Astronomers 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, called HR8799, 128 light years away from Earth.
A detailed description of the planets—showing how drastically different they are from the known worlds in the universe—was accepted Friday for publication in The Astrophysical Journal. “An image is worth a thousand words, but a spectrum is worth a million,” said lead author Rebecca Oppenheimer, associate curator and chair of the Astrophysics Department at the American Museum of Natural History.
Oppenheimer is the principal investigator for Project 1640, which uses the Hale telescope at the Palomar Observatory in California.
The project involves researchers from the California Institute of Technology, NASA’s Jet Propulsion Laboratory, Cambridge University, New York University, and the Space Telescope Science Institute, in addition to Oppenheimer’s team at the Museum.
The planets surrounding the star of this study, HR8799, have been imaged in the past. This visualization shows the location of the star HR8799 in relation to our solar system.
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.
With this system, the researchers are the first to determine the spectra of all four planets surrounding HR8799. They found them to be unlike any other known object in the universe.
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 “lukewarm” 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.