N3 Vokrouhlicky - "Yarkovsky and yorp effects paolos legacy"

YARKOVSKY and YORP effects
Paolo’s legacy

D. Vokrouhlický (Charles University, Prague)

Talk plan: a) Early days: Lageos 1 inspiration
Talk plan: b) Mid 1990s: Move to planetary
Talk plan: c) Late 1990s: First interesting planetary applications
(meteorite transport, NEAs replenishment, family structure,
detection idea)

d) > 2000: Yark/YORP mature period

EARLY YEARS: Lageos 1 inspiration

 Lageos 1 facts 

• launch on May 4, 1976
• nearly circular orbit at 5900 km and
110deg inclination
• laser-ranged with mcm accuracy
• mass  410 kg
• initial rotation period 0.6 s but has
been found to exponentially increase
with 3y ! e-fold time

• in October 1992 got a twin Lageos 2 on
a similar orbit but 52deg inclination

Orbit determination
requires empirical
accelerations …

Dave Rubincam
interpreted the mean
along-track acceleration
as the effect of thermal
thrust due to absorbed
Earth IR radiation…
(late 1980s)


From Gauss equations we know …

Hence a simple scaling provides …

Lageos meteoroid

… and thus it should be easy to bring meteoroids to the nearest resonances in the MB
(Paolo in ~ 1995).

Other landmark contributions by:

• Dave Rubincam (JGR 1995, 1998) … an independent idea for the Yarkovsky role in
meteorite transport
• Germano Afonso et al. (PSS 1995) … the first numerical integrations of Yarkovsky
migrating meteoroids with planetary perturbations

YARKOVSKY EFFECT: meteorite transport…
How much would a body move within
Meteorite precursors its estimated lifetime in the main asteroid
belt?

km size NEAs
or family members

1 … 0.002 W/m/K
2 … 0.02 W/m/K
3 … 0.2 W/m/K
4…2 W/m/K
m … 40 W/m/K
Farinella & Vokrouhlický (1998, 1999)


… and so Paolo had the clear vision of a two-stage transport process (late 1990s)


Little later technical tools allowed to directly model meteoroid drift with
planetary perturbations included … (Mira Brož)


… or couple the transport with collisional break-ups
(Vokrouhlický & Farinella 2000).

YARKOVSKY EFFECT: NEAs replenishment…

Rem. Yarkovsky migration has been since shown to be likely the sustaining
mechanism of other unstable populations (e.g., close or inside MMRs)


NEO facts: 1. About 220 bodies with H<18 (D>1km) must be
resupplied to the NEO zone every My through
the three main routes (3/1, 6 and weak resonances)
to keep the population in steady state

2. Assuming the size distribution as
N(<H) ~ 10H
in the range 15.5 < H < 18, observations give
   0.26 in the main asteroid belt
   0.35 for the NEAs

A “reasonable model” can be contructed to meet these observational
facts with Yarkovsky effect pushing the H<18 bodies out of MB

YARKOVSKY EFFECT: structure of families…

Known members of the
Astrid family:

semimajor axis vs size plot

Farinella & Vokrouhlický (1999)


Polarization of small fragments toward extreme values of semimajor
axis: a trace of their faster drift by thermal forces

• Family in (a,e) is nearly cut in two
near 2.92 AU.
• Both sides of family are bracketed by
powerful mean motion resonances
(5:2 and 7:3 MMR with Jupiter).
• Family members do not appear to
have crossed these resonances.
– No substantial contributions of
family members in both (a,e) and
(a,i) can be seen on the left side of
5:2 or right side of 7:3.

Why does this family
have such a weird shape?


Koronis family

• Observed
• Model

1. Large asteroid disrupts and ejects
multi-km fragments at velocities
consistent with hydrocode results.

2. D < 20 km bodies start drifting inward
and outward in semimajor axis a by the
Yarkovsky effect.

3. These bodies jump over or become
trapped by mean motion or secular
resonances, which may change their
(e, i) values.

4. Family members drifting far enough
reach powerful resonances capable of
pushing them onto planet-crossing
orbits.


Novel quantitative information

BLUER  Spectral slope  REDDER
about the space weathering
processes… (Nesvorný et al. 2005).

 Colors from Sloan Digital Sky Survey



 Colors from Sloan Digital Sky Survey


 Color becomes ‘redder’ over time

 Effect of space weathering:
spectral changes by solar wind
and micrometeorite impacts

 First measurement of the rate of
spectral changes for asteroids

YARKOVSKY EFFECT: detection issues etc…
YARKOVSKY EFFECT: detection issues etc…
Detection possibility of the
Yarkovsky forces noticed
in late 1990s. Requires as
accurate astrometry as
possible – naturally let to
involve planetary radar…

… since then detections
have been also achieved
for objects without radar
data. Yarkovsky forces
were also shown important
for:

• arc linkage (e.g., 1992 BF), or
• impact hazard studies (e.g.,
Apophis, 1999 RQ36)

YARKOVSKY EFFECT: post scriptum…


… what’s followed/next:

• Dave Rubincam (2000) introduced YORP as a twin phenomenon to the
Yarkovsky effect
• discovery of Karin family (2002) initiated hunt for young clusters and asteroid
structures; Yarkovsky forces are inevitable part of the age-determination
process
• Yarkovsky forces first detected (2003) through the orbit-determination of a
small NEA
• YORP first detected (2006) as an acceleration component in rotation of small
NEAs
•…


… what’s followed/next:

George Beekman (2006) discovered
the original Yarkovsky pamphlet
claimed lost by Öpik (1951)…

N3 Vokrouhlicky - "Yarkovsky and yorp effects paolos legacy"

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