Matija Ćuk Wins Prestigious Urey Prize in 2014

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Matija Ćuk Wins Prestigious Urey Prize

By David Morrison, Director of the Carl Sagan Center

SETI Institute scientist Matija Ćuk has received the highest honor for a young planetary scientist from the American Astronomical Society. The Division for Planetary Sciences of the AAS has announced the award the 2014 Harold C. Urey Prize for outstanding achievement in planetary research to Matija Ćuk. The award will be presented at the DPS meeting in November.

Matija is a specialist in planetary dynamics – the study of the effects of gravity on the motions of objects in the solar system. The AAS/DPS announcement of the prize noted that his broad-ranging research is significantly contributing to understanding the origin of the solar system’s current structure. His interests also span general aspects of planet and satellite formation. This research is driven by observations, primarily dynamical but also chemical and geophysical. He has applied his skills across a broad range of topics: the origins and evolutions of the Moon, binary asteroids, tidal evolution, orbital stability, rotational history and cratering.

Matija did his undergraduate work in astrophysics at the University of Belgrade in Serbia, and he received his Ph.D. in 2005 from Cornell University. His thesis developed an analysis of how planets capture irregular satellites, and then investigated the effects of secular resonances on their orbits. This work has been described as a technical tour de force in celestial mechanics. During this same period he devised and convincingly demonstrated the existence of the BYORP mechanism in which thermal radiation forces affect the orbital and rotational histories of binary asteroids. Other researchers have since elaborated on this mechanism, as has Matija, working with collaborators, some of whom were initially skeptical of its effectiveness.

Recently Matija has focused on the Earth-Moon system, including the evolution of the Moon’s orbit and the origin of the lunar impact cataclysm (the “late heavy bombardment”), and on aspects of the dynamics of unstable bodies in the Solar System. He found a significant flaw in the interpretation of the lunar cratering record. His study of the number density of the craters on the Orientale ejecta blanket (the youngest impact basin) indicated that fresh (class 1) craters date back to the lunar impact cataclysm. His research undercut the widely accepted assumption that the cataclysm was caused by asteroids from the main asteroid belt between Mars and Jupiter. Matija’s result challenged the status quo and solicited some strong responses, but no one identified any conceptual flaws in his arguments. New data from the Lunar Reconnaissance Orbiter support his interpretation.

Matija’s work on the origin of the Moon sought to address the observed isotopic similarity between the Earth and Moon. He identified the angular momentum constraint as a possible pathway to reconciliation between the geochemical data and giant impact hypothesis: if the early Earth-Moon system had much higher angular momentum than present day, then alternate style impact events may derive the Moon primarily from Earth’s mantle. He defined the tidal parameters that led to the largest transfer of angular momentum from the Earth-Moon system to the Earth-Sun system. Matija’s result is a major contribution to planetary science, opening new directions for understanding the origin and early evolution of the Earth-Moon system.

The SETI Institute and its Carl Sagan Center for the Study of Life in the Universe are proud to congratulate our colleague Matija Cuk, who is clearly an outstanding young researcher worthy of being recognized by the Harold C. Urey Prize.

 

 

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Matija Ćuk var hovedforfatter på en Nature artikel om månebanens udvikling fra en jord med stor hældning og hurtig rotation, som nu er blevet genoptrykt på arxiv.org:

Tidal evolution of the Moon from a high-obliquity, high-angular-momentum Earth

In the giant impact hypothesis for lunar origin, the Moon accreted from an equatorial circum-terrestrial disk; however the current lunar orbital inclination of 5 degrees requires a subsequent dynamical process that is still debated. In addition, the giant impact theory has been challenged by the Moon’s unexpectedly Earth-like isotopic composition. Here, we show that tidal dissipation due to lunar obliquity was an important effect during the Moon’s tidal evolution, and the past lunar inclination must have been very large, defying theoretical explanations. We present a new tidal evolution model starting with the Moon in an equatorial orbit around an initially fast-spinning, high-obliquity Earth, which is a probable outcome of giant impacts. Using numerical modeling, we show that the solar perturbations on the Moon’s orbit naturally induce a large lunar inclination and remove angular momentum from the Earth-Moon system. Our tidal evolution model supports recent high-angular momentum giant impact scenarios to explain the Moon’s isotopic composition and provides a new pathway to reach Earth’s climatically favorable low obliquity.

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Den traditionelle forklaring på Månens oprindelse antager, at Jorden rammes af en planet med en masse som Mars. Sammenstødet producerer en ring af partikler omkring ækvator. Denne ring samler sig hurtigt til en måne i et cirkulært kredsløb omkring ækvator. Tidevandseffekten fra Månen (og Solen) på Jordens form overfører impulsmoment fra Jorden til Månen, så Jorden roterer langsommere og Månen fjerner sig fra Jorden. Man antager, at impulsmomentet for Jord-Måne systemet er bevaret. Men denne forklaring har to problemer:

(1) Månens bane hælder 5 grader i forhold til ekliptika.

(2) Månen har overraskende samme isotopsammensæthing som Jordens kappe.

Jordens kappe og materialet i ringen over Jordens ækvator må derfor være godt blandet sammen. Dette er muligt, hvis Jorden lige efter sammenstødet havde en rotationsperiode på kun 2.5 timer. Dette kræver imidlertid, at det samlede impulsmoment for Jord-Måne systemet var 1.8 gange så stort som den nuværende værdi. Hvordan har Jord-Måne systemet mistet det overskydende impulsmoment?

Artiklen viser ved numeriske beregninger, at dette er muligt, hvis Jordens polakse starter med at have en hældning på 70 grader i forhold til ekliptikas pol. En ustabilitet i Månens bane medfører, at Månens baneplan får en hældning på hele 30 grader i forhold til ækvator. Denne hældning kombineret med perturbationer fra Solen medfører, at det totale impulsmoment reduceres til den nuværende værdi. Under processen reduceres jordaksens hældning ned til den nuværende værdi omkring 20 grader samtidigt med, at månebanens hældning i forhold til ekliptika bliver 5 grader.

Hele forløbet tager kun omkring 40 millioner år, så den spændende dynamisk er forbi, når livet opstår på Jorden.

 

 

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