- Curiosity Rover Analyzes Sample of Martian Mountain
- NASA's Dawn Spacecraft Gets Closer Views of Ceres
- Planck Reveals First Stars Were Born Late
- Hubble Captures Rare Triple-Moon Conjunction
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Posted: 06 Feb 2015 05:58 AM PST
The second bite of a Martian mountain taken by NASA's Curiosity Mars rover hints at long-ago effects of water that was more acidic than any evidenced in the rover's first taste of Mount Sharp, a layered rock record of ancient Martian environments. The rover used a new, low-percussion-level drilling technique to collect sample powder last week from a rock target called "Mojave 2." Curiosity reached the base of Mount Sharp five months ago after two years of examining other sites inside Gale Crater and driving toward the mountain at the crater's center. The first sample of the mountain's base layer came from a target called "Confidence Hills," drilled in September. A preliminary check of the minerals in the Mojave 2 sample comes from analyzing it with the Chemistry and Mineralogy (CheMin) instrument inside Curiosity. The still-partial analysis shows a significant amount of jarosite, an oxidized mineral containing iron and sulfur that forms in acidic environments.
"Our initial assessment of the newest sample indicates that it has much more jarosite than Confidence Hills," said CheMin Deputy Principal Investigator David Vaniman, of the Planetary Science Institute, Tucson, Arizona. The minerals in Confidence Hills indicate less acidic conditions of formation. Open questions include whether the more acidic water evident at Mojave 2 was part of environmental conditions when sediments building the mountain were first deposited, or fluid that soaked the site later. Both target sites lie in a outcrop called "Pahrump Hills," an exposure of the Murray formation that is the basal geological unit of Mount Sharp. The Curiosity mission team has already proposed a hypothesis that this mountain, the size of Mount Rainier in Washington, began as sediments deposited in a series of lakes filling and drying. In the months between Curiosity's drilling of these two targets, the rover team based at NASA's Jet Propulsion Laboratory, Pasadena, California, directed the vehicle through an intensive campaign at Pahrump Hills. The one-ton roving laboratory zig-zagged up and down the outcrop's slope, using cameras and spectrometer instruments to study features of interest at increasing levels of detail. One goal was to select which targets, if any, to drill for samples to be delivered into the rover's internal analytical instruments. The team chose a target called "Mojave," largely due to an abundance of slender features, slightly smaller than rice grains, visible on the rock surface. Researchers sought to determine whether these are salt-mineral crystals, such as those that could result from evaporation of a drying lake, or if they have some other composition. In a preparatory drilling test of the Mojave target, the rock broke. This ruled out sample-collection drilling at that spot, but produced chunks with freshly exposed surfaces to be examined. Mojave 2, an alternative drilling target selected at the Mojave site, has the same type of crystal-shaped features. The preliminary look at CheMin data from the drilled sample material did not identify a clear candidate mineral for these features. Possibly, minerals that originally formed the crystals may have been replaced by other minerals during later periods of wet environmental conditions. The drilling to collect Mojave 2 sample material might not have succeeded if the rover team had not recently expanded its options for operating the drill. "This was our first use of low-percussion drilling on Mars, designed to reduce the energy we impart to the rock," said JPL's John Michael Morookian, the team's surface science and sampling activity lead for the Pahrump Hills campaign. "Curiosity's drill is essentially a hammer and chisel, and this gives us a way not to hammer as hard." Extensive tests on Earth validated the technique after the team became concerned about fragility of some finely layered rocks near the base of Mount Sharp. The rover's drill has six percussion-level settings ranging nearly 20-fold in energy, from tapping gently to banging vigorously, all at 30 times per second. The drill monitors how rapidly or slowly it is penetrating the rock and autonomously adjusts its percussion level. At the four targets before Mojave 2 -- including three before Curiosity reached Mount Sharp -- sample-collection drilling began at level four and used an algorithm that tended to remain at that level. The new algorithm starts at level one, then shifts to a higher level only if drilling progress is too slow. The Mojave 2 rock is so soft, the drill reached its full depth of about 2.6 inches (6.5 centimeters) in 10 minutes using just levels one and two of percussion energy. Curiosity has also delivered Mojave 2 powder to the internal Sample Analysis at Mars (SAM) suite of instruments, for chemical analysis. The rover may drive to one or more additional sampling sites at Pahrump Hills before heading higher on Mount Sharp. NASA's Mars Science Laboratory Project is using Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. JPL, a division of the California Institute of Technology in Pasadena, built the rover and manages the project for NASA's Science Mission Directorate in Washington.
