Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing

J. P. Beaulieu*, D. P. Bennett, P. Fouqué, A. Williams, M. Dominik, U. G. Jørgensen, D. Kubas, A. Cassan, C. Coutures, J. Greenhill, K. Hill, J. Menzies, P. D. Sackett, M. Albrow, S. Brillant, J. A.R. Caldwell, J. J. Calitz, K. H. Cook, E. Corrales, M. DesortS. Dieters, D. Dominis, J. Donatowicz, M. Hoffman, S. Kane, J. B. Marquette, R. Martin, P. Meintjes, K. Pollard, K. Sahu, C. Vinter, J. Wambsganss, K. Woller, K. Horne, I. Steele, D. M. Bramich, M. Burgdorf, C. Snodgrass, M. Bode, A. Udalski, M. K. Szymański, M. Kubiak, T. Wiȩckowski, G. Pietrzyński, I. Soszyński, O. Szewczyk, Wyrzykowski, B. Paczyński, F. Abe, I. A. Bond, T. R. Britton, A. C. Gilmore, J. B. Hearnshaw, Y. Itow, K. Kamiya, P. M. Kilmartin, A. V. Korpela, K. Masuda, Y. Matsubara, M. Motomura, Y. Muraki, S. Nakamura, C. Okada, K. Ohnishi, N. J. Rattenbury, T. Sako, S. Sato, M. Sasaki, T. Sekiguchi, D. J. Sullivan, P. J. Tristram, P. C.M. Yock, T. Yoshioka

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    492 Citations (Scopus)

    Abstract

    In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars1-4. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 AU from normal stars. Here we report the discovery of a 5.5-2.7+5.5 M planetary companion at a separation of 2.6-0.6+1.5 AU from a 0.22-0.11+0.21 M M-dwarf star, where M refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.

    Original languageEnglish
    Pages (from-to)437-440
    Number of pages4
    JournalNature
    Volume439
    Issue number7075
    DOIs
    Publication statusPublished - 26 Jan 2006

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