Trans-Neptunian binaries as evidence for planetesimal formation by the streaming instability
Year: 2019
Type: article
Source: Nature Astronomy
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
Awards: Collaborative Proposal: Pebbles and Gas - The Supply Chain for Compact Planetary Systems, ANGULAR MOMENTUM TRANSPORT AND TURBULENCE WITHIN PROTOPLANETARY DISKS IS THE LEADING CANDIDATE FOR EXPLAINING THE OBSERVED EVOLUTION OF GAS DISKS ARO, ICE LINES AND IONIZATION EDGES AS CATALYSTS FOR PLANET FORMATION OBJECTIVES: THE SIMPLEST MODELS FOR PLANET FORMATION ASSUME THAT THE FIRST STEP IN T, G433322167, G4518818167, UNDERSTANDING THE PHYSICS OF ACCRETION FLOWS IN CIRCUMSTELLAR DISK PROVIDES THE FOUNDATION TO ANY THEORY OF PLANET FORMATION. THE LAST FEW YEARS HAVE WITNESSED DRAMATIC A REVISION IN THE FUNDAMENTAL FLUID DYNAMICS OF PROTOPLANETARY ACCRETION DISKS. THERE IS GROWING EVIDENCE THAT THE KEY TO ANSWERING SOME OF THE MOST PRESSING QUESTIONS SUCH AS THE ORIGIN OF DISK TURBULENCE MASS TRANSPORT AND PLANETESIMAL FORMATION MAY LIE WITHIN AND INTIMATELY LINKED TO PURELY HYDRODYNAMICAL PROCESSES IN PROTOPLANETARY DISKS. RECENT STUDIES INCLUDING THOSE FROM THE PROPOSAL TEAM HAVE DISCOVERED AND HIGHLIGHTED THE SIGNIFICANCE OF SEVERAL NEW HYDRODYNAMICAL INSTABILITIES IN THE PLANET-FORMING REGIONS OF THESE DISKS. THESE INCLUDE BUT NOT LIMITED TO: THE VERTICAL SHEAR INSTABILITY ACTIVE BETWEEN 10 TO 100 AU; THE ZOMBIE VORTEX INSTABILITY OPERATING IN REGIONS INTERIOR TO ABOUT 1AU; AND THE CONVECTIVE OVER-STABILITY AT INTERMEDIATE RADII. SECONDARY ROSSBY-WAVE AND ELLIPTIC INSTABILITIES MAY ALSO BE TRIGGERED FEEDING OFF THE STRUCTURES THAT EMERGE FROM THE ABOVE PRIMARY INSTABILITIES. THE RESULT OF THESE HYDRODYNAMIC PROCESSES RANGE FROM SMALL-SCALE TURBULENCE THAT TRANSPORTS ANGULAR MOMENTUM TO LARGE-SCALE VORTICES THAT CONCENTRATE DUST PARTICLES AND ENHANCE PLANETESIMAL FORMATION. HYDRODYNAMIC PROCESSES PERTAIN TO A WIDE RANGE OF DISK CONDITIONS MEANING THAT AT LEAST ONE OF THESE PROCESSES ARE ACTIVE AT ANY GIVEN DISK LOCATION AND EVOLUTIONARY EPOCH. THIS REMAINS TRUE EVEN AFTER PLANET FORMATION WHICH AFFECTS THEIR SUBSEQUENT ORBITAL EVOLUTION. HYDRODYNAMICAL PROCESSES ALSO HAVE DIRECT OBSERVABLE CONSEQUENCES. FOR EXAMPLE VORTICES HAVE BEING INVOKED TO EXPLAIN RECENT ALMA IMAGES OF ASYMMETRIC `DUST-TRAPS' IN TRANSITION DISKS. HYDRODYNAMIC ACTIVITIES THUS PLAY A CRUCIAL ROLE AT EVERY STAGE OF PLANET FORMATION AND DISK EVOLUTION. WE PROPOSE TO DEVELOP THEORETICAL MODELS OF THE ABOVE HYDRODYNAMIC PROCESSES UNDER PHYSICAL DISK CONDITIONS BY PROPERLY ACCOUNTING FOR DISK