How to Take Pictures of Baby Planets
Kate Follette, Amherst College
Of the thousands of known extrasolar planets, why are the dozen or so directly imaged exoplanets among the most important despite their apparently anomalous properties within the general exoplanet population (>10 astronomical units, >2x the mass of Jupiter)? What are the prospects for (and recent successes in) detecting younger, lower-mass and/or closer-in planets via direct imaging? I will discuss the current state of the art in the field of high-contrast imaging of extrasolar planets and the disks of gas and dust from which planets form (“circumstellar disks”). I will place particular emphasis on a subset of objects that host both disks and (likely) planets – the so-called “transitional disks”. These young circumstellar disks are almost certainly actively undergoing planet formation, and yet the presence of disk material complicates our ability to isolate light from planets and/or protoplanets embedded within them. I will end by discussing recent results from the Giant Accreting Protoplanet Survey (GAPplanetS) of 15 southern-hemisphere transition disks. The GAPlanetS survey aims to find protoplanets embedded in transitional disks through a distinctive signature at hydrogen wavelengths, and has so far discovered: 2-3 planets, 1 accreting M-dwarf stellar companion, and 1 disk feature masquerading as a planet.
Rethinking the Fundamentals of Classical Nova Explosions
Laura Chomiuk, MSU
Over the past few years, a revolution has been taking place in our understanding of classical novae, largely driven by the discovery of GeV gamma-rays emanating from these garden-variety explosions. These gamma-rays hint that shocks are energetically important—perhaps even dominant—in novae. I will present our burgeoning understanding of shocks in novae, from both multi-wavelength observational and theoretical perspectives, and illustrate how novae can be used as testbeds to understand other shock-powered explosions.
Solving the Puzzles of the Moon
Shun Karato, Yale University
After 50 years from the first landing of men on the Moon, about 380 kg of samples were collected by the Apollo mission. Chemical analyses of these samples together with a theory of planetary formation led to a “giant impact” paradigm (in mid 1970s). In this paradigm, the Moon was formed in the later stage of Earth formation (not the very late stage, though), when the proto-Earth was hit by an impactor with a modest size (~ Mars size) at an oblique angle. Such an impact is a natural consequence of planetary formation from a proto-planetary nebula. This collision may have kicked out mantle materials from the proto-Earth to form the Moon. This model explains mostly rocky composition of the Moon and the large angular momentum of the Earth-Moon system. High temperatures caused by an impact likely removed much of the volatile components such as water.
However, two recent geochemical observations cast doubt about the validity of such a paradigm. They include (i) not-so-dry Moon suggested from the analysis of basaltic inclusions in olivine, and (ii) the high degree of similarities in many isotopes. The first observation is obviously counter-intuitive, but the second one is also hard to reconcile with the standard model of a giant impact, because many models show that a giant impact produces the Moon mostly from the impactor. In this presentation, I will show how one can solve these puzzles by a combination of physics/chemistry of materials with some basic physics of a giant impact.