Session B1: Plenary I

Precision Cosmology: Past Successes and Future Prospects

We now have a Standard Model of cosmology, with all the well-earned pride and possible hubris that entails. We have measured the main cosmological parameters to accuracies of a few percent, and we have even tested inflation theories. But there are some pesky mysteries: dark matter and dark energy, and an apparent deficit of spatial fluctuations on the largest angular scales. And the great current challenge is testing whether gravitational waves were important in the early universe. Then, what happened to produce the galaxies, the black holes, and the remarkable complexity of astrophysics? Combining new measurements and new simulations, we have great hopes to understand a little better, and with luck, to aid in the search for the Theory of Everything, if it exists. I will sketch the history and predict the future.   

The Chelyabinsk Airburst: Observations and Models

On Feb. 15, 2013, an asteroid exploded about 40 km SSW of the Russian city of Chelyabinsk. It caused many injuries and widespread blast damage, but also yielded a plethora of data from security and dashboard cameras. Combined with seismic, infrasound, and satellite records, this serendipitous source provides a means to determine the projectile size and entry parameters and develop a self-consistent model. Analysis of video with subsequent on-site stellar calibrations enabled precise estimates of entry velocity (19 km/s), angle (17 deg) and altitude of peak brightness (29 km). The inferred pre-entry diameter was $\sim$ 20 m with a mass of $\sim$ 1200 tonnes. Satellite sensors recorded a radiated energy consistent with a total energy of $\sim$ 450 kilotons. The shallow entry angle led to an extended, near-horizontal, linear explosion. The blast was distributed over a large area, and was much weaker than it would be for a steep entry. The orientation also led to different phenomena than expected for a more vertical entry. There was no ballistic plume as calculated for Tunguska ($\sim$ 35 deg). Instead, buoyant instabilities grew into mushroom clouds and bifurcated the trail into two contra-rotating vortices. This event also suggests that the risk from airbursts is greater than previously thought.