University of Washington

ASTRONOMY DEPARTMENT

The known multiple planet systems (including the Solar System) share an intriguing trait: They all lie close to the limit of dynamical stability. If certain features of the systems are slightly different, then they are unstable and one or more planets would have been lost. In other words, these planetary systems are "packed"; there is no room for additional planets in between those that are known. I describe how packing can be measured, both through numerical and analytical methods, and discuss the known planetary systems in this context. I also show how packing is a natural consequence of some formation scenarios. Finally, I describe how the Packed Planetary Systems theory can predict the physical and orbital properties of planets. Such predictions have already been successful, and new studies may reveal terrestrial-like planets in habitable zones.

Size doesn't always matter. Canada's MOST (Microvariability & Oscillations of STars) space telescope has an aperture of only 15 cm, and the satellite has a mass of only 54 kg. But this 'orbiting suitcase' has become heavily packed with astrophysical data since leaving home.

MOST is an ultraprecise stellar photometer, a pioneer for the French CoRoT mission which has joined it in orbit two years ago, and for NASA's Kepler satellite, which went into space a few weeks ago. MOST's original one-year mission was to conduct asteroseismology - probing stellar interiors via frequency analysis of subtle surface vibrations with net luminosity amplitudes as small as a few parts per million. After over five years in orbit, MOST has extended its science to stellar activity, exo-Earth hunting, and even exoplanetary weather.

The results include: a new perspective on stellar convection and its connection to acoustic oscillations (p-modes); discovery of a new class of pulsators - the SPBe stars; a surface rotation profile for another star other than the Sun; measurements of the internal magnetic fields of stars; and the first real measure of the albedo of an exoplanet - a gas giant which is no more reflective than charcoal!

Since its arrival in the Saturn system in 2004, the Cassini spacecraft and its entry probe Huygens have revealed the surface of Titan at high resolution. The surface features that we've seen look in many ways similar to those on Earth. Interactions between Titan's icy surface, liquid water mantle, and thick rainy atmosphere are governed by the same physical processes that are at work here. So despite the unusual chemistry, exotic location, and 90K temperatures, the same processes lead to the same planetary structures. On Titan we've found sand dunes, dry river channels, mountains, rainfall, and most recently lakes and seas of liquid methane and ethane. I will discuss Cassini's views of these features and their implications for both the formation and evolution of Titan and for comparative planetology in general.

In July 2005, the Deep Impact Mission sent a projectile into comet Tempel-2 at high velocity, and observed the explosion from a flyby spacecraft. The flyby spacecraft is now being re-used in the EPOXI mission. A key component of EPOXI is the EPOCh Investigation of extrasolar planets, including characterization of the "Earth-as-an-extrasolar-planet". EPOCh also obtains precision CCD photometry of several giant exoplanets that transit bright stars. EPOCh is searching for reflected light or thermal emission from the giant planets, for rings and moons that may orbit them, and for icy or rocky planets that may also orbit the same stars as the gas giants. In favorable cases, EPOCh's sensitivity for rocky planets extends down to a size comparable to the Earth.

It can be argued that the number of habitable planets in the Milky Way is much larger than we have believed in the past. A realistic picture must include the benefits of any thermally insulating layers: deep atmospheres, thick ice layers, even the solid surface itself, all of which can lead to life-supporting surface temperatures. Even the very numerous M-star planets may be rendered habitable by a substantial atmosphere or by an eccentric orbit, which prevents synchronous rotation. The above suggests that the number of habitable planets in the Milky Way is much greater than previously thought. However, just what fraction of these might develop a technology-using species is still a very much open question. With this understanding, where do we search and how? All of the Milky Way becomes a suitable search target. This demands very powerful and time consuming search systems which can search many stars at the same time. Furthermore, the recent history of terrestrial radio technology suggests that we must search for forms of radio signals, especially spread sprectrum, which are hard to detect. If the Earth is a good example, advanced extraterrestrial technology may cause signals actually to be fainter than historical terrestrial radio transmissions. The Allen Telescope Array, a system which addresses the new paradigm, and the progress in its construction, will be described. Furthermore, our own progress in laser technology has suggested that it would be wise to search for signals from powerful pulsed lasers. Efforts to do this are described.

There is now very strong evidence that SgrA*, the compact source of radio, IR, and x-ray emission at the Galactic Center, marks the position of a 4 million solar mass black hole. Only 8 kilo-parsecs away, Very Long Baseline Interferometry (VLBI) has the potential to model, and eventually image, emission on scales of a few Schwarzschild radii, at the innermost accretion region of this black hole. This requires pushing the VLBI technique to short wavelengths where scattering by the ionized ISM is reduced and the intrinsic structure of SgrA* can be observed. VLBI observations in April 2007 at a wavelength of 1.3mm have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. More sensitive observations, using additional VLBI stations, are planned over the next few years, and will be sensitive to time variable structures predicted by models of flaring activity in SgrA*. Within this decade, it will be possible to assemble a VLBI 'Event Horizon Telescope' using existing submm facilities as well as those under construction.

The theory of planet formation has evolved significantly with the detection of more than 300 planets orbiting nearby stars. However, half of stars similar to the Sun are members of binary or multiple star systems. A function of the binary star separation, evolution from the planetesimal to planet embryo stage faces some significant dynamical challenges and is not expected to occur for binary stars with close separations. Contradicting standard theory, a few planets have now been discovered even in close binary systems and provides an impetus to reconsider mechanisms for planet formation in these challenging environments.

The carbon budget of an earth-like planet will depend on four main factors: 1) the chemical nature of the interstellar material that is incorporated into the planet-forming disk, 2) the physical conditions in the disk, 3) the thermal history of planetesimals, and 4) the dynamics of the planet-formation process. In this talk, I will focus on the first of these factors, specifically, how organics are modified in the terrestrial planet forming region of disks. Polycyclic aromatic hydrocarbons (PAHs) are observed throughout interstellar space, including in planet-forming disks. I will present recent model results that show volatile organic compounds (e.g. acetylene, methane, HCN) form as a direct consequence of thermal destruction of PAHs under conditions typical of the terrestrial planet-forming region of disks.