Properties of the NEO Population: The ACM 2005 View Richard P. Binzel (MIT) Dmitrij Lupishko (...
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Properties of the NEO Population: The ACM 2005 View Richard P. Binzel (MIT) Dmitrij Lupishko (Kharkov Observatory)
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Transcript of Properties of the NEO Population: The ACM 2005 View Richard P. Binzel (MIT) Dmitrij Lupishko (...
Properties of the NEO Population:The ACM 2005 View
Richard P. Binzel (MIT)
Dmitrij Lupishko(Kharkov Observatory)
Near-Earth Objects (NEOs)Asteroids or comets with perihelia ≤ 1.3 AU.
Near-Earth “Objects”
NEO Spectral Measurements
• Lazzarin et al.“Survey in the visible and near-IR (SINEOS)” at ESO and La Palma.
• Lazzaro et al.“Small Solar System Objects Spectro-scopic Survey (S3OS2)” at ESO.
• Dandy et al.BVRIZ colors at La Palma.
• Vernazza et al.Visible + near-IR. La Palma + IRTF.
• MIT-Hawaii-IRTFNear-IR (IRTF) public domain data.Available: smass.mit.edu
2002
2005
ALSO… P7.2 DeLeon; P7.5 Marchi; P7.10 Vernazza; …
NEO Albedo Measurements
• Delbo et al. (2003)NASA Keck
• Wolters et al. (2004)UKIRT
• Fernandez et al. (2005)Keck + UH telescopes
2002
2005
Keeping up the pace . . .
2002
2005
2002
2005
2002
2005
Discoveries Spectra Albedos
Overall Properties:
NEO population shows the full diversity of the main-belt asteroids.
NEO Population
2001 XR31: Possible R- or V-type(Marchi et al. 2004)
Additional V-types(Marchi et al. 2005)
Examples of Unusual Types
Examples of Unusual Types(33342) 1998 WT24
E-type with very low Pmax
(Kiselev et al. 2004)
Comparisons to MeteoritesOrdinary Chondrites [Q-type NEOs]
(Angeli & Lazzaro 2002)
(Lazzarin et al. 2005)
Carbonaceous Chondrites
(Lazzarin et al. 2005)
Aubrites
(Clark et al. 2004)
Also Gaffey et al. (1992), Burbine et al. (2002), Gaffey & Kelly (2004)
S-asteroid
H-chondrite
0.4 0.6 0.8 1.0
0.8
1.0
1.2
Wavelength (μm)
Relative Reflectance
The Ordinary Chondrite ProblemThe most common class of meteorites (OCs) does not match
the most common class of asteroids (S-types).
Ordinary Chondrites~80%
CarbonaceousChondrites
Irons
Achondrites
Stony-Irons
NEO Statistics S: 44% Q: 23% X: 14% C: 10%
Long debated hypothesis . . .(Wetherill & Chapman 1988; Chapman 1996; Beth Clark et al. Asteroids III)
Ordinary chondrite source bodiesdisguised by “space weathering”
to look like S-asteroids.
X-ray spectrometer at Eros provides in situ link betweenS-asteroids and ordinary chondrite meteorites. (Trombka et al. 2000)
NEAR
Progress in Laboratory Explanation for Space Weathering
Hapke et al. (1975); Pieters et al. (2000)
Progress by Many
•Moroz et al. (1996; 2000)
•Sasaki et al. (2001, 2003)
•Kurahashi et al. (2002)
•Strazzula et al. (2005)
1. Transition from ordinary chondrites to S-asteroids should be continuous.
Observable Side Effects
2. Transition dependent on surface age.–Young surfaces should look like ordinary chondrites.–Older surfaces should look like “S-asteroids”
Continuous Transition
S-asteroid
Q-asteroid
S-asteroid
H-chondrite
0.4 0.6 0.8 1.0
0.8
1.0
1.2
Wavelength (μm)
Relative Reflectance
MIT - Hawaii - IRTF NEO ReconnaissanceData available: smass.mit.edu
Continuous Transition(Lazzarin et al. 2005) Larger
“More red”
Size Dependence
(Dandy et al. 2003)
Smaller“Less red”
Spectral transition is size dependent.Transition “complete” at 5 km size.
