The meteor impact that caused Russia’s Popigai crater located in Siberia may be the cause the Eocene mass extinction event that occurred just over 33 million years ago. By measuring certain isotopes within rock samples from the Eocene period, iPLEX graduate student Matt Wielicki able to tie a short-lived, rapid cooling period in global climate to around the same time that the Popigai crater, one of the ten largest impact craters on Earth, was formed. The rapid onset of colder temperatures could be explained by a large quantity of reflecting particulates being launched into Earth’s atmosphere during the impact that blocked out the Sun. During this period, many aquatic species went extinct including the earliest types of toothed whales and many types of sea urchins and snails.
To learn more about this discovery, visit Livescience.
The ELFIN satellite currently under construction at UCLA has been selected to receive funding by the NASA Low Cost Access to Space (LCAS) program. The LCAS website describes their mission as supporting “science investigations that may be completed through suborbital flight, as well as proof-testing new technologies that may ultimately find application in free-flying Heliophysics space missions.”
ELFIN is primarily being designed and built by a group of undergraduate students supervised by Prof. Vassilis Angelopoulos. The satellite is about the size of a loaf of bread, weighs 8 pounds, and will house a magnetometer and particle detector to take space weather measurements around Earth’s poles. Learn more about the mission from the ELFIN website.
During the first million years of evolution, nascent planetary
systems are embedded in dense disk-shaped clouds of gas. These
circumstellar disks are home to a myriad of hydrodynamical processes,
which bring about turbulence and the emergence of viscous-like behavior,
enabling accretion of gas onto the protostar. Meanwhile, micronsize dust
grains embedded in the disk are growing through coagulation onto pebbles
and rocks. Turbulence has a positive effect on these small solids,
concentrating them into transient high pressure regions for long enough to
achieve gravitational collapse into km-sized bodies, forming the first
planetesimals. Giant storm systems in the disk, similar to Jupiter’s Great
Red Spot, may exist in quiescent zones of the disk. These are even more
prone to collecting solid material, producing the first terrestrial
planets and cores of giant planets. In this talk I will discuss the state
of the art and recent advances in the field of planet formation, as well
as pressing problems such as the asymmetries observed in ALMA images of
circumstellar disks, and how to interpret them.
By simulating hundreds of impacts in Mars’ equatorial region, a team of scientists have determined that the ancient Martian atmosphere was likely too thin to support flowing liquid water on the planet’s surface. The team, including iPLEX researcher Jean-Pierre Williams, identified and catalogued hundreds of large craters near the Martian equator. They then used a computer simulation to calculate what atmospheric density would have caused the range of craters observed. They concluded that the Martian atmosphere was 150 times thicker than today, a value that is only a fraction of the atmospheric pressure required to support liquid water. This presents a mystery, since many Martian geological features appear to have been carved by massive flooding. The paper’s authors suggest that the Martian atmosphere may have been temporarily thickened at times by severe volcanic activity or a large impacts that would spew large amounts of gases into the atmosphere, allowing the surface of the planet to warm up enough to allow liquid water to flow.
Read more about their Nature Geoscience paper, published on April 13, here.
I plan to discuss two topics that I have been working on:
(1) For Jupiter-like planets, the question of how cyclones and anticyclones (like the GRS and white ovals) are formed is not settled. I discuss computer simulations showing that both kinds of vortices can appear spontaneously in a rotating convection zone, much like the regions below the weather layers of Jupiter and Saturn. These vortices are long-lived, and there is no need to prescribe an artificial shear to create and maintain them.
(2) The Chinese lunar orbiters Chang’E 1 and 2 have obtained best available sets of microwave data on the moon so far. However, the two sets of data are off by 10 – 20 K, thus creating puzzle and doubts. A correction method based on taking account of possible contamination of the low temperature calibration antennas by radiation from the lunar surface is discussed. The disagreement can be reduced by a large factor.
The amount of water present in the moon may have been overestimated by scientists studying the mineral apatite, says a team of researchers led by Jeremy Boyce of the UCLA Department of Earth, Planetary and Space Sciences.
Boyce and his colleagues created a computer model to accurately predict how apatite would have crystallized from cooling bodies of lunar magma early in the moon’s history. Their simulations revealed that the unusually hydrogen-rich apatite crystals observed in many lunar rock samples may not have formed within a water-rich environment, as was originally expected.
This discovery has overturned the long-held assumption that the hydrogen in apatite is a good indicator of overall lunar water content.
