Astronomers have discovered the oldest known planets from the early days of the Universe, orbiting a star that is almost on our cosmic doorstep. 

An impression of an alien solar system. Credit: NASA/JPL-Caltech

The ancient solar system is thought to have formed around 12.8 billion years ago, just a few hundred million years after the Big Bang. Two newly detected exoplanets lie just 375 light-years away from the Earth, within our own Milky Way galaxy. But their host star was born when our galaxy was still forming.

European scientists used a giant telescope in Chile to detect two planets orbiting a star labelled HIP 11952 in the constellation of Cetus, the mythological sea monster. One planet, HIP 11952c, is the size of Jupiter while the other, HIP 11952b, is around three times the size of Jupiter. They orbit their own sun in 290 days and seven days. It is possible that there are smaller rocky worlds, though there is no direct evidence yet for these so they remain purely hypothetical. But if there was intelligent alien life inhabiting this planetary system, it could be far more advanced than that on Earth, having been around much longer.

The star raises fresh questions about how planets form because the star contains very little heavy elements other than hydrogen and helium. That is because there were almost no other elements around in the early universe. Usually planets form from cosmic clouds that include heavier chemical elements which have been produced over time inside stars and then blasted across space in a violent explosion called a supernova.

Johny Setiawan, who led the team that discovered the ancient planets, told Skymania News that they were around a hundred million years older than the previous record-holders found orbiting a dead supernova remnant called a pulsar. But he added: “HIP 11952 is still alive, not a dead star. It is also relatively very close at 375 light-years. We can imagine it is like finding an archeological discovery in our own backyard.”

On the possibility of advanced life, Dr Setiawan added: “If there is already intelligent civilization, it will have watched how the Universe started expanding after the Big Bang and how galaxies and the first stars formed. But, I wonder what kind of “blood” they have without iron element – at the time, there were almost no heavy elements available.”

The 2.2m telescope at La Silla that made the find. Credit: ESO/H.H.Heyer

A paper reporting the discovery has been accepted for publication in the journal Astronomy & Astrophysics. More than 750 so-called exoplanets have been discovered orbiting other stars since the first was detected less than 20 years ago.

The new planets were discovered using a spectrograph instrument on a telescope with a 2.2-meter light-collecting mirror at the European Southern Observatory’s La Silla site in Chile. They gave their presence away by causing a tiny wobble in their parent star’s position as they orbited it.

The star’s telephone-number name comes from its entry in the Hipparcos star catalogue, a listing of stars whose positions were measured by the Hipparcos satellite. Planets are named by adding letters to the star’s catalogue number, starting with b.

Dr Setiawan’s team from the Max-Planck-Institute for Astronomy in Heidelberg, Germany, has specialised in studying ancient, so-called metal-poor stars, meaning they are made up of just hydrogen and helium. Last year they reported finding a “hot Jupiter” in orbit around a red giant star that is thought to have been captured by our Milky Way from another galaxy.

He told us: “I’m not just looking for new planets, I’m interested in how planetary systems evolve, to find a sort of history of the life of stars and their planets. To do that, we have to look at stars which are not like the Sun and we have to search for planets around stars different from the Sun.”