Monday, 11 February 2019

India, China leading global greening effort: NASA study

India, China leading global greening effort: NASA study

 |  | Washington
India and China are leading the global greening effort, which is quite contrary to the general perception worldwide, a latest NASA study said Monday, observing that the world is a greener place than it was 20 years ago.
The NASA study based on data received and analysed from its satellite said that India and China are leading in greening on land. "China and India account for one-third of the greening but contain only 9 per cent of the planet's land area covered in vegetation," said lead author Chi Chen of Boston University.
"That is a surprising finding, considering the general notion of land degradation in populous countries from over exploitation," he said.
The study published on February 11, in the journal Nature Sustainability said that recent satellite data (2000–2017) reveal a greening pattern that is strikingly prominent in China and India and overlaps with croplands world-wide.
China alone accounts for 25 per cent of the global net increase in leaf area with only 6.6 per cent of global vegetated area.
The greening in China is from forests (42 per cent) and croplands (32 per cent), but in India it is mostly from croplands (82 percent) with minor contribution from forests (4.4 per cent), the NASA study said.
China is engineering ambitious programmes to conserve and expand forests with the goal of mitigating land degradation, air pollution and climate change.
Food production in China and India has increased by over 35 per cent since 2000 mostly owing to an increase in harvested area through multiple cropping facilitated by fertiliser use and surface- and/or groundwater irrigation.
“When the greening of the Earth was first observed, we thought it was due to a warmer, wetter climate and fertilization from the added carbon dioxide in the atmosphere,” said Rama Nemani, a research scientist at NASA's Ames Research Center and a co-author of the study.
This study was made possible thanks to a two-decade-long data record from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA's Terra and Aqua satellites. “Now with the MODIS data, we see that humans are also contributing,” she said.
Observing that once people realise there is a problem, they tend to fix it, Nemani said in the 1970s and 80s in India and China, the situation around vegetation loss was not good.
“In the 1990s, people realized it, and today things have improved. Humans are incredibly resilient. That's what we see in the satellite data,” she said.
According to the paper, how the greening trend may change in the future depends on numerous factors.
For example, increased food production in India is facilitated by groundwater irrigation. If the groundwater is depleted, this trend may change, it said.
The researchers also pointed out that the gain in greenness around the world does not necessarily offset the loss of natural vegetation in tropical regions such as Brazil and Indonesia. There are consequences for sustainability and biodiversity in those ecosystems beyond the simple greenness of the landscape, the research study said.

source: dailypioneer

Saturday, 9 February 2019

Dark matter could be detected by firing microwaves into space


09 Feb 2019
Lovell telescope
Echo location: the Lovell Telescope could be used to detect microwaves from axionic dark matter. (Courtesy: Mike Peel/Jodrell Bank Centre for Astrophysics/University of Manchester)
A powerful beam of microwaves could be fired into space to detect hypothetical dark-matter particles called axions. That is the proposal of Pierre Sikivie and Ariel Arza at the University of Florida, who hope to record a faint microwave “echo” from the dark matter thought to exist at higher concentrations in certain regions of the Milky Way.
Axions were postulated in the 1970s to overcome a problem with the strong nuclear force, but it was later realized that they could in fact make up much of the universe’s dark matter. Unlike some other dark-matter candidates, axions have unusually well-defined properties including a mass no smaller than about a millionth of an electronvolt (eV) – to make them compatible with the observed abundance of dark matter – and no larger than about 10-3 eV, given that experiments with inferior sensitivities have not discovered them.
Physicists have already tried to detect the pairs of photons that axions are predicted to decay into. One of the leading groups is the Axion Dark Matter Experiment (ADMX) at the University of Washington in Seattle. Led by Leslie Rosenberg, it uses an antenna sensitive to microwave photons at the energy of axions with a certain mass.
Like ADMX, Sikivie and Arza’s proposal boosts sensitivity to dark matter by using photons at the right frequency to stimulate axion decay. However, while ADMX goes after axions close to the apparatus – using virtual photons generated by a strong magnet surrounding a microwave cavity – the new idea involves directing a powerful beam of microwaves up from the Earth and then detecting the very few photons travelling back along the beam path following the decay of axions in space.