“The mineral apatite is the most widely used method for estimating the amount of water in lunar rocks, but it cannot be trusted,” said Boyce, who is an adjunct assistant professor in the UCLA College of Letters and Science. “Our new results show that there is not as much water in lunar magma as apatite would have us believe.”
The research was published online March 20 in the journal Science on and will be published in a future print edition.
The above image is a map of calcium within a polished thin slice of a lunar rock. The high calcium content in apatite is indicated by the bright pinks and reds, while surrounding minerals with lower calcium content are shown in blues and black. Core to rim zoning of water in crystals such as this one demonstrates the presence of the apatite fractionation, an effect responsible for the high water content of lunar apatites on an otherwise dry moon.
For decades, scientists believed the moon was almost entirely devoid of water. However, the discovery of hydrogen-rich apatite within lunar rocks in 2010 seemed to hint at a more watery past. Scientists originally assumed that information obtained from a small sample of apatite could predict the original water content of a large body of magma, or even the entire moon, but Boyce’s study indicates that apatite may, in fact, be deceptive.
Boyce believes the high water content within lunar apatite results from a quirk in the crystallization process rather than a water-rich lunar environment. When water is present as molten rock cools, apatite can form by incorporating hydrogen atoms into its crystal structure. However, hydrogen will be included in the newly crystallizing mineral only if apatite’s preferred building blocks, fluorine and chlorine, have been mostly exhausted.
“Early-forming apatite is so fluorine-rich that it vacuums all the fluorine out of the magma, followed by chlorine,” Boyce said. “Apatite that forms later doesn’t see any fluorine or chlorine and becomes hydrogen-rich because it has no choice.”
Therefore, when fluorine and chlorine become depleted, a cooling body of magma will shift from forming hydrogen-poor apatite to forming hydrogen-rich apatite, with the latter not accurately reflecting the original water content in the magma.
Understanding the story of lunar apatite has implications beyond determining how much water is locked inside lunar rocks and soil. According to the predominant theory of how the moon originally formed, hydrogen and other volatile elements should not be present at all in lunar rocks.
Many scientists theorize that the moon formed when a giant impact tore free a large chunk of Earth more than 4 billion years ago. If this “giant impact” model is correct, the moon would have been completely molten, and lighter elements such as hydrogen should have bubbled to the surface and escaped into space. Since hydrogen is a key component of water, a moon formed by a giant impact should be dry.
The majority of lunar samples are in fact very dry and missing lighter elements. Yet hydrogen-rich apatite crystals are found in a whole host of lunar samples and have presented a paradox for scientists. Somehow, despite the moon’s fiery beginning, some water and other volatiles may have remained, though perhaps not as much as apatite initially implied.
“We had 40 years of believing in a dry moon, and now we have some evidence that the old dry model of the moon wasn’t perfect,” Boyce said. “However, we need to be cautious and look carefully at each piece of evidence before we decide that rocks on the moon are as wet as those on Earth.”
This study shows that scientists still have much to learn about the composition and environment of the early moon.
“We’re knocking out one of the most important pillars of evidence regarding the conditions of the formation and evolution of the moon,” Boyce said. “Next, we plan to determine how badly apatite has distorted our view of the moon and how we can best see past it to get at the moon’s origin.”
The research was supported by a NASA Cosmochemistry grant and a NASA Lunar Advanced Science for Exploration Research grant.
Co-authors of the study include undergraduate Steven Tomlinson from UCLA, assistant research professor Francis McCubbin from the University of New Mexico, professor James Greenwood from Wesleyan University and staff scientist Allan Treiman from the NASA-funded Lunar and Planetary Institute.
On March 26, the Dawn Mission team was awarded the 2014 Trophy for Current Achievement, the Smithsonian’s highest honor bestowed on groups. The Dawn probe is the first to explore asteroids within our solar system’s main belt up close. UCLA Professor Christopher T. Russell, an iPLEX member, is the principal investigator for the Dawn mission and traveled to Washington D.C. to receive the award.
Read more about the award at the UCLA Newsroom. Find out more about Dawn on their mission homepage.
