At q = 1.81 ± 0.20 × 10-5, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio q of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent "pile-up" at q = 5-10 ×10-5. The event was observed by Spitzer, yielding a microlens-parallax πE measurement. Combined with a measurement of the Einstein radius θE from finite-source effects during the caustic crossings, these measurements imply masses of the host Mhost = 1.14+0.10-0.12 M⊙ and planet Mplanet = 7.59+0.75-0.69 M⊕, system distance DL = 3.38+0.22-0.26 kpc and projected separation a⊥ = 4.27+0.21-0.23 AU. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.

Abstract
1. INTRODUCTION
2. OBSERVATIONS
3. GROUND-BASED LIGHT CURVE ANALYSIS
4. COLOR-MAGNITUDE DIAGRAM (CMD)
5. PARALLAX ANALYSIS INCLUDING Spitzer DATA
6. PHYSICAL PARAMETERS
7. BAYESIAN TEST
8. DISCUSSION
REFERENCES

• Shude Mao(Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, National Astronomical Observatories, Chinese Academy of Sciences,)
• Todd Burdullis(CFHT Corporation)
• Andreea Petric(CFHT Corporation)
• Matthew T. Penny(Department of Astronomy Ohio State University,)
• Pascal Fouque(CFHT Corporation, Universite de Toulouse, UPS-OMP, IRAP)
• Wei Zhu(Canadian Institute for Theoretical Astrophysics, University of Toronto)
• Calen B. Henderson(IPAC)
• B. Scott Gaudi(Department of Astronomy Ohio State University)
• Sean Carey(Spitzer, Science Center)
• Geoff Bryden(IPAC)
• Charles Beichman(NASA Exoplanet Science Institute, California Institute of Technology)
• Richard W. Pogge(Department of Astronomy Ohio State University)
• Byeong-Gon Park(Korea Astronomy and Space Science Institute, University of Science and Technology, Korea (UST))
• Yongseok Lee(Korea Astronomy and Space Science Institute,School of Space Research, Kyung Hee University)
• Dong-Joo Lee(Korea Astronomy and Space Science Institute)
• Chung-Uk Lee(Korea Astronomy and Space Science Institute, University of Science and Technology, Korea (UST))
• Seung-Lee Kim(Korea Astronomy and Space Science Institute, University of Science and Technology, Korea (UST))
• Hyoun-Woo Kim(Korea Astronomy and Space Science Institute)
• Dong-Jin Kim(Korea Astronomy and Space Science Institute)
• Sang-Mok Cha(Korea Astronomy and Space Science Institute, School of Space Research, Kyung Hee University)
• Jennifer C. Yee(Center for Astrophysics j Harvard & Smithsonian)
• Yossi Shvartzvald(IPAC)
• In-Gu Shin(Korea Astronomy and Space Science Institute)
• Youn Kil Jung(Korea Astronomy and Space Science Institute)
• Kyu-Ha Hwang(Korea Astronomy and Space Science Institute)
• Cheongho Han(Department of Physics, Chungbuk National University)
• Sun-Ju Chung(Korea Astronomy and Space Science Institute, University of Science and Technology)
• Michael D. Albrow(University of Canterbury, Department of Physics and Astronomy)
• Weicheng Zang(Physics Department and Tsinghua Centre for Astrophysics, Tsinghua University)
• Sebastiano Calchi Novati(IPAC)
• Yoon-Hyun Ryu(Korea Astronomy and Space Science Institute)
• Andrew Gould(Max-Planck-Institute for Astronomy,Department of Astronomy Ohio State University)