(CORDIS) — German astronomers have discovered an ancient planetary system thought to be a survivor of one of the earliest cosmic eras, from 13 billion years ago. The system consists of the star HIP 11952 and two planets. Such an old system will help shed light on planet formation in the early Universe, which occurred under conditions quite different from those of later planetary systems such as our own.
Accepted planetary theory states that, generally speaking, a star that contains more ‘metals’, (i.e. chemical elements other than hydrogen and helium) is more likely to have planets; it is also widely accepted that planets are formed in discs of gas and dust that swirl around young stars. The team noted with interest, then, that despite this observed trend for planets to form within clouds that contain heavier chemical elements, a star containing very little bar hydrogen and helium has two planets orbiting it.
HIP 11952, which belongs in the large northern constellation Cetus, is situated about 375 light years from Earth. By carrying out a planet survey into metal-lacking stars, German researchers identified two giant planets around this star. Although these planets are not particularly unusual in themselves, it is out of the ordinary that they should orbit such an old and metal-deficient star.
These findings, published in the journal Astronomy & Astrophysics, therefore throw up questions about what it actually takes to make a planet. If metal-rich stars are more likely to form planets, how were the two planets around star HIP 11952 formed?
In the beginning, the Universe contained almost no chemical elements other than hydrogen and helium. Nearly all the heavier elements were produced over time inside stars, before being flung into space as massive stars and ending their lives in giant explosions called supernovae.
Veronica Roccatagliata from the University Observatory Munich, the principal investigator on the planet survey around metal-poor stars that led to the discovery, explains: ‘In 2010 we found the first example of such a metal-poor system, HIP 13044. 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 extremely metal poor, but, at an estimated age of 12.8 billion years, also one of the oldest systems known so far.
Johny Setiawan from the Max Planck Institute for Astronomy in Heidelberg, Germany, who led the study of HIP 11952, comments: ‘This is an archaeological find in our own backyard. These planets probably formed when our Galaxy itself was still a baby.’
Now the researchers hope to discover and study more planetary systems of this kind so they can advance their theories on planet formation.