Posted on by Nancy Atkinson

Why is Mars’ Southern Polar Cap Crooked?

Mars Express Data from Mars South Pole. Credits: ESA/ Image Courtesy of F. Altieri (IFSI-INAF) and the OMEGA team

[/caption]
Like Earth, Mars has frozen polar caps, but unlike Earth, these caps are made of carbon dioxide ice as well as water ice. During the southern hemisphere’s summer, much of the ice cap sublimates, or evaporates directly to a gas, but leaves behind what is known as the residual polar cap. The problem is that while the winter cap is symmetrical about the south pole, the residual cap is offset by some three to four degrees. Using data from ESA’s Mars Express spacecraft, scientists say two things are to blame: the Martian weather system, and interestingly, so is the largest impact crater on Mars – even though it is nowhere near the south pole.

Using the Planetary Fourier Spectrometer (PFS) onboard Mars Express, Marco Giuranna of the Istituto di Fisica dello Spazio Interplanetario CNR (IFSI), Rome, Italy, and colleagues have measured the temperature of Mars’ atmosphere from the ground up to an altitude of 50 km above the south polar region.

They charted the way the atmosphere changes in temperature and other characteristics over more than half a Martian year, and monitored the way carbon dioxide builds into the southern ice cap as the autumn turns into winter on Mars. “It is not a straightforward process. We found that two regional weather systems developed from mid-fall through the winter,” says Giuranna.

These weather systems are derived from strong eastward winds that blow straight into the Hellas Basin, the largest impact structure on Mars with a diameter of 2300 km and a depth of 7 km. The crater’s depth and the steep rise of the walls deflect the winds and create what are called Rossby waves on Earth. This creates a low pressure system near the south pole in the western hemisphere and a high-pressure system in the eastern hemisphere, again near the south pole.

Giuranna found that the temperature of the low-pressure system is often below the condensation point for carbon dioxide, so the gas condenses and falls from the sky as snow and builds up on the ground as frost. In the high-pressure system, the conditions are never appropriate for snow, so only ground frost occurs. Thus, the south polar cap is built by two different mechanisms.

The areas that have extensive snow cover do not sublimate in the summer because they reflect more sunlight back into space than the surface frost. Frost grains tend to be larger than snow grains and have rougher surfaces. The ragged texture traps more sunlight, driving the sublimation.

So the western area of the southern polar cap, built of snow and frost, not only has a larger amount of carbon dioxide ice deposited but also sublimates more slowly during the summer, while the western area built of frost disappears completely. This explains why the residual cap is not symmetrically placed around the south pole.

“This has been a martian curiosity for many years,” says Giuranna. Thanks to Mars Express, planetary scientists now understand a new facet of this amazing, alien world.

Source: ESA

Posted on by Nancy Atkinson

Earth’s Precious Metals Could Be From Meteorites and Asteroids

Artist impression of the Asteroid Kleopatra. Credit: NASA

[/caption]

Meteorites and asteroids from the inner solar system could be responsible for Earth’s store of precious metals such as platinum and iridium, brought to our nascent planet during the period of Late Heavy Bombardment, about 4,000 million years ago. Dr. Gerhard Schmidt from the University of Mainz, Germany, has calculated that about 160 metallic asteroids of about 20 kilometers in diameter would be sufficient to provide the concentrations of these metals, known as Highly Siderophile Elements (HSE), found in the Earth’s crust. “A key issue for understanding the origin of planets is the knowledge of the abundances of HSE in the crust and mantle of the Earth, Mars and the Moon. We have found remarkably uniform abundance distributions of HSE in our samples of the Earth’s upper crust. A comparison of these HSE values with meteorites strongly suggests that they have a cosmo-chemical source,” said Schmidt.

Schmidt and his colleagues have spent the last 12 years analyzing the concentrations of HSE at meteorite impact sites around the world, as well as in the samples from the Earth’s mantle and crust. In addition, he has compared the data from the Earth with data from impact breccias from the Moon brought by the Apollo missions and Martian meteorites, believed to be samples from the mantle and crust on Mars.

As the Earth formed, the heavy elements, including HSE that were present, sank to form the iron and nickel-rich metallic core. HSE were added again later by meteorite impacts, creating a veneer of material over the Earth’s surface after the core had formed, about 20-30 million years after the planet’s accretion. This could have been by the collision with a Mars-sized impactor that led to the formation of the Moon.

However, Schmidt believes that the meteorites responsible for the HSE elements on Earth are iron or stony-iron meteorites that match up with theoretical predications of asteroids formed in the Mercury-Venus region of our solar system.

