Oct

18

2020

Dr. Donald Brownlee

The Golden Age of Sample Return Missions from Space: What comet samples have told us about the origin of the solar system

Location: https://ucla.zoom.us/meeting/register/tJEqduyupj0vGd3S0_52FsbHTbPjYr0sZQUj
Time: 2:30PM

In the past 15 years, space missions have returned samples of the Sun, a comet and an asteroid for detailed study by state-of-the-art methods in laboratories around the world. Samples from two additional asteroids are being returned by current missions and return missions from the Moon and Mars are planned. Starting 30 years after the last Apollo lunar mission, some have called these new missions the Golden Age of post-Apollo sample return missions. In this talk, I will describe the Stardust mission and how the ancient rocky materials it returned from an active comet have given us important new insight into the formation of icy-bodies near the edge of the solar system. Just as Moore’s Law led to vast improvements in our computers, analogous advances in microanalytical methods have led to unprecedented capabilities for studying extraterrestrial materials. In the case of comet samples, the analyses have found abundant rocky materials that formed at incandescent temperatures, probably in the inner solar system. Such materials were profoundly unexpected components in a body whose ices formed at cryogenic temperature. Their presence in comets is evidence of large scale transport of rocky materials from the hottest regions of the early solar system to its coldest parts.

Sep

20

2020

Dr. Andrew Davis

Rocks and Minerals from Stars

Location: https://ucla.zoom.us/meeting/register/tJEqduyupj0vGd3S0_52FsbHTbPjYr0sZQUj
Time: 2:30PM

One of the most remarkable discoveries of the twentieth century is that some meteorites contain dust grains made around other stars that lived and died more than 4.5 billion years ago, before our Solar System formed. Stars only twice the mass of our Sun eventually turned into red giant stars and lost much of their mass as gas and dust. More massive stars ended with spectacular explosions called supernovae, and throw off much of their mass. Both kinds of stars return copious amounts of dust to the interstellar medium (the stuff between the stars), a portion of which formed new stars like our own, and we have recognized dust grains from both red giants and supernovae in meteorites. Each dust grain retains a chemical and isotopic record of the star around which it formed and by analyzing individual dust grains in the laboratory, we can study the interiors of stars in ways not possible by astronomy with telescopes. The study of stardust in the laboratory has led to new understanding of how the chemical elements are made in stars. Stardust was also not uniformly mixed into the solar nebula, the disk of gas and dust from which the Sun and planets formed. This caused small differences in isotopic composition among Solar System materials that have proven to be powerful tracers of the relationships between planets and different kinds of meteorites.

Aug

9

2020

Dr. Meenakshi Wadhwa

Rocks from Space – Tales from the Meteorite Vault

Location: https://ucla.zoom.us/meeting/register/tJEqduyupj0vGd3S0_52FsbHTbPjYr0sZQUj
Time: 2:30PM

Our Solar System and life as we know it could not have evolved as it did without impacts, which are perhaps the most influential among the processes shaping the surfaces of planets and moons. Early in the history of our Solar System, collisions between bodies were a key process in the growth of planets. In fact, our Moon was likely formed as the result of a giant impact on the early Earth. In the case of the Earth, the raw materials for kick-starting life may have been delivered to the surface by meteorite impacts. And the course of life on our planet has been greatly altered by the huge meteorite impacts (such as the one that killed off the dinosaurs about 65 million years ago). Are large impacts a thing of the past, or are they likely to occur in the near future? Our future may well depend on understanding and mitigating this risk. While studying samples returned from missions to asteroids will be important for this purpose, we already have many tens of thousands of asteroidal samples here on Earth that are readily and more cheaply available for us to study – these are the meteorites (rocks from space!) in our rock collections at museums and universities. While most of these meteorites indeed come from asteroids, there are also some rare kinds that come from the Moon and the planet Mars, and we can learn about the geologic histories of these planetary bodies from studying these samples. In this talk, I will discuss our current understanding of meteorites and how they are key to answering some of humanity’s biggest questions: Are we alone in the Universe or is there life elsewhere? How and when did our Solar System and planets form? Where did the water in the Earth and other planetary bodies in our Solar System come from? How did life originate on our planet?

Jul

12

2020

Dr. Cristina Thomas

DART (Double Asteroid Redirection Test): A Telescope Observer's Perspective

Location: https://ucla.zoom.us/meeting/register/tJcrfuiqpjIoGd3L-l880NKVs9ePDkLIjlQu
Time: 2:30PM

DART is NASA's first planetary defense mission, which will test asteroid deflection by kinetic impactor. The spacecraft will impact the satellite of the binary near-Earth asteroid (65803) Didymos in fall 2022. I lead the DART team responsible for observing and understanding the orbit of the moon prior to and after impact. The observed orbit change will be how the team determines the effectiveness of the experiment. We understand the orbit of the binary asteroid system using light curves, a measure of how the brightness of an object changes over time. When Didymos is close to Earth, the moon and the primary eclipse each other from the vantage point of our telescopes on the ground. Each eclipsing event causes a subtle dimming of the lightcurve known as a "mutual event". Observing these events enables us to observe the path of the satellite around the primary and predict the next mutual events. We observed the Didymos system in 2019 and have additional pre-impact observations planned for later in 2020 and early 2021. These observations will establish the state of the system before impact. We will perform similar observations in the period following the fall 2022 impact to determine the change in the satellite orbit. I will discuss how we understand the orbit of the satellite, results from our recent observations, and our future plans for observing the Didymos system.

Jun

14

2020

Dr. Frank Kyte

Spherules in Sediment Deposits from Asteroid Impact Ejecta

Location: https://ucla.zoom.us/meeting/register/tJ0ud-yppzkpH9zTgL43K75yP73wYub-w6ET
Time: 2:30PM

This talk will discuss formation of impact spherules and their occurrence in impact deposits ranging in age from 0.8 Ma (million years before present) to 3400 Ma. When asteroids impact the Earth with cosmic velocities (about 20 km/sec) they release enormous amounts of kinetic energy. A large portion of this energy is transferred to the Earth’s surface that results in seismic waves and excavation of a crater many times the asteroid’s volume. Materials ejected from this crater are deposited mostly near the crater, but in large impacts the ejecta with the highest velocity can travel above the atmosphere and return as a global deposit. The famous dinosaur-killing impact at the K/Pg (a.k.a. KT) boundary produced a global deposit that was probably only a few mm thick. It is well known that this K/Pg layer has lots of iridium from the asteroid but its most distinctive characteristic on a macro level is that it is composed mainly of small spherical particles known as impact spherules. Impact spherules are a common feature of distal impact deposits (those deposited far from the impact site). Large impacts can melt significant amounts of crustal rocks in the impact crater, producing spherules around the crater. The highest velocity ejecta likely comes from a supercritical* “ejecta plume” composed of a mixture of crustal and asteroidal materials. As this ejecta plume expands, melt droplets will form, some condensing from a vapor, and these will solidify to form the silicate spherules common in impact deposits.