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

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