 WT1190F entering the atmosphere over Sri Lanka, viewed by the airborne observation team | |
| Discovery | |
|---|---|
| Discovered by |
|
| Discovery date |
|
| Designations | |
| |
| Distant artificial satellite (before Jun 2009 to 13 November 2015) | |
| Orbital characteristics[1] | |
| Epoch 3 October 2015 (JD 2457298.5) | |
| Periapsis | 21,222 km (13,187 mi) (0.055 LD; 3.33 ER) |
| Apoapsis | 655,374 km (407,231 mi) (1.704 LD, 102.75 ER) |
| 338,298 km (210,209 mi) (0.880 LD, 53.04 ER) | |
| Eccentricity | 0.937269 |
| 22.66 days | |
Averageorbital speed | 1.1 km/s @ 0.00226 AU |
| 6.191° | |
| Inclination | 3.197° |
| 311.556° | |
| 2 October 2015 14:39:00UT | |
| 314.044° | |
| Satellite of | Earth |
| Physical characteristics | |
| Dimensions | 0.7 to 2 meters (2 to 7 ft) |
| Mass | 250 to 2,000 kilograms (550 to 4,400 lb) |
Meandensity | ~0.10 g/cm3[2] |
| 0.75 seconds[3] | |
| Albedo | >0.1 |
| ~16–23 | |
| 31.3 | |
WT1190F (9U01FF6,UDA34A3, orUW8551D) was a small temporarysatellite of Earth that impacted Earth on 13 November 2015 at 06:18:21.7 (± 0.1 seconds)UTC.[4]: 7–8 It is thought to have beenspace debris from thetrans-lunar injection stage of the 1998Lunar Prospector mission.[5][6] It was first discovered on 18 February 2013 by theCatalina Sky Survey.[2][7] It was then lost, and reacquired on 29 November 2013. It was again discovered on 3 October 2015 by astronomer Rose Garcia with the Catalina Sky Survey 60-inch telescope, and the object was soon identified to be the same as the two objects previously sighted by the team, who have been sharing their data through theInternational Astronomical Union'sMinor Planet Center (MPC).[8] An early orbit calculation showed that it was orbiting Earth in an extremely elliptical orbit, taking it from within thegeosynchronous satellite ring to nearly twice the distance of the Moon.[1] It was also probably the same object as 9U01FF6, another object on a similar orbit discovered on 26 October 2009.
WT1190F had been orbiting Earth as a temporary satellite (namedUWAIS) since mid-2009, if not longer. While it has not been positively identified with any known artificial satellites, its estimated density of 0.1 g/cm3 was much lower than would be expected of a natural object as even water has a density of 1 g/cm3. Hence,European Space Agency astronomers have concluded that the object was likely a fuel tank of some sort.[2][7]
After more observations, astronomers determined that the object would impact Earth on 13 November 2015 at 06:18 UTC (11:48 local time),[9] south ofSri Lanka.[2][7] Due to its small size, it was expected that most or all of the object would burn up in the atmosphere before impacting, but would be visible as a bright daytimefireball if the sky was not badlyovercast.[2][7]
A ground-based observational campaign was organized as a possible test for future collision events involving also natural bodies.[10]
WT1190F was first discovered by theMount Lemmon Survey, a participant in theCatalina Sky SurveyNear-Earth Object surveying program.[11] The object was identified with anapparent magnitude 19.5 on 18 February 2013, and given the temporary designation UDA34A3, but was lost soon after, with anobservation arc of only 5 hours.[12] However, it was again seen by the same survey on 29 November 2013 and given the designation UW8551D and lost again, only being observed for 1 hour 35 minutes.[12]
Most recently, it was recovered on 3 October 2015 and given the designation WT1190F. Its orbit was soon calculated and found to be orbiting Earth, but not with the orbit of any known artificial satellite. The object's orbit was soon connected, allowing more observations to be made, and severalprecovery observations have been found of the object, dating back to June 2009.[13]
The type of orbit that WT1190F had was not stable long-term. An object in this type of orbit was likely to impact into Earth or the Moon, or acquire enoughorbital speed to be ejected into orbit around the Sun.[14] It was not likely that it had been orbiting Earth for decades.[14] In 2011 the orbit had aneccentricity of 0.33 andperigee (closest approach to Earth) of 248,000 km (154,000 mi).[13] It passed about 22,000 km (14,000 mi) from the Moon on 24 May 2012.[15] By 2013 the eccentricity had increased to 0.70 and the perigee decreased to 105,000 km (65,000 mi).[12]
| Epoch | Eccentricity | Inclination | Perigee (km) | Apogee (km) |
|---|---|---|---|---|
| 2011[13] | 0.33 | 59 | 248383 | 495045 |
| 2013[12] | 0.70 | 78 | 105639 | 598686 |
| 2015[1] | 0.94 | 3 | 21221 | 655374 |
During WT1190F's orbit, it changed significantly in brightness, from anapparent magnitude 16 atperigee, to magnitude 23 atapogee. It spent most of its time dimmer than magnitude 20.[1] This, combined withsolar pressure acceleration, theYarkovsky effect, and frequent orbital perturbations by the Moon, made it difficult to precisely predict its orbit and location. About one hour before atmospheric entry, the object had a R magnitude of 13.6,[16][a] roughly the brightness ofPluto.
WT1190F madeatmospheric entry at 11 kilometers per second (25,000 miles per hour).[17] Whatever was left from the re-entry was calculated to have fallen into the ocean about 100 kilometres (62 mi) fromGalle,Sri Lanka.[8] The closest approach to Galle occurred during atmospheric flight when the object had an altitude of 45 km and a distance of 51 km.[18] For observers inColombo, Sri Lanka, the object started out[clarification needed] 30 degrees above the horizon coming in from slightly south of due west.[19] Its mass was not sufficient to cause any risk to the area, but the event still produced a bright fireball. Scientists wanted to study WT1190F to better understand the trajectory and atmospheric entry of satellites, debris, and small asteroids from translunar orbit.[20][8] The International Astronomical Center (IAC) and theUnited Arab Emirates Space Agency utilized aGulfstream 450 jet to study the re-entry from above the clouds and haze.[20] The airborne observation team successfully captured the re-entry on video.[9][21]
| Date | vmag | Distance (km) | Velocity wrt Earth (km/s)[23] |
|---|---|---|---|
| 05 | 20.8 | 602399 | 0.2 |
| 08 | 20.5 | 524608 | 0.5 |
| 10 | 20.0 | 420800 | 0.8 |
| 11 | 19.6 | 345999 | 1.0 |
| 12 | 19.0 | 246196 | 1.4 |
| 13 | 17.1 | 89914 | 2.8 |
| Impact | ~ –6[24] | 0 | 11.3 |
The International Astronomical Center (IAC) and theUnited Arab Emirates Space Agency observed WT1190F as it fell towards the Earth. The IAC chartered aGulfstream 450 jet to bring researchers such asPeter Jenniskens to the area of WT1190F's impact, at a high altitude, to view the event over clouds or haze.[20] The Next TC3 Consortium Asteroid Detection and Early Warning team narrowed the atmospheric entry time to ± 1.3 seconds.[9]
Observers on the ground could not see the fireball because of rain, but the plane was able to find an opening in the clouds. The fireball was a brightnaked eye object.Spectroscopic data was acquired to determine what the object was made of,[9] and the results published.[4]: 9
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