One million miles from Earth, a NASA camera is capturing unexpected flashes of light reflecting off our planet. The homeward-facing instrument on NOAA’s Deep Space Climate Observatory, or DSCOVR, launched in 2015, caught hundreds of these flashes over the span of a year. As keen observers from outside NASA wrote in, questioning the source of these lights, scientists deciphered the tiny cause to the big reflections: high-altitude, horizontally oriented ice crystals.
NASA’s Earth Polychromatic Imaging Camera (EPIC) instrument aboard DSCOVR is taking almost-hourly images of the sunlit planet from its spot between Earth and the sun. Alexander Marshak, DSCOVR deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, first noticed light flashes occasionally appearing over oceans as he looked through that day’s EPIC images.
Investigating the flashes, Marshak and his colleagues found that similar reflections from our pale blue dot caught the attention of astronomer Carl Sagan in 1993. Sagan was looking at images taken by the Galileo spacecraft, which launched in 1989 to study Jupiter and its moons. During one if its gravitational-assist swings around Earth, Galileo turned its instruments on this planet and collected data. Sagan and his colleagues used that to test a key question: Whether spacecraft could detect signatures of life from afar.
Flashes of light reflected off oceans—like those referenced by Sagan—could have a simple explanation, Marshak said: Sunlight hits a smooth part of an ocean or lake and reflects directly back to the sensor, like taking a flash-picture in a mirror.
But when the scientists took another took at the Galileo images, they saw something Sagan and his colleagues apparently missed—bright flashes of light over land, as well. And those flashes also appeared in the EPIC images. As the contact listed on the website that posts all EPIC images, Marshak started getting e-mails from people curious about what the flashes were.
“We found quite a few very bright flashes over land, as well,” he said. “When I first saw it, I thought maybe there was some water there, or a lake the sun reflects off of. But the glint is pretty big, so it wasn’t that.”
Instead, he and his colleagues Tamas Varnai of the University of Maryland, Baltimore County, and Alexander Kostinski of Michigan Technological University, thought of water elsewhere in the Earth system: ice particles high in the atmosphere. The scientists conducted a series of experiments, detailed in a new paper published in Geophysical Research Letters, to confirm the cause of the distant flashes.
First, the researchers cataloged all of the prospective sunlight glints over land in images from the EPIC camera. The flashes show up in three, distinct colors, because the camera takes the red, green, and blue images several minutes apart. In all, the scientists found 866 bursts between DSCOVR’s launch in June 2015 and August 2016.
The scientists reasoned that if these 866 flashes were caused by reflected sunlight, they would be limited to certain spots on the globe—spots where the angle between the sun and Earth is the same as the angle between the spacecraft and Earth, allowing for the spacecraft to pick up the reflected light. When they plotted the locations of the glints with where those angles would match, given Earth’s tilt and the spacecraft’s location, the two matched.
This helped confirm that it wasn’t something like lightning causing the flashes, Marshak said: “Lightning doesn’t care about the sun and EPIC’s location.” The researchers also plotted angles to determine that the light was reflecting off of ice particles floating in the air nearly horizontally.
Another feature of the EPIC data helped confirm that the flashes were from a high altitude, not simply water on the ground. Two channels on the instrument are designed to measure the height of clouds, and when the scientists went to the data they found high cirrus clouds, 3 to 5 miles (5 to 8 kilometers) where the glints were located.
By Kate Ramsayer
For more information about DSCOVR, visit: https://www.nesdis.noaa.gov/content/dscovr-deep-space-climate-observatory
CAPTION: A million miles from Earth, the Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory spots flash (NASA’s Goddard Space Flight Center/Katy Mersmann)
Humans Rely More on ‘Inferred’ Visual Objects than ‘Real’ Ones
Humans treat ‘inferred’ visual objects generated by the brain as more reliable than external images from the real world, according to new research published in eLife.
The study, from the University of Osnabrück, Germany, reveals that when choosing between two identical visual objects—one generated internally based on information from the blind spot and an external one—we are surprisingly likely to show a bias towards the internal information.
To make sense of the world, humans and animals need to combine information from multiple sources. This is usually done according to how reliable each piece of information is. For example, to know when to cross the street, we usually rely more on what we see than what we hear—but this can change on a foggy day.
“In such situations with the blind spot, the brain ‘fills in’ the missing information from its surroundings, resulting in no apparent difference in what we see,” says senior author Professor Peter König, from the University of Osnabrück’s Institute of Cognitive Science. “While this fill-in is normally accurate enough, it is mostly unreliable because no actual information from the real world ever reaches the brain. We wanted to find out if we typically handle this filled-in information differently to real, direct sensory information, or whether we treat it as equal.”
