[meteorite-list] Large, Distant Comets More Common Than Previously Thought
https://www.jpl.nasa.gov/news/news.php?feature=6902 Large, Distant Comets More Common Than Previously Thought Jet Propulsion Laboratory July 25, 2017 Comets that take more than 200 years to make one revolution around the Sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many "long-period comets" will never approach the Sun in a person's lifetime. In fact, those that travel inward from the Oort Cloud -- a group of icy bodies beginning roughly 186 billion miles (300 billion kilometers) away from the Sun -- can have periods of thousands or even millions of years. NASA's WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers. Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as "Jupiter family comets," whose orbits are shaped by Jupiter's gravity and have periods of less than 20 years. Researchers also observed that in eight months, three to five times as many long-period comets passed by the Sun than had been predicted. The findings are published in the Astronomical Journal. "The number of comets speaks to the amount of material left over from the solar system's formation," said James Bauer, lead author of the study and now a research professor at the University of Maryland, College Park. "We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought." The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are rare. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out during the spacecraft's primary mission before it was renamed NEOWISE and reactivated to target near-Earth objects (NEOs). "Our study is a rare look at objects perturbed out of the Oort Cloud," said Amy Mainzer, study co-author based at NASA's Jet Propulsion Laboratory, Pasadena, California, and principal investigator of the NEOWISE mission. "They are the most pristine examples of what the solar system was like when it formed." Astronomers already had broader estimates of how many long-period and Jupiter family comets are in our solar system, but had no good way of measuring the sizes of long-period comets. That is because a comet has a "coma," a cloud of gas and dust that appears hazy in images and obscures the cometary nucleus. But by using the WISE data showing the infrared glow of this coma, scientists were able to "subtract" the coma from the overall comet and estimate the nucleus sizes of these comets. The data came from 2010 WISE observations of 95 Jupiter family comets and 56 long-period comets. The results reinforce the idea that comets that pass by the Sun more often tend to be smaller than those spending much more time away from the Sun. That is because Jupiter family comets get more heat exposure, which causes volatile substances like water to sublimate and drag away other material from the comet's surface as well. "Our results mean there's an evolutionary difference between Jupiter family and long-period comets," Bauer said. The existence of so many more long-period comets than predicted suggests that more of them have likely impacted planets, delivering icy materials from the outer reaches of the solar system. Researchers also found clustering in the orbits of the long-period comets they studied, suggesting there could have been larger bodies that broke apart to form these groups. The results will be important for assessing the likelihood of comets impacting our solar system's planets, including Earth. "Comets travel much faster than asteroids, and some of them are very big," Mainzer said. "Studies like this will help us define what kind of hazard long-period comets may pose." NASA's Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA's Science Mission Directorate in Washington. The NEOWISE project is funded by the Near Earth Object Observation Program, now part of NASA's Planetary Defense Coordination Office. The spacecraft was put into hibernation mode in 2011 after twice scanning the entire sky, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects. For more information on WISE, visit: https://www.nasa.gov/wise News Media Contact Elizabeth Landau Jet Propulsion Laboratory, Pasadena, Calif. 818-354-6425
[meteorite-list] Holographic Imaging Could Be Used to Detect Signs of Life in Space
https://www.caltech.edu/news/holographic-imaging-could-be-used-detect-signs-life-space-78931 Holographic Imaging Could Be Used to Detect Signs of Life in Space Engineers explore ways to sample and identify living microbes in the outer solar system Caltech July 20, 2017 We may be capable of finding microbes in space - but if we did, could we tell what they were, and that they were alive? This month the journal Astrobiology is publishing a special issue dedicated to the search for signs of life on Saturn's icy moon Enceladus. Included is a paper from Caltech's Jay Nadeau and colleagues offering evidence that a technique called digital holographic microscopy, which uses lasers to record 3-D images, may be our best bet for spotting extraterrestrial microbes. No probe since NASA's Viking program in the late 1970s has explicitly searched for extraterrestrial life - that is, for actual living organisms. Rather, the focus has been on finding water. Enceladus has a lot of water - an ocean's worth, hidden beneath an icy shell that coats the entire surface. But even if life does exist there in some microbial fashion, the difficulty for scientists on Earth is identifying those microbes from 790 million miles away. "It's harder to distinguish between a microbe and a speck of dust than you'd think," says Nadeau, research professor of medical engineering and aerospace in the Division of Engineering and Applied Science. "You have to differentiate between Brownian motion, which is the random motion of matter, and the intentional, self-directed motion of a living organism." Enceladus is the sixth-largest moon of Saturn, and is 100,000 times less massive than Earth. As such, Enceladus has an escape velocity - the minimum speed needed for an object on the moon to escape its surface - of just 239 meters per second. That is a fraction of Earth's, which is a little over 11,000 meters per second. Enceladus's minuscule escape velocity allows for an unusual phenomenon: