Scott Sheppard studies the dynamical and physical properties of small bodies in our Solar System, such as asteroids, comets, moons and trans-neptunian objects (bodies that orbit beyond Neptune).  These objects have a fossilized imprint from the formation and migration of the major planets in our Solar System, which allow us to understand how the Solar System came to be.

The major planets in our Solar System travel around the Sun in fairly circular orbits and on similar planes. However, since the discovery of wildly varying planetary systems around other stars, and given our increased understanding about small, primordial bodies in our celestial neighborhood, the notion that our Solar System has always been so orderly is changing.

To understand solar system evolution in general and how ours came to be, Carnegie’s Department of Terrestrial Magnetism astronomer Scott Sheppard studies the dynamical and physical properties of small bodies, such as asteroids, comets, moons, trans-neptunian objects (bodies that orbit beyond Neptune), and free floating substellar objects. These small bodies in our Solar System have a fossilized imprint from the formation and migration of the major planets in our Solar System.

The known Solar System can be divided into three parts: the rocky planets like Earth, which are close to the Sun; the gas giant planets, which are further out; and the frozen objects of the Kuiper belt, which lie just beyond Neptune's orbit. Beyond this, there appears to be an edge to the Solar System where only one object, Sedna, was known to exist for its entire orbit until Sheppard and colleagues discovered a second object, dwarf planet 2012 VP113. It has a very eccentric orbit that is even more distant than Sedna. Sheppard has determined that the total population of these so called inner Oort cloud objects is likely bigger than the Kuiper Belt and main asteroid belt. Some of these inner Oort cloud objects could rival the size of Mars or Earth.

There are several competing theories for how the inner Oort cloud might have formed, but all require the Solar System to have been in a state vastly different than now since the inner Oort cloud objects are currently decoupled from any known major planet, yet have disturbed inclined, eccentric orbits. Thus the inner Oort cloud is a window into our Solar System's past. Sheppard and colleague are currently obtaining the widest and deepest survey for Solar System objects ever obtained to discover more inner Oort cloud members.

Active asteroids have stable orbits between Mars and Jupiter like other asteroids. However, unlike other asteroids, they sometimes have the appearance of comets, when dust or gas is ejected from their surfaces. The reasons for this loss of material and subsequent tail in active asteroids are unknown, although there are several theories such as recent impacts or sublimation of exposed ices. Sheppard and colleagues discovered an unexpected tail on asteroid 62412, an object which had been known as a typical asteroid for over a decade. Using Magellan Telescopic observations, Sheppard found 62412 to have a very fast rotation. It thus appears the activity in this asteroid is created by rotational fissioning of material off the surface of 62412. Sheppard and colleagues estimate that there are likely about 100 active asteroids in the main asteroid belt, based on their discovery.

Sheppard is also the co-discoverer of the first trailing Neptune Trojan and first high inclination leading Neptune Trojan. Trojans are asteroids that are locked into the same orbital period as a planet but lead or follow the planet by about 60 degrees. At these spots, the gravitational pull of the planet and the Sun combine to lock the asteroids into synchronized orbits with the planet. The presence of high inclination Trojans implies that Neptune was on a much more eccentric orbit in the past. As Neptune went through the process of becoming more circular in orbit, it gained the ability to capture high-inclination objects. Sheppard has also learned that Neptune Trojans share many similarities with their Jupiter counterparts.

In another research area, Sheppard surveys our Solar System for so-called irregular satellites. These bodies have been captured by their respective planets. Regular satellites, on the other hand, were created during disk accretion. Sheppard and colleagues have discovered over 70 of the irregular moons around Jupiter, Saturn, Uranus, and Neptune. During the survey, Sheppard determined that the giant planets all possess about the same number of irregular satellites, despite large differences in planetary mass and formation scenarios.

Sheppard discovered the first contact binary Kuiper belt object. A contact binary contains two objects that are drawn together by tidal friction like the Earth and the Moon to orbit about one another. The large amount of angular momentum in the Kuiper Belt suggests it was much denser in the distant past. Similar observations by Sheppard and his colleagues also yielded one of the first measurements of the bulk density of a KBO; the value is sufficiently low that a volatile-rich, porous structure is indicated.

Sheppard received his B.A. in physics from Oberlin College and his M.S. and Ph. D. from the University of Hawaii, where he was also a teaching assistant and a research assistant. Before becoming a staff scientist at Carnegie in 2007, he was a Carnegie Hubble Fellow. For more see http://dtm.carnegiescience.edu/people/scott-s-sheppard

Explore Carnegie Science

The Blue Ring Nebula courtesy of Mark Seibert
November 18, 2020

Pasadena, CA— The mysterious Blue Ring Nebula has puzzled astronomers since it was discovered in 2004. New work published in Nature by a Caltech-led team including Carnegie astrophysicists Mark Seibert and Andrew McWilliam revealed that the phenomenon is the extremely difficult-to-spot result of a stellar collision in which two stars merged into one.

Sixteen years ago, NASA’s Galaxy Evolution Explorer (GALEX) spacecraft discovered a large, faint blob of gas with a star at its center—an object unlike anything previously seen in our Milky Way galaxy. The blob is represented as blue in the ultraviolet images of GALEX—although it doesn't actually emit

Carnegie theoretical astrophysicist Anthony Piro engages with the VizLab wall.
November 18, 2020

Pasadena, CA— In a refurbished Southern California garage, Carnegie astrophysicists are creating the virtual reality-enabled scientific workspace of the future where they will unlock the mysteries of the cosmos.

Imagine standing in front of a wave of data and probing the mysteries of the universe’s most-ancient galaxies side-by-side with swirling, colorful simulations of galaxy formation—seeing what aligns with expectations and what needs further interrogation.  A portal to fake universes may sound like science fiction, but it is now a reality at the Carnegie Observatories. 

