 Orbital diagram ofKridsadaporn | |
| Discovery[1] | |
|---|---|
| Discovered by | R. H. McNaught |
| Discovery site | Siding Spring Obs. |
| Discovery date | 31 August 1995 |
| Designations | |
| (7604) Kridsadaporn | |
Named after | Kridsadaporn Ritsmitchai[1] (Thai astronomer) |
| 1995 QY2 · 1984 QD1 1991 CF3 | |
| Mars-crosser[1][2] unusual[3] · ACO[4][5] | |
| Orbital characteristics[2] | |
| Epoch 27 April 2019 (JD 2458600.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 33.89yr (12,379 d) |
| Aphelion | 4.8989AU |
| Perihelion | 1.3266 AU |
| 3.1127 AU | |
| Eccentricity | 0.5738 |
| 5.49 yr (2,006 d) | |
| 85.061° | |
| 0° 10m 46.2s / day | |
| Inclination | 20.449° |
| 147.24° | |
| 266.26° | |
| Earth MOID | 0.522 AU (203LD) |
| TJupiter | 2.8590 |
| Physical characteristics | |
| 12 km(est. at0.057)[6] | |
| SMASS =C[2][7] | |
| 13.3[1][2] | |
7604 Kridsadaporn, provisional designation1995 QY2, is an unusual, carbonaceousasteroid andMars-crosser on a highly eccentric orbit from the outer regions of theasteroid belt, approximately 12 kilometers (7.5 miles) in diameter. It was discovered on 31 August 1995, by Australian astronomerRobert McNaught atSiding Spring Observatory near Coonabarabran, Australia. Due to its particular orbit, theC-type asteroid belongs toMPC's list of "other"unusual objects,[3] and has been classified as an "asteroid in cometary orbit", or ACO.[4][5] The asteroid was named in memory of Thai astronomerKridsadaporn Ritsmitchai.[1]
Kridsadaporn was discovered using the0.5-m Uppsala Schmidt Telescope, as part of theSiding Spring Survey, which itself is part of a broader network ofNear-Earth object search programs. The then-unnamed asteroid was initially assigned theprovisional designation1995 QY2. In April 2005 it was renamed by its discoverer (Robert McNaught) in honour of Kridsadaporn Ritsmitchai, a then recently deceased friend and colleague at the Research School of Astronomy and Astrophysics at theAustralian National University, who worked and resided at Siding Spring Observatory. The officialnaming citation was published by theMinor Planet Center on 7 April 2005 (M.P.C. 53953).[8]
An approximation known as theTisserand criteria (T) is applied to cometary encounters with planets (such asJupiter) and used to describe their orbital inter-relationship.[9] Asteroidal-appearing bodies in elliptical orbits withJovianTisserand parametersTj < 3 only began to appear in search programs in the mid-1980s –Kridsadaporn's Jovian Tisserand parameter isTj = 2.858.[2] Before this, the failure to identify these objects was used as an argument against the existence of extinctcometary nuclei. Over the past two decades, an increasing number of asteroids, based upon their orbital and physical characteristics, have been suggested asextinct or dormant comets candidates. It is now considered likely that within the asteroid population there exist a significant number of dormant or extinct comets.[10]
More recently,Kridsadaporn has received closer attention after having been included in a number of studies relating to the analysis ofspectral properties of asteroids in cometary orbits (ACOs);[5][11] and, collisional activation processes, and the dynamic and physical properties of ACOs.[4][12] The investigation of ACOs is considered important in the understanding of formation processes of cometary dust mantles and the end states of comets, so as to determine the population ofJupiter-family comets, and, to also understand the dynamical processes involved in the transport mechanism of asteroids from typical asteroidal orbits to cometary-like ones.[5]
In earlier studies, ACOs have sometimes been referred to as cometary asteroids orcomet-asteroid transition objects.[12]
Kridsadaporn orbits the Sun at a distance of 1.3–4.9 AU once every 5 years and 6 months (2,006 days;semi-major axis of 3.11 AU). Its orbit has a higheccentricity of 0.57 and aninclination of 20° with respect to theecliptic.[2] Its elliptical orbit has similar orbital characteristics to those of theJupiter-family comets which populate the Jovian Tisserand invariant range between 2 and 3, which supports the scenario that a significant number of asteroids in cometary orbits areextinct or dormant cometary candidates.[4]