Credit: NASA
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Posted: 05 Feb 2015 02:08 PM PST
NASA's Dawn spacecraft, on approach to dwarf planet Ceres, has acquired its latest and closest-yet snapshot of this mysterious world. At a resolution of 8.5 miles (14 kilometers) per pixel, the pictures represent the sharpest images to date of Ceres. After the spacecraft arrives and enters into orbit around the dwarf planet, it will study the intriguing world in great detail. Ceres, with a diameter of 590 miles (950 kilometers), is the largest object in the main asteroid belt, located between Mars and Jupiter. Dawn is slated to arrive at Ceres on Mar. 6. “In its lowest altitude orbit, Dawn's images will have a resolution of better than 40 meters per pixel. So we will be able to see exquisite detail compared to what we have now,” Marc Rayman, Dawn Mission Director and Chief Engineer at NASA’s Jet Propulsion Laboratory told astrowatch.net.
The spacecraft will enter the dwarf planet’s orbit at an initial altitude of 13,500 km for a first full characterization. Then it will explore Ceres from survey orbit at 4,400 km, and next it will go lower to only 1,470 km. To travel from one orbit to another, it will use its extraordinary ion propulsion system to spiral lower and lower and lower.
Scientists believe that Ceres may harbor an internal ocean of liquid water under its surface. The surface is probably a mixture of water ice and various hydrated minerals such as carbonates and clay.
Dawn's mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Virginia, designed and built the spacecraft. JPL is managed for NASA by the California Institute of Technology in Pasadena.
The framing cameras were provided by the Max Planck Institute for Solar System Research, Gottingen, Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The visible and infrared mapping spectrometer was provided by the Italian Space Agency and the Italian National Institute for Astrophysics, built by Selex ES, and is managed and operated by the Italian Institute for Space Astrophysics and Planetology, Rome. The gamma ray and neutron detector was built by Los Alamos National Laboratory, New Mexico, and is operated by the Planetary Science Institute, Tucson, Arizona.
Credit: dawn.jpl.nasa.gov
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Posted: 05 Feb 2015 01:06 PM PST
New maps from ESA’s Planck satellite uncover the ‘polarised’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought. The history of our Universe is a 13.8 billion-year tale that scientists endeavour to read by studying the planets, asteroids, comets and other objects in our Solar System, and gathering light emitted by distant stars, galaxies and the matter spread between them. A major source of information used to piece together this story is the Cosmic Microwave Background, or CMB, the fossil light resulting from a time when the Universe was hot and dense, only 380 000 years after the Big Bang. "Planck can see the old light from our universe's birth, gas and dust in our own galaxy, and pretty much everything in between, either directly or by its effect on the old light," said Charles Lawrence, the U.S. project scientist for the mission at NASA's Jet Propulsion Laboratory in Pasadena, California. Thanks to the expansion of the Universe, we see this light today covering the whole sky at microwave wavelengths.
Between 2009 and 2013, Planck surveyed the sky to study this ancient light in unprecedented detail. Tiny differences in the background’s temperature trace regions of slightly different density in the early cosmos, representing the seeds of all future structure, the stars and galaxies of today.
Scientists from the Planck collaboration have published the results from the analysis of these data in a large number of scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy.
“But there is more: the CMB carries additional clues about our cosmic history that are encoded in its ‘polarisation’,” explains Jan Tauber, ESA’s Planck project scientist.
“Planck has measured this signal for the first time at high resolution over the entire sky, producing the unique maps released today.”