To do this, König and his team asked study participants to choose between two striped visual images, both of which were displayed to them using shutter glasses. Each image was displayed either partially inside or completely outside the visual blind spot. Both were perceived as identical and ‘continuous’ due to the filling-in effect; and participants were asked to select the image they thought represented the real, continuous stimulus.
“We thought people would either make their choice without preference, or with a preference towards the real stimulus, but exactly the opposite happened—there was in fact a strong bias towards the filled-in stimulus inside the blind spot,” says first author Benedikt Ehinger, researcher at the University of Osnabrück. “Additionally, in an explorative analysis of how long the participants took to make their choice, we saw that they were slightly quicker to choose this stimulus than the one outside the blind spot.”
So, why are subjects so keen on the blind-spot information when it is essentially the least reliable? The team’s interpretation is that subjects compare the internal representation (or ‘template’) of a continuous stimulus against the incoming sensory input, resulting in an error signal that represents the mismatch. In the absence of real information, no deviation and therefore no error or a smaller signal occurs, ultimately leading to a higher credibility at the decision-making stage. This indicates that perceptual decision-making can rely more on inferred rather than real information, even when there is some knowledge about the reduced reliability of the inferred image available in the brain.
“In other words, the implicit knowledge that a filled-in stimulus is less reliable than an external one does not seem to be taken into account for perceptual decision-making,” Ehinger explains.
The team says that understanding how we integrate information from different sources with different reliabilities can inform us about the exact mechanisms used by the brain to make decisions based on our perceptions.
CAPTION: Participants were asked to choose between two striped visual images, one ‘real’ and one inset in the blind spot, displayed using shutter glasses. (Photo: Ricardo Gameiro)
Genome Data from Ancient Egyptian Mummies
An international team of scientists, led by researchers from the University of Tuebingen and the Max Planck Institute for the Science of Human History in Jena, successfully recovered and analyzed ancient DNA from Egyptian mummies dating from approximately 1400 BCE to 400 CE, including the first genome-wide nuclear data from three individuals, establishing ancient Egyptian mummies as a reliable source for genetic material to study the ancient past. The study, published in March in Nature Communications, found that modern Egyptians share more ancestry with Sub-Saharan Africans than ancient Egyptians did, whereas ancient Egyptians were found to be most closely related to ancient people from the Near East.
Egypt is a promising location for the study of ancient populations. It has a rich and well-documented history, and its geographic location and many interactions with populations from surrounding areas, in Africa, Asia and Europe, make it a dynamic region. Recent advances in the study of ancient DNA present an intriguing opportunity to test existing understandings of Egyptian history using ancient genetic data.
However, genetic studies of ancient Egyptian mummies are rare due to methodological and contamination issues. Although some of the first extractions of ancient DNA were from mummified remains, scientists have raised doubts as to whether genetic data, especially nuclear genome data, from mummies would be reliable, even if it could be recovered. “The potential preservation of DNA has to be regarded with skepticism,” confirms Johannes Krause, Director at the Max Planck Institute for the Science of Human History in Jena and senior author of the study. “The hot Egyptian climate, the high humidity levels in many tombs and some of the chemicals used in mummification techniques, contribute to DNA degradation and are thought to make the long-term survival of DNA in Egyptian mummies unlikely.” The ability of the authors of this study to extract nuclear DNA from such mummies and to show its reliability using robust authentication methods is a breakthrough that opens the door to further direct study of mummified remains.
For this study, an international team of researchers from the University of Tuebingen, the Max Planck Institute for the Science of Human History in Jena, the University of Cambridge, the Polish Academy of Sciences, and the Berlin Society of Anthropology, Ethnology and Prehistory, looked at genetic differentiation and population continuity over a 1,300-year timespan, and compared these results to modern populations. The team sampled 151 mummified individuals from the archaeological site of Abusir el-Meleq, along the Nile River in Middle Egypt, from two anthropological collections hosted and curated at the University of Tuebingen and the Felix von Luschan Skull Collection at the Museum of Prehistory of the Staatliche Museen zu Berlin, Stiftung Preussicher Kulturbesitz.
The study found that ancient Egyptians were most closely related to ancient populations in the Levant, and they were also closely related to Neolithic populations from the Anatolian Peninsula and Europe.
This study counters prior skepticism about the possibility of recovering reliable ancient DNA from mummies.
CAPTION: Sarcophagus of Tadja, Abusir el-Meleq. (Photo bpk/Aegyptisches Museum und Papyrussammlung, SMB/Sandra Steiss)
Sept/Oct 2017 – #125