Origin of Phobos and Deimos — SummaryO

Ryuki HYOD
JAXA

Today’s Contents• Two leading hypothesis — Capture and giant impact‣ Capture process‣ Giant impact process- Dynamical aspects- Physical aspects- Chemical aspects (composition, volatile, etc)
• Mass transfer from Mars to its moons — regardless of the origin• Expected structures of Phobos and Deimos

Two Leading Hypothesis
captureorigingiant impact
originimpactcapturedisk

supported by spectral features

supported by orbital elements

Dark & Featureless — D-type?

Circular & Equatorial

Capture OriginPro.

A random gravitational capture
with successive orbital evolution.
Burns 1978; Murchie et al. 1991

The spectral features — Dark & Featureless —might be naturally explained.

Challenges
How were initial eccentricity andinclination damped?

Why only “two” captured?

Pro.
Giant Impact Origin
A giant impact forms a debris
disk around Mars from which
Phobos and Deimos accrete.

The orbital properties — nearly circular &equatorial — can be naturally explained.

Challenges
Why do the spectral features resemble
those of D-type asteroids?

A Giant Impact

See also,
Craddock (1994, 2011),
Citron et al. (2015)

Borealis basin-forming impact
mimp=0.03MMars, vimp=6km/s, θ=45deg
Hyodo, et al. (2017ab) (2018ab) ApJ

This impact also can form Phobos and Deimo& give ~25h Mars spin.

s Marinova+ 2008

Building Blocks — Impact Debris
Fate of debris
Building materialsof the moons
Mars
AccreteBuilding materialsof the moons

EscapeTemperature

T~2000 K  

Hyodo, et al. (2017a)

Alternative Impacts
Utopia or Hellas, an alternativelarge basin, may be responsible
for the Martian-moon forming
giant impact.
Canup & Salmon (2018)ssθimp = 45 deg
vimp = 7 km/
mimp = 0.5×10-3 MMar
Mdisk = 5×1018 kg

or

or

Alternative Impacts
Utopia or Hellas, an alternative
properties of the debris:large basin, may Phys/chem.
be responsible
for the Martian-moon
forming
Similar to the case of the Borealis basin
giant impacts
Canup & Salmon (2018) ss

θimp = 45 deg
vimp = 7 km/
mimp = 0.5×10-3 MMar
Mdisk = 5×1018 kg

Different Paths of the Giant Impact Origin
Accretion &orbital evolutions

Basinformation

direct accretion
just after basin formation
rise-and-fallTodaylate moon’s destruction
re-accretion& fi

The nal accretion time of Phobos is very different at a different path.

(a)~4 Gyr ago

Mars

Direct Accretion
Phobos and Deimos successively form
after giant impact on Mars. In this case,moons are ~4 billion years old.

~6 Mars radii

Roche limit

Synchronous radius

A low-mass extended debris disk(b)3:2MMR

2:1MMR

Massive moon(c)Hyodo et al. 2017

~3 Mars radii

Titdal evolution

TimeFormation of two small moons(d)Fall to Mars
Titdal evolution(e)
Rosenblatt+ (2016
Canup&Salmon 2018presentPhobosDeimos)© Ryuki HyodoDeimos
assuming it is already formedby another process(e.g., Rosenblatt et al. 2016
without forming Phobos)

Rise and Fall?
A 3-7 times of a rise-and-fall ofPhobos, a cycle of accumulation,
tidal evolution, and tidal
disruption, over ~4 billion years.
Today’s Phobos is the one thatcompleted its accretion in only thepast ~few Myr1,2?
Hesselbrock & Minton (2017)
1Crater analysis, suggesting the surface age of ~4 Ga (Schmedemann et al., 2014)   

2Future consideration — Can we remove the remnant rings within few Myr?

Deimos
assuming it is already formedby another process(e.g., Rosenblatt et al. 2016
without forming Phobos)

Rise and Fall?
A 3-7 times of a rise-and-fall of
Phobos, a cycle of accumulation,t i d a l e v oAnyway,l u t i o n , a n d thist i d a lalso needs a giant impact.
disruption, over ~4 billion years.
Today’s Phobos is the one thatcompleted its accretion in only thepast ~few Myr1,2?
Hesselbrock & Minton (2017)
1Crater analysis, suggesting the surface age of ~4 Ga (Schmedemann et al., 2014)   

2Future consideration — Can we remove the remnant rings within few Myr?

A single large moonAn origin of Phobos/Deimos by its disruption

The orbits of the moons might haveintersected at recently as ~1-3 billion
years ago, suggesting their progenitor
was a larger moon that impactshattered and was re-accreted to form
Phobos and Deimos1,2,3,4.
Bagheri et al. 2021
See also Brasser 2020
1Crater analysis, suggesting the surface age of ~4 Ga (Schmedemann et al., 2014
2Future consideration — impact process and successive accumulation

process are not studied yet. Why only two accumulated? Why not three, etc
see also Hyodo & Charnoz 2017?

