Vesta's surface textures get highlighted by dawn's light
[/caption]
Sunrise on Vesta highlights the asteroid’s varied surface textures in this image from NASA’s Dawn spacecraft, released on Monday, Feb. 20. The image was taken on Dec. 18 with Dawn’s Framing Camera (FC).
Just as the low angle of early morning sunlight casts long shadows on Earth, sunrise on Vesta has the same effect — although on Vesta it’s not trees and buildings that are being illuminated but rather deep craters and chains of pits!
The steep inner wall of a crater is seen at lower right with several landslides visible, its outer ridge cutting a sharp line.
Chains of pits are visible in the center of the view. These features are the result of ejected material from an impact that occurred outside of the image area.
Other lower-profile, likely older craters remain in shadow.
Many of these features would appear much less dramatic with a high angle of illumination, but they really shine brightest in dawn’s light.
A new look at old data has given scientists more insight into the Moon's core. Credit: Science
[/caption]
Last year, scientists took another look at the seismic data collected by Apollo era experiments and discovered that the lower mantle of the Moon, the part near the core-mantle boundary, is partially molten (e.g., Apollo Data Retooled to Provide Precise Readings on Moon’s Core, Universe Today, Jan. 6, 2011). Their findings suggest that the lowest 150 km of the mantle contains anywhere from 5 to 30% liquid melt. On the Earth, this would be enough melt for it to separate from the solid, rise up, and erupt at the surface. We know that the Moon had volcanism in the past. So, why is this lunar melt not erupting at the surface today? New experimental studies on simulated lunar samples may provide the answers.
It is suspected that the current lunar magmas are too dense, in comparison to their surrounding rocks, to rise to the surface. Just like oil on water, less dense magmas are buoyant and will percolate up above the solid rock. But, if the magma is too dense, it will stay where it is, or even sink.
Motivated by this possibility, an international team of scientists, led by Mirjam van Kan Parker from the VU University Amsterdam, has been studying the character of lunar magmas. Their findings, which were recently published in the Journal Nature Geoscience, show that lunar magmas have a range of densities that are dependent on their composition.
Ms van Kan Parker and her team squeezed and heated molten samples of magma and then used X-ray absorption techniques to determine the material’s density at a range of pressures and temperatures. Their studies used simulated lunar materials, since lunar samples are considered too valuable for such destructive analysis. Their simulants modelled the composition of Apollo 15 green volcanic glasses (which have a titanium content of 0.23 weight %) and Apollo 14 black volcanic glasses (which have a titanium content of 16.4 weight %).
Samples of these simulants were subjected to pressures up to 1.7 GPa (atmospheric pressure, at the surface of the Earth, is 101 kPa, or 20,000 times less than what was achieved in these experiments). However, pressures in the lunar interior are even greater, exceeding 4.5 GPa. So, computer calculations were conducted to extrapolate from the experimental results.
Apollo 15 green glass beads. Credit: NASA
The combined work shows that, at the temperatures and pressures typically found in the lower lunar mantle, magmas with low titanium contents (Apollo 15 green glasses) have densities that are less than the surrounding solid material. This means they are buoyant, should rise to the surface, and erupt. On the other hand, magmas with high titanium contents (Apollo 14 black glasses) were found to have densities that are about equal to or greater than their surrounding solid material. These would not be expected to rise and erupt.
Since the Moon has no active volcanic activity, the melt currently located at the bottom of the lunar mantle must have a high density. And, Ms van Kan Parker’s results suggest that this melt should be made of high titanium magmas, like those that formed the Apollo 14 black glasses.
A new look at old data has given scientists more insight into the Moon's core. Credit: Science
This finding is significant, because high titanium magmas are thought to have formed from titanium-rich source rocks. These rocks represent the dregs that were left at the base of the lunar crust, after all the buoyant plagioclase minerals (which make up the crust) had been squeezed upwards in a global magma ocean. Being dense, these titanium-rich rocks would have quickly sunk to the core-mantle boundary in an overturn event. Such an overturn even had been postulated over 15 years ago. Now, these exciting new results provide experimental support for this model.
