UCLA Planets

May 30, 2013: New ideas about the origin of the Earth and Moon

ivy — Fri, 24 May 2013 07:28:12 +0000

In the standard model, Earth accreted via a series of giant impacts and the last giant impact produced the Moon and fully melted the Earth. The Moon and Earth are identical in multiple isotope systems that show significant variations between most meteorite groups and planetary bodies. Thus, the simplest explanation for the isotopic similarity is that the Moon and Earth’s mantle have a common origin. However, the canonical giant impact model predicts that the Moon is primarily composed of material from the impactor, which should have had a different isotopic signature than Earth. In addition, recent data from the deep mantle demonstrate that the early Earth was not completely mixed and preserves chemical heterogeneities established during Earth’s accretion. Previous Moon-formation studies assumed that the angular momentum after the impact was similar to present day, but N-body simulations of the growth of Earth-mass planets typically find higher spin rates at the end of accretion. I will present a new model for the origin of the Earth–Moon system. A giant impact onto a fast-spinning proto-Earth can produce a disk that is massive enough to form the Moon and composed primarily of material from Earth, but the system would have had more angular momentum than today. Subsequently, the excess angular momentum can be lost during tidal evolution of the Moon via an orbital resonance. The impact energy is primarily deposited in the impacted hemisphere, and the mantle of the post-impact Earth is stably stratified, which would inhibit immediate deep convective mixing. Hence, the Moon-forming impact need not destroy pre-existing chemical heterogeneities in the deep mantle of the proto-Earth. Finally, I will discuss implications for the volatile depletion on the Moon and the formation of Earth’s early atmosphere.

May 23, 2013: The Origin of Solar and Extrasolar Planets

ivy — Wed, 22 May 2013 18:19:25 +0000

The modern wealth of data on extrasolar planets is a boon to theoretical studies of the origin and evolution of planetary systems. However the great diversity of exoplanet systems also poses challenges to the goal of a coherent, unified theory of planet formation. This talk will present dynamical models of the most crucial stages of planet growth. First I will address the origin of the solid building blocks known as planetesimals. Aerodynamic processes, highlighted by the streaming instability, play a crucial role in the emergence of planetesimals within turbulent gas disks. Such models of early planet growth can be tested with exoplanet statistics and, more directly, with studies of the Kuiper Belt. Shifting to later phases, I will address the accretion of giant planet atmospheres onto protoplanetary cores. I will present models that challenge the conventional wisdom that a 10 Earth mass core is needed to trigger runaway gas accretion. In particular lower core masses suffice in the outer regions of the protoplanetary disk. These models are crucial for understanding the HR 8799 multiplanet system and others that will be discovered in current and future imaging surveys. I will conclude by discussing future prospects for theoretical models to improve our understanding of planets near and far.

May 21, 2013: Puzzles in Giant Planet Formation

ivy — Fri, 17 May 2013 19:39:42 +0000

Despite the many hundreds of known “giant” exoplanets, theoretical models still struggle to form them. Under the core-accretion, gas-capture model of giant planet formation, it is still challenging to explain how the required ~10 Earth mass rocky/icy cores can form within the lifetime of their host gaseous circumstellar disks. In this talk I will present two different new lines of research to address this timescale dilemma. I will explore whether or not a newly identified, extremely fast aerodynamic aided accretion of “pebbles” may present a mechanism to form giant planet cores extremely rapidly. Then I will discuss how volatile loss from ice-rich cores and the subsequent enrichment of the atmosphere can alter the efficiency of core growth and potentially aid the planet formation process.

UCLA Meteorite Museum displays extensive collection to the public for the first time

kim — Thu, 16 May 2013 20:16:31 +0000

Nearly 50,000 years ago, an asteroid fragment slammed into Earth approximately forty miles east of what is now Flagstaff, Arizona. Upon impact, the celestial projectile shattered into thousands of pieces and created a mile-wide hole now known as Meteor Crater. A 357-pound chunk of that original asteroid now stands center stage in the new UCLA Meteorite Museum.

The Canyon Diablo meteorite was donated to UCLA by philanthropist William Andrews Clark, Jr. upon his death in 1934, becoming one of the first specimens entered into the UCLA Meteorite Collection. While originating from sporadic donations and purchases, it has been Professor John Wasson and researcher Alan Rubin who have spent decades building the collection to its 1500-specimen count today. Together, they have made the collection one of the most extensive in the world, but only recently have these unique bits of our solar system’s history been on display for visitors to admire. “For many years, we’ve collected beautiful exhibit specimens, but kept them locked in an inaccessible cabinet,” Rubin said. “It’s nice to put them on display for other people to see.”

Those expecting the museum to be filled with rows of indistinguishable black rocks may be surprised to learn that there are many types of meteorites, ranging from metallic to stony and everything in between. More than one exhibit emphasizes chondrites, a type of meteorite that is a subject of “endless fascination,” according to Rubin. “Chondrites are composed of thousands or millions of tiny spherules, called chondrules.” While each chondrule tells a different story, they are still very much a mystery. “It appears that chondrules formed from clumps of dust in the solar nebula, the gas and dust cloud that was here before the planets and asteroids formed, and were zapped in a way that is still unknown,” Wasson said.

