Posted on by Fraser Cain

Neutron Star With a Tail Like a Comet

Supernova remnant IC 443. Image credit: Chandra X-ray. Click to enlarge
This beautiful image shows the supernova remnant IC 443. The area in the box contains what looks like a tiny comet with a tail, but it’s actually a neutron star, moving quickly through the nebula. Neutron stars have been seen moving away from supernova remnants before, but in this case, it’s moving perpendicular. One possibility is that the former star was moving quickly through the galaxy before it exploded. The gas and dust in the nebula have slowed down and drifted away from the neutron star.

The pullout, also a composite with a Chandra X-ray close-up, shows a neutron star that is spewing out a comet-like wake of high-energy particles as it races through space.

Based on an analysis of the swept-back shape of the wake, astronomers deduced that the neutron star known as CXOU J061705.3+222127, or J0617 for short, is moving through the multimillion degree Celsius gas in the remnant. However, this conclusion poses a mystery.

Although there are other examples where neutron stars have been located far away from the center of the supernova remnant, these neutron stars appear to be moving radially away from the center of the remnant. In contrast, the wake of J0617 seems to indicate it is moving almost perpendicularly to that direction.

One possible explanation is that the doomed progenitor star was moving at a high speed before it exploded, so that the explosion site was not at the observed center of the supernova remnant. Fast-moving gusts of gas inside the supernova remnant may have further pushed the pulsar’s wake out of alignment. An analogous situation is observed for comets, where a wind of particles from the Sun pushes the comet tail away from the Sun, out of alignment with the comet’s motion.

If this is what is happening, then observations of the neutron star with Chandra in the next 10 years should show a detectable motion away from the center of the supernova remnant.

Original Source: Chandra X-ray Observatory

Posted on by Fraser Cain

Central Peaks of Zucchius Crater

Crater Zucchius captured by SMART-1. Image credit: ESA. Click to enlarge
This is a photograph of the central peaks of crater Zucchius, located on the Moon. ESA’s SMART-1 took the photo while it was about 753 kilometres (468 miles) above the surface of the Moon. The crater was formed in the Copernican era, a period that began 1.2 billion years ago. These central mountains are formed when a large object struck the Moon; the molten rocks splashed up and hardened into this shape.

This image, taken by the advanced Moon Imaging Experiment (AMIE) on board ESA’s SMART-1 spacecraft, shows the central peaks of crater Zucchius.

AMIE obtained this image on 14 January 2006 from a distance of about 753 kilometres from the surface, with a ground resolution of 68 metres per pixel.

The imaged area is centred at a latitude of 61.3 South and longitude 50.8 West. Zucchius is a prominent lunar impact crater located near the southwest limb. It has 66 kilometres diameter, but only its inside is visible in this image, as the AMIE field of view is 35 kilometres from this close-up distance.

Because of its location, the crater appears oblong-shaped due to foreshortening. It lies just to the south-southwest of Segner crater, and northeast of the much larger Bailly walled-plain. To the southeast is the Bettinus crater, a formation only slightly larger than Zucchius.

Zucchius formed in the Copernican era, a period in the lunar planetary history that goes from 1.2 thousand million years ago to present times. Another example of craters from this period are Copernicus (about 800 milion years old) and Tycho (100 million years old). Craters from the Copernican era show characteristic ejecta ray patterns – as craters age, ejecta rays darken due to weathering by the flowing solar wind.

The hills near the centre of the image are the so-called ‘central peaks’ of the crater, features that form in large craters on the Moon. The crater is formed by the impact of a small asteroid onto the lunar surface. The surface is molten and, similarly to when a drop of water falls into a full cup of coffee, the hit surface bounces back, it solidifies and then ‘freezes’ into the central peak.

The name of Zucchius crater is due to the Italian Mathematician and astronomer Niccolo Zucchi (1586-1670).

Original Source: ESA Portal

Posted on by Fraser Cain

Podcast: See the Universe with Gravity Eyes

In the past, astronomers could only see the sky in visible light, using their eyes as receptors. New technologies extended their vision into different spectra: infrared, ultraviolet, radio waves, x-rays and gamma rays. But what if you had gravity eyes? Einstein predicted that the most extreme objects and events in the Universe should generate gravity waves, and distort space around them. A new experiment called Laser Interferometer Gravitational Wave Observatory (or LIGO) could make the first detection of these gravity waves.
Continue reading “Podcast: See the Universe with Gravity Eyes”

Posted on by Fraser Cain

Science Team Determines Composition of Asteroid Itokawa

Asteroid Itokawa. Image credit: JAXA. Click to enlarge
Itokawa, a spud-shaped, near-Earth asteroid, consists mainly of the minerals olivine and pyroxene, a mineral composition similar to a class of stony meteorites that have pelted Earth in the past.