These dense, titanium-rich rocks are also expected to have a lot of radioactive elements, which tend to get left behind when other elements are preferentially taken up by mineral crystals. The resulting radiogenic heat from the decay of these elements could explain why parts of the lower lunar mantle are still hot enough to be molten. Ms van Kan Parker and her team further speculate that this radiogenic heat could also be helping to keep the lunar core partially melted even today!
Sources:
X-Rays Illuminate the Interior of the Moon, Science Daily, Feb. 19, 2012.
Neutral buoyancy of titanium-rich melts in the deep lunar interior, van Kan Parker et al. Nature Geoscience, Feb. 19, 2012, doi:10.1038/NGEO1402.
If you weren’t able to watch live, this is a fun exchange between the current astronauts in orbit, talking with one of the first people ever to see Earth from an orbital perspective. The astronauts aboard the International Space Station talked with Senator John Glenn during an in-flight call this week, to celebrate the 50th anniversary of Glenn’s historic Friendship 7 space flight. The event was part of NASA’s Future Forum at The Ohio State University in Columbus, Ohio.
Mosaic: NASA/JPL/Cornell/ASU/Marco Di Lorenzo/Kenneth Kremer
[/caption]
Opportunity, the Princess of Martian Robots, phoned home dusty new self portraits – above and below – of her beautiful bod basking in the utterly frigid sunshine during her 5th winter on the Red Planet whilst overlooking a humongous crater offering bountiful science.
NASA’s endearing robot is simultaneously carrying out an ambitious array of ground breaking science experiments this winter – providing insight into the mysterious nature of the Martian core – while sitting stationary until the energy augmenting rays of the springtime Sun shower down on Mars from the heavens above.
Opportunity’s current winter worksite is located at the rim of the vast crater named Endeavour, some 14 miles (22 kilometers) in diameter. The robot will remain parked for the winter on a slope at the north end of the crater rim segment called Cape York with an approximate 15-degree northerly tilt towards the life-giving sun to maximize solar energy production. The park-site is at an outcrop dubbed “Greeley Haven”, named in honor of Ronald Greeley, a beloved and recently deceased science team member.
The power killing dust buildup is readily apparent on the solar arrays and High Gain Antenna pictured in the new panoramic self-portraits of Opportunity’s wing-like deck. The red Martian dust also functions as a rather effective camouflage agent, sometimes blending the rover to near invisibility with the surface.
Dusty Mars Rover's Self-Portrait- Dec 2011
NASA's Mars Exploration Rover Opportunity shows dust accumulation on the rover's solar panels as the mission approached its fifth Martian winter at the rim of Endeavour Crater. Opportunity is located on the north-facing slope of a site called "Greeley Haven." This is a mosaic of images taken by Opportunity's panoramic camera (Pancam) during the 2,811th to 2,814th Martian days, or sols, of the rover's mission (Dec. 21 to Dec. 24, 2011). Credit: NASA/JPL-Caltech/Cornell/Arizona State Univ.
Indeed because Opportunity is covered with a thicker film of dust compared to her prior four Martian winters, the rover team was forced to employ the same “tilting” strategy they successfully used to keep her twin sister Spirit alive during her trio of Antarctic-like winters. This is the first winter that Opportunity did not have sufficient power to continue roving across the surface.
Since Opportunity is located just south of the Martian equator, the daylight hours for solar power generation are growing shorter until the southern Mars winter solstice occurs on March 30, 2012. As of mid- February 2012, the latest measure of solar array energy production was 274 watt-hours, compared to about 900 watt-hours at the start of the mission. See Solar Power energy graph below.
Power generation from the solar arrays has fluctuated up and down throughout Opportunity’s lifetime depending on when the completely unpredictable and fortuitous Martian wind storms chance by and miraculously clean the arrays of the rusty red dust.
Opportunity Rover Self-Portrait From 2007
Opportunity used its panoramic camera (Pancam) during the mission's sols 1282 and 1284 (Sept. 2 and Sept. 4, 2007) to take the images combined into this mosaic view of the rover. The downward-looking view omits the mast on which the camera is mounted.The deck panorama is presented in approximate true color, the camera team's best estimate of what the scene would look like if humans were there and able to see it with their own eyes.Credit: NASA/JPL-Caltech/Cornell
The rover science team is ingeniously using the lack of movement to their advantage and Opportunity is still vigorously hard at work doing breakthrough research each and every day.
