Posted on by Fraser Cain

What’s Up This Week – April 10 – April 17, 2006

Class I Flamsteed. Image credit: Ricardo Borba. Click to enlarge.
Greetings, fellow SkyWatchers! This week will be filled with meteor showers and moon shine – bright nebula and galaxies. The “Ring King” Saturn is now at its best, so get out under the stars, because…

Here’s what’s up!

Monday, April 10 – Be sure to get up before dawn to enjoy the Virginid meteor shower. The radiant point will be near Gamma in the bowl of Virgo. The fall rate of 20 per hour is above average for meteor showers, and with the Moon out of the equation this morning, you’re in for a treat!

Tonight we’ll start by identifying the large mare just south of central on the lunar disc called Oceanus Procellarum. Look almost centrally within its grey expanse for a large crater which has mostly melted down. This “ghost crater” has no name, but look along its edge for Class I Flamsteed. It is very near here that Surveyor 1 still stands. It made its landing on June 2, 1966 and sent back more than 11,000 pictures of the rock strewn, desert-like floor. This area was one of the first chosen for an Apollo mission landing, but was later scratched for a more central location.

Now let’s move on to 3.2 magnitude Mebsuta – Epsilon Geminorum. Mebsuta is the brightest star (other than Castor) in northwestern Gemini. It has a very distant 9th magnitude companion. As you observe Epsilon, keep in mind its spectral class (G8) is very similar to our Sun. Despite this, Mebsuta glows with an intensity of light 7600 times brighter. It’s one of a rare class of stars called “yellow supergiants” – stars whose nuclear cores are vastly swollen due to advanced age and which have taken on “planetary” proportions. Why planetary? Because the planet Venus would find itself orbiting inside Mebsuta’s 4600 degree C temperature photosphere!

Tuesday, April 11 – Today is the birthday of William Wallace Campbell. Born in 1862, Campbell went on to become the leader of stellar motion and radial velocity studies. He was the director of Lick Observatory from 1901 to 1930, and also served as president of the University of California and the National Academy of Sciences. Also born on this day – but in 1901 – was Donald H. Menzel – assistant astronomer at Lick Observatory. Menzel became Director of Harvard Observatory, an expert on the Sun’s coronosphere and held a genuine belief in the extraterrestrial nature of UFOs. Today in 1960, the first radio search for extraterrestrial civilizations was started by Frank Drake (Project Ozma). In 1986, Halley’s Comet closed within 65 million kilometers of the Earth ? as close as it would get.

If you would like to try out a pair of less obvious lunar features, start out again tonight at Oceanus Procellarum – a vast, grey “sea” encompassing most of the northwestern portion of the Moon. On the terminator to its southwest (and almost due west geographically), you will see two craters nearly identical in size and depth. The southern crater is Billy – one of the darkest floored areas on the Moon. Inside Billy’s bright rim, you will notice an interior as featureless as a mare. North of Billy is Hansteen, whose interior is much brighter and shows complex details. Comparing the two will show Billy was once filled with smooth lava, while Hansteen avoided that fate and shows its native scarred interior.

Although skies will be bright this evening, we can still have a look at brilliant Arcturus – a star whose distance from the Earth (10 parsecs) and radial velocity (less than 200 meters per second) can almost be considered a benchmark. By skydark you will see 0.2 magnitude Arcturus – the brightest star in Bootes and 4th brightest star in the night sky – some 30 degrees above the eastern horizon. Apparent to the eye is Arcturus’ orange color. Because a star’s intrinsic luminosity relates to its apparent brightness and distance, Arcturus’ absolute magnitude is almost precisely the same as its apparent magnitude. Just because Arcturus’ radial velocity is nearly zero doesn’t mean it isn’t on the move relative to our Sun. Arcturus star is now almost as close as it will ever get and its large proper motion – perpendicular to our line of sight – exceeds 125 kilometers per second. Every 100 years Arcturus moves almost 1 degree across the sky!