Not all the exhibits display rocks of extraterrestrial origin, however. One exhibit showcases a collection of melted tektites and Libyan desert glass that formed as a result of meteor impacts. Another exhibit offers tips on how to correctly identify meteorites. Rubin, a world expert in meteorite identification, receives phone calls nearly every day from meteorite-hunting hopefuls. While real specimens occasionally come across his desk, the vast majority of these objects come from Earth. The exhibit, entitled “Meteorwrongs,” features some of the more interesting Earthly samples Rubin has accumulated over the years.

Wasson and Rubin hope that the museum will help educate the next-generation of meteorite researchers. “The museum will be a wonderful teaching resource,” Wasson said. “Our goal is to make it the world’s best scientifically-oriented meteorite museum.” Open to the public weekdays from 9am – 4pm, the museum is located in Geology 3697. Admission is free. The museum, still incomplete, will have mounted informational tablets in its final configuration.

The UCLA Meteorite Museum is supported by the Department of Earth and Space Sciences and the Institute for Planets and Exoplanets. Those interested in providing financial support to the UCLA Meteorite Collection should visit http://giving.ucla.edu/meteorites/.

Watch a video profile of Alan Rubin here. Watch a video tour of the meteorite museum here.

May 24, 2013: Deltaic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars

ivy — Wed, 15 May 2013 21:57:38 +0000

A fundamental long-standing question regarding Mars history is whether the flat and low-lying northern plains ever hosted an ocean. The best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy. Here we use high-resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the Aeolis Dorsa region, just north of the dichotomy boundary. Observations of stacked channel bodies, switches in channel direction tied to a single node, and stratal geometries indicate that these landforms represent exhumed distributary channel deposits. Observations of depositional trunk feeder channel bodies, a lack of evidence for past topographic confinement, channel avulsions at similar elevations, and the presence of a strong break in dip slope between topset and foreset beds suggest that this distributary system was most likely a delta, rather than an alluvial fan or submarine fan. The location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary, unconfined by any observable craters, suggests a standing body of water potentially 105 km2 in extent or greater, and is spatially consistent with hypotheses for a northern ocean.

May 16, 2013: The Beginning of Life and the End of Solar Systems

ivy — Tue, 14 May 2013 18:18:52 +0000

I will address several questions related to how much life there might be in our Galaxy:
What affects whether potentially Earth-like exoplanets might be good abodes for life?
What kind of (Milankovitch-like) variations in habitability might be expected in exosolar
systems? And what does the origin of life on Earth tell us about the probability of life
elsewhere in the Galaxy? I will also discuss the longterm evolution of binary systems,
including thermal and chemical changes, and orbital evolution. In particular, Jupiter will
eventually become a hot Jupiter, and if it were somewhat closer to the Sun it would
eventually be tidally engulfed by the future-red-giant Sun.

Graduate student awarded Chateaubriand Fellowship

kim — Mon, 13 May 2013 23:11:35 +0000

Alex Grannan, a graduate student in Professor Jonathan Aurnou’s SPINLab has been awarded a Chateaubriand Graduate Exchange Fellowship. The award will provide funding for him to spend a year in the IRPHE Lab in Aix-en-Marseilles with Professor Michael Le Bars studying tidally driven resonant flows in planetary and stellar interiors.

UCLA scientists monitor collisions in space

kim — Mon, 13 May 2013 22:44:30 +0000

In a paper published in the Journal of Meteoritics and Planetary Science, UCLA Professor Christopher T. Russell and graduate student Hairong Lai present a new way of monitoring collisions between asteroids and meteroids. Their method, developed based on 30 years of observational data on these small interplanetary objects, may help scientists better predict when debris from these impacts may pose a danger to Earth.

Read more about this recent discovery at: http://newsroom.ucla.edu/portal/ucla/ucla-space-scientists-find-way-245276.aspx .

Professor Russell recently celebrated his seventieth birthday. A two-day symposium was held May 8-9 to honor his long career in planetary science.

April 26, 2012: Precise Assemblies, Clusters, Superatoms, and Cluster-Assembled Materials

ivy — Fri, 10 May 2013 23:00:27 +0000

Precise clusters offer a new set of building blocks with unique properties that can be leveraged both individually and in materials in which their coupling can be controlled by choice of linker, dimensionality, and structure. Initial measurements in both of these worlds have been made. Isolated adsorbed or tethered clusters are probed with low-temperature scanning tunneling microscopy and spectroscopy. Even closely related elements behave differently on identical substrates. Surprising spectral variations are found for repeated measurements of single isolated, tethered clusters. In periodic solids, precise clusters joined by linkers can be measured experimentally and treated theoretically with excellent agreement, in part due to the relatively weak coupling of the clusters. This coupling can be controlled and exploited to produce materials with tailored properties. Some of the rules of thumb for predicting these properties are being developed through these initial studies and the limit to which they can be applied is being explored.

April 19, 2012: Recent Insights into Planet Formation and Debris Disks

ivy — Fri, 10 May 2013 22:58:57 +0000

I will discuss recent insights that we have gained into planet formation and debris disks. In the first half of my talk, I will focus on the Kuiper belt, located at the outskirts of our planetary system, and the formation of debris disks. I will show how studying small km-sized Kuiper belt objects enables us to put our Kuiper belt into context of debris disks around other stars and I will explain how we can use the size distribution of small Kuiper belt objects and debris disks to gain insights into collisional cascades and the material properties of the objects themselves. In the second half, I will review dynamical models and geochemical constraints from the Earth, Moon and Mars and discuss their implications for the last stage of terrestrial planet formation.