enormous geysers, venting water vapor through cracks in the moon's icy shell, regularly jet out into space. When the Saturn probe Cassini flew by Enceladus in 2005, it spotted water vapor plumes in the south polar region blasting icy particles at nearly 2,000 kilometers per hour to an altitude of nearly 500 kilometers above the surface. Scientists calculated that as much as 250 kilograms of water vapor were released every second in each plume. Since those first observations, more than a hundred geysers have been spotted. This water is thought to replenish Saturn's diaphanous E ring, which would otherwise dissipate quickly, and was the subject of a recent announcement by NASA describing Enceladus as an "ocean world" that is the closest NASA has come to finding a place with the necessary ingredients for habitability. Water blasting out into space offers a rare opportunity, says Nadeau. While landing on a foreign body is difficult and costly, a cheaper and easier option might be to send a probe to Enceladus and pass it through the jets, where it would collect water samples that could possibly contain microbes. Assuming a probe were to do so, it would open up a few questions for engineers like Nadeau, who studies microbes in extreme environments. Could microbes survive a journey in one of those jets? If so, how could a probe collect samples without destroying those microbes? And if samples are collected, how could they be identified as living cells? The problem with searching for microbes in a sample of water is that they can be difficult to identify. "The hardest thing about bacteria is that they just don't have a lot of cellular features," Nadeau says. Bacteria are usually blob-shaped and always tiny - smaller in diameter than a strand of hair. "Sometimes telling the difference between them and sand grains is very difficult," Nadeau says. Some strategies for demonstrating that a microscopic speck is actually a living microbe involve searching for patterns in its structure or studying its specific chemical composition. While these methods are useful, they should be used in conjunction with direct observations of potential microbes, Nadeau says. "Looking at patterns and chemistry is useful, but I think we need to take a step back and look for more general characteristics of living things, like the presence of motion. That is, if you see an E. coli, you know that it is alive - and not, say, a grain of sand - because of the way it is moving," she says. In earlier work, Nadeau suggested that the movement exhibited by many living organisms could potentially be used as a robust, chemistry-independent biosignature for extraterrestrial life. The motion of living organisms can also be triggered or enhanced by "feeding" the microbes electrons and watching them grow more active. To study the motion of potential microbes from Enceladus's plumes, Nadeau proposes using an instrument called a digital
[meteorite-list] From Mars Rover Opportunity: Panorama Above 'Perseverance Valley'
https://www.jpl.nasa.gov/news/news.php?feature=6898 >From Mars Rover: Panorama Above 'Perseverance Valley' Jet Propulsion Laboratory July 20, 2017 NASA's Mars Exploration Rover Opportunity recorded a panoramic view before entering the upper end of a fluid-carved valley that descends the inner slope of a large crater's rim. The scene includes a broad notch in the crest of the crater's rim, which may have been a spillway where water or ice or wind flowed over the rim and into the crater. Wheel tracks visible in the area of the notch were left by Opportunity as the rover studied the ground there and took images into the valley below for use in planning its route. "It is a tantalizing scene," said Opportunity Deputy Principal Investigator Ray Arvidson of Washington University in St. Louis. "You can see what appear to be channels lined by boulders, and the putative spillway at the top of Perseverance Valley. We have not ruled out any of the possibilities of water, ice or wind being responsible." Opportunity's panoramic camera (Pancam) took the component images of the scene during a two-week driving moratorium in June 2017 while rover engineers diagnosed a temporary stall in the left-front wheel's steering actuator. The wheel was pointed outward more than 30 degrees, prompting the team to call the resulting vista Pancam's "Sprained Ankle" panorama. Both ends of the scene show portions of Endeavour Crater's western rim, extending north and south, and the center of the scene shows terrain just outside the crater. The team was able to straighten the wheel to point straight ahead, and now uses the steering capability of only the two rear wheels. The right-front wheel's steering actuator has been disabled since 2006. Opportunity has driven 27.95 miles (44.97 kilometers) since landing on Mars in 2004. On July 7, 2017, Opportunity drove to the site within upper Perseverance Valley where it will spend about three weeks without driving while Mars passes nearly behind the sun from Earth's perspective, affecting radio communications. The rover's current location is just out of sight in the Sprained Ankle panorama, below the possible spillway. Opportunity is using Pancam to record another grand view from this location. After full communications resume in early August, the team plans to drive Opportunity farther down Perseverance Valley, seeking to learn more about the process that carved it. For more information about Opportunity's adventures on Mars, visit: https://mars.nasa.gov/mer News Media Contact Guy Webster Jet Propulsion Laboratory, Pasadena, Calif. 818-354-6278 guy.webs...@jpl.nasa.gov Laurie Cantillo / Dwayne Brown NASA Headquarters, Washington 202-358-1077 / 202-358-1726 laura.l.canti...@nasa.gov / dwayne.c.br...@nasa.gov __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
[meteorite-list] Meteorite Picture of the Day
Today's Meteorite Picture of the Day: Seymchan Contributed by: Mike Miller http://www.tucsonmeteorites.com/mpodmain.asp?DD=08/24/2017 __ Visit our Facebook page https://www.facebook.com/meteoritecentral and the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com https://pairlist3.pair.net/mailman/listinfo/meteorite-list