Light is polarised when it vibrates in a preferred direction, something that may arise as a result of photons – the particles of light – bouncing off other particles. This is exactly what happened when the CMB originated in the early Universe.
Initially, photons were trapped in a hot, dense soup of particles that, by the time the Universe was a few seconds old, consisted mainly of electrons, protons and neutrinos. Owing to the high density, electrons and photons collided with one another so frequently that light could not travel any significant distant before bumping into another electron, making the early Universe extremely ‘foggy’.
Slowly but surely, as the cosmos expanded and cooled, photons and the other particles grew farther apart, and collisions became less frequent.
This had two consequences: electrons and protons could finally combine and form neutral atoms without them being torn apart again by an incoming photon, and photons had enough room to travel, being no longer trapped in the cosmic fog.
Once freed from the fog, the light was set on its cosmic journey that would take it all the way to the present day, where telescopes like Planck detect it as the CMB. But the light also retains a memory of its last encounter with the electrons, captured in its polarisation.
“The polarisation of the CMB also shows minuscule fluctuations from one place to another across the sky: like the temperature fluctuations, these reflect the state of the cosmos at the time when light and matter parted company,” says François Bouchet of the Institut d’Astrophysique de Paris, France.
“This provides a powerful tool to estimate in a new and independent way parameters such as the age of the Universe, its rate of expansion and its essential composition of normal matter, dark matter and dark energy.”
Planck’s polarisation data confirm the details of the standard cosmological picture determined from its measurement of the CMB temperature fluctuations, but add an important new answer to a fundamental question: when were the first stars born?
“After the CMB was released, the Universe was still very different from the one we live in today, and it took a long time until the first stars were able to form,” explains Marco Bersanelli of Università degli Studi di Milano, Italy.
“Planck’s observations of the CMB polarisation now tell us that these ‘Dark Ages’ ended some 550 million years after the Big Bang – more than 100 million years later than previously thought.
“While these 100 million years may seem negligible compared to the Universe’s age of almost 14 billion years, they make a significant difference when it comes to the formation of the first stars.”
The Dark Ages ended as the first stars began to shine. And as their light interacted with gas in the Universe, more and more of the atoms were turned back into their constituent particles: electrons and protons.
This key phase in the history of the cosmos is known as the ‘epoch of reionisation’.
The newly liberated electrons were once again able to collide with the light from the CMB, albeit much less frequently now that the Universe had significantly expanded. Nevertheless, just as they had 380 000 years after the Big Bang, these encounters between electrons and photons left a tell-tale imprint on the polarisation of the CMB.
“From our measurements of the most distant galaxies and quasars, we know that the process of reionisation was complete by the time that the Universe was about 900 million years old,” says George Efstathiou of the University of Cambridge, UK.
“But, at the moment, it is only with the CMB data that we can learn when this process began.”
Planck’s new results are critical, because previous studies of the CMB polarisation seemed to point towards an earlier dawn of the first stars, placing the beginning of reionisation about 450 million years after the Big Bang.
This posed a problem. Very deep images of the sky from the NASA–ESA Hubble Space Telescope have provided a census of the earliest known galaxies in the Universe, which started forming perhaps 300–400 million years after the Big Bang.
However, these would not have been powerful enough to succeed at ending the Dark Ages within 450 million years.
“In that case, we would have needed additional, more exotic sources of energy to explain the history of reionisation,” says Professor Efstathiou.
The new evidence from Planck significantly reduces the problem, indicating that reionisation started later than previously believed, and that the earliest stars and galaxies alone might have been enough to drive it.
This later end of the Dark Ages also implies that it might be easier to detect the very first generation of galaxies with the next generation of observatories, including the James Webb Space Telescope.
But the first stars are definitely not the limit. With the new Planck data released today, scientists are also studying the polarisation of foreground emission from gas and dust in the Milky Way to analyse the structure of the Galactic magnetic field.
The data have also enabled new important insights into the early cosmos and its components, including the intriguing dark matter and the elusive neutrinos, as described in papers also released today.