Wednesday, April 12 – Today in 1961, Yuri Gagarin made one full orbit of the Earth aboard Vostok 1, while also becoming the first human in space. Also today (in 1981) Columbia became the first Space Shuttle to launch.

Tonight let’s launch our lunar explorations as we head for the far north for an “on the edge” feature – Pythagoras. Named for the Greek philosopher and mathematician, you will see this smooth, walled plain as a thin, bright ellipse standing out well against the background of northern Sinus Iridum. Pythagoras is one of the deepest craters in the northern quadrant and would be even more spectacular if visible from overhead – rather than at an angle. Look for its tall and prominent central peak.

Although the Moon will interfere with most studies, we can still check out Iota Cancri – a fine wide disparate double of magnitudes 4.0 and 6.6 separated by some 30 arc seconds. This true binary is so distant from one another that they take over 60,000 years to complete a single orbit around their common center of gravity! Located slightly less than a fist’s width due north of M44, this pair is about 300 light years distant. Both stars shine with a light considerably brighter than our Sun and observers may note a subtle gold and pale blue color contrast between them.

Thursday, April 13 – Tonight’s Full Moon is often referred to as the “Pink Moon” of April. As strange as the name may sound, it actually comes from the herb moss pink- or wild ground phlox. April is the time of blossoming and the “pink” is one of the earliest widespread flowers of the spring season. As you might expect, this Full Moon is also known by other names as well. How about the “Full Sprouting Grass Moon,” the “Egg Moon,” or the coastal tribe based “Full Fish Moon” as we’ve entered the season when fish swim upstream to spawn.

Tonight let’s take a journey towards the 25th brightest star in the night sky – 1.3 magnitude Regulus. Regulus, known as “The Little King,” is the brightest star in Leo. At 77 light-years away, this star is considered a “dwarf” despite shining with a visible light almost 150 times that of Sol. The orange-red giant Arcturus and the blue white “dwarf” Regulus both share a common absolute magnitude very close to 0. The reason the two stars shine with a similar intrinsic brightness – despite widely different physical sizes – is Regulus’ photosphere is more than twice as hot (12,000 C) as Arcturus. While observing Regulus, look for a distant companion of magnitude 8.5. Normally low powers would best concentrate the companion’s light, but try a variety of magnifications to help improve contrast. For those with large aperture scopes, look for a 13.1 magnitude “companion’s companion” a little more than 2 arc seconds away!

Friday, April 14 – Today is the birthday of Christian Huygens. Born in 1629, the Dutch scientist went on to become one of the leaders in his field during the 17th century. Among his achievements were promoting the wave theory of light, patenting the pendulum clock, and improving the optics of telescopes by inventing a new type eyepiece and reducing false color through increasing the focal length of refractor telescopes. Huygens was the first to discover Saturn’s rings and largest satellite – Titan. Of the rings, Huygens said, “Saturn: encircled by a ring, thin and flat, nowhere touching, and inclined to the ecliptic.”

To honor Huygen’s achievements and get a sense just how “on the edge” his observations were at the time, consider the fact Huygens used a home built instrument of 12 foot (336.7) focal length and little more than 2 inches in aperture (57mm). Tonight, why not have a low power look at Saturn using your smallest scope. At what magnification does it become clear to you that the planet has “lost its ears” and gained a ring?

Saturday, April 15 – Tonight keep a watch for the “April Fireballs.” This unusual name has been given to what may be a branch of the complex Virginid stream which began earlier in the week. The absolute radiant of the stream is unclear, but most of its long tails will point back toward southeastern skies. These bright bolides can possibly arrive in a flurry – depending on how much Jupiter’s gravity has perturbed the meteoroid stream. Even if you only see one tonight, keep a watch in the days ahead. The time for “April Fireballs” lasts for two weeks. Just seeing one of these brilliant streaks will put a smile on your face!