)   

ux at ~1-3 Ga also needs to be studied to validate this scenario.
4Internal structure, i.e., tidal parameter, of Phobos/Deimos is still not constrained.
fl3Impact

Anyway, this also needs
a giant impact on Mars toform a progenitor.

Different Paths of the Giant Impact Origin
Accretion &orbital evolutions
Low-energy processBasinformation
High-energy process —Characterization ofthe bulk composition & chemistry

direct accretion
just after basin formation
rise-and-fallTodaylate moon’s destruction
re-accretion& fi

The nal accretion time of Phobos is very different at a different path.

ust 20

Building Blocks
Endogenous bulk composition of Martian moons- Ancient Mars crust/mantl- Impactor’s materials

disk composition

Hyodo et al.

ejected depth
Crust Mantle

impactor

mixture~50% of Martianmaterials comingfrom the mantle

Mars epanel: disk mass at different impact angles. Right panel: disk mass fraction that originated from Mars (redHyodo, et al. (2017a) ApJ

Thermal and Physical Aspects
Particle temperature
Mars origin
Impactor origin

Thermal properties (~2000 K• almost fully molte• low vapor fraction (~5%

Condensates(0.1~10µm)

Particle sizes (after cooling• solidi ed melts: ~100 μm - 10 m
• condensates from vapor: ~0.1-10 μ2000melts (100µm~10m)

Hyodo, et al. (2017a) ApJ

T~2000 K on average
Very dark (FeS, CPignatale et al (2018), ApJFeatureles
Ronnet et al (2016), ApJSpace-weathered anorthosit
Yamamoto et al (2018), GRLm )))en)sfi

Also, see Tomoki’s recent work.

Composition of Condensates
Thermodynamic equilibrium —A glimpse of chemical composition of condensates

50:50 mixing

P=10-4 barcondensation sequencecondensation sequence Pignatale et al. (2018)

Chemistry Depends on Impactor*volatile loss process is not included heresee Hyodo et al. 2018b

Pignatale et al. (2018)

Volatile Loss
- Hydrodynamic escape of the vapor- Radiation pressure on condensed dust
refractory particle

condensation lineHydrodynamic Escapecondensates~ 30% of vapor can escapeà ~ 70% of volatileelements can survive

Mar(1000-6000K)~2000 K

Radiation pressure

volatile vapor cloud

Radiation Pressure
Moderately volatile elements(condensation T > 1000 K)
are selectively removed.
Hydrodynamic escapesHyodo, et al. (2018b)

Next Topic…

Something regardless of the origin

Ejecta from Mars to its moons
PhobosPhobosA simple cone-shape distribution model

Chappaz et al. (2013Ramsley&Head (2013)

Re-evaluated —Hyodo et al. (2019) SciRepe.g. vimp=12km/s, θ=45deg×3D SPH simulations)Orbital calculations

∼10-100 Times MoreMars materials are transferred
to Phobos surface.

Transferred mass to Phobos [kg]Phobos1x1010More than 1000 ppm(>0.1%At least 1 martian particle
out of 1000 particles

1x109

1000

100

1x108
101x107
1
1x10

6

0.1
100000
Zunil

Corinto McMurdo Tooting

Mojaverelatively large crater-formin
events within the past 10 Myr

Random

260km

Martian material in the regolith [ppm]Signi cant Update From Previous Estimates

Totalwithin
the past 500 Myr

Hyodo et al. 2019, SciRep

Cubic particle
Dsg fi) D=300µm → ≳100,000 Total Particles → ≳100 Martian Particle
D=100µm → ≳3,000,000 Total Particles → ≳3,000 Martian Particles

3 g/cm3 MMX mission: ≳10 g samples

e.g. vimp=12km/s

Random nature of impacts

non-melting

Less shocked
vimp=12km/s(≲5GPa) included

Phobos×melting

ReachinPhobosMars materials are transferred
to Phobos surface.
cf. Martian meteorites:- all igneous rock- mostly young (<1.3Ga- relatively shocked (≫5GPa)

   ) 

sg

Phobos Sample
Potentially, covers all Martian geological eras &consists of all types of rocks, from sedimentary to igneous

Hyodo et al. 2019, SciRepExpected Structures — Capture Origin
Bulk Composition

Physical Properties• A kind of chondritic materia• Possibly contain “two" different origins• Particle size: Unknown

A catastrophic/erosive impact —likely? a low energy evencompared to a giant impact

Chemical Propertie• Volatile abundance: Unknown

Chondritic-1?

Primordial
Planetesimal

A rubble-pile fragmen
captured*Please note that
if a primordial object is captured
the internal structure may not be rubble-pil
but could be a layered one.