The Planck data have delved into the even earlier history of the cosmos, all the way to inflation – the brief era of accelerated expansion that the Universe underwent when it was a tiny fraction of a second old. As the ultimate probe of this epoch, astronomers are looking for a signature of gravitational waves triggered by inflation and later imprinted on the polarisation of the CMB.
No direct detection of this signal has yet been achieved, as reported last week. However, when combining the newest all-sky Planck data with those latest results, the limits on the amount of primordial gravitational waves are pushed even further down to achieve the best upper limits yet.
“These are only a few highlights from the scrutiny of Planck's observations of the CMB polarisation, which is revealing the sky and the Universe in a brand new way,” says Jan Tauber.
“This is an incredibly rich data set and the harvest of discoveries has just begun.”
The Planck data also support the idea that the mysterious force known as dark energy is acting against gravity to push our universe apart at ever-increasing speeds. Some scientists have proposed that dark energy doesn't exist. Instead, they say that what we know about gravity, as outlined by Albert Einstein's general theory of relativity, needs refining. In those theories, gravity becomes repulsive across great distances, eliminating the need for dark energy.
"So far Einstein is looking pretty good," said Martin White, a U.S. Planck team member from University of California, Berkeley. "The dark energy hypothesis is holding up very well, but this is not the end of the story."
A series of scientific papers describing the new results was published on 5 February and it can be downloadedhere.
The new results from Planck are based on the complete surveys of the entire sky, performed between 2009 and 2013. New data, including temperature maps of the CMB at all nine frequencies observed by Planck and polarisation maps at four frequencies (30, 44, 70 and 353 GHz), are also released today.
Launched in 2009, Planck was designed to map the sky in nine frequencies using two state-of-the-art instruments: the Low Frequency Instrument (LFI), which includes three frequency bands in the range 30–70 GHz, and the High Frequency Instrument (HFI), which includes six frequency bands in the range 100–857 GHz.
HFI completed its survey in January 2012, while LFI continued to make science observations until 3 October 2013, before being switched off on 19 October 2013. Seven of Planck's nine frequency channels were equipped with polarisation-sensitive detectors.
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Posted: 05 Feb 2015 08:10 AM PST
Firing off a string of action snapshots like a sports photographer at a NASCAR race, NASA's Hubble Space Telescope captured the rare occurrence of three of Jupiter's largest moons racing across the banded face of the gas-giant planet: Europa, Callisto, and Io. These so-called Galilean moons, named after the 17th century scientist Galileo Galilei, who discovered them with a telescope, complete orbits around Jupiter with durations ranging from 2 days to 17 days. They can commonly be seen transiting the face of Jupiter and casting shadows onto its cloud tops. However, seeing three moons transiting the face of Jupiter at the same time is rare, occurring only once or twice a decade.
The below Hubble image on the left shows the beginning of the event, which took place on January 24, 2015. From left to right, the moons Callisto and Io are above Jupiter's cloud tops. The shadows from Europa, Callisto, and Io are strung out from left to right. Europa is not visible in this image. Near the end of the event, approximately 42 minutes later (right-side image) Europa has entered the frame at lower left. Slower-moving Callisto is above and to the right of Europa. Fastest-moving Io is approaching the eastern limb of the planet; its shadow is no longer visible on Jupiter. Europa's shadow is toward the left side of the image, and Callisto's shadow to the right. The moons' orbital velocities are proportionally slower with increasing distance from the planet.
Missing from the sequence is Ganymede, one of the four Galilean moons that was outside Hubble's field of view and too far from Jupiter to be part of this conjunction.
The moons in these photos have distinctive colors. The ancient cratered surface of Callisto is brownish; the smooth icy surface of Europa is yellow-white; and the volcanic, sulfur-dioxide surface of Io is orange. The apparent “fuzziness” of some of the shadows depends on the moons’ distances from Jupiter. The farther away a moon is from the planet, the softer the shadow, because the shadow is more spread out across the disk. The images were taken with Hubble's Wide Field Camera 3 in visible light. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. Credit: hubblesite.org  |
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