Solar System 2.0 - four planets discovered around a star 21 light years away, arranged like in our solar system

The stunning system, named HD219134, has one giant outer planet and three super-Earths as inner stars. The proximity of the system will make it possible to explore it by various means

Astronomers from the University of Geneva (UNIGE) and the exoplanet research group NCCR have discovered a secret star system hiding in the arms of Cassiopeia, only 21 light years away.

The amazing system, named HD219134, includes one giant outer planet and three super-Earths as inner stars, one of which has transited in front of the parent star.
The super-Earth that passed in front of the star has a density similar to that of the Earth. It is by far the closest planet known today that was discovered using the transit method. This system provides ideal candidates for follow-up studies and as a means of gaining a deeper understanding of the planets' formation, internal composition and atmospheres.
The system is so close that astronomers are already dreaming of taking pictures of the planets.

The HARPS-N telescope, a northern twin of the HARPS southern telescope, was designed and built by an international consortium led by researchers from the University of Geneva. It is stationed at the Galileo telescope on the island of La Palma. This is the telescope through which the unusual system surrounding the star HD219134 was discovered. The star, a K-dwarf, is slightly smaller than the Sun, and its mass is also smaller. However, it is bright enough to be visible to the naked eye in a dark sky, near the foot of one of the W arms of the Cassiopeia group, and will be visible year-round in the Northern Hemisphere. The planetary entourage consists as mentioned of three rocky super-Earths and a huge outer planet, a configuration reminiscent of our solar system.

One of those super-Earths was discovered by the Spitzer Space Telescope

"When the initial HARPS-N radial velocity measurements indicated the presence of a planet orbiting the star HD219134 every three days, we immediately asked NASA for an observation time with the Spitzer Space Telescope," explains Ati Motelbi, an astronomer at the University of Geneva and lead author. of the article describing the discovery and which is about to appear in one of the upcoming issues of the journal Astronomy and Astrophysics.

"The idea was to check for a possible transit of the super-Earth in front of the star, a kind of mini-eclipse, which would allow us to measure the size of that planet," she continues, "to do that, we need to go into space to reach the required accuracy. " Fortune favors the brave; HD219134b did pass in front of the star. Without a doubt this planet is the closest discovered and is expected to remain so. According to the combined calculations - HD219134b's mass is 4.5 times greater than that of Earth and it is also 1.6 times greater than it, which is why it is called a super-Earth. Its average density is close to that of Earth, possibly suggesting a similar composition as well.

Two more Super Earths and a giant planet

But, there is more! The team members discovered three long-period planets, also discovered using the HARPS-N telescope. One of them is a planet 2.7 times the mass of Earth orbiting HD219134 once every 6.8 days, and a planet with a mass 8.7 times the mass of Earth orbiting the star once every 46.8 days. If, by chance, these 2 planets orbit the Sun in the same plane as the inner planet, as is often observed in compact systems, the whole family can pass in front of the star.
Members of the group have already ordered sightings in order to capture the potential transitions. In particular, they predict that the Khopo satellite that the space agency is supposed to launch, and which was developed by Swiss scientists, including from the universities of Geneva and Bern, will be the best means. Prof. Stéphane Audrey from the University of Geneva adds that "the ability to characterize three transitions of super-Earths in a close system will provide an opportunity to learn about another model of the formation of Earths."

But the story is not over yet. The system also includes a giant planet (slightly smaller than Saturn) orbiting the star at a distance of 2.1 AU, or just over three years. This system reminiscent of our own solar system in the inner planets and outer gas stars will undoubtedly gain the interest of the astronomical community.

Indeed, the proximity and brightness of the star make the system the best system for in-depth characterization of the Earth's physical properties and to study the atmosphere. Astronomers are already planning observations with spectrographs mounted on high-resolution ground-based telescopes as well as with the future James Webb Space Telescope.
During the transit of the star's light, it crosses the planet's atmosphere on its way to the observer, and it carries the spectral signature of the chemical compounds in the atmosphere. They even dream of directly imaging the outer super-Earth in the system with the new generation of giant ground-based telescopes planned for the next decade.

to the notice of the researchers