The discovery raises new questions about the migration of gas giants, as well as their formation at the margins of planetary systems.
Using the ALMA radio telescope array, astronomers have identified four breaks in the protoplanetary disk around the young star, which indicate the presence of a quartet of massive exoplanets with an extreme range of orbits - the outer planet is more than 1000 times farther from the star than the inner one. The discovery raises new questions about the migration of gas giants, as well as their formation at the margins of planetary systems. An article describing the study was presented in the Astrophysical Journal Letters.
“Models of planet formation tend to describe those that have already been observed, so new discoveries do not necessarily fit into simulations. For example, massive worlds like Saturn are formed in two main stages: first, a solid core is formed, and then a layer of gas is "stretched" over it. However, these processes must be very slow at large distances from the star, so almost all models do not lead to the creation of massive giants on the outskirts of planetary systems,”says Katie Clarke, lead author of the study at the Institute of Astronomy at the University of Cambridge (UK).
The star CI Tau, young by astronomical standards, is only 2 million years old and lives about 450 light years from Earth in the direction of the constellation Taurus. It is surrounded by a huge disk of dust and ice, in which planets, satellites, asteroids and other astronomical objects originated and continue to form. In 2016, the star rose to fame thanks to the discovery of hot Jupiter in its orbit, making CI Tau the youngest star ever to have had an exoplanet of this type. And now, thanks to new observations of ALMA, no less interesting neighbors have been found in CI Tau b.
The orbits of all four giant planets in the system are very different: the closest is approximately the same distance from CI Tau as Mercury is from the Sun, and the farthest is more than 3 times farther from the star than Neptune is from the Sun. The two outer planets are similar in mass to Saturn, while one of the inner ones is almost a complete analogue of Jupiter, and the second is "heavier" by almost 10 times.
Artistic representation of hot jupiter. Credit: ESO.
The discovery raises many questions. First, previous observations have shown that about one percent of stars contain hot Jupiters in their orbits, but most of them are hundreds of times older than CI Tau. Second, it is unclear whether the three outer planets played any role in the migration of the inner world to the star, and if so, whether this is typical of other systems. And finally, astronomers do not yet have convincing scenarios that reveal the formation of the two outer planets.
The next task, scientists call the study of this mysterious system at different wavelengths in order to obtain more information about the properties of the disk and the planets in it.
Promotional video:
Roman Zakharov