Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. [1] That is, they show a coma, tail, or other visual evidence of mass-loss (like a comet), but their orbits remain within Jupiter's orbit (like an asteroid). [2] [3] These bodies were originally designated main-belt comets (MBCs) in 2006 by astronomers David Jewitt and Henry Hsieh, but this name implies they are necessarily icy in composition like a comet and that they only exist within the main-belt, whereas the growing population of active asteroids shows that this is not always the case. [2] [4] [5]
The first active asteroid discovered is 7968 Elst–Pizarro. It was discovered (as an asteroid) in 1979 but then was found to have a tail by Eric Elst and Guido Pizarro in 1996 and given the cometary designation 133P/Elst-Pizarro. [2] [6]
Unlike comets, which spend most of their orbit at Jupiter-like or greater distances from the Sun, active asteroids follow orbits within the orbit of Jupiter that are often indistinguishable from the orbits of standard asteroids. Jewitt defines active asteroids as those bodies that, in addition to having visual evidence of mass loss, have an orbit with: [3]
Jewitt chooses 3.08 as the Tisserand parameter to separate asteroids and comets instead of 3.0 (the Tisserand parameter of Jupiter itself) to avoid ambiguous cases caused by the real Solar System deviating from an idealized restricted three-body problem. [3]
The first three identified active asteroids all orbit within the outer part of the asteroid belt. [7]
Some active asteroids display a cometary dust tail only for a part of their orbit near perihelion. This strongly suggests that volatiles at their surfaces are sublimating, driving off the dust. [10] Activity in 133P/Elst–Pizarro is recurrent, having been observed at each of the last three perihelia. [2] The activity persists for a month or several [7] out of each 5-6 year orbit, and is presumably due to ice being uncovered by minor impacts in the last 100 to 1000 years. [7] These impacts are suspected to excavate these subsurface pockets of volatile material helping to expose them to solar radiation. [7]
When discovered in January 2010, P/2010 A2 (LINEAR) was initially given a cometary designation and thought to be showing comet-like sublimation, [11] but P/2010 A2 is now thought to be the remnant of an asteroid-on-asteroid impact. [12] [13] Observations of 596 Scheila indicated that large amounts of dust were kicked up by the impact of another asteroid of approximately 35 meters in diameter.
P/2013 R3 (Catalina–PanSTARRS) was discovered independently by two observers by Richard E. Hill using the Catalina Sky Survey's 0.68-m Schmidt telescope and by Bryce T. Bolin using the 1.8-m Pan-STARRS1 telescope on Haleakala. [14] The discovery images taken by Pan-STARRS1 showed the appearance of two distinct sources within 3" of each other combined with a tail enveloping both sources. In October 2013, follow-up observations of P/2013 R3, taken with the 10.4 m Gran Telescopio Canarias on the island of La Palma, showed that this comet was breaking apart. [15] Inspection of the stacked CCD images obtained on October 11 and 12 showed that the main-belt comet presented a central bright condensation that was accompanied on its movement by three more fragments, A, B, C. The brightest A fragment was also detected at the reported position in CCD images obtained at the 1.52 m telescope of the Sierra Nevada Observatory in Granada on October 12. [15]
