Small Rocky Planet Discovered In Our Galaxy

Media Resources
Embargoed till 5am Thursday Jan 26
Australian Eastern Summer Time
Contacts
Local
Tasmanian contacts from the University of Tasmania, School of
Mathematics and Physics.
Dr John Greenhill : John.Greenhill@utas.edu.au
phone: (03) 6226 2429 (w)
Dr Kym
Hill : Kym.Hill@utas.edu.au
phone: (03) 6226 2437 (w)
Dr Stefan Dieters :
Stefan.Dieters@utas.edu.au phone: (03) 6226
2438 (w)
The University of Tasmania Press
Office can be contacted:
Phone: (03) 6226 2124 Mobile: 0417 517 291
press.office@utas.edu.au
Other Australian contacts:
Dr Andrew Williams, Perth Observatory :
phone (08)
9293 8255
andrew@physics.uwa.edu.au
Professor Penny Sackett, Research School of Astronomy and
Astrophysics ANU :
phone (02) 6125 0266
director@mso.anu.edu.au
Links
- The
University of Tasmania press release (word).
- The
Perth Observatory (pdf)
press release.
- The
European Southern Observatory (ESO) (pdf) press release.
- The
NSF/NASA/Hubble (txt)
press release and site.
- PPARC
(UK) (txt) media
release.
- Nature Journal ; where
scientific paper is being published.
- PLANET group home page.
- Perth Observatory
event information page.
- European Southern
Observatory press information.
Photos/Images
The Milky Way runs vertically, with
Scorpio in the centre, with Sagittarius just below center. The large
glow (just below centre) marks the location where OGLE-2005-BLG-390L
and it's planet are located, which is toward the center of our galaxy.
- Close
up view of sky around Sagittarius.
Credit: Desktop Universe Shevill
Mathers
The cloud of stars seen in this image is
near the centre of our galaxy, about 30,000 light years away. These are
generally stars much brighter than our Sun. Between us and them there
are many stars, most too faint to be seen. These foreground stars orbit
the centre of the galaxy. If one of these foreground star becomes
nearly perfectly aligned with a background star, it's gravity acts like
a giant lens, creating miniture multiple micro-images of the background
star. These images combine, and make the background star brighten. For
a single foreground (lens) star and a single background star the
brightness of the background star increases and decreases in a
characteristic manner. These microlensing events are very rare because
the alignment has to be nearly exact and stars are very small compared
to the distances between them. In order to find a resonable number of
microlensing events the brightness of millions of stars needs to be
monitored on a nightly basis. This is done very sucessfully by
the OGLE and MOA groups.
- Colour
view of the star field
with the location of OGLE-2005-BLG-390Lb marked Credit:
Planet Group
- Two
images of the field taken with the Mt Canopus telescope; one showing OGLE-2005-BLG-390Lb
when it is faint
and the other when it is bright. In each
case OGLE-2005-BLG-390Lb is marked. Credit: UTas
Note that the images taken from Mt
Canopus are rotated 45 degrees with respect to images taken by the
PLANET group.
- Still
images of the combined images from the planet and background star from
the beginning , middle, and end, (png format) of the
planetary anomaly. Credit Andrew
Williams & David Bennett
The position of the planet is not marked
but is between the small yellowish star image from the planet and
larger star image formed by the foregroud star (star of planet). At the
middle of the planetary anomaly the images combine to give a donut
shaped image of the background star. The planet is located in the
middle of the donut. Changes in these combined images cause the small
brightening of the background star as shown in the lightcurve.
- Artist
impression of the planet and its parent star. Credit STSci/G.Bacon
The parent star is
only one fifth the mass of the Sun. It is a much cooler, and so shines
with a red colour. These stars are called red dwarfs and are the most
common type of star in our galaxy. Even though the planet obirts only 3
times further out from its star than the Earth about the Sun, it is
much colder; about the temperature of Neptune or Pluto in our solar
system. The mass of the planet (only 5 Earth Masses) is too small to be
a gas planet like Jupiter (317 Earth masses). So it is probably made
largly of rock and ice; a giant Pluto or Europa (large moon of Jupiter).
