Discovery of Ice Crystals on Earth
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When we send astronomical satellites out to explore the solar system, we also take the opportunity to set them to look back on Earth. This tradition dates back to the time of the late 1970s when astronomer Carl Sagan requested a view of Earth from the Voyager 1 satellite from vantage point of Saturn.

In that famous photo, the entire Earth occupies a scant couple of pixels on the image. Since that time, many pictures of Earth have ben taken at still higher spatial resolution. As the level of our ability to see fine details grew, we started noticed something curious about the images.

In addition to seeing the beauty of our tiny marble-colored planet, we also saw brief surges of light appear on the surface. The source of such "twinkles" went undiscovered from their first occurrence in 1993 until 2016.

At first planetary scientists attributed these mysterious twinkles to reflections off of the water, except that the twinkling took place both on water and on land. Then lightning was cited as the cause, except that the events did not take place all over the planet as would be expected of electrical storms. Instead, the events showed a restriction in latitudes. It was this clue led us to the most likely solution, that the twinkling is caused by sunlight reflecting off of the Earth.

With just the right angle between the Sun, Earth and satellite, such a twinkle can be generated by ice crystals. This study was conducted based on analyzing 860 twinkles appearing over a span of 23 years. Note the satellites that produced the images of the Earth from space were positioned typically one million miles from Earth (yes one million), yet the ice crystals are smaller than the size of a single poppy seed (50 - 100 micrometers).

If ice crystals are really so bright and shiny, then in principle, one can apply a similar technique to make the first discoveries of ice crystals (and potentially water) on planets orbiting other stars.

Dr. Brenda Frye

About Dr. Brenda Frye

Brenda L. Frye is an observational cosmologist at the Department of Astronomy/Steward Observatory, University of Arizona. She earned her Ph. D. in Astrophysics from the University of California at Berkeley, assisted by a National Science Foundation Graduate Research Fellowship.

Her thesis work involved measuring the concentration of the total mass of visible plus dark matter in the fields of massive galaxy clusters, a program requiring the use of some of the largest telescopes in the world.

Moving a mile from her Ph. D. institution, she assumed a postdoctoral position with the Supernova Cosmology Project at Lawrence Berkeley National Laboratory under the direction of Professor Saul Permutter.

She then treked across the country to take a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship and a Princeton Council on Sciences and Technology Fellowship both at Princeton University.

Moving further east, she became a Lecturer in Physics at Dublin City University in Dublin, Ireland, where a number of European collaborations were formed.

From there she crossed back across the pond to the west coast of the U. S. to become a tenure-track Assistant Professor of Physics at the University of San Francisco.

Her travels have now landed her at her Alma Mater in Tucson, where she teaches and does research. The aims of her research continue to be to use gravitational telescopes in space as 'lenses' to study the properties of dark matter and those of distant galaxies back to when the universe was <900 million years old.

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