Discovery of a Cool Planet of 5.5 Earth Masses: OGLE-2005-BLG-390

OGLE-2005-BLG-390 was detected by the OGLE EWS [opens in new window] System on July 11, 2005.

True-colour image of the OGLE-2005-BLG-390 field (as observed by the PLANET team with the Danish 1.54m telescope).
The event resembled the typcal single lens light curve for most of its duration. But for a period of about a few hours on the night of August 10, 2005 the gravitational field of the planet caused a short-lived planetary deviation lasting several hours. It was noticed first by the PLANET team. Observations of the beginning of the deviation were taken from Chile by PLANET and OGLE, while the second part of the deviation was well covered by the PLANET observing station in Perth, Australia. The MOA collaboration also secured images of the microlens when testing its new telescope and confirmed the observed anomaly.

Discovery paper:
Beaulieu et al., 2006,
Nature, 439 (7075), 437-440
pdf version

Modeling of the light curve indicates that the deviation in the light curve of OGLE-2005-BLG-390 is caused by a record small mass planet. The new planetary system is also the most distant among all known extrasolar planetary system.

Parameters of the OGLE-2005-BLG-390 event


(Mass ratio of the lens components)



(Orbital distance assuming circular orbit in Einstein ring units)



(Position angle)

2.756±0.003 [rad]


(Impact parameter in Einstein ring units)



(Time of the closest approach to the center of mass)

31.231±0.005 July 2005


(Einstein ring crossing time)

11.03±0.11 [days]


(Unmagnified brightness of the source star in the I-band)

15.561±0.002 [mag]


(I-band magnitude of the blend at baseline)

15.561±0.002 [mag]

Estimation of parameters of the lensing system:


(Mass of the star)

0.22+0.21-0.11 [MSun]


(Mass of the planet)

5.5+5.5-2.7 [MEarth]


(Projected distance)

2.6+1.5-0.6 [AU]


(Distance to the lensing system)

6.6±1.0 [kpc]

Equatorial coordinates of OGLE-2005-BLG-390:

RA=17:54:19.19 DEC=-30:22:38.3 (J2000.0)

OGLE photometric data of OGLE-2005-BLG-390

(regularly updated when additional observations of the lens field are collected) are available from the OGLE-2005-BLG-390 EVENT PAGE [opens in new window].

PLANET photometric data of OGLE-2005-BLG-390

are available HERE:

  • Danish Telescope at ESO La Silla, Chile
  • Perth Observatory, Australia
  • Canopus Observatory, Tasmania, Australia
  • RoboNet

    MOA-2 photometric data of OGLE-2005-BLG-390

    are available here.

    Additional information can be found on the

    PLANET team WWW pages [opens in new window].