 C/2019 Y4 (ATLAS) imaged on March 14, 2020 | |
| Discovery | |
|---|---|
| Discovered by | ATLAS–MLO |
| Discovery date | December 28, 2019 |
| Designations | |
| |
| A10j7UG | |
| Orbital characteristics[1] | |
| Epoch | March 7, 2020 (JD 2458915.5) |
| Observation arc | 115 days |
| Number of observations | 1250 |
| Aphelion | 660.9626±3.2491AU |
| Perihelion | 0.2528 AU |
| Semi-major axis | 330.6077±1.6252 AU |
| Eccentricity | 0.99924 |
| Orbital period | 6011.43±44.33yr |
| Inclination | 45.3839° |
| 120.5721° | |
| Argument of periapsis | 177.4084° |
| Last perihelion | 31 May 2020 |
| TJupiter | 0.454 |
| EarthMOID | 0.631177 AU (94,422,700 km) |
| JupiterMOID | 1.39373 AU |
| Physical characteristics[2][3] | |
| Dimensions | 0.4–1.0 km (0.25–0.62 mi) |
Mean diameter | 0.6 km (0.37 mi) |
| Comet total magnitude (M1) | 9.9±0.9 |
| Comet nuclear magnitude (M2) | 13.1±0.7 |
| 7.0 (2021 apparition) | |
C/2019 Y4 (ATLAS) was acomet with anear-parabolic orbit discovered by theATLAS survey on December 28, 2019.[4] Early predictions based on the brightening rate suggested that the comet could become as bright as magnitude 0 matching the brightness ofVega.[5] It received widespread media coverage due to its dramatic increase in brightness and orbit similar to theGreat Comet of 1844, but on 22 March 2020, the comet started disintegrating.[6][7] Such fragmentation events are very common forKreutz Sungrazers. The comet continues to fade and did not reach naked eye visibility.[5] By mid-May, comet ATLAS appeared very diffuse even in a telescope. C/2019 Y4 (ATLAS) has not been seen since 21 May 2020.[8]
C/2019 Y4 (ATLAS) was the brightest on March 30 when it had anapparent magnitude of about 7, but after disintegrating, it continued to fade, until it was last observed on May 21. It is located in the constellation Monoceros but is no longer visible. It reached its nearest point to Earth on May 23 and come toperihelion (closest to the Sun) on May 31.
In April 2020, astronomers reported, onThe Astronomer's Telegram, the possible disintegration of Comet ATLAS.[6][7][9] The comet has fragmented into at least 4 pieces.[10][11] NASA subsequently reported that the Hubble Space Telescope has identified that there could be as many as roughly "30 fragments on April 20, and 25 pieces on April 23."[12] The fragmentation may be the result of outgassing causing an increase in the centrifugal force of the comet.
TheSolar Orbiter flew through the ion tail of comet ATLAS between May 31 and June 1 and the dust tail on June 6.[13][14]
Comet ATLAS was discovered onCCD images taken on December 28, 2019, with a 0.5 m (20 in)reflecting telescope atopMauna Loa inHawaii.[15] The images were taken as part of theAsteroid Terrestrial-impact Last Alert System (ATLAS). At the time of its discovery, the comet shone atmagnitude 19.6 in the constellationUrsa Major as viewed from Earth.[16][17] Larry Denneau was the first to identify the object's cometary appearance,[16] placing the object on theMinor Planet Center's Possible Comet Confirmation Page, alerting other astronomers. Further observations over subsequent days identified acoma; acomet tail became increasingly apparent as observations continued.[15]
Between the beginning of February and near the end of March, Comet ATLAS brightened from magnitude 17 to magnitude 8, representing a 4000-fold increase in brightness.[18] In March 2020, the comet's brightness increased four magnitudes.[17] C/2019 Y4's green or aqua colour arose from emissions of diatomic carbon with a 1.2° or 10' or3.3 million km multicolour tail, more than twice as wide as the Sun. As a diffuse object, the comet would need to reach anapparent magnitude of around 3–4 to be obvious to the casual observer in a dark sky. A 4th magnitude comet in bright twilight is not very impressive nor obvious. In early April, the comet faded due to a significant fragmentation event.[19] On April 14, 2020, initial estimates of water production by the comet were reported, and found "a water production rate of 1.25×1028 +/− 5×1025 mol/sec within an aperture of 100,000 km".[20]
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At the time of its discovery Comet ATLAS was nearly 3 astronomical units (AU) from the Sun.[17] The first orbital calculations for the comet were published on theMinor Planet Electronic Circular, and were based on observations taken between December 28, 2019, and January 9, 2020, which indicating a 4,400-yearorbital period and aperihelion of 0.25 AU. Similarities were noted between the orbital elements of C/2019 Y4 and theGreat Comet of 1844 (C/1844 Y1), suggesting that C/2019 Y4 is a fragment of the same parent body, split about five thousands years ago.[21][22][15][23]
TheJPL Small-Body Database using anepoch of February 18, 2020, shows C/2019 Y4 (ATLAS) with an orbital period of approximately 6,000 years, but this solution includes misleadingperturbations while inside of the planetary region. A more useful barycentric solution before the comet entered the planetary region shows an inbound orbital period of about 4,800 years.[24] The comet reached its nearest point to the Sun on May 31, 2020.[2] After leaving the planetary region, the comet will have an outbound orbital period of about 5,200 years.
The fragmentation of C/2019 Y4 in late March 2020,[22] has changed the velocities of the fragments by up to 10 meters/second (25000 km/month). This small change in velocity can cause a big change in the long-term orbital period of these near-parabolic fragments. The short observation arc of ~10 days for fragments D&E results in large uncertainties in the orbital periods. Fragment B was observed the longest. Fragment D may have come the closest to Earth but due to the short observation arc has an uncertainty of ±2 million km in the close approach distance.[25]
| Fragment | Orbital period (years) | Closest Approach to Earth | obs arc (days) |
|---|---|---|---|
| C/2019 Y4-A | ejection[26] | 0.7858 AU (117.55 million km) | 27 |
| C/2019 Y4-B | 17200±2300[27] | 0.7816 AU (116.93 million km) | 40 |
| C/2019 Y4-C | ejection[28] | 0.7824 AU (117.05 million km) | 26 |
| C/2019 Y4-D | 126±86[29] | 0.7777 AU (116.34 million km) | 8 |
| C/2019 Y4-E | 88±32[30] | 0.7794 AU (116.60 million km) | 6 |
During January to March 2020, the comet was located in the constellation ofUrsa Major. Throughout the month of April, the comet was in the constellation ofCamelopardalis. On May 12 it moved intoPerseus. It was 0.78 AU (117 million km; 300 LD) from Earth on May 23 during anew moon when the comet was 17 degrees from the Sun. At itsperihelion on May 31, it was in theTaurus constellation 12 degrees from the Sun.[31] Then, through June and July, it passed throughOrion andMonoceros.
2020 in space | ||
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| Impact events | ||
| Selected NEOs | ||
| Exoplanets |
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| Discoveries |
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| Comets | ||
| Space exploration |
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