Caustic rings

The proposal relies on certain assumptions about the type of dark matter “halo” thought to envelop our galaxy. Most astrophysicists assume that the halo is thermal, which means that particles of dark matter drawn in from outside interact with the particles already there, maximizing entropy and yield a halo of uniform temperature. Instead, Sikivie and Arza reckon that the infalling particles interact too slowly to reach thermal equilibrium and generate flows of dark matter with well-defined velocities. In turn, those flows would yield higher density regions of dark matter known as caustic rings.
As Sikivie explains, the frequency of the microwave beam would have to be adjusted slightly to account for the Doppler shift of the moving axions. So a smaller spread of axion velocities would increase the detection rate for a beam of a given frequency. The existence of caustic rings, meanwhile, would boost the density of axions in the line of sight, assuming the beam is pointed at the right spot on the sky.
Sikivie is confident that his astrophysics is correct, arguing that satellite observations support the idea that Earth is close to one of the Milky Way’s caustic rings – a crucial factor in determining detection sensitivities. He has yet to sketch out his scheme in detail but says one option would be to fire microwaves from perhaps 100 small dishes arranged around a much larger, existing, receiver, such as the Green Bank Telescope in West Virginia or the Lovell Telescope in the UK. As he points out, the Doppler shift comes in handy here as it would in principle mean being able to pick out the echo – at a miniscule 10-21 W – from the vastly more powerful outgoing beam.
Sikivie argues that such an experiment could target a much wider range of frequencies, and therefore axion masses, than ADMX. If the axion does exist and does constitute dark matter, he claims, the experiment “would have an excellent chance of finding it”.

Astronomical electricity bill

Sikivie cautions that, unlike ADMX, the new scheme only exists “on paper” and that it remains to be seen how much it would cost. Electricity consumption alone could amount to $100m, he says, assuming that 10 MW-years of energy is needed for every doubling in frequency (at $1 per watt-year). But he says that this estimate is quite sensitive to assumptions about the nature of galactic dark matter and could be as low as $5m.
Rosenberg is enthusiastic about the proposal. “I don’t think there’s much question that this is sensible,” he says, regarding the basic principle of axion echo generation. But he considers the astrophysical analysis to be “more speculative”, although still potentially correct. And he argues that neither radar facilities nor astronomical observatories are set up to carry out such a search – the former lacking suitable low-noise receivers while the latter typically don’t fire beams into space.
Axel Lindner, who studies dark matter at DESY in Germany, is more upbeat on this point. He says that the new proposal “basically rests on existing technologies”, arguing that it could in fact “be realized rather quickly” if someone sketched out a more concrete plan.
The proposal is described in a preprint on the arXiv server.

Friday, 8 February 2019

2018 fourth hottest year on record: NASA


Washington: Earth’s global surface temperatures in 2018 were the fourth warmest since 1880 and the planet will warm further, especially since greenhouse gas emissions are continuing to rise, NASAand the National Oceanic and Atmospheric Administration (NOAA) have said. Global temperatures in 2018 were 0.83 degrees Celsius warmer than the 1951 to 1980, according to scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York. Globally, 2018’s temperatures ranked behind those of 2016, 2017 and 2015. The past five years are, collectively, the warmest years in the modern record.
“2018 is yet again an extremely warm year on top of a long-term global warming trend,” GISS Director Gavin Schmidt said in a statement on Wednesday. Since the 1880s, the average global surface temperature has risen about 1 degree Celsius. This warming has been driven in large part by increased emissions into the atmosphere of carbon dioxide and other greenhouse gases caused by human activities. “Weather dynamics often affect regional temperatures, so not every region on Earth experienced similar amounts of warming,” said NOAA.
Warming trends are strongest in the Arctic region, where 2018 saw the continued loss of sea ice. “In addition, mass loss from the Greenland and Antarctic ice sheets continued to contribute to sea level rise. (IANS)

source: sentinelassam

Wednesday, 6 February 2019

Astronomers Map a Black Hole Using ‘Echoes’ of Light

By Alison Klesman | February 5, 2019 5:30 pm

This artist’s interpretation shows the black hole MAXI J1820+070 and its companion star, along with J1820’s accretion disk (orange) and corona (blue).
(Credit: Aurore Simonnet and NASA’s Goddard Space Flight Center)Black holes pepper our universe, but like their name implies, most are invisible — until something happens to change that. That something is often material flowing into the black hole. And in March 2018, one such previously invisible black hole flared to life when a flood of matter fell inward, allowing astronomers to spot and track the event, ultimately mapping out the region close to a black hole in finer detail than ever before.

