An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb

Weicheng Zang, Cheongho Han, Iona Kondo, Jennifer C. Yee, Chung Uk Lee, Andrew Gould, Shude Mao, Leandro de Almeida, Yossi Shvartzvald, Xiangyu Zhang, Michael D. Albrow, Sun Ju Chung, Kyu Ha Hwang, Youn Kil Jung, Yoon Hyun Ryu, In Gu Shin, Sang Mok Cha, Dong Jin Kim, Hyoun Woo Kim, Seung Lee KimDong Joo Lee, Yongseok Lee, Byeong Gon Park, Richard W. Pogge, John Drummond, Thiam Guan Tan, José Dias do Nascimento, Dan Maoz, Matthew T. Penny, Wei Zhu, Ian A. Bond, Fumio Abe, Richard Barry, David P. Bennett, Aparna Bhattacharya, Martin Donachie, Hirosane Fujii, Akihiko Fukui, Yuki Hirao, Yoshitaka Itow, Rintaro Kirikawa, Naoki Koshimoto, Man Cheung Alex Li, Yutaka Matsubara, Yasushi Muraki, Shota Miyazaki, Greg Olmschenk, Clément Ranc, Nicholas J. Rattenbury, Yuki Satoh, Hikaru Shoji, Stela Ishitani Silva, Takahiro Sumi, Daisuke Suzuki, Yuzuru Tanaka, Paul J. Tristram, Tsubasa Yamawaki, Atsunori Yonehara, Andreea Petric, Todd Burdullis, Pascal Fouqué

Research output: Contribution to journalArticlepeer-review


We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q2 = 0:9- 1:2 × 10-5 = 3-4 q⊕ at 1σ, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries (4. q=q⊕. 6), it fills out the previous empty sector at the bottom of the triangular (log s; log q) diagram, where s is the planet-host separation in units of the angular Einstein radius θE. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets. Due to the extreme magnification of the event, Amax ∼ 1450 for the underlying single-lens event, its light curve revealed a second companion with q3 ∼ 0:05 and j log s3j ∼ 1, i.e., a factor ∼ 10 closer to or farther from the host in projection. The measurements of the microlens parallax ∼E and the angular Einstein radius ∼E allow estimates of the host, planet and second companion masses, (M1;M2;M3) ∼ (0:3M⊙; 1:0M⊙; 17MJ ), the planet and second companion projected separations, (a⊥;2; a⊥;3) ∼ (1:5; 0:15 or 15) au, and system distance DL ∼ 1 kpc. The lens could account for most or all of the blended light (I ∼ 19:3) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by COVID-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program.

Original languageEnglish
Article number239
JournalResearch in Astronomy and Astrophysics
Issue number9
StatePublished - Sep 2021


  • Gravitational lensing: Micro


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