NASA reported on a series of images taken by the Hubble Space Telescope between October 29, 2013, and January 14, 2014, that show the increasing separation of the four main bodies. [16] The Yarkovsky–O'Keefe–Radzievskii–Paddack effect, caused by sunlight, increased the spin rate until the centrifugal force caused the rubble pile to separate. [16]
By smashing into the asteroid moon of the binary asteroid 65803 Didymos, NASA's Double Asteroid Redirection Test spacecraft made Dimorphos an active asteroid. Scientists had proposed that some active asteroids are the result of impact events, but no one had ever observed the activation of an asteroid. The DART mission activated Dimorphos under precisely known and carefully observed impact conditions, enabling the detailed study of the formation of an active asteroid for the first time. [17] [18] Observations show that Dimorphos lost approximately 1 million kilograms after the collision. [19] Impact produced a dust plume that temporarily brightened the Didymos system and developed a 10,000-kilometer (6,200 mi)-long dust tail that persisted for several months. [20] [21] [22] The DART impact is predicted to have caused global resurfacing and deformation of Dimorphos's shape, leaving an impact crater several tens of meters in diameter. [23] [24] [25] The impact has likely sent Dimorphos into a chaotically tumbling rotation that will subject the moon to irregular tidal forces by Didymos before it will eventually return to a tidally locked state within several decades. [26] [27] [28]
Some active asteroids show signs that they are icy in composition like a traditional comet, while others are known to be rocky like an asteroid. It has been hypothesized that main-belt comets may have been the source of Earth's water, because the deuterium–hydrogen ratio of Earth's oceans is too low for classical comets to have been the principal source. [29] European scientists have proposed a sample-return mission from a MBC called Caroline to analyse the content of volatiles and collect dust samples. [10]
Identified members of this morphology class (TJup>3.08) include: [30] : 17
Name | Semi-major axis (AU) | Perihelion (AU) | Eccentricity | TJup | Orbital class | Diameter (km) | Rotation period (hr) | Cause | Activity discovery year | Recurrent? |
---|---|---|---|---|---|---|---|---|---|---|
1 Ceres | 2.766 | 2.550 | 0.078 | 3.310 | main-belt (middle) | 939.4 | 9.07 | Water sublimation [3] | 2014 | |
493 Griseldis | 3.116 | 2.568 | 0.176 | 3.140 | main-belt (outer) | 41.56 | 51.94 | Impact [31] | 2015 | ✗ |
596 Scheila | 2.929 | 2.45 | 0.163 | 3.209 | main-belt (outer) | 159.72 | 15.85 | Impact [32] [33] [34] | 2011 | ✗ |
2201 Oljato | 2.174 | 0.624 | 0.713 | 3.299 | NEO (Apollo) | 1.8 | >26 | Sublimation [35] | 1984 | ✗ |
3200 Phaethon | 1.271 | 0.140 | 0.890 | 4.510 | NEO (Apollo) | 6.26 | 3.60 | Thermal fracturing, dehydration cracking, and/or rotational disintegration [36] | 2010 | ✓ |