Video/animations
Just below the centre of the frame are
two round star images. The left hand image is that of
OGLE-2005-BLG-390Lb. As the
microlensing event progresses the star first brightens then fades with
a brief resurgence in brightness. As the unseen foreground star moves
closer into line with the background which we see here, the gravity of
the foreground star acts like a giant lens. The star brightens as the
alignment between foreground and background star becomes closer and
then fades as they move appart. Briefly the star brightens again as the
planet's gravity creates another image.
- Animation
(gif) made up of OGLE-2005-BLG-390Lb
images from the Danish 1.5
m telescope at La Silla Observatory, Chile. Credit: PLANET group / ESO (=European
Southern Observatory).
- Movie
(mpeg 1.3 mb) mostly showing an artists impression of
the planet. Credit ESO
- Movie
(mpeg 0.8 mb) showing how the gravity of the foreground star changes the brightness of
the background star. Credit: ESO
- Movie
(medium
resolution mpeg 96 mb) combining above material, and explanation
about planet formation theories, the Danish telescope, and interviews. Credit ESO
- Animations
showing the images created by the foreground star and planet: Credit: Andew Williams and David Bennett. (Perth Observatory event information page)
This is a simulation of
the images a hypothetical super high resolution telescope would see. We
observe the combined image and measure the the brightness of the
background star as these images change. The position of the foreground
star is shown as a small green circle. The viewpoint is centred on the
foreground star and so the position of the background star (a small red
circle) seems to move. The blue circle is the Einstein ring. If the
alignment was perfect a circular image of the background star would be
seen here. Initially the foreground star creates two images (yellowish)
images of the background star. As the foreground star and background
star move relative to each other the images move and grow larger
corresponding to a brightening of the background. The whole
microlensing event lasts 40 days. Toward the end, the animation slows
down and zooms in upon one of the primary images created by the
foreground lens star. A third very small image created by the planet
appears. The postion of the planet is marked by a blue dot. As the
planet moves it's image grows larger and merges with the primary image
from the star (circle with hole). This coresponds to the 12 hour long
brightening of the background star causing the bump in the lightcurve.
Later the images separate and the planetary image rapidly fades away.
Adaptive view (whole event with zoom for planentary anomaly)
1280x720 pixel
MPEG4
720x576 pixel
broadcast-ready view MPEG
Whole event view
1280x720 pixel MPEG4
720x576 pixel broadcast
ready view MPEG
Zoomed view of the planetary anomaly only
1280x720 pixel MPEG4
720x576 pixel broadcast
ready view MPEG
Graphs/Plots
- Lightcurve
(gif, pdf), showing how
brightness of OGLE-2005-BLG-390Lb changed. Credit: PLANET group
This is a plot of brightness versus time
for the background star of OGLE-2005-BLG-390Lb. As the unseen
foreground star aligns with the background star it's gravity acts like
a giant lens. As the alignment changes the brightness of the background
star varies in a characteristic manner; a smooth rise and fall.
If the foreground star has a planet, the planet's gravity distorts the
gravitational lens adding extra micro-images, causing an extra
brightening of
the background stars overall image. The length of this extra bump
(anomaly) depends mostly
on the planets mass. The larger the planet the longer the deviation in
brightness. For OGLE-2005-BLG-390Lb the deviation lasted about 12
hours.
(See the insert of the lightcurve plot). In this case the Perth
Observatory got most of the brightness measurements during the anomaly
caused by the planet. Each colour on the plot represents a
separate telescope. The changing bands of colour shows how as daylight
approaches at one telescope the next telescope takes over, giving
roughly continous coverage.
- Extra-solar
planet properties summary
Credit: Kieth Horne, Andrew
Williams
- Map showing
location of telescopes in the PLANET group. Credit PLANET group
As the Earth rotates at least one of the telescopes is in
darkness, so the between them the PLANET telescopes have 24hours of
darkness for the 3-4 months of the observing campaign.
Mt Canopus with a 1 m diameter telescope is near Hobart Tasmania and is
run by the School of Mathematics and Physics of the University of
Tasmania.
The Perth Observatory has a 0.6m diameter telescope and is run by (CALM
= Conservation and Land Management) department of the West Australian
state government.

Planet
Infomation Page
Optical and X-ray Astronomy home page
URL:
http://www.phys.utas.edu.au/physics/optastr/planet0390/media_OB390.htm
Jan 2006