Different classes of meteorites have characteristic elemental ratios of HSE that give indications where in the Solar System they formed. Chondrites are stony meteorites that represent the pristine material from the early Solar System, and iron or stony-iron meteorites, which are fragments of larger asteroids that had enough internal heat in the past to form a molten metal core. These most likely would have formed in the inner solar system.

The ratios of HSE found in Earth’s crust bear a much closer resemblance to iron or stony-iron meteorites, and Schmidt believes these meteorites came from the inner solar system.

There’s a problem, however. Of the 175 known impact craters on Earth, remains of the projectiles have been found for about 40, and none of these meteorites have been identified as being formed in the region between Mercury and Venus.

Intriguingly, some of the Martian meteorites found in Antarctica, which are probably represent samples of the Martian crust also have HSE values that resemble groups of iron meteorites and stony irons, suggesting that a similar process took place on Mars.

Rock on Mars found by Opportunity rover, believed to be a meteorite. Credit: NASA/JPL
Rock on Mars found by Opportunity rover, believed to be a meteorite. Credit: NASA/JPL

Also, the first meteorite found on Mars by the Opportunity Mars Exploration Rover in 2005 was an iron
meteorite.

Dr. Schmidt presented his findings at the European Planetary Science Congress in Muenster on Monday, 22nd September.

Source: European Planetary Science Conference Press Release

Posted on by Nancy Atkinson

Gamma Ray Burst From the Edge of the Universe

Swift's Ultaviolet and optical telescope captured a far away gamma ray burst. Credit: NASA/Swift/Stefan Immler

[/caption]

NASA’s Swift satellite captured the most distant gamma-ray burst ever detected. The blast came from an exploding star 12.8 billion light-years away, near the edge of the visible universe. Swift saw the explosion on September 13 at 1:47 am EDT. But because light moves at finite speed, and looking farther into the universe means looking back in time, this means the burst occurred less than 825 million years after the universe began, or when the universe was less than one-seventh its present age. This star was probably from the earliest generations of stars ever formed. “This is the most amazing burst Swift has seen,” said the mission’s lead scientist Neil Gehrels at NASA’s Goddard Space Flight Center.

Gamma rays from the far-off explosion triggered Swift’s Burst Alert Telescope, and the spacecraft established the event’s location in the constellation Eridanus. It quickly turned to examine the spot, and less than two minutes after the alert, Swift’s X-Ray Telescope began observing the position. There, it found a fading, previously unknown X-ray source. The burst has been designated as GRB 080913.

Astronomers on the ground were alerted as well and a group using ESO’s 2.2 meter telescope at the LaSilla Observatory were able to make observations one minute after Swift started observing. An hour and a half later, the Very Large Telescope at Paranal, Chile, targeted the afterglow.

Astronomers look for the redshift of these objects to determine distance. The light that is emitted from an object is shifted towards the red, or less energetic end, of the electromagnetic spectrum, due to the Doppler Effect. In certain colors, the brightness of a distant object shows a characteristic drop caused by intervening gas clouds. The farther away the object is, the longer the wavelength where this fade-out begins.

Analysis of the spectrum for GRB 080913 established the blast’s redshift at 6.7 — among the most distant objects known.

Gamma-ray bursts are the universe’s most luminous explosions. Most occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, gas jets — driven by processes not fully understood — punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, which generates bright afterglows.

Source: NASA

Posted on by Nancy Atkinson

The Cepheids Aren’t Falling

Cepheid variable stars have been used for years as a way to determine distance to other galaxies. The correlation between their period of variability and absolute luminosity provides a cosmic yardstick to measure distances out to a few tens of millions of light-years. Additionally, Cepheids closer to home are used as tools to investigate how the Milky Way spins. But the motion of the Cepheids in our galaxy has confused astronomers, as these neighborhood Cepheids appear to fall towards the sun. A debate has raged for decades as to whether this phenomenon was truly related to the actual motion of the Cepheids and, consequently, to a complicated rotating pattern of our galaxy, or if it was the result of effects within the atmospheres of the Cepheids. But new observations with the HARPS (High Accuracy Radio Velocity Planet Searcher) spectograph shows that the Cepheids aren’t falling, and that the much debated, apparent ‘fall’ does in fact stem from properties of the atmospheres around these variable stars.

“The motion of Milky Way Cepheids is confusing and has led to disagreement among researchers,” says astrophysicist Nicolas Nardetto. “If the rotation of the Galaxy is taken into account, the Cepheids appear to ‘fall’ towards the Sun with a mean velocity of about 2 km/s.”

