Scientists discover water on the sun’s surface
WATERLOO, Ont. — Water has been discovered on the surface of the sun in sunspots where it causes a sort of “stellar greenhouse effect” that affects the sunspot’s energy output.
“There’s a perception that the sun is too hot to form water on its surface, but we have proved that it exists in sunspots because they are cooler,” said Peter Bernath, a chemistry professor at the University of Waterloo.
Scientists from UW and the National Optical Astronomy Observatories in Tucson, Ariz., recorded evidence of water – – not in liquid form because the sun is too hot, but as vapor or steam — in dark sunspots.
The discovery is of fundamental importance for understanding the atmospheres of the sun and stars. Hot water molecules are the most important absorbers of infrared radiation in the atmospheres of cool stars, such as “variable red giants.” Studying the physical effects of hot water in these red giant stars may be central to determining the rate at which they evolve and eject material into space.
Dark sunspots can be 2,000 degrees C cooler than the surrounding bright surface of the sun, allowing detailed studies of regions that mimic the surfaces of red giant stars. Sunspots are caused by magnetic fields that float to the surface of the sun and locally suppress energy flow from the core.
Bernath, an expert in molecular astronomy, said it is surprising to find water vapor on the sun because its surface temperature of 5,700 degrees C causes it to break into atoms of hydrogen and oxygen. Since sunspots are cooler, the atoms can recombine to form water vapor that can absorb escaping infrared radiation.
“This formation of water vapor affects the energy flow from sunspots, creating a kind of stellar greenhouse effect,” he said. Bernath believes, however, this has no effect on climate on earth.
Astronomers Lloyd Wallace, William Livingston and Kenneth Hinkle of the Arizona-based observatories worked with collaborators to obtain infrared spectra that reveal a large number of water absorption features originating on the sun.
The research was carried out at the National Solar Observatory McMath-Pierce telescope at Kitt Peak in Arizona using an instrument called a Fourier transform spectrometer. The Kitt Peak work was supported by the U.S. National Science Foundation.
Laboratory spectroscopy was conducted in Canada by Bernath, who is also a senior research scientist at the University of Arizona (Tucson), with Waterloo master of science student Jennifer Busler, Dr. Bujin Guo and Keqing Zhang, a PhD student. The laboratory work was supported by Canada’s Natural Sciences and Engineering Research Council and the U.S. National Aeronautics and Space Administration.
The lab research, in which the team recorded an infrared emission spectrum of hot water at 1,550 degrees C, supported the results obtained from the telescope measurements. By comparing the lab spectrum with the sunspot spectrum, it proved for the first time that hot water vapor is present on the sun, Bernath said.
The results of the research, which are being published in the journal Science, will help to “emphasize that water is an important absorber in the sun and stars that is underappreciated,” Livingston said. He hopes this research will encourage further laboratory work for the purpose of understanding the astrophysical importance of the water spectrum in the sun and stars.
“Since the temperatures of cool stars are very difficult to produce in the laboratory, these results are unique and show that current theory is not adequate to model these spectra and that a basic understanding of the behavior of water must be explored further by scientists,” he said.
Bernath said the spectrum of hot water is also important here on earth. “For example, the exhaust of a rocket contains hot water vapor. This rocket plume provides a signature that can be used to identify the type of rocket. The spectrum of water also serves as a continuing challenge to theoreticians. New theoretical techniques in spectroscopy are often tested using the water spectrum.”
The discovery was only possible through the use of sophisticated equipment including the world’s largest solar telescope and a high-resolution infrared spectrometer, Bernath said. This allowed the recording of a high- resolution spectrum of a sunspot followed by the laboratory work to record new hot water spectra.
“This interdisciplinary collaboration between astronomers and chemists was also necessary in order to make the identification,” Bernath added.
Dr. Peter Bernath, UW, (519) 888-4814
From Jim Fox, UW News Bureau, (519) 888-4444
Release no. 84 — May 25, 1995
University of Waterloo
200 University Avenue West
Waterloo, Ontario, Canada N2L 3G1
+1 519 888 4567