While thinking of Jupiter, why not search for the planet’s ghost? The “Ghost of Jupiter” sits after skydark in the constellation Hydra. Start at Alpha Hydrae and head east about a fist’s width to find Lambda within a field of nearby fainter stars. Continue less than a fist southeast and locate Mu. You’ll find the “Ghost of Jupiter” (NGC 3242) lurking in the dark less than a finger-width due south. At magnitude 9, the NGC 3242 gives a strikingly blue-green appearance in even small scopes – despite being more than 1500 light years away.

Before we call it a night, let’s visit with Luna as we look along the southern shore of Mare Humorum and identify ancient crater Vitello. Notice how this delicate ring resembles earlier study Gassendi on the opposite shore.

Sunday, April 16 – With the later rise of the Moon, this is a fine opportunity to have a look at a group of galaxies between Leo’s paws. Start at Regulus and look due east toward Iota Leonis. Halfway between the two (less than a fist from Regulus) and two finger-widths northeast of Rho Leonis, you’ll encounter Messier Galaxies M95 and M96 – both within the same low power field of view. At magnitude 9.2, the brighter – and slightly rounder – M96 lies northeast of 9.7 magnitude M95. Pierre M?chain discovered both galaxies on March 20, 1781 and Messier added them to his catalog 4 days later. These two galaxies are two of the brightest members of the Leo I galaxy group located some 38 million light-years away.

To see another Messier member of the Leo I group, center on M96 and shift the galaxy south. From the north side of the low power field, the 9.3 magnitude galaxy M105, nearby 10th magnitude NGC 3384, and 12th magnitude NGC 3389 will come into view. M105 was discovered by M?chain on the night Messier catalogued M95 and 96 but was not formally added to Messier’s catalog. Based on M?chain’s observing notes, Helen Sawyer Hogg added it to Messier’s list in 1947 – along with galaxy M106 and globular cluster M107. M?chain failed to notice M105’s bright neighboring galaxy – NGC 3384. NGC 3384 is actually slightly brighter than the faintest Messier discovered – M91.

We’re not done yet! If you center on M105 and shift due north less than a degree and a half you will encounter 10th magnitude NGC 3377 – a small elongated galaxy with a stellar core. There are a dozen galaxies visible to moderate amateur instruments (through magnitude 12) in the Leo I region of the sky!

If you are out late enough to study the Moon, relocate previous study Petavius on the southern terminator. Just beyond its east wall, look for a bright ridge that extends from north to south separated by darkness from Petavius. This is Palitzsch, a very strange, gorge-like formation that looks as if it was caused by a meteor plowing through the Moon’s surface. Palitzsch’s true nature wasn’t known until 1954 when Patrick Moore resolved it as a “crater chain” using the 25″ Newall refractor at Cambridge University Observatory.

May all your journeys be at light speed… ~Tammy Plotner with Jeff Barbour.

Posted on by Fraser Cain

New Spacecraft Will Search for Lunar Ice

An artist’s conception of LRO on its way to the moon. Image credit: NASA Click to enlarge
NASA announced a new spacecraft today that will search for ice at the Moon’s southern pole: the Lunar CRater Observation and Sensing Satellite (LCROSS). The spacecraft will launch as a secondary payload with the Lunar Reconnaissance Orbiter in 2008. As it approaches the Moon, LCROSS will split into two spacecraft. The first will smash into the Moon’s south pole, and the second will fly through the resulting plume, analyzing it for traces of water. This mission will be developed on a shoestring; NASA has allocated a total of $80 million for its development.

NASA today announced that a small, ‘secondary payload’ spacecraft, to be developed by a team at NASA Ames Research Center, Moffett Field, Calif., has been selected to travel to the moon to look for precious water ice at the lunar south pole in October 2008.

The smaller secondary payload spacecraft will travel with the Lunar Reconnaissance Orbiter (LRO) satellite to the moon on the same rocket, the Evolved Expendable Launch Vehicle (EELV), to be launched from Kennedy Space Center, Florida. The NASA Ames team proposed the secondary payload mission, which will be carried out by the Lunar CRater Observation and Sensing Satellite (LCROSS).