THERMODYNAMICS DUST DYNAMICS DISK SELF-GRAVITY AND THREE-DIMENSIONAL EFFECTS. BY INCLUDING THESE EFFECTS WE GO WELL-BEYOND PREVIOUS WORKS BASED ON IDEALIZED DISK MODELS. THIS EFFORT IS NECESSARY TO UNDERSTAND HOW THESE INSTABILITIES OPERATE AND INTERACT IN REALISTIC PROTOPLANETARY DISKS. THIS WILL ENABLE US TO PROVIDE A UNIFIED PICTURE OF HOW VARIOUS HYDRODYNAMIC ACTIVITIES FIT TOGETHER TO DRIVE GLOBAL DISK EVOLUTION. WE WILL ADDRESS KEY QUESTIONS INCLUDING THE STRENGTH OF THE RESULTING HYDRODYNAMIC TURBULENCE THE LIFETIME OF LARGE-SCALE VORTICES UNDER REALISTIC DISK CONDITIONS AND THEIR IMPACT ON THE EVOLUTION OF SOLIDS WITHIN THE DISK. INCLUSION OF THESE ADDITIONAL PHYSICS WILL LIKELY UNCOVER NEW YET-UNKNOWN HYDRODYNAMIC PROCESSES. OUR GENERALIZED MODELS ENABLES A DIRECT LINK BETWEEN THEORY AND OBSERVATIONS. FOR EXAMPLE A SELF-CONSISTENT INCORPORATION OF DUST DYNAMICS INTO THE THEORY OF HYDRODYNAMIC INSTABILITIES IS PARTICULARLY IMPORTANT SINCE IT IS THE DUST COMPONENT THAT IS USUALLY OBSERVED. WE WILL ALSO ESTABLISH THE CONNECTION BETWEEN THE PROPERTIES OF LARGE-SCALE OBSERVABLE STRUCTURES SUCH AS VORTICES TO THE UNDERLYING DISK PROPERTIES SUCH AS DISK MASS AND VERTICAL STRUCTURE WHICH ARE DIFFICULT TO INFER DIRECTLY FROM OBSERVATIONS. WE ALSO PROPOSE TO STUDY FOR THE FIRST TIME THE DYNAMICAL INTERACTION BETWEEN HYDRODYNAMIC TURBULENCE AND PROTO-PLANETS AS WELL AS THE INFLUENCE OF LARGE-SCALE VORTICES ON DISK-PLANET INTERACTION. THIS IS NECESSARY TOWARDS A REALISTIC MODELING OF THE ORBITAL EVOLUTION OF PROTO PLANETS AND THUS IN PREDICTING THE FINAL ARCHITECTURE OF PLANETARY SYSTEMS. THE PROPOSAL TEAM'S EXPERTISE AND EXPERIENCE RANGING FROM MATHEMATICAL ANALYSES TO STATE-OF THEART NUMERICAL SIMULATIONS IN ASTROPHYSICAL FLUID DYNAMICS PROVIDES A MULTI-METHOD APPROACH TO THESE PROBLEMS. THIS IS NECESSARY TOWARDS ESTABLISHING A RIGOROUS UNDERSTANDING OF THESE FUNDAMENTAL HYDRODYNAMICAL PROCESSES IN PROTOPLANETARY ACCRETION DISKS., G58316358, G6273510985, HOW 100 KM PLANETESIMALS FORM FROM SMALLER MM-CM SIZED PEBBLES IS ONE OF THE BIGGEST UNANSWERED QUESTIONS IN SOLAR SYSTEM FORMATION. WITH THE DISCOVERY OF THE STREAMING INSTABILITY A ROBUST CANDIDATE HAS EMERGED FOR CLUMPING THESE PEBBLES TO THE POINT OF GRAVITATIONAL COLLAPSE ALLOWING THEM TO FORM LARGER BODIES. HOWEVER THERE REMAIN TWO LARGELY UNRESOLVED ISSUES WITH THIS PROCESS. FIRST THE STREAMING INSTABILITY WILL ONLY TRIGGER CLUMPING FOR A SUFFICIENTLY LARGE CONCENTRATION OF PEBBLES A CONDITION THAT IS NOT ALWAYS EASILY MET IN DISKS WITH A SMOOTH MONOTONIC RADIAL STRUCTURE. ADDITIONALLY THE INITIAL