Kepler K2 Campaign 9: II. First space-based discovery of an exoplanet using microlensing

D. Specht, R. Poleski, M. T. Penny, E. Kerins, I. McDonald, Chung-Uk Lee, A. Udalski, I. A. Bond, Y. Shvartzvald, Weicheng Zang, R. A. Street, D. W. Hogg, B. S. Gaudi, T. Barclay, G. Barentsen, S. B. Howell, F. Mullally, C. B. Henderson, S. T. Bryson, D. A. CaldwellM. R. Haas, J. E. Van Cleve, K. Larson, K. McCalmont, C. Peterson, D. Putnam, S. Ross, M. Packard, L. Reedy, Michael D. Albrow, Sun-Ju Chung, Youn Kil Jung, Andrew Gould, Cheongho Han, Kyu-Ha Hwang, Yoon-Hyun Ryu, In-Gu Shin, Hongjing Yang, Jennifer C. Yee, Sang-Mok Cha, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, M. K. Szymański, I. Soszyński, K. Ulaczyk, P. Pietrukowicz, Sz Kozłowski, J. Skowron, P. Mróz, Shude Mao, Pascal Fouqué, Wei Zhu, F. Abe, R. Barry, D. P. Bennett, A. Bhattacharya, A. Fukui, H. Fujii, Y. Hirao, Y. Itow, R. Kirikawa, I. Kondo, N. Koshimoto, Y. Matsubara, S. Matsumoto, S. Miyazaki, Y. Muraki, G. Olmschenk, C. Ranc, A. Okamura, N. J. Rattenbury, Y. Satoh, T. Sumi, D. Suzuki, S. I. Silva, T. Toda, P. J. Tristram, A. Vandorou, H. Yama, C. Beichman, G. Bryden, S. Calchi Novati

Research output: Contribution to journalArticlepeer-review


We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens-source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data, and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass-position-velocity degeneracy and measure the planet's mass directly. We find a host mass of 0.58 ± 0.04M and a planetary mass of 1.1 ± 0.1MJ. The system lies at a distance of 5.2 ± 0.2 kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be 4.2 ± 0.3 au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}$ au and orbital period $P = 13^{+9}_{-2}$ yr. This makes K2-2016-BLG-0005MLb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models....
Original languageEnglish
Pages (from-to)6350-6366
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date31 Jan 2023
Publication statusPublished - 1 Apr 2023


  • gravitational lensing
  • micro
  • methods
  • data analysis
  • telescopes
  • surveys
  • Planets and satellites
  • detection


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