Researcher Emily Rickman along with other planet hunters from Geneva Observatory, Switzerland have discovered 3 new massive planets and 2 new low mass brown dwarfs.
Discovering planets outside of the Solar System, known as exoplanets, is vital in trying to understand how Earth and the Solar System formed. Different detection techniques are used to find these far away worlds, but many observational biases exist that can make planets so far away difficult to detect.
Researchers at Geneva Observatory have been carrying out an ongoing survey of stars in the Southern hemisphere for over 20 years in order to detect exoplanets. These stars are similar to the Sun in size and temperature and nearby to our own Solar System, known as the ‘Solar neighbourhood’. The survey is carried out using the Swiss telescope based at La Silla observatory in the Atacama desert, Chile – an optimal place to observe the night sky due to low light pollution and dry clear conditions for most days in the year.
There are several techniques that can be used to detect exoplanets – one of the most popular and successful techniques is called the ‘radial velocity’ technique. As a planet orbits a star, this causes it to wobble as both the star and the planet in the system orbit their centre of mass. As the star wobbles, or moves towards or away from us as the planet orbits it, this causes the light received from the star to be compressed (making the wavelength observed bluer) or to be stretched (making the wavelength observed redder), as demonstrated in the image.
The best example of this in everyday life is when an ambulance with its siren on speeds past you. As it is approaching the sound wave is compressed and the siren has a higher frequency, but as the ambulance passes you and moves away, the sound wave is stretched and the frequency of the sound decreases, giving this infamous high to low sound as it moves past.
The radial velocity technique, otherwise known as the Doppler method, uses the same phenomenon. We observe and measure the Doppler shift of the spectrum of the host star of an exoplanet. This creates what’s called a radial velocity curve. From this we can pull out information like the orbital period of a planet, i.e. how long it takes the planet to orbit a star as well as the mass of the planet.
Using this 20 year survey of measuring radial velocities, Rickman et al. report the discovery of 3 new exoplanets and 2 low mass brown dwarfs (objects that are bigger than a planet, but not quite a star). These planets are at very long distances away from their star, greater than 5 times the distance of Earth to the Sun. They take longer than 15 Earth years to orbit their star, which is why this long term survey is vital in detecting these objects. They are also giant planets which masses of several Jupiter masses or more, far bigger than any planet in our Solar System.
Some of these planets are also very eccentric, which means that its orbit around its star is not very circular like that of Earth’s. It means that at some points in its orbit it is extremely close to its star, which means that the planet would likely be very hot and at other points in its orbit it would be very far away from its star meaning that the planet would likely be very cold – not very ideal conditions for alien life!
Because these planets are so massive and at such wide separations away from their star, it is possible to directly image some of these planets – quite literally taking an image of a planet next to a star. When an image is taken of a planet or brown dwarf, the spectrum of its atmosphere can also be observed helping to understand these objects even more. These observations can be pieced together to help constrain how these planets formed – which in the long run help astronomers understand how our own Solar System formed. So stay tuned for the next stage in investigating these new planets!
Check out the paper at: https://arxiv.org/abs/1904.01573
Reference: Rickman et al. 2019, The CORALIE survey for southern extrasolar planets XVIII. Three new massive planets and two low mass brown dwarfs at separation larger than 5 AU