The dynamics of peer participation, or churn, are an inherent property of Peer-to-Peer (P2P) systems that should be incorporated in both the design and evaluation of P2P systems. This requires a proper characterization of churn in real-world P2P networks. However, the few previous measurement-based studies on the characterization of P2P systems have used either unrepresentative group of peers or coarse-grain measurements. In this extended abstract, we characterize churn in the Gnutella network based on fine-grained monitoring of the entire population. We developed a new crawler that can capture a complete snapshot of Gnutella network within a few minutes. This not only improves the accuracy, by reducing distortion in captured snapshots, but it also increases the granularity of captured dynamics. We present our preliminary characterizations of peer uptime and discuss their implications. In particular, we show that peer uptime follows a power-law distribution rather than the commonly assumed Poisson distribution. In a nutshell, a large portion of up peers are highly stable, yet the remaining peers turnover very quickly.