An international team of astronomers has discovered an ancient planetary system that is likely to be a survivor from one of the earliest cosmic eras.
An artist’s impression of HIP 11952 and its two Jupiter-like planets (Timotheos Samartzidis)
As part of a survey targeting especially metal-poor stars, the team has identified two giant planets orbiting a star known as HIP 11952 with periods of 290 and 7 days respectively.
By themselves, these planets called HIP 11952b and HIP 11952c are not unusual. What is unusual is the fact that they orbit such an extremely metal-poor and very old star.
Planets usually form within clouds that include heavier chemical elements, but the star HIP 11952 contains very little other than hydrogen and helium.
This system, located in the constellation Cetus about 375 light years away, promises to shed light on planet formation in the early universe – under conditions quite different from those of later planetary systems, such as our own.
The discovery will be published in a forthcoming issue of the journal Astronomy & Astrophysics.
For classical models of planet formation, which favor metal-rich stars when it comes to forming planets, planets around such a star should be extremely rare.
“In 2010 we found the first example of such a metal-poor system, HIP 13044,” said Dr. Veronica Roccatagliata of the University Observatory Munich, the principal investigator of the planet survey around metal-poor stars that led to the discovery. “Back then, we thought it might be a unique case; now, it seems as if there might be more planets around metal-poor stars than expected.”
HIP 13044 became famous as the “exoplanet from another galaxy” – the star is very likely part of a so-called stellar stream, the remnant of another galaxy swallowed by our own billions of years ago.
Compared to other exoplanetary systems, HIP 11952 is not only one that is extremely metal-poor, but, at an estimated age of 12.8 billion years, also one of the oldest systems known so far.
“This is an archaeological find in our own backyard,” said Dr. Johny Setiawan of the Max Planck Institute for Astronomy, who led the study. “These planets probably formed when our Galaxy itself was still a baby.”
“We would like to discover and study more planetary systems of this kind,” explained Dr. Anna Pasquali of the Center for Astronomy at Heidelberg University, a co-author on the study. “That would allow us to refine our theories of planet formation. The discovery of the planets of HIP 11952 shows that planets have been forming throughout the life of our Universe.”
