Although our Sun is an ordinary star, the Solar System is the only planetary system known to harbor life. Studying the Solar System enables us to learn how stable planetary systems form and how planets develop the conditions needed for life.
Many gravitational triple systems are in a hierarchical configuration, where two objects orbit each other in a relatively tight inner binary while the third object is on a much wider orbit. If the third object is sufficiently distant, an analytic, perturbative approach can be used to calculate the evolution of the system. In the secular approximation , the two orbits torque each other and exchange angular momentum, but not energy. Therefore the orbits can change shape and orientation (on timescales much longer than their orbital periods), but not semimajor axes.
A large number of TA researchers work on projects connected to celestial mechanics, with many looking at the stability and evolution of planetary systems in general, as well as the specific evolution of the Solar System.
Highlights to (and links to) some current research in this area by department members include:
The solar system is comprised of a variety of bodies, from giant planets like Jupiter to the smallest asteroids and everything in between. RG astronomers use the Submillimeter Array to measure both the thermal emission from solar system objects and spectral lines from their atmospheres. These measurements allow one to infer surface temperatures as well as atmospheric composition, thermal structure, and dynamics on bodies as diverse as Neptune, Mars, Titan, and Pluto.
The CfA has joined the Pan-STARRS-1 Science Consortium. Pan-STARRS-1 is a 1.8m aperture telescope located on Haleakala. Its 1.4 gigapixel, 7 square degree camera will repeatedly image the entire sky north -30 degrees declination. Roughly 60% of the observing time of the PS1 telescope will be dedicated to the "3pi steradian" survey with an observing cadence that is optimized for the detection of near-Earth asteroids and slow-moving solar system bodies.
The solar wind originates in the million-degree solar corona and flows out from the Sun at 300 to more than 800 km/sec (roughly one to two million miles per hour). Most of the ions in the wind are hydrogen and helium, but a small fraction are heavier elements such as carbon, oxygen, and neon. When those heavy ions, which have lost most or all of their electrons, collide with neutral gas in comets, planetary atmospheres, or very tenuous gas throughout the solar system, they emit X-rays via a process called charge exchange.
Solar and Stellar X-Ray Group (SSXG) researchers study solar and stellar atmospheres, which are composed of extremely hot, highly dynamic plasma. Activities include designing, testing, building and operating instruments, analyzing space and ground-based observations, and creating theoretical models. SSXG researchers lead or are major partners in a number of instrumentation projects, links to which can be found below.
The heliosphere is a bubble of hot gas in interstellar space stretching from the Sun to greater than 100 Sun-Earth distances. It contains some fraction of inflowing neutral interstellar hydrogen and helium atoms. Highly charged positive ions emanate from the Sun in the solar wind and impact the neutral material. The ions capture electrons from the atoms into high excited states that radiate primarily in the soft X-ray spectral region. The spectra provide information about the solar wind composition and velocity and the distribution of atoms in the heliosphere.
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.
Every planetary system forms in a thin disk of gas and dust orbiting a young star. Small dust grains, a micron or two in size, collide and merge into large aggregates that settle into the midplane of the disk. In the midplane, aggregates grow into planetesimals with diameters of roughly 1 km. Collisions between planetesimals produce planets. SSP scientists use theoretical calculations to understand how dust grains evolve and how planetesimals become planets.