To observe the planets around stars distant light years, scientists have to engineer a lot. In this case, however, they went further. Astronomers have indeed observed the traces of planets in formations around a very young star, HD 163296.
The discovery was made thanks to a very powerful radio telescope, ALMA (Atacama Large Millimeter / submillimeter Array), in the Atacama desert in Chile. ALMA is made up of 66 sensitive antennas designed to capture the millimeter and submillimetric radiation coming from the cold objects of the Universe . This wavelength corresponds to a band between the infrared and the radio waves.
The solar system being studied in this case is very interesting, and could be considered a distant relative of ours. The central star, HD 163296, is only four million years old, has a mass equal to “only” twice that of our Sun and is about 330 light years from Earth, in the constellation of Sagittarius.
Using an innovative technique, two astronomers, quite independently, have discovered that the traces present in the protoplanetario disk of HD 163296 are due to the presence of planets in formation. The technique consists in studying the doppler effect on millimeter radiation emitted by carbon monoxide (CO) molecules. When the gas interacts with a very massive body, such as a planet in formation, locally it undergoes variations in its motion, which translate into a variation in the frequency of the emitted radiation.
By studying these imperceptible variations, the team led by Richard Teague, of the Monash University in Australia and the Institut de Planétologie et d’Astrophysique of Grenoble, has identified two planets in formation, respectively 12 and 21 billion km from the star.
Independently, the team led by Christophe Pinte, of the University of Michigan, has identified a planet in formation at 39 billion km from the star.
The two groups of astronomers have used very similar techniques but with some differences. The Teague method in fact consists in studying average variations of the gas flow, while the Pinte technique consists in measuring this flow directly. In the first case, it is possible to identify flux variations up to a few percentage points and is therefore more precise, while the second technique is more suitable for the outer areas of the planetary disc, but it is less precise and requires flow variations greater than 10%.
About the discovery, here are the words of Teague:
Measuring the flow of gas inside a protoplanetary disk gives us much more certainty that there are planets orbiting a young star. This technique offers a new, promising direction to understand how planetary systems are formed.
While these were the words of Pinte:
We examined the small-scale localized motion of the gas in the protoplanetary disc of the star. It is a completely new approach that could make us discover some of the youngest planets in the galaxy, thanks to the high resolution images produced by Alma.