Pan-STARRS 1 spots free-floating planet
A unique Jupiter-like planet, “floating in space on its own” without a sun or star, was initially detected by the Pan-STARRS 1 telescope atop Haleakala.
“We have never before seen an object free-floating in space that looks like this,” said Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa, in a news release announcing the discovery.
Astronomers with Pan-STARRS 1 were part of an international team that located the young planet, identified as PSO J318.5-22. The planet is estimated to have formed 12 million years ago, is 80 light years from Earth and has a mass six times larger than Jupiter (Jupiter’s mass is 317 times that of the Earth’s).
Most planets orbit stars, but that is not the case with PSO J318.5-22, said Liu.
“It’s not attached to a star. It’s floating in space on its own,” said Liu in an interview with The Maui News on Wednesday. “It’s just driving through space all by itself.”
PSO J318.5-22 was located in the constellation of Capricornus from its faint and unique heat signature by the Pan-STARRS 1 wide-field survey telescope. Observations from other telescopes in Hawaii indicated that the planet has properties similar to those of gas-giant planets found orbiting around young stars.
Gas giants, such as Jupiter, Saturn, Uranus and Neptune, may have a rocky or metallic core, but most of their mass consists of the gases hydrogen and helium with traces of water, methane, ammonia and other hydrogen compounds, according to the website ScienceDaily.
What makes the discovery of this planet even more special is that astronomers are able to get a clean look at the planet, the news release from the IfA said. About a thousand extrasolar planets have been discovered in the past decade through indirect methods, such as wobbling or dimming of their host stars by the planet, but only a handful have been directly imaged – and all of them are around young stars.
Trying to observe those planets is like having a firefly next to a spotlight, said Liu. In the case of PSO J318.5-22, “the firefly is moving all by itself,” he said.
“PSO J318.5-22 is not orbiting a star so it will be much easier for us to study,” said Niall Deacon of the Max Planck Institute for Astronomy in Germany and a co-author of the study. “It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth.”
Pan STARRS 1, a wide-field telescope, “is great at finding these things,” said Liu.
The telescope design, developed at the IfA, involves a combination of relatively small mirrors with very large digital cameras that create a viewing system that can observe the entire sky several times each month, the website said. Astronomers get to visit the whole visible sky about 20 times a year.
“We often describe looking for rare celestial objects as akin to searching for a needle in a haystack. So we decided to search the biggest haystack that exists in astronomy, the dataset from PS1,” said Eugene Magnier of IfA and the other co-author of the study.
The total Pan STARRS 1 dataset to date is about 4,000 terabytes, which is larger than the sum of the digital versions of all the movies ever made, all books ever published and all the music albums ever released, the news release said.
PSO J318.5-22 was discovered during a search for brown dwarfs, objects that are larger than planets but too small to ignite the nuclear fusion to become stars, said the news release. The image was taken in September 2010, according to the study.
Due to their relatively cool temperatures, brown dwarfs are very faint and have very red colors, but Pan STARRS 1 has a camera sensitive enough to detect their heat signatures.
“PSO J318.5-22 stood out as an oddball, redder than even the reddest known brown dwarfs,” the news release said.
Liu explained that “very red” means “it’s very, very low temperature.” He said that the planet is not producing energy but is “glowing.”
“It is just not producing its own energy,” he said. “It is releasing trapped energy.”
The team followed up the Pan STARRS 1 discovery with multiple telescopes on Mauna Kea, the news release said. Infrared spectra taken with the NASA Infrared Telescope Facility and the Gemini North Telescope showed that PSO J318.5-22 was not a brown dwarf.
By regularly monitoring the position of PSO J318.5-22 over two years with the Canada-France-Hawaii Telescope, the team concluded that PSO J318.5-22 belongs to a collection of young stars and objects called the Beta Pictoris that formed about 12 million years ago, the news release said.
They formed as clusters “in the same birth cloud and scattered,” Liu said. “All are relatively newly born and drifted from their birthplace.”
The discovery paper of PSO J318.5-22 is being published by Astrophysical Journal Letters and is available at arxiv.org/abs/1310.0457.
* Lee Imada can be reached at email@example.com.