Q
S
5 km
Main beltaverage(S-types)
(ordinary chondrites)
Running Box AverageQ- and S-types
What are the relative roles of weathering
vs. regolith retention?Binzel et al. (2004)
Smaller sizes = “younger, fresher” surfaces.
Larger sizes = older “weathered” surfaces.
Cheng (2004)Collision
fragmentsPrimordialsurvivors
Albedo DependenceTrend toward brighter “fresher” surfaces at smaller sizes.
(Delbo et al. 2003)
NEOs
MainBelt Harris-DLR (2005)
Near-Earth “Objects”
Major Advances:Physical measurements of comet nuclei
and “asteroids” in comet-like orbits.Abell et al. (2005) Fernandez et al. (2001, 2005)
Jewitt (2004, Comets II)
ALSO… P3.1 Abell; P3.9 Lamy; P14.1Alvarez-Candel; P14.8 DeMeo; P14.19 Lowry;
Tell “Tail” Signs forLow Albedo NEOs
• Standard Thermal Model (Lebofsky & Spencer 1989) shows low albedo asteroids in near-Earth space are warm enough to emit in the near-IR.
• First application using IRTF SpeX (2.5μm) to NEOs (1998 ST27) reported by Abell (ACM 2002; Thesis 2003).
• Model templates for application to NEOsby Rivkin et al. (2005).
Determining the Fraction of “Dead Comets” in NEO Space
• Criterion #1.Have orbits similar to Jupiter-family comets: Tj< 3.
Q
Q
Q
Q Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
QQQ
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
Q
T < 3
2.0 2.5 3.0 3.5 4.0
0.0
0.2
0.4
0.6
0.8
Tisserand
Albedo
Must debias NEO discovery statistics for low albedo objects.
Must debias NEO discovery statistics for low albedo objects.
Must debias NEO discovery statistics for low albedo objects.
Must debias NEO discovery statistics for low albedo objects.
Must debias NEO discovery statistics for low albedo objects.
Must debias NEO discovery statistics for low albedo objects.
Fernandez et al. (2001)
Debiased NEO Population(Stuart 2003 Ph.D. Thesis; Stuart & Binzel 2004)
KEY RESULT:30% of the total NEO population
resides in orbits having T<3.
(Fernandez et al. 2005 set threshold < 0.075) Or Have “C-, D-, P-type” spectra (as a proxy for low albedo).
-->Fernandez et al. (2005): 53 +/- 9 %-->Binzel et al. (2004): 50 +/- 10%
• Criterion #1: Debiased T<3 population• Criterion #2:
Also have comet-like albedo.
Determining the Fraction of “Dead Comets” in NEO Space
T<3 NEOs
• Criterion #1: Debiased T<3 population = 30% of all NEOs
• Criterion #2: 50% of T<3 NEOs have “comet-like” albedos/colors
Results for the Fraction of “Dead Comets” in NEO Space
RESULT: 0.50 x 0.30 = 0.15
15 +/- 5% of the total NEO populationare extinct comet candidates.
CONCLUSIONS• Space weathering has come of age.
– S asteroid connection to ordinary chondrites.– Transition at 5 km may be key to unraveling
weathering vs. regolith particle size/retention.
• T<3 population has a distinct character.– Bias corrected: 30% of all NEOs reside T<3.
• 15 +/- 5% of the total NEO population are “dead comet” candidates.
• Ongoing & future challenge:Further scrutiny of comet candidates.
FIN
Properties of the Near-Earth Object Population
Richard P. Binzel(MIT)
Dmitrij Lupishko(Kharkov Observatory)
