The dwarf and the 7 planets


 Illustration: NASA



A small och faint star in the constellation of Aquarius has been proven to have seven planets.The initial discovery was made by a team led by the Belgian astronomer Michaël Gillon, who used a small 60 cm telescope at ESO, La Silla (see right). Continued observations with, among others, the Very Large Telescope and the infrared space telescope Spitzer have revealed more information.

The seven planets orbiting this star all are of Earth size. Of these, three planets are considered to lie inside the habitable zone (i.e. where the heat influx allows liquid water).


trappist1 system

Illustration: NASA

The figure above shows the layout of the new system. It actually is strongly reminiscent of a scaled-up Jovian system. Trappist-1 is a very small and faint star (10 times smaller than the Sun, 2000 times fainter). To at all be able to observe this system so successfully is explained by the fact that its orbital plane is very exactly aligned towards Earth. This allows for very detailed transit based observations, where very small variations in the light of the star have been observable.

All the planets lie very close to their star, far inside the corresponding orbit of Mercury. Further studies show that so tight planetary systems not only force each planet to have bound rotation (i.e. always show the same hemisphere towards its star), but also have orbits that are mutually bound in gravitational resonances. This explains why such a tight system still can remain stable. 

Very little is known about the planets, except that they appear Earth-like, i.e. rocky planets and not gas planets. It is doubtful whether any of the planets have conditions suitable for life. As an example, it is known that they are exposed to much higher levels of extreme ultraviolet radiation than is the case for Earth. This would affect any hypothetical atmosphere.

But nevertheless, this planetary system constitutes a very exciting discovery which with certainty will spark  a lot of further interest and will be an obvious target when the world's largest telescope, the E-ELT, begins operation in a few years.


Moore info:

Basic data
Trappist's own home page
Observations of extreme UV