“The LCROSS mission gives the agency an excellent opportunity to answer the question about water ice on the moon,” said Daniel Andrews of NASA Ames, whose team proposed the LCROSS mission. “We think we have assembled a very creative, highly innovative mission, turning the upper stage of the rocket that brought us to the moon into a substantial impactor on the moon.”

After launch, the secondary payload LCROSS spacecraft will arrive in the lunar vicinity independent of the LRO satellite. On the way to the moon, the LCROSS spacecraft’s two main parts, the Shepherding Spacecraft (S-S/C) and the Earth Departure Upper Stage (EDUS), will remain coupled.

As the spacecraft approaches the moon’s south pole, the upper stage will separate, and then will impact a crater in the south pole area. A plume from the upper stage crash will develop as the Shepherding Spacecraft heads in toward the moon. The Shepherding Spacecraft will fly through the plume, and instruments on the spacecraft will analyze the cloud to look for signs of water and other compounds. Additional space and Earth-based instruments also will study the 2.2-million-pound (1000-metric-ton) plume.

“The LCROSS mission will help us determine if there is water hidden in the permanently dark craters of the moon’s south pole,” said Marvin (Chris) Christensen, Robotic Lunar Exploration Program (RLEP) manager, and acting director of NASA Ames. “If we find substantial amounts of water ice there, it could be used by astronauts who later visit the moon to make rocket fuel,” Christensen added.

Earlier, NASA had requested proposals internally from its NASA field centers for existing or reasonably matured concepts for secondary payloads that would offer cost-effective contributions to RLEP.

To prepare for the return of astronauts to the moon, NASA will conduct various RLEP robotic missions from 2008 to potentially 2016 to study, to map and to learn about the lunar surface. These early missions will help determine lunar landing sites and whether resources, such as oxygen, hydrogen and metals, are available for use in NASA’s long-term lunar exploration objectives.

“Establishing research stations on the moon will give us the experience and capabilities to extend to Mars and beyond,” noted robotics deputy program manager Butler Hine of Ames.

“An exploration science program with a sustained human presence on the moon gives us the opportunity to conduct fundamental science in lunar geology, history of the solar system, physics and the biological response to partial (Earth) gravity,” said Christopher McKay, lunar exploration program scientist at Ames.

The space agency specified that the winning proposal must demonstrate an affordable concept beneficial to RLEP, according to the document that asked NASA centers to submit suggestions for the secondary payload. NASA noted that the secondary payload mission should cost no more than $80 million. NASA also required that the payload mass not exceed 2,205 pounds (1,000 kilograms).

NASA encouraged its field centers to team with industry to develop proposals. On Jan. 10, NASA issued a request for information to industry to allow businesses to provide secondary payload concepts to NASA. Each NASA center reviewed ideas from industry as well as secondary payload concepts developed internally.

NASA asked that the concepts advance the Vision for Space Exploration to include missions that evolve lunar science, characterize the lunar environment and support identification sites for future human missions as well as the utility of those sites.

The space agency said that it was looking for missions that demonstrate technology that could enhance future exploration, that show operational schemes to support exploration, that develop or emplace infrastructure in support of exploration, that advance commercial opportunities and those missions that would collect engineering data to support the Constellation program. That program is developing NASA’s new spaceship, the Crew Exploration Vehicle.