PLANETESIMAL SIZE DISTRIBUTION THAT ARISES FROM NUMERICAL SIMULATIONS IS SIGNIFICANTLY MORE TOP-HEAVY COMPARED WITH OBSERVED SMALL BODY SOLAR SYSTEM POPULATIONS. ANOTHER ADVANCEMENT IN RECENT YEARS HAS BEEN THE REALIZATION THAT PRESSURE TRAPS I.E. LOCAL GAS PRESSURE ENHANCEMENTS ARE LIKELY PREVALENT IN PROTOPLANETARY DISKS ARISING FROM A VARIETY OF PROCESSES E.G. THE OUTER EDGE OF PLANET-INDUCED GAPS. WHILE THE IMPORTANCE OF THESE TRAPS HAS BEEN REALIZED IN THE CONTEXT OF PLANET FORMATION AS A WHOLE THEIR ROLE IN PLANETESIMAL FORMATION VIA THE STREAMING INSTABILITY HAS ONLY BARELY BEEN EXPLORED. THUS STUDYING THE INTERACTION BETWEEN THESE PRESSURE TRAPS AND STREAMING-INDUCED PLANETESIMAL FORMATION IS ESSENTIAL FOR SEVERAL REASONS. FIRST AS MENTIONED ABOVE THESE TRAPS ARE MORE LIKELY THAN NOT TO EXIST IN PROTOPLANETARY DISKS. SECOND WHILE THESE TRAPS MAY LOCALLY ENHANCE THE CONCENTRATION OF PEBBLES TO STREAMING-UNSTABLE VALUES THESE EFFECTS MUST COMPETE WITH MOMENTUM FEEDBACK FROM THE PEBBLES ONTO THE PRESSURE TRAP WHICH COULD DEFORM THE TRAP AND ACTUALLY REDUCE CLUMPING. FINALLY IF THESE TRAPS CAN SURVIVE THEY COULD POTENTIALLY CHANGE THE INITIAL PLANETESIMAL SIZES (SINCE STREAMING-UNSTABLE WAVELENGTHS WILL DECREASE NEAR THE TRAP PEAK) AND/OR THE SIZE DISTRIBUTION (IF THE TRAPS MAINTAIN A PEBBLE CONCENTRATION CLOSE TO GRAVITATIONALLY INSTABILITY PLANETESIMALS MAY FORM ONE-BY-ONE EACH OF ROUGHLY THE SAME SIZE EQUATING TO A MORE BOTTOM HEAVY DISTRIBUTION). THUS WE AIM TO TEST WHETHER PRESSURE TRAPS WILL (A) SURVIVE THE MOMENTUM FEEDBACK FROM PEBBLES TO PRODUCE SIGNIFICANT CLUMPING AND (B) CHANGE THE RESULTING PLANETESIMAL SIZES AND/OR SIZE DISTRIBUTION. PRESSURE TRAPS COULD ALSO PLAY A CRUCIAL ROLE IN PLANET FORMATION. FOR EXAMPLE AS JUPITER IS BEING FORMED IT WILL OPEN A GAP THAT GENERATES A PRESSURE TRAP EXTERIOR TO ITS ORBIT. PLANETESIMALS FORMED FROM THIS TRAP COULD CRITICALLY INFLUENCE THE EVOLUTION OF THE SOLAR SYSTEM IN ANY COMBINATION OF THREE POSSIBILITIES: THESE PLANETESIMALS MAY MERGE AND/OR ACCRETE PEBBLES TO EVENTUALLY FORM SATURN BE SCATTERED AWAY FROM THE PLANET SOME OF WHICH MAY BE DEPOSITED AS VOLATILE RICH ASTEROIDS IN THE MAIN BELT AND/OR BE ACCRETED BY JUPITER PROVIDING THE SOURCE OF JUPITER'S OBSERVED SUPER-SOLAR METALLICITY. IN THIS PROPOSAL WE WILL USE STATE-OF-THE-ART CODES ATHENA (A GAS+PARTICLE DYNAMICS CODE) AND LIPAD (A PLANET FORMATION CODE) TO CARRY OUT THE MOST IN-DEPTH STUDY TO DATE TO TEST THESE CRITICAL IDEAS. SPECIFICALLY OUR PROPOSED WORK IS OUTLINED INTO THREE TASKS: TASK 1: USE ATHENA TO TEST WHETHER PRESSURE TRAPS WILL