From: Andy Soos, ENN
Published March 13, 2013 09:44 AM

Nearby Stars and Planets

The stars are so very far away. But they seem to be creeping closer all the time with the advent of new discoveries and studies. For example. a pair of newly discovered stars is the third-closest star system to the Sun, according to a paper that will be published in Astrophysical Journal Letters. The duo is the closest star system discovered since 1916 and is about 6.5 light years distant. The closest still remain the trio of stars known as Alpha Centauri at a little over 4 light years away. Even more amazing is that researchers have conducted a remote reconnaissance of a distant solar system with a new telescope imaging system that sifts through the blinding light of stars. Using a suite of high-tech instrumentation and software called Project 1640, the scientists collected the first chemical fingerprints, or spectra, of this system's four red exoplanets, which orbit a star 128 light years away from Earth. It makes one wonder what astronomers on other worlds are seeing on Earth itself.


Both stars in the new binary system are "brown dwarfs," which are stars that are too small in mass to ever become hot enough to ignite hydrogen fusion. As a result, they are very cool and dim, resembling a giant planet like Jupiter more than a bright star like the Sun.

"The distance to this brown dwarf pair is 6.5 light years -- so close that Earth's television transmissions from 2006 are now arriving there," Luhman said. "It will be an excellent hunting ground for planets because it is very close to Earth, which makes it a lot easier to see any planets orbiting either of the brown dwarfs." Since it is the third-closest star system, in the distant future it might be one of the first destinations for manned expeditions outside our solar system, Luhman said. 

The other nearby stars are Barnard's Star (a red dwarf) and the three located near Alpha Centauri (two yellow types like our sun and a red dwarf). 

By combining the detections of the star system from the various surveys, Luhman was able to measure its distance via parallax, which is the apparent shift of a star in the sky due to the Earth's orbit around the Sun. He then used the Gemini South telescope on Cerro Pachón in Chile to obtain a spectrum of it, which demonstrated that it had a very cool temperature, and hence was a brown dwarf. "As an unexpected bonus, the sharp images from Gemini also revealed that the object actually was not just one but a pair of brown dwarfs orbiting each other," Luhman said.

Planets are far more difficult to image due to the brightness of the parent stars.  Nevertheless, the planets surrounding the star of this study, HR 8799, have been imaged in the past. But except for a partial measurement of the outermost planet in the system, the star's bright light overwhelmed previous attempts to study the planets with spectroscopy, a technique that splits the light from an object into its component colors—as a prism spreads sunlight into a rainbow. Because every chemical, such as carbon dioxide, methane, or water, has a unique light signature in the spectrum, this technique is able to reveal the chemical composition of a planet's atmosphere.

The results are "quite strange," Oppenheimer, the lead researcher on this study, said. "These warm, red planets are unlike any other known object in our universe. All four planets have different spectra, and all four are peculiar. The theorists have a lot of work to do now." One of the most striking abnormalities is an apparent chemical imbalance. Basic chemistry predicts that ammonia and methane should naturally coexist in varying quantities unless they are in extremely cold or hot environments. Yet the spectra of the HR 8799 planets, all of which have temperatures of about 1000 Kelvin (1340 degrees Fahrenheit), either have methane or ammonia, with little or no signs of their chemical partners. Other chemicals such as acetylene, previously undiscovered on any exoplanet, and carbon dioxide may be present as well. The planets also are "redder," meaning that they emit longer wavelengths of light, than celestial objects with similar temperatures. This could be explained by significant but patchy cloud cover on the planets, the authors say.

With 1.6 times the mass and five times the brightness, HR 8799 itself is very different from our Sun. The brightness of the star can vary by as much as 8 percent over a period of two days and produces about 1,000 times more ultraviolet light than the Sun. All of these factors could impact the spectral fingerprints of the planets, possibly inducing complex weather and sooty hazes that could be revealed by periodic changes in the spectra. More data is needed to further explore this solar system's unusual characteristics.

For further information see Brown Dwarf and HR 8799.

Local Neighborhood image by Janella Williams via Penn State.

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