Nardetto and his colleagues observed eight Cepheids with the high precision HARPS spectrograph, attached to the 3.6-m ESO telescope at La Silla, 2400 m up in the mountains of the Chilean Atacama Desert. HARPS, or the High Accuracy Radial Velocity Planetary Searcher, is best known as a very successful planet hunter, but it can also be used to resolve other complicated cases, where its ability to determine radial velocities – the speed with which something is moving towards or away from us – with phenomenally high accuracy is invaluable. “Our observations show that this apparent motion towards us almost certainly stems from an intrinsic property of Cepheids,” says Nardetto.

The astronomers found that the deviations in the measured velocity of Cepheids were linked to the chemical elements in the atmospheres of the Cepheids considered. “This result, if generalized to all Cepheids, implies that the rotation of the Milky Way is simpler than previously thought, and is certainly symmetrical about an axis,” concludes Nardetto.

Source: ESO

Posted on by Nancy Atkinson

Two Shuttles on the Pad — The Last Time

It’s a rare event anyway, but this is the last time ever. Two shuttles are now sitting on NASA’s two launchpads at Kennedy Space Center. Space shuttle Endeavour completed a 4.2-mile journey to Launch Pad 39B Friday morning, Sept. 19, at 6:59 a.m. EDT, and this is the first time a shuttle has stood by as a rescue vehicle. Atlantis, over at Pad 39A is preparing for its mission to the Hubble Space Telescope, currently scheduled for Oct. 10 (although there might be an problem with that date –see below). Since Atlantis won’t be going to the International Space Station which would be a “safe haven” in the event of an emergency, Endeavour will stand by in the unlikely event a rescue mission is necessary. After Endeavour is cleared from its duty as a rescue vehicle, it will move to Launch Pad 39A for the upcoming STS-126 mission to the International Space Station. That flight is targeted for launch Nov. 12. This Saturday, there will be a good photo op as the Rotating Service Structures for Endeavour will be rolled back, making both the shuttles more visible. Robert Pearlman at CollectSPACE.com has a full list of the 17 times in history two shuttles sat on the launchpads, and some great pictures, too.

A small glitch occurred this week in preparing for the Hubble servicing mission. Trouble with a cleaning system connected to a canister housing fresh batteries and a new camera bound for the Hubble Space Telescope somehow blew insulation into protective bagging around the cargo carrier.. Work to inspect and clean the canister will delay its delivery to the shuttle Atlantis at launch pad 39A by at least 24 hours. While a corresponding launch delay is possible, NASA is sticking with its current Oct. 10 launch target until managers get a better sense of how much lost time can be made up.

And for those you that have questions as to why Endeavor will be moved to 39A, its because that pad is being prepared for being able to launch the Ares rockets for the upcoming Constellation program. It will work in a pinch to launch the shuttle, but NASA officials would much rather launch it from 39A to avoid any problems. And even if the shuttle program is extended in order to shorten the gap between the time the shuttle flights end and Constellation begins, shuttles will probably not launch from 39B again.

If you missed seeing Endeavour’s crawl out to the pade, video file of rollout will be available on NASA Television.

Posted on by Nancy Atkinson

Flyby Anomalies Explained?

Artist impression of the Rosetta flyby of Earth. Credit: ESA

[/caption]
Several different spacecraft have exhibited unexplained changes in speed during gravity assists when flying by Earth. First there was Galileo in 1990 and 1992, NEAR, which flew by Earth in January 1998, and then Cassini in August of 1999. Rosetta — the ESA spacecraft that recently flew by an asteroid – swung by the home planet in March 2005, followed by MESSENGER in August of the same year. All these probes showed an expected change in speed during the flyby. The largest anomaly was recorded for NEAR, whose velocity changed 13 millimeters per second more than it should have. Earlier this year, a group of JPL researchers that had been working on the problem for years basically threw up their hands, saying they hoped other physicists could come up with a solution. They had concluded the anomaly was too large to be explained by known effects related to Einstein’s general theory of relativity. But a new paper proposes that Special Relativity may explain everything.