Kridsadaporn is amongst another group of bodies [Mars-crossing (MC) and/or near-Earth object (NEO) populations] that may have originated from themain asteroid belt as fragments injected into amean-motion resonance orsecular resonance, developing increasingly higher orbital eccentricity over time resulting in theperihelion distance becoming smaller than theaphelion distances of theinner planets. At their birth, near-earth asteroids (NEAs) and MC orbits are in resonance, and when their orbital eccentricity becomes large enough, to the point that their orbits cross those of the inner planets, their orbits then become modified in arandom-walk fashion. This results in a complex interplay between planetary encounters and resonances which may lead to a range of unexpected outcomes including cometary-type orbits; solar collisions; or, eventual ejection from theSolar System.[12][13]
Detailed investigations intoKridsadaporn's dynamic evolution have been carried out by creating 15 "clone" orbits, integrated forward over a period of 12 million years, by changing the last digit of its orbital parameters. Nine (9) clones demonstrated moderate chaotic behavior jumping between the Jovian mean-motion resonances of 15:7, 9:4, and 11:5 with some orbits becomingEarth-crossers within the integration period. The remaining six (6) clones grew in orbital eccentricity until becomingJupiter-crossers, and then, behaving asJupiter-family comets, they were ejected from the Solar System over periods in the order of 105 years.[12]
There are several prominent dips in the distribution of asteroids in the main belt. These gaps are more sparingly populated with objects of higher orbital eccentricity. Known asKirkwood gaps, these dips in distribution density correspond to the location oforbital resonances with Jupiter. Objects with eccentric orbits continue to increase in orbital eccentricity over longer time-scales to eventually break out of resonance due to close encounters with a major planet.[14]Kridsadaporn, with a semi-major axis of 3.11 AU,[2] corresponds to a very narrow gap associated with the 11:7 resonance[12] within a series of weaker and less sculpted gaps.
In theSMASS classification,Kridsadaporn is a common, carbonaceousC-type asteroid.[2][7]
A number of studies[5][11] includedKridsadaporn within a sample of asteroids in cometary orbits in order to understand the relationships inspectral characteristics between ACOs, the Jupiter-family comets, and the outer main belt asteroids. The only finding was that comets present neutral or red feature-less spectra.[5] Earlier studies[15] suggested that comets in all stages of evolution - active; dormant; and, dead - were very dark, often reddish, objects with spectra similar toD-type,P-type andC-type asteroids of theouter Solar System with probably carbonaceous dust containing reddishorganic compounds controlling their colour andalbedo characteristics.[5]
Studies analyzing the albedo distribution of a sample of asteroids in cometary orbits,[16] found in general that they exhibit lower albedos than objects withTj > 3 and further concluded that all ACOs in that sample withTj < 2.6 had albedospV < 0.075 - similar to those measured for cometary nuclei - suggesting cometary origins.[5]
A sample of objects, which includedKridsadaporn, was used in a study[5] of the relationship between the Jovian Tisserand invariant and spectral properties of asteroids in cometary orbits, which determined that all observed ACOs within the sample withTj < 2.9 were feature-less.Kridsadaporn, with its Jovian Tisserand invariant of 2.858,[2] falls within the feature-less (without bands) comet-like spectral group. These studies also concluded that ACOs with featured spectra (with bands) typical of the main belt hadTj ≥ 2.9 while those withTj < 2.9 demonstrated comet-like spectra, suggesting that the subsample of ACOs with 2.9 ≤Tj ≤ 3.0 could be populated by a large fraction of interlopers from the inner part of the belt.[4]
Kridsadaporn has a perihelion distanceq = 1.3224AU.[2]A study of the relationship between the size distribution profile and perihelion distances of ACOs[17] concluded that a sub-sample of ACOs with a perihelion distanceq > 1.3AU had a size distribution profile similar to that of the Jupiter family comets, suggesting that sub-sample to be composed of a significant fraction of dormant comets, while a large fraction of ACOs withq < 1.3AU could more likely be scattered objects from the outer main belt.[4]
Objects with a Jovian Tisserand invariantTj ≤ 3 and taxonomic properties consistent with a low albedo, however, are not enough to imply that they are dormant or extinct comets. The fraction of low albedo,Tj ≤ 3, objects actually being dormant or extinct comets is estimated to be 65% ± 10%.[11]