From her stationary position, Opportunity is conducting her first ever radio science Doppler tracking measurements to support geo-dynamic investigations and to elucidate the unknown structure of the Martian interior and core. The team was eager for the long awaited chance to carry out the radio tracking experiment with the High Gain Antenna (HGA) and determine if Mars core is liquid or solid. Months of data collection are required while the rover stays stationary.
“This winter science campaign will feature two way radio tracking with Earth to determine the Martian spin axis dynamics – thus the interior structure, a long-neglected aspect of Mars,” Ray Arvidson told Universe Today. Arvidson, of Washington University in St. Louis, is the deputy rover Principal Investigator.
Opportunity has nearly finished snapping the 13 filter, 360 degree stereo Greeley” panorama. The rover deployed the robotic arm onto the surface of the “Amboy” outcrop to collect multi-sol integrations with the Mössbauer Spectrometer and the largest ever mosaic campaign using the Microscopic Imager.
“We’ll do good science while we’re at Greeley Haven. But as soon as we catch a wind gust or the seasons change, we’ll be on our way again,” Steve Squyres told Universe Today. Squyres, of Cornell University is the rover Science Principal Investigator
“The Martian southern winter solstice occurs at the end of March. A few months after that date we will drive her off the outcrop and further explore Cape York,” Arvidson told me
The team will drive Opportunity in search of further evidence of the gypsum mineral veins like “Homestake” – indicative of ancient water flow – previously discovered at Cape York. Thereafter they’ll rove further south to investigate deposits of phyllosilicates, the clay minerals which stem from an earlier epoch when liquid water flowed on Mars eons ago and perhaps may have been more favorable to sustaining life.
Graph shows Opportunity’s Solar power energy generation over the past 1000 Sols, or Martian Days, from Sol 1900 up to February 2012. Credit: NASA/JPL/Marco Di Lorenzo Mars from Earth on Feb 18, 2012 is nearly at opposition (occurs March 3) in this image taken using a Celestron 11 inch telescope in Leesburg, Florida. Astrophotographer Credit: Ernie Rossi
Opportunity is now well into her 9th year exploring hitherto unknown terrain on Mars, far exceeding anyone’s expectation. She landed inside a tiny crater on Jan. 24. 2004 for what was expected to be a mission of merely 90 Martian days, or Sols.
Today is Martian Sol 2873, that’s 32 times beyond the rover designers “warranty” for NASA’s Opportunity rover.
Altogether, Opportunity has journeyed more than 21 miles (34 kilometers) across the Red Planet’s surface, marking the first overland expedition on another Planet. See our route map below.
Opportunity Rover Traverse Map at Meridiani Planum on Mars - 2004 to 2012
Traverse map shows the 8 Year Journey of Opportunity from Eagle Crater landing site on Sol 1- Jan. 24, 2004 - to 5th Winter Haven worksite at Greeley Haven at Endeavour Crater rim in January 2012. Opportunity embarked on a crater tour and discovered bountiful evidence for the flow of liquid water on Mars billions of years ago. Endeavour Crater is 14 miles 22 kilometers) in diameter. Opportunity has driven more than 21 miles (34 km). Credit: NASA/JPL/Cornell/UA/Marco Di Lorenzo/Kenneth Kremer
Meanwhile, NASA’s Curiosity Mars Science Laboratory rover is rocketing through space and on course for a pinpoint touchdown inside the layered terrain of Gale Crater on August 6, 2012. Curiosity is now America’s last planned Mars rover following the cancellation of the joint NASA/ESA ExoMars rover mission in the Obama Administrations newly announced Fiscal 2013 NASA budget.
Artist's impression of a binary system containing a stellar-mass black hole called IGR J17091-3624
[/caption]
Astronomers using NASA’s Chandra X-ray Observatory have reported record-breaking wind speeds coming from a stellar-mass black hole.
The “wind”, a high-speed stream of material that’s being drawn off a star orbiting the black hole and ejected back out into space, has been clocked at a staggering 20 million miles per hour — 3% the speed of light! That’s ten times faster than any such wind ever measured from a black hole of its size!
The black hole, dubbed IGR J17091-3624 (IGR J17091 for short), is located about 28,000 light-years away in the constellation Scorpius. It is part of a binary system, with a Sun-like star in orbit around it.
