it was known that on 12 October 2017 at 5:42 UT, the asteroid would pass 0.0003352 AU (50,150 km; 31,160 mi) from Earth.^[2] Then at 19:19 UT, the asteroid would pass 0.001856 AU (277,700 km; 172,500 mi) from the Moon.^[2]2012 TC₄ peaked at about apparent magnitude 12.9,^[23] and was too faint to be seen without a telescope. The Earth approach of 2017 increased the asteroid's orbital period from 1.67 years to 2.06 years.^[24]

2012 TC₄ reached a maximum apparent magnitude of 12.9 just prior to its closest approach, soon after which it came too close to the Sun to be seen with telescopes.^[23] It was last observed on 14 December 2017 at an apparent magnitude of 25,^[4]

Size reference of2012 TC4, based on radar observations.

Studies of the asteroid'slight curve in October 2012, found it to have arotation period of 0.2038 hours (or 12 minutes and 14 seconds) with a brightness variation of 0.93magnitude (U=3-), which is indicative for a non-spherical shape.^[9][a]2012 TC₄ is afast rotator, which is rather typical for its small size. The fastest rotator currently known is2014 RC, a similarly sized NEO, with a period of only 16 seconds.Lightcurves obtained during the 2017 encounter confirmed that2012 TC₄ is in a non-principal axis rotation, commonly known astumbling.^[7][5] The spin axis varies on timescales of minutes, with a second period of 0.142 hours (or 8.5 minutes).^[8] The lightcurve amplitude suggests a ratio of largest to smallest axis of at least 2.3.^[7]

Radar images were taken fromGoldstone Observatory andGreen Bank Telescope on 12 October 2017. The delay-doppler images had a range resolution of 1.9 meters/pixel, the highest resolution ever obtained using Goldstone transmissions.^[6][1] The images showed that2012 TC₄ was a very elongated object about 50 feet (15 meters) long and roughly 25 feet (8 meters) wide.^[5] The high circular polarization ratio found for2012 TC₄ is consistent with results seen fromE- andV-type NEAs previously.^[6] Observations fromArecibo Observatory were planned, but had to be cancelled due to damage to the observatory as a result ofHurricane Maria.^[25]

The spectrum of2012 TC₄ is that of anE- orXe-type asteroid.^[7][6] E-type asteroids tend to have a high albedo (>0.30). This agrees with the albedo of 0.35 found for2012 TC₄.^[1] This type of asteroids is commonly found in theinner Main Belt.^[26]

2012 TC₄ is composed ofigneous material.^[5] The short rotation period of2012 TC₄ implies that it is not arubble pile but rather a monolithic object of non-negligible strength, which is typical for very small asteroids.^[7]

As a result of2012 TC₄'s frequent approaches to Earth, its orbit changes significantly over short periods of only decades. Its two observed close approaches and their effects are shown below:

Between 2012 and 2017,2012 TC₄'s average distance from the Sun increased by almost 0.4 AU, with the time it takes to orbit the sun increasing by 250 days. Its closest approach to the Sun also increased significantly, from 90% of the Earth's distance to the Sun to 97%, and its inclination lowered slightly, going from 1.4 degrees to less than 0.5 degrees relative to Earth's orbit.

As a result of non-gravitational forces such as theYarkovsky effect on small bodies, it is difficult to constrain its orbit more than a few decades into the past or future.

• List of asteroid close approaches to Earth
• List of asteroid close approaches to Earth in 2012
• List of asteroid close approaches to Earth in 2017
• NASAPlanetary Defense Coordination Office

• Interesting Asteroids Past Earth Close encounters —Sormano Astronomical Observatory
• Image and animation of 2012 TC4 – Virtual Telescope Project
• Asteroid 2012 TC4 On Track For Close Earth Flyby AstroBob 10/3/17
• Asteroid 2012 TC4: House-Sized Asteroid Almost Hits Earth (PHOTO, VIDEO) 13 October 2012
• 2012 TC4 orbit and observations,Minor Planet Center
• 2012 TC4 atNeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
• 2012 TC4 atESA–space situational awareness
  • Ephemerides · Observations · Orbit · Physical properties · Summary
• 2012 TC4 at theJPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• Apollo asteroids
• Minor planet object articles (unnumbered)
• Discoveries by Pan-STARRS
• Near-Earth objects removed from the Sentry Risk Table
• Fast rotating minor planets
• Near-Earth objects in 2012
• Near-Earth objects in 2017
• Astronomical objects discovered in 2012

• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from February 2018