That work, published January 9 in Nature, was led by Erin Kara of the University of Maryland and NASA’s Goddard Space Flight Center. Kara also presented the results at a press conference the same day at the 233rd meeting of the American Astronomical Society in Seattle. Using NASA’s Neutron star Interior Composition Explorer (NICER) aboard the International Space Station (ISS), the team watched the stellar-mass black hole (designated MAXI J1820+070, or J1820 for short), which flared to life March 11, every day for months. In that time, they used light echoes, which occur when light from near the black hole is absorbed by the accretion disk farther out and then emitted again in a sort of “echo,” to map out the region close to the black hole and watch how that it changed over time.
“Similar to how bats use echolocation to map out a dark cave that they can’t see, we are using these light echoes to put constraints on what it must look like around this black hole that we cannot resolve spatially with our telescopes,” Kara explained in the press conference.

Black hole geometry

While many black holes are simply sitting calmly in space without nearby material to consume, some are in binary systems where one star has become a black hole, while the companion is at an earlier stage in its life. This is the case for J1820 — the black hole is pulling material off a star, which forms a swirling disk of material that heats up as it falls inward toward the event horizon and disappears. The accretion disk is relatively flat and thin, as its name implies, shining at a temperature of about 18 million degrees Fahrenheit (10 million degrees Celsius). Closer to the black hole lies a spherical “corona” of even hotter electrons, protons, and positrons at almost 2 billion F (1 billion C).
Outbursts such as the one that allowed the team to spot J1820 occur when an instability in the disk, such as a clump of material, causes a sudden rush of matter toward the black hole, making the system to flare hotter and brighter. The first instrument to find the flaring black hole was the Japan Aerospace Exploration Agency’s Monitor of All-sky X-ray Image (MAXI), which is also installed on the ISS. Once MAXI spotted the event, NICER swung into place to pinpoint its location and study the X-rays streaming from the black hole in greater detail.

Making a Map

During an outburst, the hot corona shines in all directions. Some of that light hits the accretion disk, which absorbs it, heats up, and then emits light of its own. The time it takes for this to happen is the time it takes light to travel (at the speed of light) from the corona to different parts of the accretion disk. Any delay in the echoes between light from the corona and light from the accretion disk tells astronomers how far out in the disk the echoes came from. The timing differences allow researchers to then piece together a picture of what the accretion disk looks like.
NICER “has this incredibly fast, high time resolution,” Kara said, which means it takes separate measurements quickly so that astronomers can watch what’s happening in greater detail. That greater detail meant “we were able to measure shorter light echoes than had ever been seen before in a stellar-mass black hole system. And that means we’re probing closer to the black hole with these light echoes than ever before possible,” Kara said.

Closing In

But something else was happening. “As we watched the system over several weeks, we saw that the light echoes got closer and closer together. That was indicating that something in the system was getting smaller – so either the accretion disk coming inwards, or the corona shrinking,” Kara said.
How could they differentiate one from the other? Light echoes from parts of the accretion disk closer to the black hole are redder, because the light is stretched out as it tries to escape the black hole’s immense gravity. This is called gravitational redshifting. Looking at the maximum stretching that occurred told the team how close the accretion disk got to the black hole, as well as whether that distance changed over time.
“We noticed that the most gravitationally redshifted emission – the emission coming from the innermost regions – the amount of that emission did not change at all. So that suggested to us that the disk itself is close to the central black hole and does not evolve over time. But because the light echoes got shorter and shorter, closer and closer together, that must mean that the corona was shrinking,” she said.
Her team estimated that over several weeks, “the corona shrinks from something like 100 miles [160 kilometers] to only 10 [16 km],” Kara said.
“This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution,” study co-author Jack Steiner at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research said in a press release. “The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself.”

The Bigger Picture

This first-of-its kind observation will not only help astronomers better understand the workings of stellar-mass black holes, which are tens of times the mass of the Sun, but can also be applied to supermassive black holes, which are millions or billions of times the mass of the Sun.
“In stellar-mass black holes [these outbursts] evolve over timescales of several weeks to months. So we can watch this evolution happening in real time and we find now that it’s the corona that’s driving that evolution,” Kara said. But in supermassive black holes, she added, such outbursts occur over billions of years. By scaling up what’s going on around smaller black holes over shorter time periods, she explained, astronomers can learn more about how material falls in and causes changes in the region around supermassive black holes on much larger scales. That will, in turn, allow astronomers to better understand how these behemoths affect their local environment, which in turn affects the evolution of the galaxy around them.
“These stellar-mass black holes are a great analogue for studying the evolution of the corona and the accretion geometry in real time,” she said.

Sunday, 3 February 2019

Curiosity makes unexpected discovery on Mars, NASA says planet is 'uncanny valley of Earth

NASA's Mars Curiosity rover has successfully taken measurements of the density of a mountain on the red planet and finds it more porous than originally thought.