The campus has just undertaken its new experiential

unWISE / NASA/JPL-Caltech / D.Lang (Perimeter Institute).
November 2, 2020

Pasadena, CA- La quinta generación del Sloan Digital Sky Survey recogió sus primeras observaciones del cosmos a la 1:47 a.m. del 24 de octubre de 2020. Este innovador estudio del cielo reforzará nuestra comprensión de la formación y evolución de las galaxias- incluyendo nuestra Vía Láctea- y los agujeros negros supermasivos que acechan en sus centros.  

El recién lanzado SDSS-V continuará la tradición pionera establecida por las generaciones anteriores, con un enfoque en el siempre cambiante cielo nocturno y los procesos físicos que ocurren en los objetos que componen nuestra visió

unWISE / NASA/JPL-Caltech / D.Lang (Perimeter Institute).
November 2, 2020

Pasadena, CA— The Sloan Digital Sky Survey’s fifth generation collected its very first observations of the cosmos at 1:47 a.m. MDT on October 24, 2020. This groundbreaking all-sky survey will bolster our understanding of the formation and evolution of galaxies—including our own Milky Way—and the supermassive black holes that lurk at their centers.  

The newly-launched SDSS-V will continue the path-breaking tradition set by the survey's previous generations, with a focus on the ever-changing night sky and the physical processes that drive these changes, from flickers and flares of supermassive black holes to the back-and-forth shifts of stars

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The fund supports a postdoctoral fellowship in astronomy that rotates between the Carnegie Science departments of Terrestrial Magnetism in Washington, D.C., and the Observatories in Pasadena California. 

The Earthbound Planet Search Program has discovered hundreds of planets orbiting nearby stars using telescopes at Lick Observatory, Keck Observatory, the Anglo-Australian Observatory, Carnegie's Las Campanas Observatory, and the ESO Paranal Observatory.  Our multi-national team has been collecting data for 30 years, using the Precision Doppler technique.  Highlights of this program include the detection of five of the first six exoplanets, the first eccentric planet, the first multiple planet system, the first sub-Saturn mass planet, the first sub-Neptune mass planet, the first terrestrial mass planet, and the first transit planet.Over the course of 30 years we have

The Giant Magellan Telescope will be one member of the next class of super giant earth-based telescopes that promises to revolutionize our view and understanding of the universe. It will be constructed in the Las Campanas Observatory in Chile. Commissioning of the telescope is scheduled to begin in 2021.

The GMT has a unique design that offers several advantages. It is a segmented mirror telescope that employs seven of today’s largest stiff monolith mirrors as segments. Six off-axis 8.4 meter or 27-foot segments surround a central on-axis segment, forming a single optical surface 24.5 meters, or 80 feet, in diameter with a total collecting area of 368 square meters. The GMT

Along with Alycia Weinberger and Ian Thompson, Alan Boss has been running the Carnegie Astrometric Planet Search (CAPS) program, which searches for extrasolar planets by the astrometric method, where the planet's presence is detected indirectly through the wobble of the host star around the center of mass of the system. With over eight years of CAPSCam data, they are beginning to see likely true astrometric wobbles beginning to appear. The CAPSCam planet search effort is on the verge of yielding a harvest of astrometrically discovered planets, as well as accurate parallactic distances to many young stars and M dwarfs. For more see  http://instrumentation.obs.carnegiescience.edu/

Johanna Teske became the first new staff member to join Carnegie’s newly named Earth and Planets Laboratory (EPL) in Washington, D.C., on September 1, 2020. She has been a NASA Hubble Fellow at the Carnegie Observatories in Pasadena, CA, since 2018. From 2014 to 2017 she was the Carnegie Origins Postdoctoral Fellow—a joint position between Carnegie’s Department of Terrestrial Magnetism (now part of EPL) and the Carnegie Observatories.

Teske is interested in the diversity in exoplanet compositions and the origins of that diversity. She uses observations to estimate exoplanet interior and atmospheric compositions, and the chemical environments of their formation

Phillip Cleves’ Ph.D. research was on determining the genetic changes that drive morphological evolution. He used the emerging model organism, the stickleback fish, to map genetic changes that control skeletal evolution. Using new genetic mapping and reverse genetic tools developed during his Ph.D., Cleves identified regulatory changes in a protein called bone morphogenetic protein 6 that were responsible for an evolved increase in tooth number in stickleback. This work illustrated how molecular changes can generate morphological novelty in vertebrates.

Cleves returned to his passion for coral research in his postdoctoral work in John Pringles’ lab at Stanford

Brittany Belin joined the Department of Embryology staff in August 2020. Her Ph.D. research involved developing new tools for in vivo imaging of actin in cell nuclei. Actin is a major structural element in eukaryotic cells—cells with a nucleus and organelles —forming contractile polymers that drive muscle contraction, the migration of immune cells to  infection sites, and the movement of signals from one part of a cell to another. Using the tools developed in her Ph.D., Belin discovered a new role for actin in aiding the repair of DNA breaks in human cells caused by carcinogens, UV light, and other mutagens.

Belin changed course for her postdoctoral work, in

Evolutionary geneticist Moises Exposito-Alonso joined the Department of Plant Biology as a staff associate in September 2019. He investigates whether and how plants will evolve to keep pace with climate change by conducting large-scale ecological and genome sequencing experiments. He also develops computational methods to derive fundamental principles of evolution, such as how fast natural populations acquire new mutations and how past climates shaped continental-scale biodiversity patterns. His goal is to use these first principles and computational approaches to forecast evolutionary outcomes of populations under climate change to anticipate potential future