“This is like the cosmic equivalent of winds from a category five hurricane,” said Ashley King from the University of Michigan, lead author of the study. “We weren’t expecting to see such powerful winds from a black hole like this.”
IGR J17091 exhibits wind speeds akin to black holes many times its mass… such winds have only ever been measured coming from black holes millions or even billions of times more massive.
“It’s a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes,” said co-author Jon M. Miller, also from the University of Michigan.
Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss)
Stellar-mass black holes are formed from the gravitational collapse of stars about 20 to 25 times the mass of our Sun.
“This black hole is performing well above its weight class,” Miller added.
IGR J17091 is also surprising in that it seems to be expelling much more material from its accretion disk than it is capturing. Up to 95% of the disk material is being blown out into space by the high-speed wind which, unlike polar jets associated with black holes, blows in many different directions.
While jets of material have been previously observed in IGR J17091, they have not been seen at the same time as the high-speed winds. This supports the idea that winds can suppress the formation of jets.
Chandra observations made two months ago did not show evidence of the winds, meaning they can apparently turn on and off. The winds are thought to be powered by constant variations in the powerful magnetic fields surrounding the black hole.
The study was published in the Feb. 20 issue of The Astrophysical Journal Letters.
This image, acquired by NASA’s MESSENGER spacecraft on December 12, 2011, reveals the blue coloration of the 32-mile (52-km) -wide Degas crater located in Mercury’s Sobkou Planitia region.
Degas’ bright central peaks are highly reflective in this view, and may be surrounded by hollows — patches of sunken, eroded ground first identified by MESSENGER last year.
Such blue-colored material within craters has been increasingly identified as more of Mercury’s surface is revealed in detail by MESSENGER images. It is likely due to an as-yet-unspecified type of dark subsurface rock, revealed by impact events.
The slightly larger, more eroded crater that Degas abuts is named Brontë.
The image was acquired with MESSENGER’s Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS), using filters 9, 7, 6 (996, 748, 433 nanometers) in red, green, and blue, respectively.
Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
SDO AIA image of the Sun and Moon at 14:11 UT on Feb. 21, 2012
[/caption]
The Sun seems to be glowing in traditional Mardi Gras colors in this image, made from three AIA channels taken today at approximately 14:11 UT (about 9:11 a.m. EST) as the Moon passed between it and the Solar Dynamics Observatory spacecraft. Looks like it’s that time of year again!
During portions of the year, the Moon transits the Sun on a regular basis from the perspective of NASA’s SDO spacecraft, which lies within the Moon’s orbit. When this happens we are treated to an improvised eclipse… and it gives SDO engineers a way to fine-tune the observatory’s calibration as well.
Here are more AIA views of the same event captured in different wavelengths:
Lunar transit on 2-21-12; AIA 304Lunar transit on 2-21-12; AIA 193Lunar transit on 2-21-12; AIA 4500
…and here’s an interesting image taken in HMI Dopplergram:
HMI Dopplergram image of transit
While the AIA (Atmospheric Imaging Assembly) images the Sun in light sensitive to different layers of its atmosphere, the Helioseismic and Magnetic Imager (HMI) studies oscillations in the Sun’s magnetic field at the surface layer.
And if you happen to be reading this as of the time of this writing (appx. 10:06 a.m. EST) you can keep up with the latest images coming in on the SDO site at http://sdo.gsfc.nasa.gov/.
It’s Mardi Gras and the Moon doesn’t want to miss out on any of the fun!
Images courtesy of NASA/SDO and the AIA, EVE, and HMI science teams. Hat-tip to Mr. Stu Atkinson who called the AIA alert on Twitter.
GJ1214b, shown in this artist’s view, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)
[/caption]
Would Kevin Costner’s character in the movie “Waterworld” be at home on this exoplanet? The planet GJ 1214b was discovered in 2009 and was one of the first planets where an atmosphere was detected. In 2010, scientists were able to measure the atmosphere, finding it likely was composed mainly of water. Now, with infrared spectra taken during transit observations by the Hubble Space Telescope, scientists say this world is even more unique, and that it represents a new class of planet: a waterworld underneath a thick, steamy atmosphere.
“GJ 1214b is like no planet we know of,” said Zachary Berta of the Harvard-Smithsonian Center for Astrophysics (CfA). “A huge fraction of its mass is made up of water.”
