CARNEGIE INSTITUTION FOR SCIENCE 1530 P Street, NW Washington, D.C. 20005-1910 202.387.6400 President Eric D. Isaacs ..... Director, Department of Embryology Yixian Zheng ..... Director, Geophysical Laboratory Michael Walter ..... Acting Director, Department of Global Ecology Joe Berry ..... Director, The Observatories Crawford H. Greenewalt Chair John Mulchaey ..... Acting Director, Department of Plant Biology Zhiyong Wang ..... Director, Department of Terrestrial Magnetism Richard Carlson ..... Chief Operating Officer Timothy Doyle ..... Chief Development Officer Ann McElwain ..... Editor Tina McDowell ..... Science Writer Natasha Metzler Over the past few weeks, I’ve been thinking about how best to define the “Carnegie Difference.” Certainly, we take great pride in our exceptional investigators and their willingness to tackle some of the greatest scientific challenges of our time, across a wide range of disciplines. Yet talent and intellectual ambition are by no means unique to Carnegie; institutions around the world attract gifted researchers whose insights and determination lead to transformative discovery. Instead, I believe that what truly sets us apart is our willingness to champion unconventional interdisciplinary approaches that can lead to unexpected and important results. This issue of Carnegie Science offers important insights into the ways that the “Carnegie Difference” informs and deepens our work. One excellent example can be found in the recent discovery of the most distant known object orbiting the Sun—a mysterious, pink-tinted, icy world nicknamed “Farout” by Carnegie astronomer Scott Sheppard and his team. Several years ago, they proposed the existence of Planet X, a massive Neptune-like planet orbiting far beyond Pluto. Since then, they have been probing the most distant reaches of the Solar System in search of the hypothetical planet, and their assiduous efforts have led to the discovery of 62 distant objects floating far beyond Pluto. This latest discovery–fascinating in itself–ultimately could provide valuable clues to the size and location of Planet X. Here on Earth, Global Ecology’s Anna Michalak is using a data-driven approach to investigate greenhouse gas emissions at a global scale, with a focus on methane emissions in China. In 2010, China enacted a suite of strict regulations intended to reduce the massive methane emissions related to coal mining. However, Anna and her coauthors’ atmospheric modeling and analysis of satellite data from 2015 found that the tough new regulations had no discernible impact; overall, Chinese methane emissions actually increased by 50%. These results indicate a disappointing missed opportunity by Chinese officials to support aspirational public policies with the infrastructure and technology investments necessary to meet their stated environmental goals. New work from a team led by Will Ludington, in our Department of Embryology, addresses the significant–and so far unpredictable–health effects of the gastrointestinal microbiome, a diverse ecosystem of thousands of microbial species living within the human body. To better understand the complex relationships between these microbes and their hosts, Ludington and his team looked at the relatively simple microbiome of five bacterial species found in fruit fly intestines. Using complex mathematical models, Ludington found that different combinations of bacteria varied dramatically in their effects on fruit fly development, fertility, and longevity. These findings suggest that we have only begun to understand the ways in which these dynamic and taxonomically complex microbe communities affect human health and physiology. These highlights represent only a few examples of the wide-ranging, entrepreneurial, and intriguing research that has distinguished this institution for more than a century. As you read this issue of Carnegie Science, I know you will gain new perspectives on the people, the partnerships, the processes, and the results that constitute the “Carnegie Difference.” L E T T E R F R O M T H E P R E S I D E N T Eric D. Isaacs President Defining the “Carnegie Difference”