6478 Gault | 2.305 | 1.860 | 0.193 | 3.461 | main-belt (inner) | 5.6 | 2.49 | Rotational disintegration [37] [38] [39] | 2019 | ✓ |
(62412) 2000 SY178 | 3.159 | 2.909 | 0.079 | 3.197 | main-belt (outer) | 10.38 | 3.33 | Rotational disintegration [40] | 2014 | ✗ |
65803 Didymos/Dimorphos | 1.643 | 1.013 | 0.383 | 4.204 | NEO (Apollo) | 0.77 / 0.15 | 2.26 | Human-caused impact | 2022 | ✗ |
101955 Bennu | 1.126 | 0.896 | 0.204 | 5.525 | NEO (Apollo) | 0.48 | 4.29 | (unknown) [30] : 22 Electrostatic lofting, impacts, thermal fracturing, or dehydration cracking | 2019 | ✓ |
(588045) 2007 FZ18 | 3.176 | 2.783 | 0.124 | 3.188 | main-belt (outer) | 2023 | ||||
2002 CW116 | 2.690 | 2.068 | 0.231 | 3.319 | main-belt (middle) | 0.5 | 2024 | |||
2008 BJ22 | 3.071 | 2.943 | 0.042 | 3.199 | main-belt (outer) | <0.4 | 2022 | ✗ | ||
2010 LH15 | 2.744 | 1.770 | 0.355 | 3.230 | main-belt (middle) | 1.483 | 2023 | ✓ | ||
2015 BC566 | 3.062 | 2.957 | 0.034 | 3.201 | main-belt (outer) | 2023 | ✗ | |||
2015 FW412 | 2.765 | 2.319 | 0.161 | 3.280 | main-belt (middle) | 2023 | ||||
2015 VA108 | 3.128 | 2.451 | 0.217 | 3.160 | main-belt (outer) | 2023 | ||||
2023 JN16 | 2.696 | 2.300 | 0.147 | 3.351 | main-belt (middle) | 2023 | ||||
107P/4015 Wilson–Harrington | 2.625 | 0.966 | 0.632 | 3.082 | NEO (Apollo) | 6.92 | 7.15 | Sublimation [41] [42] | 1949 | ✗ |
133P/7968 Elst–Pizarro | 3.165 | 2.668 | 0.157 | 3.184 | main-belt (outer) | 3.8 | 3.47 | Sublimation/rotational disintegration [43] [44] | 1996 | ✓ |
176P/118401 LINEAR | 3.194 | 2.578 | 0.193 | 3.167 | main-belt (outer) | 4.0 | 22.23 | Sublimation [45] | 2005 | ✗ |
233P/La Sagra (P/2009 WJ50) | 3.033 | 1.786 | 0.411 | 3.081 | main-belt (outer) | 3.0 | 2010 | ✗ | ||
238P/Read (P/2005 U1) | 3.162 | 2.362 | 0.253 | 3.153 | main-belt (outer) | 0.8 | Sublimation [46] | 2005 | ✓ | |
259P/Garradd (P/2008 R1) | 2.727 | 1.794 | 0.342 | 3.217 | main-belt (middle) | 0.60 | Sublimation [47] | 2008 | ✓ | |
288P/(300163) 2006 VW139 | 3.051 | 2.438 | 0.201 | 3.203 | main-belt (outer) | 1.8 / 1.2 | Sublimation [48] | 2011 | ✓ | |
311P/PanSTARRS (P/2013 P5) | 2.189 | 1.935 | 0.116 | 3.660 | main-belt (inner) | 0.4 | >5.4 | Rotational disintegration [49] [50] [51] | 2013 | ✓ |
313P/Gibbs (P/2003 S10) | 3.154 | 2.391 | 0.242 | 3.133 | main-belt (outer) | 2.0 | Sublimation [52] | 2003 | ✓ | |
324P/La Sagra (P/2010 R2) | 3.098 | 2.621 | 0.154 | 3.099 | main-belt (outer) | 1.1 | Sublimation [53] | 2010 | ✓ | |
331P/Gibbs (P/2012 F5) | 3.005 | 2.879 | 0.042 | 3.228 | main-belt (outer) | 3.54 | 3.24 | Rotational disintegration [54] [55] | 2012 | ✗ |
354P/LINEAR (P/2010 A2) | 2.290 | 2.004 | 0.125 | 3.583 | main-belt (inner) | 0.12 | 11.36 | Impact [56] | 2010 | ✗ |
358P/PanSTARRS (P/2012 T1) | 3.155 | 2.410 | 0.236 | 3.134 | main-belt (outer) | 0.64 | Sublimation [57] | 2012 | ✗ | |
426P/PanSTARRS (P/2019 A7) | 3.188 | 2.675 | 0.161 | 3.103 | main-belt (outer) | 2.4 | 2019 | ✗ | ||
427P/ATLAS (P/2017 S5) | 3.171 | 2.178 | 0.313 | 3.092 | main-belt (outer) | 0.90 | 1.4 | Sublimation/rotational disintegration [58] | 2017 | ✗ |
432P/PanSTARRS (P/2021 N4) | 3.045 | 2.302 | 0.244 | 3.170 | main-belt (outer) | <1.4 | 2021 | ✗ | ||
433P/(248370) 2005 QN173 | 3.067 | 2.374 | 0.226 | 3.192 | main-belt (outer) | 3.2 | Sublimation/rotational disintegration | 2021 | ✓ | |