Mars Curiosity rover, NASA's Mars Curiosity rover, Mars Curiosity rover NASA, NASA's mission to Mars, Mount Sharp, Gale crater Mars, Red planet, NASA's Mars Curiosity, Earth, mars insight, rover mars, mission to mars NASA
Curiosity rover used the Mars Hand Lens Imager to capture a set of 55 high-resolution images, which were stitched together to create this full-color self-portrait. The mosaic shows the rover at 'Rocknest,' the spot in Gale Crater where the mission's first scoop sampling took place. (Image: NASA/JPL-Caltech/Malin Space Science Systems)
ocks on Mars are more porous and less compacted than scientists expected, according to a study that used data from NASA's Curiosity rover.
Researchers, including those from Arizona State University (ASU) in the US, measured the density of rock layers in 154-kilometre-wide Gale Crater on Mars.
"What we were able to do is measure the bulk density of the material in Gale Crater," said Travis Gabriel, a graduate student at Arizona State University.

Findings of the study

The findings, published in the journal Science, show that the layers are more porous than scientists had suspected.
The discovery also gives scientists a novel technique to use in the future as the rover continues its trek across the crater and up Mount Sharp, a five-kilometre-high mountain at its centre.

NASA's Mars rover Curiosity captured this composite image, which looks toward the higher regions of Mount Sharp, on September 9, 2015.(Image: NASA/JPL-Caltech/MSSS)
As Curiosity ascended Mount Sharp, the gravitational force increased - but not as much as scientists expected.
"The lower levels of Mount Sharp are surprisingly porous," said Kevin Lewis of Johns Hopkins University in the US.
"We know the bottom layers of the mountain were buried over time. That compacts them, making them denser. But this finding suggests they weren't buried by as much material as we thought," Lewis said.

How did the scientists reach this conclusion?

1. Gabriel worked on computing what the grain density should be for the rocks and ancient lake-bed sediments the rover has been driving over.
"Working from the rocks' mineral abundances as determined by the chemistry and mineralogy instrument, we estimated a grain density of 2810 kilogrammes per cubic metre," he said in a statement.
"However, the bulk density that came out of our study is a lot less - 1680 kilogrammes per cubic metre," said Gabriel.
2. The much lower figure shows that the rocks have a reduced density, most likely resulting from the rocks being more porous.
3. This means the rocks have been compressed less than scientists have thought.
4. The engineering sensors used in the study were accelerometers, much like those found in every smartphone to determine its orientation and motion.
5. Curiosity's sensors do the same, but with much greater precision, helping engineers and mission controllers navigate the rover across the Martian surface.

Mars, you are my density.

In '72, Apollo 17 astronauts measured gravity on the Moon with a special tool called a gravimeter. I repurposed accelerometers to take similar measurements on Mars. Turns out Mount Sharp isn't as dense as expected 🤔 

6. Curiosity's accelerometers can also be used as a gravimeter - an instrument that can measure gravity - to reveal secrets about Martian geology.
7. Even when Curiosity is stationary, the accelerometers are constantly detecting the slight changes in gravity on Mars, as Curiosity rolls further up Mount Sharp.
8. Researchers used over 700 measurements from Curiosity's accelerometers taken between October 2012 and June 2017. These were calibrated to filter out 'noise', such as the effects of temperature and the tilt of the rover during its climb.
9. The calculations were then compared to models of Mars' gravity fields to ensure accuracy.

Mystery mountain

There are many mountains within craters or canyons on Mars, but few approach the scale of Mount Sharp.
Scientists still aren't sure how the mountain grew inside of Gale Crater. One idea is that the crater was once filled with sediment. How much of it was filled remains a source of debate, but the thinking is that many millions of years of wind and erosion eventually excavated the mountain.

A computer generated image showing Mount Sharp rising from the center of the Gale Crater.(Image: NASA/JPL-Caltech/ASU/UA)
If the crater had been filled to the brim, all that material should have pressed down, or compacted, the many layers of fine-grained sediment beneath it.
But the new paper suggests Mount Sharp's lower layers have been compacted by only a half-mile to a mile (1 to 2 kilometers) - much less than if the crater had been completely filled.
"There are still many questions about how Mount Sharp developed, but this paper adds an important piece to the puzzle," said study co-author Ashwin Vasavada, Curiosity's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

Mars and Earth are planetary siblings

Lewis said that Mars holds plenty of mystery beyond Mount Sharp. Its landscape is like Earth's, but sculpted more by wind and blowing sand than by water. They're planetary siblings, at once familiar and starkly different.

"To me, Mars is the uncanny valley of Earth," Lewis said. "It's similar but was shaped by different processes. It feels so unnatural to our terrestrial experience."

source and credits: indiatoday