Astronomers: Dying solar system once harbored vast amounts of water

Approximately 150 light years away lies the star GD 61, a white dwarf nearing the end of its life. GD 61 was once three times more massive than our Sun. Once the star had used up its supply of hydrogen, it began fusing helium into carbon and swelled into a red giant. However, GD 61 lacked sufficient mass to begin fusing carbon, allowing carbon and oxygen to build up in its center. Eventually, the dying star shed its outer layers, leaving an exceptionally dense stellar remnant with a mass comparable to our Sun but with a volume comparable to that of Earth.

A new study led by Jay Farihi of the University of Cambridge has discovered a fragmented dwarf planet around GD 61. Unlike the more than 900 exoplanets discovered around younger stars, the broken dwarf planet orbiting GD 61 has been shattered by the intense gravity of the white dwarf, allowing scientists to study its composition. Debris from the planet has been drawn close to GD 61, and so the team used ultraviolet measurements from the Cosmic Origins Spectrograph on the Hubble Space Telescope to determine the amount of oxygen present in the atmosphere of the white dwarf star.

The ultraviolet measurements allowed the researchers to detect the abundances of magnesium, silicon, iron, and other elements in the contaminated atmosphere of the star. This allowed them to predict how much oxygen should be present in the atmosphere of the star. Farihi and team found significantly more oxygen than they expected. The team ruled out comets as a source of the oxygen because comets, in addition to carrying oxygen in water molecules, also bear large amounts of carbon, and the atmosphere of GD 61 is devoid of carbon. This means that the excess oxygen was probably delivered in water molecules contained within the shattered dwarf planet.

So rich in water was the fragmented dwarf planet that water accounted for 26% of its mass, similar to Ceres, a dwarf planet and the largest object in our solar system’s asteroid belt. By comparison, the blue planet Earth is only 0.02% water mass; indeed, most of the water on Earth was probably delivered by water-rich asteroids early in the planet’s history.

The discovery of a water-rich body in the GD 61 star system provides a glimpse ahead at what our solar system will be like in six billion years, as our own Sun nears the end of its life. It also suggests that habitable planets might have once existed around GD 61. “The finding of water in a large asteroid means the building blocks of habitable planets existed – and maybe still exist – in the GD 61 system, and likely also around a substantial number of similar parent stars,” Farihi explained in a University of Cambridge press release.

The existence of a shattered dwarf planet in the GD 61 system also suggests the presence of one or more gas giants, the gravity of which would have pushed the dwarf planet and other water-rich bodies closer to the white dwarf star. As they moved closer to GD 61, the star’s gravity tore them apart, giving Farihi and colleagues their unique look inside an object in another solar system.

The new study was published in the October 11 issue of the journal Science.

Source:http://thespacereporter.com

Astronomers say they've spotted lonesome planet without a sun

 Eighty light-years from Earth, there's a world that's just six times more massive than Jupiter, floating all alone without a sun to keep it warm, astronomers reported Wednesday.

Such free-floaters have been reported before, but in the past, it hasn't always been clear whether these were orphaned planets or failed stars. This time, the scientists say they're sure it's a planet.

"We have never before seen an object free-floating in space that that looks like this," team leader Michael Liu of the Institute for Astronomy at the University of Hawaii at Manoa said in a news release. "It has all the characteristics of young planets found around other stars, but it is drifting out there all alone. I had often wondered if such solitary objects exist, and now we know they do."

The heat signature of the world, known as PSO J318.5-22, was identified by the Pan-STARRS 1 wide-field survey telescope on Haleakala, on the Hawaiian island of Maui. The light coming from the object is about 100 billion times fainter in optical wavelengths than the planet Venus. Most of its energy is emitted in infrared wavelengths.

In a report being published in Astrophysical Journal Letters, Liu and his colleagues said the object has properties similar to those of gas-giant planets found orbiting young stars.

Past reports of "rogue planets" have been murky, due to the fact that it can be hard to discriminate between large planets and a class of failed stars known as brown dwarfs. Some astronomers insist on a definition of planets that would apply only to objects that form around stars. They'd prefer to call objects like PSO J318.5-22 "planetary-mass objects," orplanemos for short.

PSO J318.5-22 was discovered while the researchers was combing through data from Pan-STARRS 1 for readings from brown dwarfs. Brown dwarfs are typically faint and red, but Liu and his colleagues said PSO J318.5-22 stood out because it was redder than the reddest known brown dwarfs.

N. Metcalfe & Pan-STARRS 1 Science Consortium

A multicolor image from the Pan-STARRS 1 telescope shows the free-floating planet PSO J318.5-22, in the constellation of Capricornus.

They followed up with observations using the Gemini North Telescope and the NASA Infrared Telescope Facility telescopes on the summit of Hawaii's Mauna Kea, and concluded that its infrared signature was more consistent with a young planetary-mass object. The science team also monitored the object for two years using the Canada-France-Hawaii Telescope, to determine its direction of motion and its distance from Earth. That's how they figured out it was 80 light-years away.

The team concluded that PSO J318.5-22 is associated with a collection of young stars called the Beta Pictoris moving group, which formed about 12 million years ago. The best-known star in that group, Beta Pictoris, is known to harbor a gas-giant planet that's about eight times as massive as Jupiter.

Gravitational perturbations may have kicked PSO J318.5-22 out of its planetary cradle soon after it was born, or it may have been formed by a different method. Either way, Niall Deacon of the Max Planck Institute for Astronomy in Germany, a co-author of the study, said PSO J318.5-22 should help scientists get a better understanding of other planets that aren't quite as lonely.

“Planets found by direct imaging are incredibly hard to study, since they are right next to their much brighter host stars," Deacon said in the news release. "PSO J318.5-22 is not orbiting a star, so it will be much easier for us to study. It is going to provide a wonderful view into the inner workings of gas-giant planets like Jupiter shortly after their birth.”

Source:www.nbcnews.com