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

Decker French
July 24, 2019

Pasadena, CA— Carnegie’s K. Decker French was recognized by the Astronomical Society of the Pacific with its Robert J. Trumpler Award, which is presented to a recent Ph.D. graduate “whose research is considered unusually important to astronomy.” French completed her doctorate at the University of Arizona Tucson in 2017 and is currently a Hubble Fellow at the Carnegie Observatories.

Her research focuses on a radio survey of the gas clouds within galaxies that have recently ended the star-forming phase of their evolution.  The lack of star formation in these galaxies has long been assumed to be caused by a depletion of the cold, dense molecular gases

Vera measuring spectra with DTM measuring engine, courtesy of Carnegie Science.
July 24, 2019

Washington, DC—The House approved yesterday a bill to name the Large Synoptic Survey Telescope in honor of late Carnegie scientist Vera Rubin, who confirmed the existence of dark matter.

Rubin received the National Medal of Science for her research on how stars orbit their galactic centers. She revealed that stars at varying distances from the center of a spiral galaxy orbit at the same speed, rather than at decreasing speeds away from the center, providing undeniable evidence that each galaxy is embedded in a halo of dark matter holding its mass together.

She died in December 2016.

“Vera demonstrated intellectual courage and a tireless commitment to

An image of the Hubble Space Telescope floating against the background of space courtesy of NASA.
July 16, 2019

Pasadena, CA—A team of collaborators from Carnegie and the University of Chicago used red giant stars that were observed by the Hubble Space Telescope to make an entirely new measurement of how fast the universe is expanding, throwing their hats into the ring of a hotly contested debate. Their result—which falls squarely between the two previous, competing values—will be published in The Astrophysical Journal.

Nearly a century ago, Carnegie astronomer Edwin Hubble discovered that the universe has been growing continuously since it exploded into being during the Big Bang. But precisely how fast it’s moving—a value termed the Hubble constant in his

This cartoon courtesy of Anthony Piro illustrates three possibilities for the origin of the mysterious hydrogen emissions from the Type IA supernova called ASASSN-18tb that were observed by the Carnegie astronomers.
May 7, 2019

Pasadena, CA—Detection of a supernova with an unusual chemical signature by a team of astronomers led by Carnegie’s Juna Kollmeier—and including Carnegie’s Nidia Morrell, Anthony Piro, Mark Phillips, and Josh Simon—may hold the key to solving the longstanding mystery that is the source of these violent explosions. Observations taken by the Magellan telescopes at Carnegie’s Las Campanas Observatory in Chile were crucial to detecting the emission of hydrogen that makes this supernova, called ASASSN-18tb, so distinctive.   

Their work is published in Monthly Notices of the Royal Astronomical Society.

Type Ia supernovae play a

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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/

Staff Associate Kamena Kostova joined the Department of Embryology in November 2018. She studies ribosomes, the factory-like structures inside cells that produce proteins. Scientists have known about ribosome structure, function, and biogenesis for some time. But, a major unanswered question is how cells monitor the integrity of the ribosome itself. Problems with ribosomes have been associated with diseases including neurodegeneration and cancer. The Kostova lab investigates the fundamental question of how cells respond when their ribosomes break down using mass spectrometry, functional genomics methods, and CRISPR genome editing.

Kostova received a B.S. in Biology from the

Sally June Tracy applies cutting-edge experimental and analytical techniques to understand the fundamental physical behavior of materials at extreme conditions. She uses dynamic compression techniques with high-flux X-ray sources to probe the structural changes and phase transitions in materials at conditions that mimic impacts and the interiors of terrestrial and exoplanets. She is also an expert in nuclear resonant scattering and synchrotron X-ray diffraction. She uses these techniques to understand novel behavior at the electronic level.  Tracy received her Ph.D. from the California Institute of

The Ludington lab investigates complex ecological dynamics from microbial community interactions using the fruit fly  Drosophila melanogaster. The fruit fly gut carries numerous microbial species, which can be cultured in the lab. The goal is to understand the gut ecology and how it relates to host health, among other questions, by taking advantage of the fast time-scale and ease of studying the fruit fly in controlled experiments. 

Nick Konidaris is a staff scientist at the Carnegie Observatories and Instrument Lead for the SDSS-V Local Volume Mapper (LVM). He works on a broad range of new optical instrumentation projects in astronomy and remote sensing. Nick's projects range from experimental to large workhorse facilities. On the experimental side, he recently began working on a new development platform for the 40-inch Swope telescope at Carnegie's Las Campanas Observatory that will be used to explore and understand the explosive universe.

 Nick and his colleagues at the Department of Global Ecology are leveraging the work on Swope to develop a new airborne spectrograph that will be