Research in the Solar, Stellar, and Planetary Sciences (SSP) Division is directed toward understanding star and planet formation and the physical processes in the Sun, stars, and stellar systems. Division research on the Sun addresses its basic stellar properties, its atmosphere and corona, and its effects on the Earth. Studies of other stars seek to measure the age and chemical composition and to understand the structure of surrounding disks, magnetic fields, and winds. Searches for objects in our own solar system and for extra-solar planets inform theoretical investigations of star and planet formation and evolution. Observational data are obtained from ground-based observatories (such as the MMT Observatory, Magellan, and the Whipple Observatory) and from satellites including the Solar and Heliospheric Observatory, the Transition Region and Coronal Explorer, the Far Ultraviolet Spectrographic Explorer, the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope.


Pandora is a general-purpose non-LTE computer program for calculating stellar atmosphere models and detailed line and continuum spectra.

Minor Planet Center (MPC)

The MPC is responsible for the designation of minor planets, comets, and natural satellites in the solar system. The MPC is also responsible for the efficient collection, computation, checking, and dissemination of astrometric observations and orbits for minor planets and comets.

Solar System

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Sedna distorted orbit

Roughly 4.5 Gyr ago, the Solar System formed in a disk surrounding the proto-Sun. Within this disk, the gas giants grew to their current sizes in a few Myr; the rocky planets took a few tens of Myr to reach their present masses.

Besides keeping track of the myriad objects in the Solar System, SSP scientists use data on the compositions, masses, and positions of these objects along with theoretical models to learn how planets form and evolve in time.

Stellar Variability

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the sun

All stars vary in brightness. On geological time scales, main sequence stars become bright red giants and end their lives as dim white dwarfs, neutron stars, or black holes. As stars evolve, some pulsate regularly on time scales ranging from seconds to years. Other stars vary irregularly. SSP scientists study these variations to learn about the structure and life history of stars.

Stellar Coronae/Winds

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TW Hydrae

Cool stars like the Sun are surrounded by a corona, a million degree plasma extending far beyond the visible photosphere. The stellar wind is ionized gas ejected from the outer portions of the corona at speeds of hundreds of km/sec. SSP scientists are world leaders in applying spectroscopy to study the physical conditions of stellar coronae and winds and in developing theoretical models to explain these observations.


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HAT discovers its first planet

In the last two decades, new discoveries have improved our understanding of other planetary systems. By measuring the brightnesses and motions of nearby stars, astronomers have detected more than 200 planets in 170 planetary systems. Most planets are gas giants like Jupiter or Neptune. Others are icy super-Earths. SSP scientists use ground-based and space-based instruments to detect and to characterize exoplanets.

Stellar Atmospheres

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dark absorption bands

In 1925, Cecilia Payne first applied the new science of quantum mechanics to the analysis of stellar spectra. Besides relating stellar spectral types to photospheric temperatures, Payne showed that stars - and hence most of the observable universe - are composed mostly of hydrogen. Today, SSP scientists and other astronomers analyze spectra to measure chemical abundances and other physical properties of stellar atmospheres. In addition to providing information on the structure and evolution of stars, these measurements constrain the ages and masses of the oldest stars in the galaxy.

Binary Stars

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X-rays from Nova RS Oph

Many stars are in binary or multiple star systems, where two or more stars orbit a common center of mass. Because the stars in a multiple star system have the same age, widely separated binaries and multiple stars provide good tests of stellar evolution theory. In close binary systems, the two stars often exchange mass and angular momentum, which changes their evolution compared to single stars. SSP scientists study the physical processes associated close and wide binary stars.


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oscillations in nearby bright stars

Asteroseismology applies seismology to stars. On Earth, seismologists measure motions and waves in the crust and mantle to learn about their structure and composition. In the Sun and other stars, asteroseismologists measure changes in the brightness and velocity to learn about the structure of the atmosphere and interior of a star. Because the changes are small (velocities of meters per second), CfA scientists use special purpose instruments to study the structure of nearby bright stars.

Star Formation

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Taurus-Auriga is a nearby star forming region

Stars form in the cold dense cores of giant molecular clouds. All newly-formed stars are surrounded by a circumstellar disk containing enough material to make a planetary system. SSP scientists use observations and theoretical data to understand how the central star and the surrounding disk evolve with time.

Many stars form in clusters. The clusters range in size from small groups of 5-10 times to dense clusters of thousands of stars. SSP scientists study the origin, structure, and evolution of young star clusters.