SURVIVE FEEDBACK FORCES TO ENHANCE CLUMPING. TASK 2: USE ATHENA TO TEST WHETHER PRESSURE TRAPS WILL CHANGE THE SIZES AND/OR SIZE DISTRIBUTION OF PLANETESIMALS. TASK 3: USE LIPAD TO DETERMINE WHETHER PLANETESIMALS PRODUCED IN A PRESSURE TRAP INDUCED BY PROTO-JUPITER WILL LEAD TO THE FORMATION OF SATURN'S CORE BE SCATTERED INTO THE ASTEROID BELT AND/OR ENRICH JUPITER'S ATMOSPHERE., MAGNETIC FIELDS AND SELF-GRAVITY ARE LIKELY TO PLAY IMPORTANT AND INTERCONNECTED ROLES IN THE EVOLUTION OF PROTOSTELLAR DISKS AROUND NEWLY FORMED STARS. WE PROPOSE TO USE A COMBINATION OF NUMERICAL SIMULATIONS AND ANALYTIC MODELS TO UNDERSTAND HOW NET MAGNETIC FIELDS EVOLVE DURING A SELF-GRAVITATING DISK PHASE AND WHETHER CONDITIONS IN SUCH DISKS ALLOW FOR THE COLLISIONAL GROWTH OF ICY PARTICLES AS A PRE-REQUISITE FOR EARLY PLANET FORMATION. WE WILL SPECIFICALLY SEEK TO ANSWER THREE MAIN QUESTIONS: (1) HOW DO SELF-GRAVITATING PROTOSTELLAR DISKS THREADED BY NET MAGNETIC FIELDS EVOLVE? TO ADDRESS THIS QUESTION WE WILL DEVELOP SIMULATIONS THAT INCLUDE SELF-GRAVITY AND EITHER IDEAL MAGNETOHYDRODYNAMICS (MHD) OR NON-IDEAL MHD INCLUDING AMBIPOLAR DIFFUSION. WE WILL QUANTIFY THE EFFECT OF NET FIELDS ON ANGULAR MOMENTUM TRANSPORT IN SELF-GRAVITATING DISKS AND DEVELOP A PHYSICAL UNDERSTANDING OF NET FLUX TRANSPORT THAT CAN BE USED IN LONG-TERM EVOLUTIONARY MODELS. (2) HOW DOES THE NET FLUX OF PROTOSTELLAR DISKS EVOLVE OVER LONG TIME SCALES? WE WILL DEVELOP SIMPLIFIED NUMERICAL MODELS THAT BUILD ON PRIOR WORK BY LUBOW PAPALOIZOU&PRINGLE (1994) AND GUILET&OGILVIE (2014). (3) HOW IS ENERGY DISSIPATED IN SELF-GRAVITATING DISKS? WE WILL USE IDEALIZED NUMERICAL EXPERIMENTS TO QUANTIFY THE BALANCE BETWEEN DISSIPATION IN LARGE-SCALE SPIRAL STRUCTURES VERSUS SMALL-SCALE TURBULENCE. WE WILL USE THE RESULTS TO BETTER UNDERSTAND WHETHER CONDITIONS IN EARLY PROTOSTELLAR DISKS ALLOW FOR THE INITIAL GROWTH OF ICY SOLID PARTICLES TO LARGER SIZES. THE PROPOSED STUDY IS A THEORETICAL INVESTIGATION INTO HOW BASIC PHYSICAL PROCESSES - DISK SELF-GRAVITY AND MAGNETIC FLUX TRANSPORT - AFFECT THE EVOLUTION OF PROTOSTELLAR DISKS DURING THE FORMATION OF STARS AND PLANETARY SYSTEMS. THE EXPECTED RESULTS ARE RELEVANT TO THE DIRECT IMAGING OF DISK STRUCTURE WITH SPACE ASTROPHYSICS MISSIONS AND TO THE INTERPRETATION OF EXOPLANET POPULATIONS VIA THEORETICAL MODELS THAT START WITH THE COLLISIONAL GROWTH OF SMALL PARTICLES., G767601387, I PROPOSE TO PERFORM THREE-DIMENSIONAL (3D) PROTOPLANETARY DISK SIMULATIONS TO BETTER UNDERSTAND THE FORMATION OF PLANETESIMALS, THE SUPER-KILOMETER, G8210229802
OpenAlex ID: W2952048505