The speed of the spacecraft is measured by the Doppler shift in radio signals from the spacecraft to the antennas of the Deep Space Network. In a very short and concise paper, (reading it is like watching Will Hunting solve the MIT professor’s equation), Jean Paul Mbelek from CEA-Saclay in France says that the relative motion of the spacecraft and the spinning Earth have not been properly accounted for. When a well known but overlooked effect of Special Relativity is taken into account, where the transverse Doppler effect of the Earth’s spin and the velocity of the craft are factored in, there is no flyby anomaly. “Thus, GR (General Relativity) does not need to be questioned and the flyby anomaly is merely due to an incomplete analysis using conventional physics,” says Mbelek.

flyby-anomaly. credit: arXiv blog
flyby-anomaly. credit: arXiv blog

Other explanations had proposed dark matter or “Unruh radiation” could be the answer. But Mbelek says we just haven’t been doing the physics right. He concludes that spacecraft “flybys of heavenly bodies may be viewed as a new test of Special Relativity which has proven to be successful near the Earth.” He proposes a follow-up of tracking the spacecraft trajectories beyond just the probes’ closest approach to Earth to test this hypothesis further.

Sources: arXiv, arXiv blog

Posted on by Nancy Atkinson

See Doomed Spacecraft Before Its Fiery Demise

ATV. credit: ESA

[/caption]

The Jules Verne Automated Transfer Vehicle (ATV) has done its duty – it even went above and beyond its expected capabilities. But the end is nigh, and soon, on September 29 the ATV will become a fireball and burn up in the Earth’s atmosphere, never to be seen again. But before it does, people in North America and Europe have the perfect opportunity to see it sail overhead this weekend in its low Earth orbit, and according to Spaceweather.com, the ATV will glow about a brightly as the North Star, Polaris. To find out when and where to look for the ATV in the evening or early morning skies, check out Spaceweather.com’s great satellite tracking webpage. Just plug in your zip code and you’ll be able to get tracking information for all the satellites that will be visible for the next few days. Also, Heavens Above is a great site to find tracking information, as well. So get out there and bid Jules Verne adieu. Here’s some of the great things the ATV accomplished while on orbit at the ISS, and a movie of its undocking too…


The Jules Verne spent five months docked to the space station where it delivered supplies (and fun things like a manuscript written by its namesake.) The supply ship turned into a tug boat when its engines were fired up to help the ISS avoid a piece of space junk. It also served as an impromptu bedroom for the space station crew.

When will the next ATV fly? Sometime in 2010, and the name for that ship has not yet been revealed. It will follow the debut of another space station cargo ship, Japan’s H-2A Transfer Vehicle, set for next year.

Here’s a movie of the Jules Verne undocking from the ISS.

Source: Spaceweather.com

Posted on by Nancy Atkinson

Star Blasting Water From Its Surroundings

A jet of gas firing out of a very young star can be seen ramming into a wall of material in this infrared Spitzer image. Image credit: NASA/JPL-Caltech/Harvard-Smithsonian CfA

[/caption]

The Spitzer Space Telescope has spied water in a cloud of gas and dust around a nascent star. That’s interesting in itself, but even more remarkable, the water is being blasted apart by the young star’s laser-like jets. Spitzer’s spectrometer was used to get a better look at these jets and analyze the jet’s molecules. To the astronomers’ surprise, Spitzer picked up the signature of rapidly spinning fragments of water molecules, called hydroxyl, or OH. “This is a truly unique observation that will provide important information about the chemistry occurring in planet-forming regions, and may give us insights into the chemical reactions that made water and even life possible in our own solar system,” said Achim Tappe, of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

A young star forms out of a thick, rotating cloud of gas and dust. Like the two ends of a spinning top, powerful jets of gas emerge from the top and bottom of the dusty cloud. As the cloud shrinks more and more under its own gravity, its star eventually ignites and the remaining dust and gas flatten into a pancake-like disk, from which planets will later form. By the time the star ignites and stops accumulating material from its cloud, the jets will have died out.

Tappe and his colleagues used Spitzer’s infrared eyes to cut through the dust surrounding the star, called HH 211-mm, to analyze the jets. The astronomers were surprised to see water molecules in the data. But the results showed the hydroxyl molecules have absorbed so much energy (through a process called excitation) that they are rotating around with energies equivalent to 28,000 Kelvin (27,700 degrees Celsius). This far exceeds normal expectations for gas streaming out of a stellar jet. Water, which is abbreviated H2O, is made up of two hydrogen atoms and one oxygen; hydroxyl, or OH, contains one oxygen and one hydrogen atom.

The results reveal that the jet is ramming its head into a wall of material, vaporizing ice right off the dust grains it normally coats. The jet is hitting the material so fast and hard that a shock wave is also being produced.

“The shock from colliding atoms and molecules generates ultraviolet radiation, which will break up water molecules, leaving extremely hot hydroxyl molecules,” said Tappe.

