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arXiv · 2009.12377

A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event

P. Mroz·R. Poleski·A. Gould·A. Udalski·T. Sumi·M. K. Szymanski·I. Soszynski·P. Pietrukowicz·S. Kozlowski·J. Skowron·K. Ulaczyk·M. D. Albrow·S. -J. Chung·C. Han·K. -H. Hwang·Y. K. Jung·H. -W. Kim·Y. -H. Ryu·I. -G. Shin·Y. Shvartzvald·J. C. Yee·W. Zang·S. -M. Cha·D. -J. Kim·S. -L. Kim·C. -U. Lee·D. -J. Lee·Y. Lee·B. -G. Park·R. W. Pogge
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Abstract

Some low-mass planets are expected to be ejected from their parent planetary systems during early stages of planetary system formation. According to planet-formation theories, such as the core accretion theory, typical masses of ejected planets should be between 0.3 and 1.0 $M_{\oplus}$. Although in practice such objects do not emit any light, they may be detected using gravitational microlensing via their light-bending gravity. Microlensing events due to terrestrial-mass rogue planets are expected to have extremely small angular Einstein radii (< 1 uas) and extremely short timescales (< 0.1 day). Here, we present the discovery of the shortest-timescale microlensing event, OGLE-2016-BLG-1928, identified to date ($t_{\rm E} \approx 0.0288\ \mathrm{day} = 41.5 \mathrm{min}$). Thanks to the detection of finite-source effects in the light curve of the event, we were able to measure the angular Einstein radius of the lens $θ_{\rm E} = 0.842 \pm 0.064$ uas, making the event the most extreme short-timescale microlens discovered to date. Depending on its unknown distance, the lens may be a Mars- to Earth-mass object, with the former possibility favored by the Gaia proper motion measurement of the source. The planet may be orbiting a star but we rule out the presence of stellar companions up to the projected distance of 8.0 au from the planet. Our discovery demonstrates that terrestrial-mass free-floating planets can be detected and characterized using microlensing.

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P. Mroz, R. Poleski, A. Gould, A. Udalski, T. Sumi, M. K. Szymanski, I. Soszynski, P. Pietrukowicz, S. Kozlowski, J. Skowron, K. Ulaczyk, M. D. Albrow, S. -J. Chung, C. Han, K. -H. Hwang, Y. K. Jung, H. -W. Kim, Y. -H. Ryu, I. -G. Shin, Y. Shvartzvald, J. C. Yee, W. Zang, S. -M. Cha, D. -J. Kim, S. -L. Kim, C. -U. Lee, D. -J. Lee, Y. Lee, B. -G. Park, R. W. Pogge. 2020-10-20. A terrestrial-mass rogue planet candidate detected in the shortest-timescale microlensing event. https://doi.org/10.3847/2041-8213%2Fabbfad

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