26 planets and 11 systems for Kepler

To date, the Kepler space telescope has discovered more than 2,000 potential extrasolar planets. 26 of these planets that orbit suns other than our own have just been confirmed in 11 star systems.

 

The Kepler space telescope (illustration). Credit: NASA

Since 2009, Kepler has been observing the same region of the sky, examining the slightest variation in luminosity of 155,453 stars. A temporary drop in the brightness of these other suns could be caused by the fact that a planet is passing in front of it, and thereby blocking out part of the light. This is what is known as the transit method (the planet transits in front of the star around which it is orbiting). To date, NASA’s space telescope has found almost 2,300 “planet candidates”, that is to say drops in luminosity which have the characteristics of other worlds passing in front of their sun. However, before these extrasolar planets can be “validated”, their existence has to be verified by means of other methods, notably by using ground telescopes. On 26 January 2012, as a result of such verification, the American Space Agency announced the confirmation of 26 planets spread throughout 11 star systems.

Kepler’s catalogue of extrasolar planets (planets that orbit suns other than our own) arranged by stars (same column). The 26 new worlds are shown in green. In blue, on the left-hand side, are the planets in our solar system for size comparison (Sol-b is Mercury, Sol-c is Venus, Sol-d is the Earth, Sol-e is Mars, Sol-f is Jupiter, Sol-g is Saturn, Sol-h is Neptune and Sol-i is Uranus). Credit: NASA

What variety!
Kepler’s new authenticated harvest stands out because of its great variety. Although all these planets orbit near to their star (nearer than Venus is to our Sun), their sizes range from being 1.5 times that of the Earth to being bigger than Jupiter (the biggest in our solar system). Fifteen of them have a diameter between 1.5 times that of the Earth and that of Neptune. One year on these worlds lasts from 6 to 143 Earth days. Other observations will be necessary to determine which extrasolar planets are gaseous and which are telluric (that is to say rocky, like our own planet). The 11 systems are all situated in our immediate galactic neighbourhood as Kepler “sees” up to about 3,000 light years away, and they each contain between 2 and 5 planets.
The video below explains how by measuring transit times, we manage to detect the fact that there is one or more planets around the same star.



As we previously mentioned, none of these worlds is further away from its star than Venus is from our Sun (which is 108 million km as opposed to 150 million km for the Earth). We are, therefore, looking at rather “compact” planet systems. To such a point that astronomers have noticed that these extrasolar planets mutually disturb one another due to gravitational interaction, thereby causing acceleration or deceleration in their orbit around their star. In this respect, the Kepler-33 system stands out with its 5 worlds that orbit a star which is older and more massive than our own. And these 5 planets revolve in a “restrained” area (in terms of astronomical distances obviously) since all are nearer to their star than Mercury is to the Sun. And yet, Mercury is the planet in our solar system that is nearest to our Sun!

Orbital resonance
Scientists have also noticed so-called “orbital resonance” phenomena, which is when the orbital periods of objects orbiting other objects have a ratio that is a simple fraction. For instance, for the 5 Kepler-25, 27, 30, 31 and 33 systems, one pair has been detected where the planet nearer to the star orbits its sun exactly twice whilst the planet further away only completes one orbit. For the 4 Kepler-23, 24, 28 and 32 systems, the nearer world completes three orbits whereas the one further away only completes two. However, “orbital resonance” is nothing new and our own solar system features a good example with Neptune that orbits the Sun three times to Pluto’s twice.
The animation video below shows how Kepler’s 26 new worlds orbit their respective star.



Published on 27 January 2012