Pictured here are the following members of the Dawn team (from left to right): Grant Faris, Carol Polanskey, Chris Russell, Steve Joy, Greg Whiffen, Marc Rayman, Robert Mase, Tim Weise, Brett Smith, Nick Mastrodemos, Paul Fieseler, Carol Raymond and Don Han. Image credit: Smithsonian National Air and Space Museum
One of the expanding fields of exoplanet research is the detailed characterization of exoplanets, including the properties of their atmospheres. This is currently being done for a growing sample of the so-called hot Jupiters – gas-giant planets orbiting close-in to their host star – a class of planets with no Solar System analog. I will present the results of our atmospheric study of the unique transiting exoplanet Kepler-13Ab. It is one of only two known short-period (1.76 day) transiting planets orbiting a bright hot A-type star (Teff = 7,650 K), and the host star is part of a hierarchical triple system. We have studied the planet’s emission spectrum by observing the planet’s occultation (secondary eclipse; when the planet moves behind the host star) using data from the optical to the IR, obtained with the Kepler and Spitzer space telescopes along with a ground-based observation in the near-IR. We derive a temperature of 2,750 K of the planet’s day-side hemisphere, as hot as the smallest main-sequence stars. We find evidence for a high geometric albedo (~0.3), a few times larger than that of most other hot Jupiters, and for the presence of atmospheric inversion. In addition, our revised planetary radius (1.4 Jupiter radius) is significantly smaller than previously thought, and our revised planetary mass, from measuring the beaming effect and ellipsoidal distortion in the Kepler orbital phase curve, is 5 – 8 Jupiter mass. Therefore, Kepler-13Ab is a massive high-density hot Jupiter. Time allowing, I will show how the difference between the Kepler occultation time and transit (primary eclipse) time is half a minute shorter than expected from the light travel time delay across the orbit, and discuss possible causes.
A new dwarf planet has been discovered in the ‘interplanetary no man’s land’ found between the Kuiper Belt and the Oort Cloud that astronomers originally thought was just empty space. The new planet called 2012 VP113 is 280 miles across and orbits at a distance of 80 astronomical units (AU),where an AU is the distance from the Earth to the Sun. This orbit takes the new planet far beyond the Kuiper Belt which stretches between 30 and 55 AU. Pluto, a Kuiper Belt Object, never orbits further than 49 AU from the Sun. The dwarf planet 2012 VP113 is not far enough away to be considered part of the Oort Cloud, a shell of icy objects orbiting thousands of AU from the Sun, but its discovery may indicate the existence of an ‘inner Oort Cloud’.
Read more about the story from the LA Times, including commentary from iPLEX Director Dave Jewitt.
Recent observations have discovered several objects that are evidently experiencing some sort of mass shedding or breakup. The interpretations of such objects can be across this spectrum; for example, P/2013 P5 may be experiencing mass shedding, while P/2013 R3 may be breaking up into several components. P/2010 A2, on the other hand, could be some combination of these effects. Detailed observations of these bodies can be interpreted as being consistent with rotational break-up of the objects, based on the spectrum and magnitude of ejecta speeds plus some aspects of the morphology of their debris tails. An interesting hypothesis is whether all of these outcomes could have singularly arisen from the YORP effect. Specifically, could rotational instability lead to such different failure modes? The present study considers failure modes of irregularly shaped rubble-pile bodies due to a YORP-type spin up, comparing perfectly ellipsoidal shapes with actual shape models (based on radar observations and spacecraft imaging). Failure modes may be categorized into two different modes: structural failure, a process of plastic deformation finally leading to fission or global redistribution in a catastrophic way, and surface shedding at which particles sitting on the surface are lofted from there due to centrifugal accelerations exceeding gravitational accelerations prior to structural failure. We have developed dynamical and structural analysis techniques to determine the failure modes of rubble pile objects given their shape, mass, and spin rate. This talk discusses correlations between the shape and the failure mode due to a YORP-type spin up, using 21 sample asteroid models. The primary result of this study shows that irregular asteroids can be categorized into four shape classes: (i) spherical bodies undergoing structural failure, (ii, iii) ellipsoidal bodies experiencing either structural failure or surface shedding, and (iv) bifurcated bodies failing by structural failure. We discuss what the observational implications of these failure modes may be.
The meteor impact that caused Russia’s Popigai crater located in Siberia may be the cause the Eocene mass extinction event that occurred just over 33 million years ago. By measuring certain isotopes within rock samples from the Eocene period, iPLEX graduate student Matt Wielicki able to tie a short-lived, rapid cooling period in global climate to around the same time that the Popigai crater, one of the ten largest impact craters on Earth, was formed. The rapid onset of colder temperatures could be explained by a large quantity of reflecting particulates being launched into Earth’s atmosphere during the impact that blocked out the Sun. During this period, many aquatic species went extinct including the earliest types of toothed whales and many types of sea urchins and snails.
