LOTUS

While 4000 of exoplanets have been confirmed so far, direct comparison of exoplanets with solar planets is still difficult because most transiting exoplanets discovered so far have orbital period shorter than 1 year. Using Graphic Processing Unit (GPU) computing and techniques in machine learning, we surveyed signals of transiting planets whose orbital period is larger than 2 years in 200,000 stars observed by the {it Kepler} spacecraft. Most of such signals were overlooked because it occurs only one or two transits in 4 year light curves and were difficult to be identified by standard periodic analysis of the detection pipelines. We identified dozens of long-period transiting exoplanets and finally published the catalog of long-period planets including Jupiter-like gas giants. Also, we found that Neptunian-sized planets around the snow line (at a few au) is common around FGK stars. It is difficult to explain this population for current formation theory.

Known exoplanets near the snow line are located too far to measure its nature even for its mass. Nearby targets are crucial for further study by ground-based large telescopes or space observatory. To find nearby such systems, we are working on the nano-satellite mission, LOTUS (Long-period transiting exoplanet surveyor), in collaboration with the University of Tokyo (Nakasuka lab), NAOJ, and Princeton university. LOTUS has a very wide (33 deg x 33 deg) 7.5 cm telescope in a nano-satellite bus system (20 kg) and plans to observe north/south poles continuously. The field of nano satellite is now growing rapidly and has significant potential as a key innovation of astronomy in the next decade.

References

Transiting Planet Candidates Beyond the Snow Line Detected by Visual Inspection of 7557 Kepler Objects of Interest

Sho Uehara, Hajime Kawahara, Kento Masuda, Shin’ya Yamada, Masataka Aizawa, ApJ, 822, 2 (2016), arXiv:1602.07848,

Transiting Planets near the Snow Line from Kepler. I. Catalog

Hajime Kawahara, Kento Masuda, AJ 157, 6 (2019), arXiv:1904.04980,

LOTUS: wide-field monitoring nanosatellite for finding long-period transiting planets

Kawahara et al. SPIE, SPIE (2021)