Minton

Was The Earth always at 1 AU?

(and was the Sun always 1 Solar Mass?)David Minton

Purdue University

CollaboratorsRenu Malhotra (U. of Arizona/LPL)Hal Levison (SwRI)Bill Bottke (SwRI)David Nesvorn (SwRI)

Alessandro Morbidelli (OCA)David Vokrouhlick (Charles)Bruce Simonson (Oberlin)

Thursday, April 12, 2012

The FYSP solved 3 ways

1. Mass-losing Sun

2. Jumping Earth

3. Archean Bombardment


The problem

How to keep this line

Above this line

1-D radiative balance:(Pollack 1979)

Time varying solar luminosity:(Gough 1981)


Solving the FYSP by fiddling with basic solar system parameters



Whitmire (1995)



Orbital adiabatic invariant



Conserved




Conserved


More massive early Earth?...not considered here.



Conserved




Conserved


Simple: Change the gravitational constant of the

universe.



Conserved




Conserved


Increasing mass also decreases aSo lets try this first...


Minton & Malhotra (2007)Thursday, April 12, 2012

Present-day mass loss~30% due to solar wind

~70% due to E=mc2.


2.5%? That doesnt sound so bad!



2.5% Msun=26 Jupiters



2.5% Msun=26 Jupiters

Sustained mass loss


Based on measurements of stellar winds from Wood et al. (2005)


Mass-losing Sun

A mass-losing Sun could in principle solve the FYSP

But you need sustained high rates of mass loss over ~2 Gy

Required mass loss rates are at odds with inferred stellar wind mass loss rates of Sun-like stars


What about just semimajor axis?


Ways of changing semimajor axis

Type 1 & II migration (Goldreich & Tremaine 1979; Lin, and Papaloizou)

Requires gas: T

Planet-Planet Scattering

Terrestrial planet system with an extra planet near Mars can stay stable for as long as ~1 Gy before losing the extra planet (Chambers 2007)

~1 % of simulations of our solar system lose Mercury within 5 Gy. In 1 out of ~2500 simulations ALL terrestrial planets went unstable 3 Gy into the future (Laskar & Gastineau 2009)

Video from Fred Rasio Credit: Trent Schindler, National Science Foundation

...and Planet-Planet Collisions


Laskar & Gastineau 2009


Flaps w

ings

Doesnt flap wings

1 year later 3 Gy later


0.75 Venus

Earth

0.25 Venus

Planet-planet scattering


Earth

Venus


Jumping Earth


Could Earth have moved 2 Gy ago?

Planet-planet scattering could, in principle, solve the FYSP

Late-stage accretion simulations rarely have such large mergers beyond ~100 My

Maybe standard late-stage initial conditions are not quite right? (stay tuned for Minton & Levison 2012!)


How can we test this?

Hypothesis: Venus didnt finish accreting until ~2.5 Gy ago, and proto-Venus scattered Earth outward to 1 AU prior to the final giant impact.



Hypothesis:

Is there evidence of relatively recent catastrophic resurfacing on Venus?

Venus didnt finish accreting until ~2.5 Gy ago, and proto-Venus scattered Earth outward to 1 AU prior to the final giant impact.



Hypothesis:



Yes!



Hypothesis:





Hypothesis:


Does Venus have some unusual differentiation history (Hf-W)?

How much debris does this impact generate, and is it consistent with inner solar system cratering?



Science Science FictionThis idea


Solving the Faint Young Sun Paradox is possible by invoking a more massive Sun, but requires sustained high solar rates of mass loss for ~2 Gy that may not be observed in solar analogue stars.

Solving the Faint Young Sun Paradox is possible by invoking planet-planet scattering of proto-Venuses (Venii?) 2.5 Gy ago, but this may not be compelling in the face of minimal constraints.

(Dont stop trying to solve it with atmospheric chemistry)


A funny thing happened on the way to understanding some details in the modeling of the

Late Heavy Bombardment...

The asteroid belt looks like the source of the LHB impactors (Strom et al. 2005; Richardson 2009; Head et al. 2010)

But if the LHB was caused by giant planet migration & associated resonances sweeping across the main belt and exciting/depleting asteroids, it doesnt look like it lost more than ~50% of its mass (Minton & Malhotra 2009; 2011; Morbidelli et al. 2010)

Thats not enough mass to make all the craters!


6

The dynamical structure of the asteroid belt


The E-Belt

We placed bodies on main belt-like orbits in gap.

Pre-LHB: -600 My to 0 My Jovian planets in circular orbits between 5-12 AU.Mars started on a low-e orbit

Mars-Crossing Boundary

Hungaria Asteroids

Hungaria Asteroids

6 Resonance

Mars

Mars


E-Belt and the Hungaria Asteroids

Our model E-belt objects after 4 Gy compared to the known H < 14 Hungarias.

Observed Hungarias (H < 14)

Mars

Mars

E-belt survivors after 4 Gy

The E-belt makes Hungarias!


Depletion of E-Belt Population

Using observed Hungaria population, we predict Initial E-belt had population density similar to pre-LHB main belt. It produced ~9-10 lunar basins, with ~2-3 Imbrium/Orientale-sized.

Hungaria Population Today

Pre

-LH

BLH

B


Basin Formation on the Earth and Moon

If the E-belt produced ~9 lunar basins:Normalize using youngest basin Orientale with age of 3.7-3.8 Ga.This predicts LHB starts at ~4.1-4.2 Ga and lasts ~400 My on Moon.

Earth

Moon

Archean Proterozoic


Basin Formation on the Earth and Moon

If the E-belt produced ~9 lunar basins:Normalize using youngest basin Orientale with age of 3.7-3.8 Ga.This predicts LHB starts at ~4.1-4.2 Ga and lasts ~400 My on Moon.

Earth

Moon

LHB

Archean Proterozoic

Orientale (~3.7-3.8 Ga)

~900 km diameter


The LHB doesnt really end on Earth until the late Archean/early Proterozoic (~ 2 Gy ago)

Supported by spherule layer abundances Could the high impact rate be related to climate and

biochemistry changes on Earth?

i.e. Providing a pathway for phosphorous reduction? (Pasek et al. 2007)

Can impacts be a factor in the oxidation of the atmosphere?

The E-Belt

Hot off the presses, April 26, 2012 in Nature

An Archean Heavy Bombardment From a Destabilized Extension of the Asteroid Beltby Bottke, Vokrouhlick, Minton, Nesvorn, Morbidelli, Brasser, Simonson, & Levison

(also check out the companion paper on impact spherules by Johnson & Melosh)


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