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July 21, 2014 at 11:10 am

Asteroid Named in Honor of Professor Thomas Statler

Professor Thomas Statler

Astronomy Professor Thomas Statler

It’s not every day you learn an asteroid bears your name. This month, Dr. Thomas Statler, Professor of Physics & Astronomy, attended the triennial “Asteroids, Comets, Meteors” conference in Helsinki, Finland, the leading international gathering in the field of small Solar System bodies, where it’s a tradition to announce new asteroid names at the conference banquet. Statler was surprised and delighted to receive this professional honor, along with a few dozen other planetary scientists in attendance.

“My namesake was the 9536th asteroid to be discovered, found by astronomers at the Massachusetts Institute of Technology in 1981,” Statler explained. “The discoverers get to suggest a name, and if it’s approved by the International Astronomical Union it becomes official. So now it’s (9536) Statler.”

The International Astronomical Union is the only body with globally recognized authority to name objects in space.

There are more than 300,000 asteroids now known, so finding a new one is not particularly remarkable, according to Statler. Discovery teams like the one at MIT have, over the years, honored scientists, public figures, and others by naming asteroids after them.

Currently there are about 18,000 asteroids with names, and about 20 times more without. “Because asteroid discoverers have eclectic tastes, the asteroidal “Who’s Who” is a bit odd,” Statler explains. “(9536) Statler travels in the company of (1815) Beethoven and (2001) Einstein, but also (15092) Beegees and (214476) Stephencolbert—not to mention (9007) James Bond and (13681) Monty Python.”

The full list of asteroid names can be found at The International Astronomical Union Minor Planet Center.

There are still 360,000 opportunities to name an asteroid (if you discovered it). “It’s a professional honor,” Statler said. “A very quirky one, to be sure, as there are asteroids named after house pets, dinosaurs, convicted murderers, etc.—but a fun one that is permanently on the books and one to make your parents proud.”

Conference Presentations

At the conference, Statler co-authored with Derek Richardson, Kevin Walsh, Yang Yu, and Patrick Michel a presentation on “Mechanism of self-reinforcing YORP acceleration for fast-rotating asteroids.”

Abstract: The YORP effect is an important process that directly alters the spin states, and indirectly alters the orbits,of small Solar System bodies. It has been suggested that YORP may be able simultaneously to account for the high fraction of binaries among the near-Earth-asteroid (NEA) population, the frequent radar detections of objects shaped like child’s tops, and the abundance of top-shaped asteroids with binary companions. In a compelling demonstration, Walsh et al. (2008, Nature 454, 188) simulated the evolution of idealized, gravitationally bound rubble piles, to which they continually added angular momentum. The centrifugal force caused material to move from mid-latitudes toward the equator, generating the characteristic top shape. Continued spin-up caused the equatorial ridge to shed material, which reaccreted in orbit to form a binary companion. But this mechanism rests on the assumption that YORP will provide all the angular momentum needed to form axisymmetric tops, accelerate them to the mass-shedding limit, and drive enough mass into orbit to form an observable companion. This assumption is problematic, as a truly axisymmetic body would experience no YORP effect at all, and small surface changes on an object with approximate large-scale axisymmetry can easily change the sign of the torque and decelerate the spin (Statler 2009, Icarus 202, 502). So the search is on for a mechanism that can ensure a continual increase in angular momentum to overcome the stochastic effect of topographic changes. One intriguing suggestion is ”tangential YORP” (Golubov and Krugly 2012, ApJL 752, L11), which arises from asymmetric east-west heat conduction across small exposed structures, and always produces an eastward torque. But tangential YORP relies on structures at a preferred size scale, which shrinks to millimeters as the rotation rate approaches periods of a few hours. How the effects generated at these tiny scales are diluted by the mesoscale (meters to hectometers) topography in which they are embedded is still unknown. Here we suggest a different process, in which the accelerating rotation itself alters the mesoscale topography so as to bias the ordinary YORP effect toward continued acceleration. This process begins during the stage when increasing centrifugal forces initiate migration of material toward the equator. We assume that a significant part of that migration occurs in the form of surface avalanches, preferentially occurring on equator-facing slopes that have been destabilized by the centrifugal deflection of the local effective gravity. At rotation periods of a few hours, the Coriolis force on the moving avalanche will be significant, causing a westward deflection of the flow. The accumulated effect from many avalanches will result in a global tendency for shallower slopes to face southwest in the northern hemisphere and northwest in the southern hemisphere, a topographic chirality to which YORP will couple. Because a shallow slope is illuminated for a larger fraction of the day than a steep slope, the tendency will be to increase the eastward component of the recoil force and accelerate the spin. And because it does not rely on heat conduction, this topographic self-reinforcement process can act either in concert with, or independently of, tangential YORP. In this presentation we will demonstrate the circumstances under which topographic self-reinforcement can produce a significant bias in the fraction of rapid rotators that continue to gain angular momentum when already close to the mass-shedding limit.

He also co-authored, with D. Cotto-Figueroa, T. Statler, D. Richardson, and P. Tanga, Coupled spin and shape evolution of small rubble-pile asteroids and self-limitation of the YORP effect.

Abstract: We present the results of the first simulations that self-consistently model the YORP effect on the spin states of dynamically evolving aggregates. Extensive analyses of the basic behavior of the YORP effect have been previously conducted leading to the idea of the classical ”YORP cycle”. These studies are based on the assumption that the objects are rigid bodies, but evidence from lightcurve observations strongly suggests that most asteroids are aggregates. The timescales over which mass reconfiguration occur are much shorter than the timescales over which YORP changes the spin states and Statler [2009] has shown that the YORP effect has an extreme sensitivity to the topography of the asteroids (Icarus 202, 501–513). As the YORP effect changes the spin, the change in spin results in a change of the shape, which subsequently changes the YORP torques. The continuous changes in the shape of an aggregate result in a different evolution of the YORP torques and therefore aggregates do not evolve through the YORP cycle as a rigid body would. Instead of having a spin evolution ruled by long periods of rotational acceleration and deceleration as predicted by the YORP cycle, the YORP effect is self-limiting on aggregate asteroids exhibiting a stochastic behavior and/or a self-governed behavior. We provide a description of the stochastic and self-governed behaviors of the YORP effect along with the results of shape evolution including the types, magnitudes, and frequencies of movement and shedding of material. Although rotational acceleration for long periods of time is not achieved, a fraction of objects do present mass-shedding episodes at lower spin rates than the critical spin limit for aggregate asteroids. We also provide the bulk properties of the obtained distribution of changes in the spin rates, which are necessary in order to model correctly the coupled Yarkovsky/YORP evolution.

 

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