GJ 1214b is a super-Earth — smaller than Uranus but larger than Earth — and is about 2.7 times Earth’s diameter. That gives it a volume 20 times as great as Earth yet it has less than seven times as much mass, so it’s actually kind of a lightweight. This world is also hot: it orbits a red-dwarf star every 38 hours at a distance of 2 million kilometers, giving it an estimated temperature of 230 degrees Celsius.
Berta and a team of international astronomers used Hubble’s Wide Field Camera 3 (WFC3) to study GJ 1214b when it crossed in front of its host star. During such a transit, the star’s light is filtered through the planet’s atmosphere, giving clues to the mix of gases.
“We’re using Hubble to measure the infrared color of sunset on this world,” Berta said.
Hazes are more transparent to infrared light than to visible light, so the Hubble observations help to tell the difference between a steamy and a hazy atmosphere. They found the spectrum of GJ 1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.
Since the planet’s mass and size are known, astronomers can calculate the density, of only about 2 grams per cubic centimetre. Water has a density of 1 gram per cubic centimetre, while Earth’s average density is 5.5 grams per cubic centimetre. This suggests that GJ 1214b has much more water than Earth does, and much less rock.
As a result, the internal structure of GJ 1214b would be extraordinarily different from that of our world.
“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’, substances that are completely alien to our everyday experience,” Berta said.
Theorists expect that GJ 1214b formed further out from its star, where water ice was plentiful; later the planet migrated inward towards the star. In the process, it would have passed through the star’s habitable zone, where surface temperatures would be similar to Earth’s. How long it lingered there is unknown.
GJ 1214b is located in the constellation of Ophiuchus (The Serpent Bearer), and just 40 light-years from Earth. Scientists say it will be a prime candidate for study by the NASA/ESA/CSA James Webb Space Telescope, planned for launch later this decade.
The Atacama Desert of Chile has been called “an astronomer’s paradise,” with its stunningly dark, steady and transparent skies. It is home to some of the world’s leading telescopes, such as the Very Large Telescope (VLT) is located on Paranal. Babak Tafreshi, an astronomer, journalist and director of The World at Night (TWAN) is creating a series of timelapse videos from Paranal, and this is his latest. Just beautiful. You can see more at his Vimeo page.
Newly detected series of narrow linear troughs are known as graben, and they formed in highland materials on the lunar farside. These graben are located on a topographic rise with several hundred meters of relief revealed in topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images (blues are lower elevations and reds are higher elevations). Image Credit: NASA/GSFC/Arizona State University/Smithsonian Institution
[/caption]
Recent images from NASA’s Lunar Reconnaissance Orbiter Camera provide evidence that the lunar crust may be pulling apart in certain areas. The images reveal small trenches less than a kilometer in length, and less than a few hundred meters wide. Only a small number of these features, known as graben, have been discovered on the lunar surface.
There are several clues in the high-resolution images that provide evidence for recent geologic activity on the Moon.
The LROC team detected signs of contraction on the lunar surface as early as August of 2010. The contractions were in the form of lobe-shaped ridges known as lobate scarps. Based on the data, the team suggests the widely-distributed scarps indicate the Moon shrank in diameter, and may be continuing to shrink. Interestingly enough, the new image data featuring graben presents a contradiction, as they indicate lunar crust being pulled apart and theorize that the process that created the graben may have occurred within the past 50 million years.
“We think the Moon is in a general state of global contraction due to cooling of a still hot interior, said thomas Watters from the Center for Earth and Planetary Studies. “The graben tell us that forces acting to shrink the Moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the Moon cannot be large, or the small graben might never form.”
Based on the size of the graben, the forces responsible for contraction of the lunar surface are assumed to be fairly weak. It is further theorized that, unlike the early terrestrial planets, the Moon was not completely molten during its early history.
“It was a big surprise when I spotted graben in the farside highlands,” said Mark Robinson, LROC Principal Investigator at Arizona State University. “I immediately targeted the area for high resolution stereo images so we could create a 3-dimensional view of the graben. It’s exciting when you discover something totally unexpected. Only about half the lunar surface has been imaged in high resolution. There is much more of the Moon to be explored.”
If you’d like to learn more about the recently discovered graben on the moon, you can watch a short video by Thomas Watters below:
