* Astronomy

Title: A Terrestrial Planet in a ~1 AU Orbit Around One Member of a ~15 AU Binary
Author: A. Gould, A. Udalski, I.-G. Shin, I. Porritt, J. Skowron, C. Han, J. C. Yee, S. Kozlowski, J.-Y. Choi, R. Poleski, L. Wyrzykowski, K. Ulaczyk, P. Pietrukowicz, P. Mróz, M.K. Szymanski, M. Kubiak, I. Soszynski, G. Pietrzynski, B.S. Gaudi, G.W. Christie, J. Drummond, J. McCormick, T. Natusch, H. Ngan, T.-G. Tan, M. Albrow, D.L. DePoy, K.-H. Hwang, Y.K. Jung, C.-U. Lee, H. Park, R.W. Pogge, F. Abe, D. P. Bennett, I. A. Bond, C. S. Botzler, M. Freeman, A. Fukui, D. Fukunaga, Y. Itow, N. Koshimoto, P. Larsen, C. H. Ling, K. Masuda, Y. Matsubara, Y. Muraki, S. Namba, K. Ohnishi, L. Philpott, N. J. Rattenbury, To. Saito, D. J. Sullivan, T. Sumi, D. Suzuki, P. J. Tristram, N. Tsurumi, K. Wada, N. Yamai, P. C. M. Yock, A. Yonehara, Y. Shvartzvald, D. Maoz, S. Kaspi, et al. (1 additional author not shown)

We detect a cold, terrestrial planet in a binary-star system using gravitational microlensing. The planet has low mass (2 Earth masses) and lies projected at a_{\perp,ph} ~ 0.8 astronomical units (AU) from its host star, similar to the Earth-Sun distance. However, the planet temperature is much lower, T<60 Kelvin, because the host star is only 0.10--0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host is itself orbiting a slightly more massive companion with projected separation a_{\perp,ch}=10--15 AU. Straightforward modification of current microlensing search strategies could increase their sensitivity to planets in binary systems. With more detections, such binary-star/planetary systems could place constraints on models of planet formation and evolution. This detection is consistent with such systems being very common.

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