435P/PanSTARRS (P/2021 T3) | 3.018 | 2.056 | 0.319 | 3.090 | main-belt (outer) | 2021 | ✗ | |||
455P/PanSTARRS (P/2021 S9) | 3.156 | 2.193 | 0.305 | 3.087 | main-belt (outer) | <1.6 | 2017 | ✗ | ||
456P/PanSTARRS (P/2021 L4) | 3.165 | 2.788 | 0.119 | 3.125 | main-belt (outer) | <4.4 | 2021 | ✗ | ||
457P/2020 O1 (Lemmon–PanSTARRS) | 2.647 | 2.329 | 0.120 | 3.376 | main-belt (middle) | 0.84 | 1.67 | Sublimation/rotational disintegration [59] | 2020 | ✓ |
P/2013 R3 (Catalina–PanSTARRS) | 3.033 | 2.205 | 0.273 | 3.184 | main-belt (outer) | ~0.4 | Sublimation/rotational disintegration [60] | 2013 | ✗ | |
P/2015 X6 (PanSTARRS) | 2.755 | 2.287 | 0.170 | 3.318 | main-belt (middle) | <1.4 | Sublimation [61] | 2015 | ✗ | |
P/2016 G1 (PanSTARRS) | 2.583 | 2.041 | 0.210 | 3.367 | main-belt (middle) | <0.8 | Impact [62] | 2016 | ✗ | |
P/2016 J1-A/B (PanSTARRS) | 3.172 | 2.449 | 0.228 | 3.113 | main-belt (outer) | <1.8 / <0.8 | Sublimation [63] | 2016 | ✓ | |
P/2018 P3 (PanSTARRS) | 3.007 | 1.756 | 0.416 | 3.096 | main-belt (outer) | <1.2 | Sublimation | 2018 | ✓ | |
P/2019 A3 (PanSTARRS) | 3.147 | 2.313 | 0.265 | 3.099 | main-belt (outer) | <0.8 | 2019 | ✗ | ||
P/2019 A4 (PanSTARRS) | 2.614 | 2.379 | 0.090 | 3.365 | main-belt (middle) | 0.34 | 2019 | ✗ | ||
P/2021 A5 (PanSTARRS) | 3.047 | 2.620 | 0.140 | 3.147 | main-belt (outer) | 0.30 | Sublimation | 2021 | ✗ | |
P/2021 R8 (Sheppard) | 3.019 | 2.131 | 0.294 | 3.179 | main-belt (outer) | 2021 | ✗ | |||
P/2022 R5 (PanSTARRS) | 3.071 | 2.470 | 0.196 | 3.148 | main-belt (outer) | 2022 | ||||
P/2023 S4 (Hogan) | 3.134 | 2.542 | 0.189 | 3.185 | main-belt (outer) | 2023 | ||||
P/2024 L4 (Rankin) | 2.231 | 0.672 | 0.699 | 3.255 | NEO (apollo) | <0.4 | Rotational disintegration? | 2024 |
Castalia is a proposed mission concept for a robotic spacecraft to explore 133P/Elst–Pizarro and make the first in situ measurements of water in the asteroid belt, and thus, help solve the mystery of the origin of Earth's water. [64] The lead is Colin Snodgrass, from The Open University in the UK. Castalia was proposed in 2015 and 2016 to the European Space Agency within the Cosmic Vision programme missions M4 and M5, but it was not selected. The team continues to mature the mission concept and science objectives. [64] Because of the construction time required and orbital dynamics, a launch date of October 2028 was proposed. [64]
On January 6, 2019, the OSIRIS-REx mission first observed episodes of particle ejection from 101955 Bennu shortly after entering orbit around the near-Earth asteroid, leading it to be newly classified as an active asteroid and marking the first time that asteroid activity had been observed up close by a spacecraft. It has since observed at least 10 other such events. [4] The scale of these observed mass loss events is much smaller than those previously observed at other active asteroids by telescopes, indicating that there is a continuum of mass loss event magnitudes at active asteroids. [65]
Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets, and is the prototype of active asteroids. Its orbit keeps it within the asteroid belt, yet it displayed a dust tail like a comet while near perihelion in 1996, 2001, and 2007.
