A space-based probe called Gaia, launched in December 2013, has been circling the Sun 1.5 million kilometres (nearly a million miles) beyond Earth's orbit and has been discreetly snapping pictures of the Milky Way. The satellite's billion-pixel camera, the largest ever in space, is so powerful it would be able to gauge the diameter of a human hair at a distance of 1,000 kilometres, meaning nearby stars have been located with unprecedented accuracy. Just over half-way through its five-year mission, Gaia's two telescopes have located a billion stars. That's still only one percent of the Milky Way's estimated stellar population, scattered over an area 100,000 light years in diameter. But it is enough to keep professional stargazers busy for years to come, said Francois Mignard, an astronomer at France's National Centre for Scientific Research and a member of the Gaia Science Team. "Over the centuries we have sought to catalogue the content of the skies," he told AFP. "But never have we achieved anything so complete or precise—it is a massive undertaking." The first data dump "opens a new chapter in astronomy," he added, and is certain to generate hundreds of scientific studies. Gaia maps the position of the Milky Way's stars in a couple of ways. Not only does it pinpoint their location, the probe—by scanning each star about 70 times—can plot their movement as well. This is what allows scientists to calculate the distance between Earth and each star, a crucial measure, explained Mignard. Both types of data will be available Wednesday for more than two million stars. "That's 20 times more than what we had before," Mignard said. "And all in one fell swoop!" By the end of 2017, Gaia will have done the same for a billion. At the same time, it will collect vital data about each star's temperature, luminosity and chemical composition, vastly expanding current knowledge. Tens of thousands of previously undetected objects will be discovered, including asteroids that may one day threaten Earth, planets circling nearby stars, and exploding supernovas. "It seems like a good bet that the mission will reveal thousands of new worlds," Gregory Laughlin, an astronomer at Yale University, told the science journal Nature. By identifying stars from smaller galaxies long ago swallowed up by our own, Gaia will also help scientists better understand the Milky Way's origin and evolution. Astrophysicists, meanwhile, hope to learn more about the distribution of dark matter, the invisible substance thought to hold the observable universe together. They also plan to test Albert Einstein's general theory of relativity by watching how light is deflected by the Sun and its planets. "Gaia is going to revolutionise what we know about stars and the Galaxy," David Hogg, an astronomer at New York University working on the project told Nature. The spacecraft is controlled from the European Space Operations Centre in Darmstadt, Germany, using ground stations in Cebreros, Spain and New Norcia in Australia. More than 50 companies across Europe were involved in building Gaia and its instruments. Mission scientists are scheduled to brief journalists on some of the initial findings Wednesday afternoon. Explore further: Gaia mapping the stars of the Milky Way
Loescher H.,Science Team |
Loescher H.,University of Colorado at Boulder |
Ayres E.,Science Team |
Ayres E.,University of Colorado at Boulder |
And 5 more authors.
PLoS ONE | Year: 2014
Soils are highly variable at many spatial scales, which makes designing studies to accurately estimate the mean value of soil properties across space challenging. The spatial correlation structure is critical to develop robust sampling strategies (e.g., sample size and sample spacing). Current guidelines for designing studies recommend conducting preliminary investigation(s) to characterize this structure, but are rarely followed and sampling designs are often defined by logistics rather than quantitative considerations. The spatial variability of soils was assessed across ∼1 ha at 60 sites. Sites were chosen to represent key US ecosystems as part of a scaling strategy deployed by the National Ecological Observatory Network. We measured soil temperature (Ts) and water content (SWC) because these properties mediate biological/ biogeochemical processes below- and above-ground, and quantified spatial variability using semivariograms to estimate spatial correlation. We developed quantitative guidelines to inform sample size and sample spacing for future soil studies, e.g., 20 samples were sufficient to measure Ts to within 10% of the mean with 90% confidence at every temperate and subtropical site during the growing season, whereas an order of magnitude more samples were needed to meet this accuracy at some high-latitude sites. SWC was significantly more variable than Ts at most sites, resulting in at least 10x more SWC samples needed to meet the same accuracy requirement. Previous studies investigated the relationship between the mean and variability (i.e., sill) of SWC across space at individual sites across time and have often (but not always) observed the variance or standard deviation peaking at intermediate values of SWC and decreasing at low and high SWC. Finally, we quantified how far apart samples must be spaced to be statistically independent. Semivariance structures from 10 of the 12- dominant soil orders across the US were estimated, advancing our continental-scale understanding of soil behavior. © 2014 Loescher et al. Source
