Astronomers Find Oldest Exoplanet Yet, With A Bonus
With the boom of exoplanet discoveries lately, astronomers have seen a lot more of our stellar neighborhood than ever before on their quest to find habitable planets at the right distance from their host stars. Here recently, one such a planet has caught their attention. A group of planets about 13 light-years away orbiting a red dwarf called Kapteyn’s Star have a planet among them in the Goldilocks zone called Kapteyn b.
Kapteyn b isn’t just captivating because of its distance from Kapteyn’s Star, but it’s also the oldest exoplanet yet discovered by astronomers. At 11.5 billion years old, it’s just a couple billion years younger than the universe itself. This also makes it over twice the Earth’s age, and being in the habitable zone, as ever it intrigues scientists all the more.
"It does make you wonder what kind of life could have evolved on those planets over such a long time," said study lead author Guillem Anglada-Escude of Queen Mary University of London.
During the observation of Kapteyn’s Star, astronomers noticed a slight color shift in the light being emmitted. This indicated to them that there could possibly be a planet or planets that were gravitationally pulling on the star. After the HARPS spectrometer made the initial discovery, Keck’s HIRES and Chile’s Magellan II’s PFS instrument were able to confirm the findings. It was hard to accept, though, because habitable planets aren’t expected around a red dwarf, especially one that’s only one third the mass of our Sun.
"We were surprised to find planets orbiting Kapteyn’s Star. Previous data showed some moderate excess of variability, so we were looking for very short-period planets when the new signals showed up loud and clear," said Anglada-Escude.
Kapteyn b has a 48 day orbital period where its colder neighbor, Kapteyn c, has a 121 day orbit. So how does an 11.5 billion year old planetary system show up in our galaxy?
Astronomers believe that the Kapteyn system was once part of a dwarf galaxy that was assimilated by our Milky Way and has now likely taken its new identity as the Omega Centauri globular cluster 16,000 light years away. They believe this because Omega Centauri contains many thousands of stars that are around the 11.5 billion year age range.
IMAGE CREDIT: PHL @ UPR Arecibo, Aladin Sky Atlas (artistic rendition)