This asteroid ingredient list, published in Science, comes courtesy of Hayabusa, the spacecraft launched in 2003 by the Japanese Aerospace Exploration Agency (JAXA). The mission of Hayabusa is to bring back first-ever samples from an asteroid to better understand their role as building blocks of the solar system.

Itokawa, an elongated rocky object nearly as long as five football fields, circles the sun more than 321 million miles away from Earth. Along with a few hundred known asteroids, Itokawa’s orbit is close to Earth’s orbit and was discovered by the Lincoln Near-Earth Asteroid (LINEAR) program, which detects near-Earth asteroids and provides advance warning if any are bound for Earth. Itokawa doesn’t currently pose such a threat, but its close proximity made it a tempting scientific target.

A near-infrared spectrometer aboard Hayabusa helped identify Itokawa’s mineralogy, mostly a mixture of the rock-forming minerals olivine and pryroxene, and possibly some plagioclase and metallic iron. But to truly understand what they had, the team turned to Takahiro Hiroi, a Brown University researcher who is expert in determining the composition of asteroids and meteorites, bits of asteroids that have fallen to Earth.

Hiroi is a senior research associate in the Department of Geological Sciences at Brown and the operations manager of the University’s NASA-funded Reflectance Experiment Laboratory (RELAB). For the Hayabusa project, Hiroi obtained samples of meteorites from museums, measured them at RELAB, and compared these results with spectral data from Itokawa.

Hiroi was able to determine that the mineral composition of the surface of Itokawa was similar to that of LL chondrites, a common class of stony meteorites relatively low in metallic iron. This link helped the team place a probable source of origin for Itokawa: the inner portion of the main asteroid belt, a ring of tens of thousands of rocks orbiting the sun between Mars and Jupiter.

Using Hayabusa data, the team was also able to better describe the surface of Itokawa. Much of it is studded with boulders, although the asteroid contains a smoother area known as Muses Sea. This diversity of terrain, the team concludes, may be the result of past meteoroid impacts and space weathering, a rock-altering process due to bombardments by dust particles and solar wind.

“We’ve never had a close-up look at such a small asteroid until now,” Hiroi said. “Large asteroids such as Eros are completely covered with a thick regolith, a blanket of looser material created by space weathering. With Itokawa, we believe we have witnessed a developing stage of the formation of this regolith. And these boulders sitting on Itokawa are no different from the meteorites that have fallen on Earth. So we may be seeing an earlier stage of asteroid evolution, of a type that has touched this planet.”

NASA and JAXA funded the work.

Original Source: Brown University

Posted on by Fraser Cain

Titan Behind the Rings

Titan behind Saturn’s icy ring. Image credit: NASA/JPL/SSI Click to enlarge
Titan peeks from behind Saturns rings in this recent Cassini photograph. The dark Enke gap and narrow F-ring are visible. Cassini took this image on April 28, 2006 when it was approximately 1.8 million kilometers (1.1 million miles) from Titan.

Saturn’s largest moon, Titan, peaks out from under the planet’s rings of ice.

This view looks toward Titan (5,150 kilometers, or 3,200 miles across) from slightly beneath the ringplane. The dark Encke gap (325 kilometers, or 200 miles wide) is visible here, as is the narrow F ring.

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were taken with the Cassini spacecraft narrow-angle camera on April 28, 2006 at a distance of approximately 1.8 million kilometers (1.1 million miles) from Titan. Image scale is 11 kilometers (7 miles) per pixel on Titan.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Metal in Planets Depends on Their Stars

Correlation between the heavy elements in transiting planets and the metallicity of their parents. Image credit: A&A. Click to enlarge
Of the 188 extrasolar planets discovered, 10 are transits; we see them because they dim their parent star as they pass in front. This gives astronomers an opportunity to study the actual composition of these planets. European astronomers have discovered that the metal content of these “hot Jupiters” depends on the amount of metal in their parent star, which changes the size of their cores.

A team of European astronomers, led by T. Guillot (CNRS, Observatoire de la Cote d’Azur, France), will publish a new study of the physics of Pegasids (also known as hot Jupiters) in Astronomy & Astrophysics. They found that the amount of heavy elements in Pegasids is correlated to the metallicity of their parent stars. This is a first step in understanding the physical nature of the extrasolar planets.

