The Smallest Planet Orbiting the Smallest Star

David BennettUniversity of Notre Dame

for the MOA & OGLE Collaborationsmobile phone: 574-315-6621

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

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

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

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

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

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

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

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

David Bennett - Smallest Planet Orbits Smallest Star

snow at t = 1 Myr

steam at t = 1 Myr

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 Collaboration2OGLE Collaboration3PLANET CollaborationUS effort funded by the NSF and NASA

David Bennett - Smallest Planet Orbits Smallest Star