Two Ancient Worlds Discovered In Neighboring Galactic Cluster
June 4, 2014

Two Ancient Worlds Discovered In Neighboring Galactic Cluster

Lawrence LeBlond for - Your Universe Online

Using new data from the HARPS spectrometer at the ESO’s La Silla observatory in Chile, an international team of scientists have discovered two exoplanets orbiting a nearby ancient star. Kapteyn’s star, named after Jacobus Kapteyn, who discovered the star in the 19th century, is a red dwarf and one of the two planets in its grasp sits at the right spot where life could form.

Led by Queen Mary University of London, the international team, which included scientists from UC Irvine, UC Santa Cruz and Carnegie, discovered the planets by measuring tiny periodic changes in the motion of the host star. Using the Doppler Effect, which shifts the star’s light spectrum depending on velocity, the team can work out some of the properties of the two planets, such as mass and orbital period.

The study also combined data from HIRES at Keck Observatory in Hawaii and PFS at Magellan/Las Campanas Observatory; these spectrometers helped secure the detection of the planets.

"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," explained lead author Dr Guillem Anglada-Escude, from QMUL's School of Physics and Astronomy.

"That we can make such precise measurements of such subtle effects is a real technological marvel," added Jeff Crane of the Carnegie Observatories.

The team’s work is published in the Monthly Notices of the Royal Astronomical Society.

Kapteyn’s star is the second fastest moving star in the night sky as seen from Earth, and belongs to the galactic halo – an extended cloud of stars orbiting the Milky Way Galaxy. With just a third of the mass of our own sun, this red dwarf can be seen in the southern constellation of Pictor with an amateur telescope.

Based on the collected data, planet Kapteyn b is at least five times more massive than Earth and was found to orbit its host star once every 48 days. This discovery means the planet is warm enough for liquid water to be present on the surface, meaning life as we know it could be capable of forming. The second planet, Kapteyn c is a more massive super-Earth and quite different from b. Its orbit around the star takes 121 days and early estimates suggest it is too cold to support liquid water.

"Finding a stable planetary system with a potentially habitable planet orbiting one of the very nearest stars in the sky is mind blowing. This is one more piece of evidence that nearly all stars have planets, and that potentially habitable planets in our Galaxy are as common as grains of sand on a beach," Pamela Arriagada, the second author, and a Carnegie postdoctoral researcher, said in a statement.

Currently, the researchers only know approximate masses, orbital periods and distances to the host star. By continuing to study the exoplanets, the team hopes to determine the atmospheric compositions using next-generation instruments and ultimately determine if either can and/or does bear liquid water.

To date, most planetary systems discovered by NASA’s Kepler mission have been hundreds of light years away. However, Kapteyn’s star is relatively close to us. It is the 25th nearest star to the sun and is only 13 light years away from Earth, meaning it is literally sitting in our own backyard in astronomical terms.

Another difference in this discovery is the somewhat strange story of the star. Kapteyn’s star was born in a dwarf galaxy that was absorbed and subsequently disrupted by the early Milky Way. The galactic disruption put Kapteyn’s star in a fast halo orbit. The likely remnant core of the original dwarf galaxy is Omega Centauri, a globular cluster 16,000 light years from Earth which contains hundreds of thousands of similarly ancient stars. Based on this data, the team believes the Kapteyn b and c planets are about 11.5 billion years old – about 2.5 times older than Earth and roughly 2 billion years younger than the Universe itself.

"It does make you wonder what kind of life could have evolved on those planets over such a long time," noted Dr Anglada-Escude.

"This discovery is very exciting. It suggests that many potentially habitable worlds will be found in the next years around nearby stars by ground-based and space-based observatories, such as PLATO. Until we have detected a larger number of them, the properties and possible habitability of the near-most planetary systems will remain mysterious," Prof Richard Nelson, Head of the Astronomy Unit at QMUL, who was not involved in the research, commented on the work.