The Smallest Planet Orbiting the Smallest Star

1. The Smallest Planet Orbiting the Smallest Star David Bennett University of Notre Dame for the MOA & OGLE Collaborations mobile phone: 574-315-6621

2. Summary of Finding • MOA-2007-BLG-192Lb is a ~3 Earth-mass planet • this is the smallest discovered to date • Its host star has a mass of 6  3% of the mass of the Sun • Most likely, it is < 8% of a Solar mass, which is too small to sustain nuclear reactions - a brown dwarf • The system is at a distance of 3000 light years • The planet’s orbital radius is about the same as that of Venus (70% of the Earth-Sun distance) David Bennett - Smallest Planet Orbits Smallest Star

3. Host Color Is Probably Magenta • “Brown” Dwarfs are magenta • Adam Burrows et al (2001) (520-603-3297) • due to atmospheric absorption by Sodium and Potassium David Bennett - Smallest Planet Orbits Smallest Star

4. Possibly a Low-Mass Red-Dwarf Star Future observations with the Hubble Space Telescope or the European Southern Observatory’s Very Large Telescope will decide this issue. David Bennett - Smallest Planet Orbits Smallest Star

5. The Microlensing Method • Uses a background star as a source of light • Gravitational field of star and planet act as a lens • requires no light from the planetary host • Observed signal is changing magnification • Required alignment is very rare, so the very dense Galactic bulge fields are observed David Bennett - Smallest Planet Orbits Smallest Star

6. Source Star Moves Across Lens Magnification Pattern Observed brightness changes as source star crosses lens system magnification pattern. (credit: Fumio Abe, MOA Collaboration) David Bennett - Smallest Planet Orbits Smallest Star

7. Observed Light Curve • planetary signal captured by MOA • due to new wide field-of-view telescope and camera David Bennett - Smallest Planet Orbits Smallest Star

8. New MOA Telescope Enabled Discovery • 1.8m MOA-2 telescope • Mt. John Observatory, NZ • MOA-cam3 CCD Camera • Images 2.2 sq. deg. • 13 times the area of the full moon • Entire Galactic Bulge imaged every hour • All microlensing events monitored for planets • Similar telescopes are needed in Chile (OGLE-IV) and South Africa David Bennett - Smallest Planet Orbits Smallest Star

9. Comparison to Other Exoplanets Microlensing discoveries in red, transit discoveries in blue and Doppler discoveries in black. Letters indicate Solar System planets. The snow-line relates to the conditions steam at t = 1 Myr snow at t = 1 Myr David Bennett - Smallest Planet Orbits Smallest Star

10. Credits & Further Info for further info, contact David Bennett (cell phone: 574-315-6621) or go to http://www.nd.edu/~bennett/moa07blg192/ Scientific Paper to be published in the Astrophysical Journal (arXiv:0806.0025) Authors: D.P. Bennett1, I.A. Bond1, A. Udalski2, T. Sumi1, F. Abe1, A. Fukui1, K. Furusawa1, J.B. Hearnshaw1, S. Holderness1, Y. Itow1, K. Kamiya1, A.V. Korpela1, P.M. Kilmartin1, W. Lin1, C.H. Ling1, K. Masuda1, Y. Matsubara1, N. Miyake1, Y. Muraki1, M. Nagaya1, T. Okumura1, K. Ohnishi1, Y.C. Perrott1, N.J. Rattenbury1, T. Sako1, To. Saito1, S. Sato1, L. Skuljan1, D.J. Sullivan1, W.L. Sweatman1, P.J. Tristram1, P.C.M. Yock1, M. Kubiak2, M.K. Szymanski2, G. Pietrzynski2, I. Soszynski2, O. Szewczyk2, L. Wyrzykowski2, K. Ulaczyk2, V. Batista3, J.P. Beaulieu3, S. Brillant3, A. Cassan3, P. Fouque3, P. Kervella, D. Kubas3, and J.B. Marquette3 1MOA Collaboration 2OGLE Collaboration 3PLANET Collaboration US effort funded by the NSF and NASA David Bennett - Smallest Planet Orbits Smallest Star