Population of small asteroid systems - We are still in a survey phase

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Population of small asteroid systems- We are
still in a survey phase

• P. Pravec, P. Scheirich, P. Kušnirák, K. Hornoch,
  A. Galád
• Astronomical Institute AS CR, Ondrejov, Czech
  Republic
• The 3rd Workshop on Binaries in the Solar System
• Hawaii, the Big Island, 2013 June 30 July 2

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Spin-up fission asteroid systems

• Current sample
• Our binary asteroid parameters database (Pravec
  and Harris 2007, update June 2013)
• 39 NEA systems
• 79 MBA/MC systems (smaller than 20 km)
• We have also identified 158 asteroid pairs
  (Vokrouhlický and Nesvorný 2008, Pravec and
  Vokrouhlický 2009, Pravec et al. 2010, plus
  others in prep.)
• Many known binaries appear to be KW4-like
  systems, but we have found several unusual cases
• Primaries of asteroid pairs being binary (or
  ternary)
• Semi-wide binaries with super-critical angular
  momentum
• Binaries with a second, non-synchronous
  rotational component

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Spin-up fission asteroid systems

• Primary sizes
• Largest D1 10 km
• (1052) Belgica 10.3 1.3 km (Franco et al.
  2013)
• (3868) Mendoza 9.3 1.0 km (Pravec et al. 2012)
• Smallest D1 0.15 km
• 2004 FG11 0.15 0.03 km (Taylor et al. 2012)
• 2003 SS84 0.12 km (Nolan et al. 2003, no unc.)
• This primary diameter range 0.15 to 10 km is the
  same range where we observe the spin barrier
  (gravity dominated regime, predominantly
  cohesionless, rubble-pile asteroid structure
  implied).
• The upper limit on D1 seems to be because
  asteroids larger than 10 km dont get quite to
  the spin barrier where they would fission
  asteroid spin rates fall off from the spin
  barrier at D gt 10 km. (Are they too big to be
  spun up to the spin barrier by YORP during their
  lifetime? But see the talk by Holsapple.)
• The lower limit on D1 is likely because asteroids
  smaller than 0.15 km are predominantly not
  rubble piles. But the observational selection
  effect against detection of smaller binaries has
  to be checked.

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Spin-up fission asteroid systems

• Secondary relative sizes
• Largest D2/D1 close to 1 (Double Asteroids)
• (69230) Hermes, (809) Lundia, (854) Frostia,
  (1089) Tama, (1139) Atami, (1313) Berna, (2478)
  Tokai, (4492) Debussy, (4951) Iwamoto all D2
  /D1 between 0.8 and 1
• Smallest D2/D1 (observational sensitivity-limited)
  
• (1862) Apollo D2/D1 0.04 (Ostro et al. 2005,
  unc. factor 2)
• Systems with D2/D1 lt 0.4-0.5 abundant.
• Decrease at D2/D1 lt 0.3 and especially below 0.2
• maybe observational bias.

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Spin-up fission asteroid systems

• Distances between components
• Shortest Porb 11.9 h
• (65803) Didymos 11.91 0.02 h (Pravec et al.
  2006)
• 2006 GY2 11.7 0.2 h (Brooks 2006)
• Corresponds to a/D1 1.5 0.2. Consistent with
  the Roches limit for strengthless satellites at
  a/D1 1.27 (for same densities of the two
  bodies) that corresponds to Porb 9.5 h for the
  bulk density of 2 g/cm3.
• Decreasing number density at Porb gt 1 day
• - a real decrease plus observational selection
  effect.
• Largest separation infinity
• many asteroid pairs

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Small telescopes, but a lot of timeNEOSource
project,1.54-m Danish telescope, La Silla
Study of non-gravitational asteroid evolution
processes via photometric observations PI Petr
Pravec, Co-PI David Vokrouhlický 2012 October
2016 December, remote observations on 80
nights/year with the 1.54-m telescope at La
Silla A number of other projects with 0.35-1 m
telescopes.
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1. Primaries of asteroid pairs being binary (or
ternary)
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Primaries of asteroid pairs being binary (or
ternary)

• Five cases so far
• (3749) Balam, (6369) 1983 UC, (9783) Tensho-kan,
  (10123) Fideoja, (80218) 1999 VO123
• Similar to our other photometrically detected
  binaries in the main belt
• D1 1 to 6 km
• D2/D1 0.23 to 0.45
• P1 2.40 to 3.15 h
• Porb 29.5 to 56.5 h (possible lack of the
  closest
• orbits with orbital periods lt 1 day)
• The unbound component (secondary of the asteroid
  pair)
• Dsec/D1 0.15 to 0.9 (four of them 0.15 to
  0.35)
• Age between 120 kyr and gt 1 Myr (these are times
  before present when
• geometric and Yarkovsky clones of the orbits of
  the two components
• converge)
• Another (fourth) component distant satellite
  present in (3749) Balam.

