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| Space on Sep 15, 2012

How and when did the first planets form in our universe?

At an estimated age of 12.8 billion years, the HIP 11952 exoplanet system is one of the oldest systems known so far.

While conducting a survey of metal-poor or very ancient stars, astronomers discovered one of the oldest planetary systems known so far. Astronomers hope to use this system to begin to understand how and when the first planets formed in our universe.

In late March, 2012, European astronomers announced that they had discovered a planetary system around a metal-poor star, that is, a star containing mainly hydrogen and helium, the two ingredients thought to have been present at the Big Bang. In other words, this star and its two Jupiter-sized planets appear to be survivors from the extremely early universe. The star is HIP 11952, and it’s not the only very ancient star known to have planets. But, at an estimated age of 12.8 billion years, this exoplanet system is one of the oldest systems known so far.

Artist's concept of the metal-poor and very ancient star HIP 11952 and its two planets. How did planets form in the early universe? And when did the first planets form? Image credit: Timotheos Samartzidis

HIP 11952 is located in the direction of the constellation Cetus the Whale at a distance of about 375 light-years from Earth. Its planets – HIP 11952b and HIP 11952c – have orbital periods of 290 and 7 days, respectively.

We know these are not planets like our own Earth. Our sun is at least a second-generation star. How do we know? We know because the sun and Earth and everything around us on Earth, including our own bodies, contain chemical elements heavier (more complex) than hydrogen and helium. All chemical elements heavier than hydrogen and helium are thought to have formed inside stars, via the process of thermonuclear fusion that enables stars to shine. These elements or metals were released into space via supernova eruptions. It’s the “we are star stuff” idea that Carl Sagan popularized a few decades ago and that still resonates with so many. Sagan also said:

We are a way for the cosmos to know itself.

In the video above, Sagan is talking about the universe we know best: our Earth, our own solar system, other second- or third-generations stars that lie relatively near us in space. The HIP 11952 system is not like these familiar stars and planets. Instead, the system is a relic from a much earlier era of the cosmos.

And so astronomers want to use these planets and their star HIP 11952 to begin to understand that early time in the universe, say, 13 billion years ago. For example, we believe we know how planets like our Earth form. We believe they form from vast rotating clouds of gas and dust swirling around a star. Presumably the first planets formed in much the same way, but no one can be sure. Also, when did the first planets form? The planetary system HIP 11952 might help lead astronomers along the path of finding answers to these questions.

These astronomers found the planets around HIP 11952 while conducting a survey targeting especially metal-poor stars. They say planets around such a star should be extremely rare. Veronica Roccatagliata of University Observatory Munich was principal investigator of the planet survey. She said in a press release:

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.

Anna Pasquali from the Center for Astronomy at Heidelberg University, a co-author of the paper, added:

We would like to discover and study more planetary systems of this kind. 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.

Bottom line: While conducting a survey of metal-poor or very ancient stars, European astronomers discovered one of the oldest planetary systems known so far. HIP 11952 is now known to have two Jupiter-sized planets. The system is thought to be some 12.8 billion years old. Astronomers hope to use this system to begin to understand how and when the first planets formed in our universe.

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