Vega's Likeness for New Planets
All of the hundred or so planets that have been discovered around other stars have been very large gaseous (Jupiter-like) planets orbiting close to their star. This is very unlike our own Solar System. New computer modelling techniques have shown that observations of the structure of a faint dust disk around Vega can be best explained by a Neptune-like planet orbiting at a similar distance to Neptune in our own solar system and having similar mass. The wide orbit of the Neptune-like planet means that there is plenty of room inside it for small rocky planets similar to the Earth - the Holy Grail for astronomers wanting to know whether we are alone in the Universe.
|SCUBA image with the position of the star (*) and the predicted position and direction of the planet (x) marked. The distance between the star and the planet is equivalent to twice that between the Sun and Neptune. Credit: SCUBA
The modelling, which was described in the December 2003 issue of The Astrophysical Journal, is based on observations taken with the world's most sensitive submillimetre camera, SCUBA. The camera, built at the ATC, is operated on the James Clerk Maxwell Telescope in Hawaii. The SCUBA image shows a disk of very cold dust (-180 degrees centigrade) in orbit around the star.
The false color image represents the heat emitted from the dust disk around Vega. The image shows the disk seen face-on. The disk structure includes two bright clumps, represented by the yellow and red colors. The star is barely noticeable and is located at the center of the image, mid-way between the two clumps. The dust were seeing is actually confined to a region relatively far from the star: more than twice as far as the distance from the Sun to Neptune. The lack of dust close to the star is the first indication that a planetary system is hiding in the hole. The modelling published today implies that this system looks very much like our own Solar System.
"The irregular shape of the disk is the clue that it is likely to contain planets" explains astronomer Mark Wyatt, the author of the paper. "Although we can't directly observe the planets, they have created clumps in the disk of dust around the star."
The modelling suggests that the Neptune-like planet actually formed much closer to the star than its current position. As it moved out to its current wide orbit over about 56 million years, many comets were swept out with it, causing the dust disk to be clumpy.
"Exactly the same process is thought to have happened in our Solar System", said Wyatt, "Neptune was 'pushed' away from the Sun because of the presence of Jupiter orbiting inside it". So it appears that as well as having a Neptune-like planet, Vega may also have a more massive Jupiter-like planet in a smaller orbit.
The model can be tested in two ways as Wayne Holland, who made the original observations, explains "The model predicts that the clumps in the disk will rotate around the star once every three hundred years. If we take more observations after a gap of a few years we should see the movement of the clumps. Also the model predicts the finer detail of the disk's clumpiness which can be confirmed using the next generation of telescopes and cameras."
Paradoxically the star barely appears in the SCUBA image because it is far too hot to be seen with this kind of detector. Vega is, however, easily seen with the naked eye. It is the third brightest star visible from Northern latitudes and is bluish-white in color.
Facts about Vega
- Vega is the fifth brightest star in the sky and the third brightest visible in the Northern hemisphere.
- It is 25 light years away from the Sun (1AU is the distance between the Earth and Sun).
- It has a diameter three times bigger than the Sun.
- It is 58 times brighter than the Sun.
- Together with Deneb and Altair, Vega forms the summer triangle.
- Vega is the brightest star in the constellation Lyra, the Harp. The lyre, or harp, is supposed to have been invented by the Greek God Hermes who gave it to his half-brother Apollo. Apollo then gave it to his son Orpheus, the musician of the Argonaughts.
- Vega was the first star ever to be photographed. During the night of July 16-17 1850 the historic picture was taken at Harvard Observatory using a 15 inch refractor telescope during a 100 second exposure.
Related Web Pages
NASA Kepler Mission
European Southern Observatory
Astrobiology Magazine New Planets
Extrasolar Planets Encyclopedia
Planet Quest (JPL)
Space Interferometry Mission