Up to now, astronomers have discovered 188 extrasolar planets, among which 10 are known as “transiting planets”. These planets pass between their star and us at each orbit. Given the current technical limitations, the only transiting planets that can be detected are giant planets orbiting close to their parent star known as “hot Jupiters” or Pegasids. The ten transiting planets known thus far have masses between 110 and 430 Earth masses (for comparison, Jupiter, with 318 Earth masses, is the most massive planet in our Solar System).

Although rare, transiting planets are the key to understanding planetary formation because they are the only ones for which both the mass and radius can be determined. In principle, the obtained mean density can constrain their global composition. However, translating a mean density into a global composition needs accurate models of the internal structure and evolution of planets. The situation is made difficult by our relatively poor knowledge of the behaviour of matter at high pressures (the pressure in the interiors of giant planets is more than a million times the atmospheric pressure on Earth). Of the nine transiting planets known up to April 2006, only the least massive one could have its global composition determined satisfactorily. It was shown to possess a massive core of heavy elements, about 70 times the mass of the Earth, with a 40 Earth-mass envelope of hydrogen and helium. Of the remaining eight planets, six were found to be mostly made up of hydrogen and helium, like Jupiter and Saturn, but their core mass could not be determined. The last two were found to be too large to be explained by simple models.

Considering them as an ensemble for the first time, and accounting for the anomalously large planets, Tristan Guillot and his team found that the nine transiting planets have homogeneous properties, with a core mass ranging from 0 (no core, or a small one) up to 100 times the mass of the Earth, and a surrounding envelope of hydrogen and helium. Some of the Pegasids should therefore contain larger amounts of heavy elements than expected. When comparing the mass of heavy elements in the Pegasids to the metallicity of the parent stars, they also found a correlation to exist, with planets born around stars that are as metal-rich as our Sun and that have small cores, while planets orbiting stars that contain two to three times more metals have much larger cores. Their results will be published in Astronomy & Astrophysics.

Planet formation models have failed to predict the large amounts of heavy elements found this way in many planets, so these results imply that they need revising. The correlation between stellar and planetary composition has to be confirmed by further discoveries of transiting planets, but this work is a first step in studying the physical nature of extrasolar planets and their formation. It would explain why transiting planets are so hard to find, to start with. Because most Pegasids have relatively large cores, they are smaller than expected and more difficult to detect in transit in front of their stars. In any case, this is very promising for the CNES space mission COROT to be launched in October, which should discover and lead to characterization of tens of transiting planets, including smaller planets and planets orbiting too far from their star to be detected from the ground.

What of the tenth transiting planet? XO-1b was announced very recently and is also found to be an anomalously large planet orbiting a star of solar metallicity. Models imply that it has a very small core, so that this new discovery strengthens the proposed stellar-planetary metallicity correlation.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Aram Chaos on Mars

This false colour image, taken by ESA’s Mars Express spacecraft, shows the heavily eroded Aram Chaos region on Mars. The region is a 280-km (174-mile) wide circular structure located between two outflow channels. Scientists think that the eastern portion of the nearby Valles Marineris was responsible for torrents of ice and water that chopped up the landscape millions of years ago.

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, show Aram Chaos, 280-km-wide circular structure characterized by chaotic terrain.

The HRSC obtained these images during orbit 945 with a ground resolution of approximately 14 metres per pixel. The images show the region of Aram Chaos, at approximately 2 North and 340 East.

Aram Chaos is a 280-km-wide almost-circular structure located between the outflow channel Ares Vallis and Aureum Chaos. It is one of many regions located east of Valles Marineris and characterized by chaotic terrain.

As the name ‘chaos’ suggests, this terrain comprises large-scale remnant massifs, large relief masses that have been moved and weathered as a block. These are heavily eroded and dominate the circular morphology, or structure, which may have formed during an impact. As seen in the colour image, these remnant massifs range from a few kilometres to approximately ten kilometres wide and have a relative elevation of roughly 1000 metres.

The western region of the colour image is characterized by brighter material, which seems to be layered and could be the result of sedimentary deposition. Distinct layering, causing a terrace-like appearance, is also visible east of this brighter material and in the relatively flat region located in the northwest of the colour image.

***image4:left***Some scientists believe that the numerous chaotic regions located in the eastern part of Valles Marineris were the source of water or ice thought to have created the valleys that extend into Chryse Planitia. These regions are particularly interesting because they may yield clues to the relationship between Valles Marineris, the chaotic terrain, the valleys and the Chryse basin.

The colour scenes have been derived from the three HRSC-colour channels and the nadir channel. The perspective view has been calculated from the digital terrain model derived from the stereo channels. The anaglyph image was calculated from the nadir and one stereo channel.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Saturn’s Moon Enceladus Rolled Over

An illustration of the interior of Saturn’s moon Enceladus. Image credit: NASA. Click to enlarge
Saturn’s moon Enceladus has a strange hot spot at its southern pole; a region that should be one of its coldest places. Scientists think that warm material inside the moon created an instability. The moon eventually rolled over, repositioning the spot at its southern pole. Other bodies in the Solar System, such as Uranus’ moon Miranda, have probably undergone similar rolls in the past.