Tappe said this same process of ice being vaporized off dust occurs in our own solar system, when the sun vaporizes ice in approaching comets. In addition, the water that now coats our world is thought to have come from icy comets that vaporized as they rained down on a young Earth. This discovery provides a better understanding of how water — an essential ingredient for life as we know it — is processed in emerging solar systems.

Source: JPL

Posted on by Nancy Atkinson

Saturn’s Glowing Rings

Saturn's G ring straight on. Credit: NASA/JPL

[/caption]

The Cassini spacecraft recently flew through the plane of Saturn’s rings and took this straight-on image of the G ring, showing a bright arc of material seen here as it rounds the ring’s edge, or ansa. The spacecraft also took images of the moons Mimas and Calypso (see below). In the image here, the diffuse glow at left shows the extended nature of this faint ring. The view looks toward the sunlit side of the rings from less than a degree below the ringplane. The ring moved against the background stars during this exposure, creating the star trails seen here. Cassini scientists and engineers are preparing for an upcoming flyby of the moon Enceladus on October 9. This is the second of seven targeted Enceladus fly-bys in the Extended Mission., and the spacecraft will pass through the moon’s geyser-like plumes in an attempt to measure fields and particles.

Cassini spacecraft scientists think the bright arc in the G Ring contains relatively large, icy particles held in place by a gravitational an orbital resonance with the moon Mimas. Micrometeoroids collide with the large particles, releasing smaller, dust-sized particles that brighten the arc. The plasma in the giant planet’s magnetic field sweeps through this arc continually, dragging out the fine particles and creating the G ring. The ring arc orbits Saturn along the inner edge of the G ring. The image was taken with the Cassini spacecraft narrow-angle camera on Aug. 22, 2008, from about 1.2 million kilometers (740,000 miles) from Saturn.

Here’s the image of Mimas and the rings:
Mimas and Saturn's Rings. Credit: NASA/JPL

And one of Calypso, too:

Calypso and Saturn's Rings. Credit: NASA/JPL

Source: Cassini web page, Twitter

Posted on by Nancy Atkinson

Companion Dwarf Galaxy Almost Invisible

Segue 1 is 50 times dimmer than the star cluster pictured above but is 1000 times more massive, meaning most of its mass must be made up of dark matter. (Credit: Sloan Digital Sky Survey)

A team of astronomers has discovered the least luminous, most dark matter-filled galaxy known to exist. The Segue 1 galaxy is one of about two dozen small satellite galaxies orbiting our own Milky Way. This is a very faint galaxy, a billion times less bright than the Milky Way. But despite its small number of visible stars, Segue 1 is nearly a thousand times more massive than it appears, meaning most of its mass must come from dark matter. “Segue 1 is the most extreme example of a galaxy that contains only a few hundred stars, yet has a relatively large mass,” said Marla Geha, an assistant professor of astronomy at Yale and lead author on a paper about Segue 1.

Geha and her colleagues have observed about half of the dwarf satellite galaxies that orbit the Milky Way. These objects are so faint and contain so few stars that at first they were thought to be globular clusters – tightly bound star clusters that also orbit our host galaxy. But by analyzing the light coming from the objects using the Keck telescope in Hawaii, the researchers determined these objects are actually galaxies, but just very faint.

Looking only at the light emitted by these ultra-faint galaxies, Geha and her colleagues expected them to have correspondingly low masses. Instead, they discovered that they are between 100 and 1000 times more massive than they appear. Invisible dark matter, she said, must account for the difference.

Although dark matter doesn’t emit or absorb light, scientists can measure its gravitational effect on ordinary matter and believe it makes up about 85 percent of the total mass in the universe. Finding ultra-faint galaxies like Segue 1, which is so rife with dark matter, provides clues as to how galaxies form and evolve, especially at the smallest scales.

“These dwarf galaxies tell us a great deal about galaxy formation,” Geha said. “For example, different theories about how galaxies form predict different numbers of dwarf galaxies versus large galaxies. So just comparing numbers is significant.”

It’s only recently that astronomers have discovered just how prevalent these dwarf satellite galaxies are, thanks to projects like the Sloan Digital Sky Survey, which imaged large areas of the nighttime sky in greater detail than ever before. In the past two years alone, the number of known dwarf galaxies orbiting the Milky Way has doubled from the dozen or so brightest that were discovered during the first half of the twentieth century.

Geha predicts astronomers will find even more as they continue to sift through new data. “The galaxies I now consider bright used to be the least luminous ones we knew about,” she said. “It’s a totally new regime. This is a story that’s just unfolding.”

Source: Yale University