12 years ago, we didn't even know planets could exist around distant stars.

Today, we know of almost 300 of them!

The exosolar planet session here at this year's NAM began with the announcement by Rachael Smith (Institute of Astronomy, University of Cambridge) of the astonishing discovery of two asteroid belts orbiting the star eta Tel.


 

Such a system may sound familiar to you... that is because we have two asteroid belts in our own solar system! In our solar system, one is between the orbits of Mars and Jupiter (the asteroid belt) and one is at the very edge of our solar system (the Kuiper-Edgeworth belt, of which Pluto appears to be the closest and largest member).


 

However, eta Tel is a very young system, only 12 million years old (our solar sytem is 4,500 million years old), and so eta Tel reminds us of how our solar system must have looked long ago, before Jupiter and Saturn formed. In fact, the asteroid belts in eta Tel may began to stick together to form two large planets in the future.


 

Following on with the same theme, Martin Dominik (University of St Andrews) described a system called Ogle-2006-BLG-109, which contained two Jupiter-sized planets at 2.3 & 4.6 times the Sun-Earth separation - again, very similar to the planets Jupiter & Saturn in our solar system. In total, astronomers now know of 26 multiple planet systems, and 4 of these planets are in habitable zones - the location around a star that is neither too hot or too cold for life.


 

Astronomer Elain Simpson of the Queen's University Belfast announced the discovery of 5 more planets using SuperWASP, with 2 more suspect planets.

Elain initially discovered 44 possible planets, and by observing each and every one in more detail using the Nordic Optical Telescope, she discovered the 5 planets. All these planets are hot Jupiters - large planets, very close to their parent star.


 

It makes us all wonder when the first Earth-like planet will be found - This year? There is a European Space Agency mission being planned called Darwin which has the aim of finding traces of water, ozone & carbon dioxide around some of these distant planets, helping us to identify Earth-like planets in the very near future.


 

source: Royal Observatory Greenwich
 

Exosolar planet atmosphers
 

One of the newest topic in astronomy presented at this year's NAM was the atmosphere's in exosolar planets session.

I find it staggering that astronomers can now study the atmospheric composition of planets orbiting distant stars!

The ultimate aim is to find an atmosphere around a planet that could sustain life. That has not been found yet, but it is only a matter of time...

There are two ways to study the atmosphere of a distant exoplanet. If the planet ever passes in front of the parent star, some starlight is blocked by the planet itself, but some of the star-light is absorbed by the planet's atmosphere - and by looking at what wavelength's of starlight is absorbed by the planet's atmosphere, you can work out what chemicals are present in the planet's atmosphere. Also, when the planet moves around to the far side of the star, it can reflect starlight in our direction, and by looking at that reflected starlight astronomers can work our what chemicals are doing the reflection.


 

Doing this in reality is incredibly difficult, due to the parent star being so bright, and the planets being so small and faint.


 

The highlight of the session was the research done by Tommi Koskinen at the University College London, on a planet called HD17156b.

This planet was actually discovered by amateur astronomers! It is very impressive what new science can be achieved by experienced amateur astronomers. In this example, the planet moved in front of its parent star, hiding 0.6% of the light coming from the star - and this is enough for skilled amateur astronomers to detect the planet.


 

While amateurs monitor the entire sky, professionals scrutinise individual objects, and this is exact what Tommi and his colleagues have done.

They discovered that the orbit of the planet around the parent star is very elliptical (strongly oval shaped), and so the temperature of the planet can vary by a staggering 1000^oC depending on where it is in its orbit. They also discovered that when the planet is close to the star it rotates at the same rate at which it orbits, but when it is further away from the star it rotates quicker.


 

source: Royal Observatory Greenwich