Exoplanets & Exomoons

Free-Floating Planet Mass Function from MOA-II 9-year Survey Towards The Galactic Bulge

By Keith Cowing
Status Report
March 16, 2023
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Free-Floating Planet Mass Function from MOA-II 9-year Survey Towards The Galactic Bulge
This illustration shows a rogue planet traveling through space. Credit: NASA/JPL-Caltech/R. Hurt (Caltech-IPAC)

We present the first measurement of the mass function of free-floating planets (FFP) or very wide orbit planets down to an Earth mass, based on microlensing data from the MOA-II survey in 2006-2014. The shortest duration event has an Einstein radius crossing time of tE=0.057±0.016days and an angular Einstein radius of θE=0.90±0.14μas.

There are seven short events with tE<0.5 day, which are likely to be due to planets. The detection efficiency for short events depends on both tE and θE, and we measure this with image-level simulations for the first time. These short events can be well modeled by a power-law mass function, dN4/dlogM=(2.18+0.52−1.40)×(M/8M⊕)−α4 dex−1star−1 withα4=0.96+0.47−0.27 for M/M⊙<0.02. This implies a total of f=21+23−13 FFP or wide orbit planets in the mass range 0.33<M/M⊕<6660 per star, with a total FFP mass of m=80+73−47M⊕ per star.

The number of FFP is 19+23−13 times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α∼0.9, which would imply a total number of 22+23−13 planets star−1 and a total mass of 171+80−52M⊕ star−1.

Takahiro Sumi, Naoki koshimoto, David P. Bennett, Nicholas J. Rattenbury, Fumio Abe, Richard Barry, Aparna Bhattacharya, Ian A. Bond, Hirosane Fujii, Akihiko Fukui, Ryusei Hamada, Yuki Hirao, Stela Ishitani Silva, Yoshitaka Itow, Rintaro Kirikawa, Iona Kondo, Yutaka Matsubara, Shota Miyazaki, Yasushi Muraki, Greg Olmschenk, Clement Ranc, Yuki Satoh, Daisuke Suzuki, Mio Tomoyoshi, Paul . J. Tristram, Aikaterini Vandorou, Hibiki Yama, Kansuke Yamashita (MOA collaboration)

Comments: 12 pages, 6 figures, submitted to AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2303.08280 [astro-ph.EP] (or arXiv:2303.08280v1 [astro-ph.EP] for this version)
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Submission history
From: Takahiro Sumi
[v1] Wed, 15 Mar 2023 00:00:45 UTC (1,144 KB)

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