Regardless of the origin(Hyodo et al. 2019)

els,tt  Chondritic-2© Ryuki Hyodo

Martian ejecta (~1,000ppm)+Late accretion (~10,000ppm)

Expected Structures — Giant Impact
Bulk Composition (Hyodo et al. 2017ab)• ~50wt.% Martian materia↪ Ancient martian crust and mantle• ~50wt.% impactor’s material (as a result of giant impact on Mars)

Physical Properties (Hyodo et al. 2017ab)• Solidi ed melts: 100µm-10• Condensed dust: 0.1-1µm↪ featureless (Ronnet et al. 2016)*In the case where a late destruction and re-accretion occurs —materials from a late impactor may be potentially mixed (as the third bulk material).

Chemistry of the Condensed Dus• Chemistry strongly depends on the impactor (Pignatale et al. 2018)↪ A clue to understand the impacto• Volatile element would be depleted (Hyodo et al. 2018b)

Condensed dust(≲5wt%)

Impactor-originate
material (initially melted)*Some of blue/red would be fully mixed
before cooling/solidi cation
But, its fraction is not constrained yet.

Regardless of the origin(Hyodo et al. 2019)

Ancient Martian materiat lr dml. 

fifi(initially melted)© Ryuki Hyodo

Martian ejecta (~1,000ppm)+Late accretion (~10,000ppm)

Even if the initial disk is
not in the Martian equatorial plane
Hyodo et al. 2017bSphere

Oblate Mars J2 effect

Martian “Eureka” Trojan asteroids- Seven out of known nine Mars Trojan Trojans — Oivine-rich features- They form a family, called “Eureka family”(121514) 1999 UJ7(X-type)

Eureka60 degA-typeEureka
2001 DH47

Martian meteorits

2001 DH47Sa-type2007 NS2

Martian meteorits

60 degX-typeS-typeMartian meteorits
C-typeMars surface

Eureka family(A or Sa-types)- Eureka- 2001 DH47
- 2007 NS2- etc.

Polishook 2017 Nature Ast.

Any connection witha giant impact on Mars?

Martian meteorites• Olivin-rich features are found in some Martian meteorites(e.g. Chassigny and Allan Hills: McSween 1985)
A-type asteroids• Rare A-type asteroids are found in Hungaria and Main belt
regions (e.g. DeMeo&Carry 2014)
Mars Trojan• 7 of 9 Mars Trojan are olivine-rich (e.g. Polishook 2017)

1AU

1.5AU

Hungarians

Main belt

1.7-2AU2-3.3AU

Martian material• Olivine is a major mineral of the Martian upper mantle with ∼60 wt% (Bertka & Fei 1997; Zuber 2001)• At the surface of Martian grabens, such as Nili Fossae, an olivine-rich signature is detected(Hoefen et al. 2003; Mustard et al. 2009) Hyodo et al. 2017b

A fraction of giant impact ejecta
is distributed
outside Mars gravitational eld

Phobos/Deimosbuilding block(black particles)

Escaping eject(blue&red particles)

White particles
escaping ejecta from the gravity of Mars
Hyodo, & Genda 2018, ApJLfi  s as:

Escaping ejecta can be the source of(1) Mars Trojan(2) A fraction of rare A-type asteroids

Composition of the escaping ejecta
Mass of the debris

Composition
Ejected depth

Phobos/Deimosbuilding block(black particles)

Escaping eject(blue&red particles)

Results of the typical impact• Total debris mass Mdebris ~ 2% of MMar
• ~20wt% of Mdebris originates from Mar• ~50wt% of Mars-debris comes from Martian mantle (< 50km depth)

s: asHyodo, & Genda 2018, ApJL

Mars’ giant impact is recorded in meteorites?
Hyodo & Genda 2018, ApJL

Ejecta from impact on Mars
high-velocity
collision
Primordial asteroid

40Ar-39Ar resetting age

Moon-forming impact?
(Bottke et al. 2015)

High-velocity collisions btw asteroids and the ejecta- Produce 40Ar-39Ar age resetting ?
- Produce U-Pb age resetting ?
- Produce impact melts ?
- etc ?

U-Pb resetting age

Moon-forming impact?
(Bottke et al. 2015)see also Bottke et al. 2015, Sciencefor the case of the Moon-forming giant impact

A single event can explain many?
The same single giant impact on Mars can potentially explain:- produce the Borealis basin- produce Phobos and Deimos- produce Mars Trojans and a fraction of the rare A-type asteroids- record the signatures of high-velocity impacts in meteorites- deliver ancient Martian material to the Earth and Moon
Mars Trojans
Ancient delivery

Implantation of rare A-type asteroids

Hungarians

Phobos & Deimos

Main belt

High-velocity collision with asteroids