Three exoplanets around the 150 light year -distant star HD3167 show how dramatically a solar system can be messed up in its early days. While one of the planets usually revolves around the equator of his mother's star, the other two migrate to orbits that lead over the poles of the star. This is the result of a working group around Vincent Bourrier from the Université de Genève based on data from the very large telescope in Chile and the Cheops space telescope, together with older measurements of the Harps-N instrument at the Italian Galileo National Telescope on the Canary Island of La Palma.
As the team reports in "Astronomy & Astrophysics", the system's innermost planet, a rocky planet with about five Earth masses, orbits its star on a fairly ordinary equatorial orbit, albeit with 23 hours in a very short time. The other two components of the system, two mini-Neptunes with orbital periods of 8.5 and about 30 days, travel around the star at an angle of about 110 degrees to its equator – almost perpendicular to the orbit of the inner planet.
Of course you cannot see an exoplanet at such a large distance along the star. The working group indirectly measured the angles of the orbits with the help of the Rossiter-Mclaghlin effect, in which a temporary planet only covers the half of the star to the observer and then those that turn away from it. The change in the Doppler effect of the star rotation can be measured in the light of the star and thus open up the positions of the planet during the transit. In fact, Bourrier and his team did this with the two inner planets - from the earth, the appearance does not pass in front of the star. They opened up its orbit based on the railway data of the middle companion.
Despite the very different orbits, the three planets almost certainly all emerged from the original dust disk around the star, the team writes. Only later were their orbits tilted into the curious angle. The working group blames another object in this system, which also orbits the central star and caused the orbits of the exoplanets to tilt from their original orientation due to its gravity. The inner planet, on the other hand, orbits so close to the star that its influence kept it in its original orbit.
The fourth companion has so far been undiscovered - Bourrier's team now wants to track it down using further measurements. The curious planetary system around HD3167 promises new knowledge about the evolution of planetary systems. Among other things, you could illuminate how the culprit that caused the moon came about - or why the ice giant Uranus is almost on the side.