Saturn’s moon Enceladus – an active, icy world with an unusually warm south pole ? may have performed an unusual trick for a planetary body. New research shows Enceladus rolled over, literally, explaining why the moon’s hottest spot is at the south pole.

Enceladus recently grabbed scientists’ attention when the Cassini spacecraft observed icy jets and plumes indicating active geysers spewing from the tiny moon’s south polar region.

“The mystery we set out to explain was how the hot spot could end up at the pole if it didn’t start there,” said Francis Nimmo, assistant professor of Earth sciences, University of California, Santa Cruz.

The researchers propose the reorientation of the moon was driven by warm, low-density material rising to the surface from within Enceladus. A similar process may have happened on Uranus’ moon Miranda, they said. Their findings are in this week’s journal Nature.

“It’s astounding that Cassini found a region of current geological activity on an icy moon that we would expect to be frigidly cold, especially down at this moon’s equivalent of Antarctica,” said Robert Pappalardo, co-author and planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We think the moon rolled over to put a deeply seated warm, active area there.” Pappalardo worked on the study while at the University of Colorado.

Rotating bodies, including planets and moons, are stable if more of their mass is close to the equator. “Any redistribution of mass within the object can cause instability with respect to the axis of rotation. A reorientation will tend to position excess mass at the equator and areas of low density at the poles,” Nimmo said. This is precisely what happened to Enceladus.

Nimmo and Pappalardo calculated the effects of a low-density blob beneath the surface of Enceladus and showed it could cause the moon to roll over by up to 30-degrees and put the blob at the pole.

Pappalardo used an analogy to explain the Enceladus rollover. “A spinning bowling ball will tend to roll over to put its holes — the axis with the least mass — vertically along the spin axis. Similarly, Enceladus apparently rolled over to place the portion of the moon with the least mass along its vertical spin axis,” he said.

The rising blob (called a “diapir”) may be within either the icy shell or the underlying rocky core of Enceladus. In either case, as the material heats up it expands and becomes less dense, then rises toward the surface. This rising of warm, low-density material could also help explain the high heat and striking surface features, including the geysers and “tiger-stripe” region suggesting fault lines caused by tectonic stress.

Internal heating of Enceladus probably results from its eccentric orbit around Saturn. “Enceladus gets squeezed and stretched by tidal forces as it orbits Saturn, and that mechanical energy is transformed into heat energy in the moon’s interior,” added Nimmo.

Future Cassini observations of Enceladus may support this model. Meanwhile, scientists await the next Enceladus flyby in 2008 for more clues.

This research was supported by grants from NASA. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of Caltech, manages the mission for NASA’s Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images and information about the Cassini mission, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

Original Source: NASA News Release

Posted on by Fraser Cain

Astrophoto: NGC 4631 by Bernd Wallner

NGC 4631 by Bernd Wallner
People have populated the night sky with animals, mythical heroes, and scientific instruments by connecting the stars into constellations. Similar leaps of imagination have also led observers to give names to nebulas and galaxies based on their resemblance. Thus, M51 is called the Whirlpool Galaxy, M27 is named the Dumbbell Nebula and M57 is known as the Ring. NGC 4631 reminded someone of a Whale, complete with barnacles, and like a harpoon the name stuck to it.

NGC 4631 is an enormous spiral galaxy about the same size as the Milky Way but, by chance, it is turned to us so that we only see its edge. Vast veins of dark dust are visible crisscrossing its length. This matter is a fundamental ingredient to create future solar generations. Not surprisingly, the dark lanes are intermingled with the bright red and blue glows of young star clusters that have just left their nebula nests.

Slightly to the left of center is the golden tale-tale glow of this galaxy’s central region. It’s a side view that’s partially obscured by the front edge of spiral arms we see. Images from the Chandra X-Ray Observatory have shown that NGC 4631 has a halo of hot gases blown from clusters of massive stars in this area. The Milky Way has a similar halo, too.

NGC 4631 belongs to a group of galaxies that are approximately 25 million light years from Earth in the direction of the northern constellation Canes Venatici. The fourteen members of this gathering are located so close together that they interact with each other gravitationally. For example, the small oval shaped companion galaxy seen in this picture may have previously been much larger but lost matter to NGC 4631 as a price for approaching too close and being captured. Also, a slight warp, or curve, is noticeable in this galaxy’s profile. It is thought to be caused by the gravitational tug of other galaxies in this group. Even more noticeable is the effect this galaxy has on one of its neighbors, NGC 4656 (located close-by but outside this picture’s field of view). It is a galaxy so disturbed that it has been named the Hockey Stick.

