We have known for some time now that water exists in permanently shadowed regions of lunar craters near the north and south poles of the moon. We now have evidence that water also exist in sunlit regions of the moon. How was this data obtained?
When we use devices like prisms to spread out the wavelengths of light, we see dark and bright bands in different places on this spectrum. Those bright and dark bands are chemical signatures that alert us to the presence of specific elements and molecules.
Observing and interpreting these spectral features is called spectroscopy. The difficulty in assessing whether water exists elsewhere in the solar system comes from the fact that water is abundant in Earth’s atmosphere. Water vapor is also a prime cause of atmospheric distortion, so the largest telescopes in the world are located at high altitudes or in regions of low humidity — often both — to mitigate the obscuring effect of the atmosphere.
Unfortunately for observers, even telescopes located on mountains in the desert are unable to sort out atmospheric water from extraterrestrial water. In addition to distorting images, atmospheric water vapor blocks infrared light, limiting our ability to observe this portion of the spectrum.
Stratospheric Observatory for Infrared Astronomy (SOFIA) overcomes those challenges. Researchers using SOFIA, a joint mission of NASA and the German Aerospace Center (DLR) that consists of a 2.7 meter reflecting telescope housed in a highly modified Boeing 747, announced in October of last year that they detected water on the sunlit surface of the moon.
SOFIA, in operation since 2010, is a marvel of technology. Designed primarily as an infrared telescope, it studies comets, planetary atmospheres, newly forming stars and so much more. It makes observations while flying at an altitude of 41,000 feet, above nearly all the water vapor in the atmosphere. SOFIA also has advantages over space-based telescopes in that it can change out instrumentation and be serviced here on Earth.
It is believed that the water detected on the lunar surface is locked up in droplets of glass formed by meteorite impacts. The abundance of water in sunlit areas of the moon is 100 times less than the driest desert on Earth, but it underscores the value of making use of materials already present in solar system objects that humans wish to visit.
The Morning Sky
The summer triangle asterism is now an early morning object. Look to the eastern morning sky to find Altair (in Aquilla), Vega (in Lyra) and Deneb (in Cygnus) forming the points of a large triangle. Look above Vega to find the constellation Hercules, home to the globular cluster M13. Use a star chart and binoculars to find this beautiful cluster comprised of hundreds of thousands of stars.
The Evening Sky
The moon was full on Jan 28. Mars stands high in the south west after dark. Just below Mars is distant Uranus, looking greenish-blue and lonely. Use binoculars to find this planet, whose lone visitor was Voyager 2 in 1986. Sirius, the brightest star in the night sky, rises in the east just before 6 p.m.
Dan Price is a NASA/JPL Solar System Ambassador and informal educator. He leads the Night Sky Tours at Josephine Sculpture Park. Have a question about astronomy or space science? Send an email to email@example.com and it might be featured in a future column.