Planetary Collisions outside the Solar System: Time Domain Characterization of Extreme Debris Disks

Luminous debris disks of warm dust in the terrestrial planet zones around solar-like stars are recently found to vary, indicative of ongoing large-scale collisions of rocky objects. We use Spitzer 3.6 and 4.5 {\mu}m time-series observations in 2012 and 2013 (extended to 2014 in one case) to monitor 5 more debris disks with unusually high fractional luminosities ("extreme debris disk"), including P1121 in the open cluster M47 (80 Myr), HD 15407A in the AB Dor moving group (80 Myr), HD 23514 in the Pleiades (120 Myr), HD 145263 in the Upper Sco Association (10 Myr), and the field star BD+20 307 (>1 Gyr). Together with the published results for ID8 in NGC 2547 (35 Myr), this makes the first systematic time-domain investigation of planetary impacts outside the solar system. Significant variations with timescales shorter than a year are detected in five out of the six extreme debris disks we have monitored. However, different systems show diverse sets of characteristics in the time domain, including long-term decay or growth, disk temperature variations, and possible periodicity.Comment: 50 pages, 14 figures, 9 tables; Accepted for publication in the Astrophysical Journa

Governing agriculture-forest landscapes to achieve climate change mitigation

This introduction to the special section on Governing Agriculture-Forest Landscapes to Achieve Climate Change Mitigation reviews external interventions to improve forest conditions and reduce deforestation, and by extension, influence carbon storage in agriculture-forest landscapes. The review is based on a careful survey of 123 cases of project-based and policy interventions to influence land use and forest cover outcomes. We propose that outcomes of interventions can be explained in terms of rights, incentives, and technologies related to land use and apply this framework to examine 12 types of interventions in agriculture-forest landscapes. The analysis of the identified 123 cases raises concerns about consistency of data and comparability of cases. Our preliminary evidence suggests limited association between the stated objective of an intervention and its success. This evidence also suggests that smaller scale and effective enforcement may be positively associated with improved forest outcomes. But the effectiveness of interventions across different agriculture-forest landscapes varies and available evidence does not permit easy generalizations. The variable effects of interventions across different agriculture-forest landscapes point to the need to better understand the forms and functions of interventions and to problems associated with assessing their relative efficacy