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Multiple system (3749) Balam

• Hierarchy
• Primary, D1 4.2 km (from WISE data, unc. 10),
  P1 2.80 h, nearly spheroidal (A 0.10 mag)
• Close satellite, D2/D1 0.45, Porb 33.4 h
  (Marchis et al. 2008), moderate eccentricity
• Distant satellite, D3/D1 0.22, Porb 1300-3900
  h, e 0.3-0.8 (Vachier et al. 2012)
• Unbound secondary, Dsec/D1 0.15 (from ?H),
  300-kyr old pair (Vokrouhlický 2009)
• The inner couple (the primary the close
  satellite) looks like a classical KW4-type
  binary,
• also its angular momentum is close to critical
  (aL 1.30 0.14)
• BUT
• The orbit is moderately eccentric (e 0.06) and
  we have not been able to fit the
• available 4-apparition data (2007, 2009, 2010 and
  2012) with an orbit model with apsidal
• precession only suspect non-zero inclination of
  the orbit wrt the primarys equator, hence

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Multiple system (3749) Balam
e 0.06 0.02 (3 sigma), apsidal precession
rate d?/dt 0.7-1.2 deg/day. Note that d?/dt 1
deg/day corresponds to J2 0.10 (moderately
flattened spheroid).
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Paired binaries (6369) and (9783)
They look pretty much like classical
(semi-)asynchronous binaries ---except for their
relatively long orbital periods--- with
near-critical total angular momentum and
nearly-spheroidal primary. But well look
forward towards seeing more data from their
return apparitions.
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Paired binaries (10123) and (80218)
The second rotational period of 38.8 h in (10123)
is unusually long, probably slowed down by some
process. If it belongs to the secondary with
Porb 56.5 h, could perhaps it be at a closer
(synchronous) orbit with Porb 38.8 h before
the asteroid pair 10123-117306 formed some 1-2
Myr ago?? (But the secondarys spin rate might
change during the pair formation too .)
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2. Semi-wide binaries withsuper-critical angular
momentum
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Semi-wide binaries with super-critical angular
momentum

• Three cases so far
• (1717) Arlon
• (4951) Iwamoto
• (32039) 2000 JO23
• Total angular momentum content super-critical
• aL 1.8, 2.25 and 2.9 (uncertainties
  0.2-0.6).
• Common feature Large satellite
• D2/D1 0.6 to 0.9 ( 0.1)
• and distant, of course (with large fraction of
  the angular momentum being in the orbital)
• Porb 117, 118, and 360 h

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(1717) Arlon
D2/D1 0.5 P1 5.15 h P2 18.22 h Porb 117.0
h Assuming P1 belongs to the primary and P2
belongs to the secondary aL 1.82 (unc.
25) Is the assumption right? And, again, we
may speculate Couldnt the satellite be at
a synchronous orbit with Porb 18 h before it
was moved to its current distant orbit??
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(4951) Iwamoto
D2/D1 0.88 0.1 P1 Porb 117.9 0.2 h (at
least one component is synchronous) aL 2.25
(unc. 25) No way how aL could be close to 1.
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(32039) 2000 JO23
D2/D1 0.58 P1 3.30 or 6.60 h P2 11.10
h Porb 360 h aL 2.3 Again, no way how aL
could be close to 1.
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Semi-wide binaries with super-critical angular
momentum
A (semi-)asynchronous, KW4-like
binaries B fully synchronous, near
equal-sized binaries (double asteroids)
(Pravec and Harris 2007)
Present update
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Semi-wide binaries with super-critical angular
momentum
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3. Binaries with a second, non-synchronous
rotational component
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Binaries with a second, non-synchronous
rotational component
We detected seven such cases so far
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(1830) Pogson
(Pravec et al. 2012)
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(2006) Polonskaya
(Pravec et al. 2012)
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(2577) Litva
(Warner et al. 2009)
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(16635) 1993 QO
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Binaries with a second, non-synchronous
rotational component
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(2486) Metsahovi
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(3982) Kastel
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(5474) Gingasen
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(114319) 2002 XD58
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Binaries with a second, non-synchronous
rotational component
The second, non-synchronous rotational lightcurve
component observed in 7 of the 79 MBA binaries
(9) of our current binary sample. In some cases
with short Porb, the (even much shorter) P2 may
actually belong to another, probably more
distant satellite (i.e., the system is ternary)
the P2 lightcurve component doesnt disappear in
total secondary events when the close satellite
producing the observed mutual events fully
disappears behind the primary. The four observed
cases with two rotational components, but no
mutual events, may be relatively wide
non-synchronous systems.
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Conclusions
Classical close (semi-)asynchronous binaries
(KW4-like) represent only a, and actually the
easiest observable, part of the population of
spin-up fission asteroid systems among 1-10 km
sized MBAs. Some systems apparently went
formation/evolution paths leading to more distant
satellites or including ejection of a body from
the system (producing an asteroid pair with
primary being binary).
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Thank you