Bernd Wallner took this beautiful picture of NGC 4631 over three late-April nights this year from his private observatory near Burghausen. Bavaia, Germany. Bernd used his 24-inch Cassegrain reflector telescope and an 11 mega-pixel camera to record 70 separate images that were digitally combined to form this eight and a half hour exposure.

Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.

Written by R. Jay GaBany

Posted on by Fraser Cain

The Ozone Layer’s Recovering

The Antarctic ozone hole. Image credit: NASA.
Over the last few decades, scientists have been tracking the depletion of the ozone layer in the Earth’s atmosphere. A large hole still opens up over Antarctica, but ozone levels worldwide have stopped declining. The question is why. The relatively recent reduction of ozone-destroying gasses shouldn’t make an improvement so quickly. NASA scientists think that atmospheric wind patterns could be transferring ozone around the planet, helping with the recovery. At this rate, we’ll return to 1980 levels between 2030 and 2070.

Think of the ozone layer as Earth’s sunglasses, protecting life on the surface from the harmful glare of the sun’s strongest ultraviolet rays, which can cause skin cancer and other maladies.

People were understandably alarmed, then, in the 1980s when scientists noticed that manmade chemicals in the atmosphere were destroying this layer. Governments quickly enacted an international treaty, called the Montreal Protocol, to ban ozone-destroying gases such as CFCs then found in aerosol cans and air conditioners.

Today, almost 20 years later, reports continue of large ozone holes opening over Antarctica, allowing dangerous UV rays through to Earth’s surface. Indeed, the 2005 ozone hole was one of the biggest ever, spanning 24 million sq km in area, nearly the size of North America.

Listening to this news, you might suppose that little progress has been made. You’d be wrong.

While the ozone hole over Antarctica continues to open wide, the ozone layer around the rest of the planet seems to be on the mend. For the last 9 years, worldwide ozone has remained roughly constant, halting the decline first noticed in the 1980s.

The question is why? Is the Montreal Protocol responsible? Or is some other process at work?

It’s a complicated question. CFCs are not the only things that can influence the ozone layer; sunspots, volcanoes and weather also play a role. Ultraviolet rays from sunspots boost the ozone layer, while sulfurous gases emitted by some volcanoes can weaken it. Cold air in the stratosphere can either weaken or boost the ozone layer, depending on altitude and latitude. These processes and others are laid out in a review just published in the May 4th issue of Nature: “The search for signs of recovery of the ozone layer” by Elizabeth Westhead and Signe Andersen.

Sorting out cause and effect is difficult, but a group of NASA and university researchers may have made some headway. Their new study, entitled “Attribution of recovery in lower-stratospheric ozone,” was just accepted for publication in the Journal of Geophysical Research. It concludes that about half of the recent trend is due to CFC reductions.

Lead author Eun-Su Yang of the Georgia Institute of Technology explains: “We measured ozone concentrations at different altitudes using satellites, balloons and instruments on the ground. Then we compared our measurements with computer predictions of ozone recovery, [calculated from real, measured reductions in CFCs].” Their calculations took into account the known behavior of the sunspot cycle (which peaked in 2001), seasonal changes in the ozone layer, and Quasi-Biennial Oscillations, a type of stratospheric wind pattern known to affect ozone.

What they found is both good news and a puzzle.

The good news: In the upper stratosphere (above roughly 18 km), ozone recovery can be explained almost entirely by CFC reductions. “Up there, the Montreal Protocol seems to be working,” says co-author Mike Newchurch of the Global Hydrology and Climate Center in Huntsville, Alabama.

The puzzle: In the lower stratosphere (between 10 and 18 km) ozone has recovered even better than changes in CFCs alone would predict. Something else must be affecting the trend at these lower altitudes.

The “something else” could be atmospheric wind patterns. “Winds carry ozone from the equator where it is made to higher latitudes where it is destroyed. Changing wind patterns affect the balance of ozone and could be boosting the recovery below 18 km,” says Newchurch. This explanation seems to offer the best fit to the computer model of Yang et al. The jury is still out, however; other sources of natural or manmade variability may yet prove to be the cause of the lower-stratosphere’s bonus ozone.

Whatever the explanation, if the trend continues, the global ozone layer should be restored to 1980 levels sometime between 2030 and 2070. By then even the Antarctic ozone hole might close–for good.

Original Source: NASA News Release