The Smallest Planet Orbiting
the Smallest Star
David Bennett
University of Notre Dame
for the MOA & OGLE Collaborations
mobile 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 (OGLEIV) and South Africa
David Bennett - Smallest Planet Orbits Smallest Star
Comparison to Other Exoplanets
steam at
t = 1 Myr
snow at
t = 1 Myr
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
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