The New Horizons Science Team Meeting in Boulder, Colorado, in November 2015. Mission scientists enjoyed the fruits of their labor by viewing stereographic projections of geology 3-D terrain maps of Pluto and Charon. Credit: Constantine Tsang It's amazing that we've come such a long way in our exploration of the Pluto system, and it's only been five months since the close flyby of New Horizons. From the exceptionally young ice-covered plain informally named Tombaugh Regio on Pluto to the deep canyons cut into Charon, the terrains we're seeing are just amazing. Everyone, from the mission scientists to the general public, seems to be having a field day coming up with pet theories and comparisons with other places in our solar system to explain the alien Pluto system worlds we're seeing. To put this into context, I'd like to take us back a few weeks just prior to the July 14 flyby, before we got the exquisitely detailed images we routinely downlink now. During that phase, we were getting longer range, low-resolution views of Pluto and Charon, and my job was to create approach movies showing New Horizons rushing up to meet the pair in space. In workrooms at the Johns Hopkins Applied Physics Lab (JHUAPL) in Laurel, Maryland, I and many of the science team members had arrived for the flyby, and were working seven days a week to keep on top of the data flowing in. The majority of the science data being received at this time were in the form of panchromatic (black and white) images from the telescopic LORRI imager on New Horizons. These Optical Navigation images, or "OpNavs," came in different flavors, in part based on their exposure times. These images are used to refine the approach trajectory of New Horizons and to search for hazards on approach. Sequencing these images together had the added benefit of allowing us to make movies of Charon and Pluto rotating on their axes and orbiting one another at closer and closer range. The Pluto System in the Barycentric Reference Frame The procedure I used to make these movies was not trivial, mind you. Each movie imager, or "frame," from LORRI was, in fact, a stack of four separate images, taken at slightly different times. This allowed us to "sub-sample" Pluto's (and eventually Charon's) disk to get the best possible spatial resolution out of the LORRI telescope. This work was mainly done by science team member and image processing expert Tod Lauer at the National Astronomical Optical Observatories. Because we wanted to get the best resolution out of the data, Tod and I enhanced the images using a technique called image deconvolution, which sharpens them. The practical problem with this was we didn't sometimes know what features were real on Pluto and Charon (because we've never been there before!), and what were potentially introduced as artifacts by the deconvolution process. So we deconvolved the images separately, using multiple techniques, and then compared our results to see what features at the edge of resolution were common to differing image processing techniques—we knew we could trust those. Needless to say, I was gratified to see such features pop out from the LORRI images consistently. Because Pluto was in a slightly different place in each frame, I then co-registered and centered Pluto to create a single movie Plutocentric frame that gave the approach movies the appearance of a motionless Pluto at the center of each movie. Every few days, another set of images was taken and I repeated the procedure. But I wasn't quite done. To remove the barycentric "wobble" caused by Pluto and Charon tugging on each other, I then took each of the frames and co-registered them against a background star that appeared in the field of view of all the frames. Every 6.4 days, Charon would make a full rotation around Pluto, and I could compile a new rotation movie of Charon going around Pluto (see Figure 1). In these movies the features on Pluto would rotate, getting bigger in the field of view with each image, and we could finally begin to see the surface details that are so obvious now (see Figure 2). On each movie frame, I also printed in ancillary data such as distance to Pluto and time to closest approach. I was humbled to be part of the process of giving the world its first look at the Pluto system up close. As time went on, and we got data from the MVIC color camera aboard New Horizons, I could also overlay the color information on the monochromatic images to colorize the movie. You may wonder why this process is at all relevant now, given the incredible high resolution images we got later. Well, here are a couple of reasons. First, the approach movies contain data on parts of Pluto and Charon that were not imaged at closest approach. These images will be used to get as much information out as possible about the Pluto system, its global geography, its surface properties, and potential temporal variations as we approached. Second, the barycentric movies are a great visualization of the two-body binary system and provide an invaluable teaching tool for educators and the general public. Finally, I think it just looks cool! It puts into perspective how we on New Horizons and NASA are always exploring, and how far we have come to explore the Pluto system.