Forming habitable planets on the computer Anders Johansen Lund University, Department of Astronomy and Theoretical Physics 1/9
Two protoplanetary discs (Andrews et al., 2016) (ALMA Partnership, 2015) Two ALMA images of protoplanetary discs HL Tau is 450 light years away, 1 million years old TW Hydrae is 176 light years away, 10 million years old Emission comes mainly from its the 1% mass in mm-sized pebbles Pebbles are formed by collisions between micron-sized dust grains Protoplanetary discs live for a few million years 2 / 9
Big questions in planet formation Size and time Dust µ m Pebbles mm cm Planetesimals 10 1,000 km Planets 10,000 km How do pebbles gather to form km-scale planetesimals? How do the cores of giant planets accrete rapidly enough to accrete gas? How are the different planetary classes gas giants, ice giants, super-earths and terrestrial planets formed? How are habitable planets seeded with life-essential molecules like H 2O? 3 / 9
Forming planetesimals through the streaming instability ESA 9 9 ESA ESO (Johansen et al., PPVI, 2014) I Dense pebble filaments emerge through the streaming instability (Youdin & Goodman, ApJ, 2005; Johansen et al., Nature, 2007; Bai & Stone, ApJ, 2010) I Filaments collapse by gravity to form planetesimals with sizes from 10 km to several 100 km (Johansen et al., 2015, Science Advances; Simon et al., ApJ, 2016) I Most mass in 100-km-scale planetesimals, as in asteroid belt I Small bodies like comet 67P/Churyumov-Gerasimenko are piles of primordial pebbles, as observed for 67P (Poulet et al., MNRAS, 2016) I Many planetesimals form as binaries, similar to those observed in the Kuiper belt beyond Neptune (Noll et al., Icarus, 2008) 4/9
Pebble accretion Hill radius marks the region of gravitational influence of a growing protoplanet Planetesimal is scattered by protoplanet Most planetesimals that enter the Hill sphere of a protoplanet are simply scattered less than 0.1% are accreted Pebble spirals towards protoplanet due to gas friction Pebbles spiral in towards the protoplanet due to gas friction Very high pebble accretion rates Core growth to 10 M Possible to form solid cores of 0 6 Earth masses before the gaseous 10 5 Pebbles protoplanetary disc is accreted 10 4 after a few million years r/au (Johansen & Lacerda, MNRAS, 2010; Ormel & Klahr, A&A, 2010; Lambrechts & Johansen, A&A, 2012) t/yr 10 8 10 7 Planetesimals Fragments 5 / 9
Growth tracks of giant planets J S t = 0.00 Myr U N 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.37 Myr U N Solid core 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.54 Myr U N Solid core Slow gas contraction 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.63 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.71 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.79 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.88 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.79 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.86 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.91 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 0.99 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 1.03 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 1.30 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of giant planets J S t = 1.32 Myr U N Solid core Slow gas contraction Run away gas accretion 0 0 30 40 Planet formation model including the evolving protoplanetary disc, growth by pebble and gas accretion and migration (Bitsch et al., A&A, 2015; Johansen & Lambrechts, Annual Review of Earth and Planetary Sciences, 2017) Giant planets form solid core first (blue line), then gas envelope contracts slowly (red) and finally undergoes run-away collapse (yellow) Giant planets take approximately 1 Myr to form Protoplanets undergo substantial migration during their growth 6 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 0.0 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 0.2 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 0.4 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 0.6 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 0.8 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 1.0 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 1.2 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Growth tracks of terrestrial planets (?) Only rock Ice + rock t = 1.4 Myr V E Me Ma 0 1 2 3 4 5 Inside water ice line at 2.5 AU particles contain no water ice Protoplanets overshoot the terrestrial masses and form super-earths Rocky super-earths form inside of ice line, water worlds migrate from outside the ice line In good agreement with prevalence of super-earths around other stars How are terrestrial planets formed then? 7 / 9
Terrestrial planet formation with Jupiter t = 0.0 Myr V E Me Ma 0 5 5 Jupiter blocks the flow of material into the terrestrial planet zone Protoplanet growth quenched at Mars-mass planetary embryos Embryos grow to terrestrial planets after 100 Myr of mutual collisions The debris from one of these impacts likely created our Moon Another giant impact with an icy protoplanet could have delivered all the Earth s budget of water, carbon and nitrogen 8 / 9
Terrestrial planet formation with Jupiter t = 0.2 Myr V E Me Ma 0 5 5 Jupiter blocks the flow of material into the terrestrial planet zone Protoplanet growth quenched at Mars-mass planetary embryos Embryos grow to terrestrial planets after 100 Myr of mutual collisions The debris from one of these impacts likely created our Moon Another giant impact with an icy protoplanet could have delivered all the Earth s budget of water, carbon and nitrogen 8 / 9
Terrestrial planet formation with Jupiter t = 0.4 Myr V E Me Ma 0 5 5 Jupiter blocks the flow of material into the terrestrial planet zone Protoplanet growth quenched at Mars-mass planetary embryos Embryos grow to terrestrial planets after 100 Myr of mutual collisions The debris from one of these impacts likely created our Moon Another giant impact with an icy protoplanet could have delivered all the Earth s budget of water, carbon and nitrogen 8 / 9
Terrestrial planet formation with Jupiter t = 0.6 Myr V E Me Ma 0 5 5 Jupiter blocks the flow of material into the terrestrial planet zone Protoplanet growth quenched at Mars-mass planetary embryos Embryos grow to terrestrial planets after 100 Myr of mutual collisions The debris from one of these impacts likely created our Moon Another giant impact with an icy protoplanet could have delivered all the Earth s budget of water, carbon and nitrogen 8 / 9
Future of planet formation modeling Solar System Kepler 11 WASP 47 HD 108874 HR 8799 Model growth from protoplanetary disc to diverse planetary systems Include dust growth, planetesimal formation, planetesimal accretion, pebble accretion, gas accretion and planetary migration Multiple protoplanets growing and interacting gravitationally Self-consistent calculations of volatile delivery to habitable terrestrial planets and super-earths Formation of moon systems around giant planets and super-earths Understanding the necessary requirements to make planets habitable 9 / 9