3200 Phaethon, provisionally designated 1983 TB, is an active Apollo asteroid with an orbit that brings it closer to the Sun than any other named asteroid. For this reason, it was named after the Greek myth of Phaëthon, son of the sun god Helios. It is 5.8 km (3.6 mi) in diameter and is the parent body of the Geminids meteor shower of mid-December. With an observation arc of 35+ years, it has a very well determined orbit. The 2017 Earth approach distance of about 10 million km was known with an accuracy of ±700 m.
276 Adelheid is a dark Alauda asteroid from the outer region of the asteroid belt, approximately 121 kilometers in diameter. It was discovered by Austrian astronomer Johann Palisa at Vienna Observatory on 17 April 1888. The meaning of the asteroids's name is unknown.
596 Scheila is a main-belt asteroid and main-belt comet orbiting the Sun. It was discovered on 21 February 1906 by August Kopff from Heidelberg. Kopff named the asteroid after a female English student with whom he was acquainted.
Gaussia, provisional designation 1923 OA, is a dark background asteroid from the outer regions of the asteroid belt, approximately 73 kilometers in diameter. It was discovered on 8 August 1923, by Soviet astronomer Sergey Belyavsky at the Simeiz Observatory on the Crimean peninsula. The asteroid was named after German mathematician Carl Friedrich Gauss. Gauss computed the orbit of Ceres, and 1001 Gaussia was named along with 1000 Piazzia, and 1002 Olbersia in part for their work on Ceres, with names for Giuseppe Piazzi, who found Ceres, and Heinrich Wilhelm Matthias Olbers, who recovered it later that year.
Arago, provisional designation 1923 OT, is a dark asteroid from the outer regions of the asteroid belt, approximately 55 kilometers in diameter. It was discovered on 5 September 1923, by Russian astronomer Sergey Belyavsky at the Simeiz Observatory on the Crimean peninsula. The asteroid was named after French mathematician François Arago.
1159 Granada, provisional designation 1929 RD, is a dark background asteroid and relatively slow rotator from the inner regions of the asteroid belt, approximately 30 kilometers in diameter. It was discovered on 2 September 1929, by astronomer Karl Reinmuth at the Heidelberg Observatory in southwest Germany. The asteroid was named for the Spanish city and province of Granada.
2906 Caltech, provisional designation 1983 AE2, is an asteroid from the outer region of the asteroid belt, approximately 56 kilometers in diameter. It was discovered on 13 January 1983 by American astronomer Carolyn Shoemaker at Palomar Observatory in the United States. It is named after the California Institute of Technology.
2637 Bobrovnikoff, provisional designation A919 SB, is a background asteroid from the inner regions of the asteroid belt, approximately 6 kilometers in diameter. It was discovered on 22 September 1919, by German astronomer Karl Reinmuth at the Heidelberg-Königstuhl State Observatory in Heidelberg, Germany. The presumed spherical S-type asteroid has a rotation period of 4.79 hours. It is named after astronomer Nicholas Bobrovnikoff, who was the director of the Perkins Observatory in Ohio, United States.
1337 Gerarda, provisional designation 1934 RA1, is a dark background asteroid from the outer regions of the asteroid belt, approximately 40 kilometers in diameter. It was discovered on 9 September 1934, by Dutch astronomer Hendrik van Gent at the Union Observatory in Johannesburg, South Africa. The asteroid was named after Gerarda Prins, the wife of an orbit computer at Leiden Observatory.
1650 Heckmann, provisional designation 1937 TG, is a rare-type Nysian asteroid from the inner regions of the asteroid belt, approximately 29 kilometers in diameter. It was discovered on 11 October 1937, by German astronomer Karl Reinmuth at Heidelberg Observatory in southern Germany, and later named after astronomer Otto Heckmann.
1582 Martir, provisional designation 1950 LY, is a carbonaceous background asteroid from the outer regions of the asteroid belt, approximately 37 kilometers in diameter. It was discovered on 15 June 1950, by Argentine astronomer Miguel Itzigsohn at the La Plata Astronomical Observatory in Argentina. The asteroid was named after the First Lady of Argentina, Eva Perón.
1525 Savonlinna, provisional designation 1939 SC, is an asteroid from the central region of the asteroid belt, approximately 12 kilometers in diameter. It was discovered on 18 September 1939, by Finnish astronomer Yrjö Väisälä at the Turku Observatory in southwestern Finland. It was later named after the eastern Finnish town Savonlinna.
1648 Shajna, provisional designation 1935 RF, is a stony asteroid from the inner regions of the asteroid belt, approximately 9 kilometers in diameter. It was discovered on 5 September 1935, by Russian astronomer Pelageya Shajn at Simeiz Observatory on the Crimean peninsula. Two weeks later, it was independently discovered by Cyril Jackson at Johannesburg Observatory, South Africa. It was later named after the discoverer and her husband, Russian astronomers Grigory Shajn.
1263 Varsavia, provisional designation 1933 FF, is an asteroid from the central region of the asteroid belt, approximately 40 kilometers in diameter. It was discovered on 23 March 1933, by Belgian astronomer Sylvain Arend at Uccle Observatory in Belgium. It is named for the city of Warsaw.
354P/LINEAR, provisionally designated P/2010 A2 (LINEAR), is a small main-belt asteroid that was impacted by another asteroid sometime before 2010. It was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) at Socorro, New Mexico on 6 January 2010. The asteroid possesses a dusty, X-shaped, comet-like debris trail that has remained nearly a decade since impact. This was the first time a small-body collision had been observed; since then, minor planet 596 Scheila has also been seen to undergo a collision, in late 2010. The tail is created by millimeter-sized particles being pushed back by solar radiation pressure.
The five-planet Nice model is a numerical model of the early Solar System that is a revised variation of the Nice model. It begins with five giant planets, the four that exist today plus an additional ice giant between Saturn and Uranus in a chain of mean-motion resonances.
324P/La Sagra is an active asteroid with an orbital period of 5.44 years. It has been found to be active in more than one perihelia, indicating that the source of activity is sublimation.
P/2013 R3 (Catalina–PanSTARRS) was an active main-belt asteroid that disintegrated from 2013 to 2014 due to the centrifugal breakup of its rapidly-rotating nucleus. It was discovered by astronomers of the Catalina and Pan-STARRS sky surveys on 15 September 2013. The disintegration of this asteroid ejected numerous fragments and dusty debris into space, which temporarily gave it a diffuse, comet-like appearance with a dust tail blown back by solar radiation pressure. Observations by ground-based telescopes in October 2013 revealed that P/2013 R3 had broken up into four major components, with later Hubble Space Telescope observations showing that these components have further broken up into at least thirteen smaller fragments ranging 100–400 meters (330–1,310 ft) in diameter. P/2013 R3 was never seen again after February 2014.
483P/PanSTARRS is a pair of active main-belt asteroids that split apart from each other in early 2010. The brightest and largest component of the pair, P/2016 J1-A, was discovered first by the Pan-STARRS 1 survey at Haleakalā Observatory on 5 May 2016. Follow-up observations by the Canada-France-Hawaii Telescope at Mauna Kea Observatory discovered the second component, P/2016 J1-B, on 6 May 2016. Both asteroids are smaller than 1 kilometre (0.62 mi) in diameter, with P/2016 J1-A being roughly 0.6 km (0.37 mi) in diameter and P/2016 J1-B being roughly 0.3 km (0.19 mi) in diameter. The two components recurrently exhibit cometary activity as they approach the Sun near perihelion, suggesting that their activity is driven by sublimation of volatile compounds such as water.