For images related to the LCROSS mission, please visit:
http://www.nasa.gov/centers/ames/multimedia/images/2006/lunarorbiter.html

For additional high-resolution images of the and historic information, please visit:
http://www.nasa.gov/centers/ames/news/releases/2004/moon/moon.html

http://lunar.arc.nasa.gov/

http://nssdc.gsfc.nasa.gov/planetary/lunarprosp.html

http://science.nasa.gov/newhome/headlines/ast31jul99_1.htm

Original Source: NASA News Release

Posted on by Fraser Cain

Astrophoto: Leo 1 by Bernhard Hubl

Leo 1 by Bernhard Hubl
Astronomers are beginning to see a pattern in what was previously viewed as the random distribution of galaxies tossed across the universe. Emerging is an understanding that the galaxies are distributed on the surface of huge bubbles whose interiors are void or contain material yet to be discovered. These bubbles are of various sizes but, in general, there are lots of them thus a helpful mental image of the universe’s organization may be something similar in appearance to soap suds. Where the edges of these bubbles meet, groups of galaxies tend to collect in bunches and this agrees with the observational evidence.

Our home Galaxy is called the Milky Way because the ancient Greeks rationalized its broad band of light arcing across the night sky was milk from the breast of the Queen of Gods, Hera. The Milky Way galaxy and thirty or more others which include M31, its two large satellites and M33 comprise what’s known as the Local Group. The Local Group of galaxies, in turn, interacts with four other nearby galaxy concentrations and it is thought that each of these clusters probably exchange members over some regular, but enormous, time scale.

Some of the members of the Local Group are actually satellites of our galaxy. Almost all of them are called dwarfs due to their small size and irregular shape. So far, twelve, maybe thirteen, have been identified, including the Large and Small Magellanic Clouds – more will likely be discovered. One of the most distant of these attendants, pictured here, is located about 900,000 light years from Earth and is called Leo 1.

Leo 1 was unknown until 1950 and was only visible through long exposure photographs until it was finally visually observed around 1990. The challenge with seeing or photgraphing this galaxy has less to do with its brightness than with the fact that it appears extremely close to the brightest star in the constellation Leo, which is called Regulus. Regulus is thousands of times more brilliant and the glare seen in optical instruments can wash out the presence of this small galaxy.

This remarkable photograph was produced by astronomer, Bernhard Hubl, at his imaging site in Schlierbach, Austria over a period of three nights during mid-March, 2006. This picture required over eight hours of exposure and was produced through a four inch aperture refractor with a 2 mega-pixel astronomical camera.

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

Star Explodes Inside Another Star

Artist’s impression of the explosion of RS Ophiuchi. Image credit: David A. Hardy. Click to enlarge
Astronomers recently noticed that the normally dim star RS Ophiuchi had brightened enough to be visible without a telescope. This white dwarf star has brightened like this 5 times in the last 100 years, and astronomers believe it’s about to collapse into a neutron star. RS Ophiuchi is in a binary system with a much larger red giant star. The two stars are so close that the white dwarf is actually inside the envelope of the red giant, and explodes from within it every 20 years or so.

On 12 February 2006, amateur astronomers reported that a faint star in the constellation of Ophiuchus had suddenly become clearly visible in the night sky without the aid of a telescope. Records show that this so-called recurrent nova, RS Ophiuchi (RS Oph), has previously reached this level of brightness five times in the last 108 years, most recently in 1985. The latest explosion has been observed in unprecedented detail by an armada of space- and ground-based telescopes.

Speaking today (Friday) at the RAS National Astronomy Meeting at Leicester, Professor Mike Bode of Liverpool John Moores University and Dr Tim O’Brien of Jodrell Bank Observatory will present the latest results which are shedding new light on what happens when stars explode.

RS Oph is just over 5,000 light years away from Earth. It consists of a white dwarf star (the super-dense core of a star, about the size of the Earth, that has reached the end of its main hydrogen-burning phase of evolution and shed its outer layers) in close orbit with a much larger red giant star.

The two stars are so close together that hydrogen-rich gas from the outer layers of the red giant is continuously pulled onto the dwarf by its high gravity. After around 20 years, enough gas has been accreted that a runaway thermonuclear explosion occurs on the white dwarf’s surface. In less than a day, its energy output increases to over 100,000 times that of the Sun, and the accreted gas (several times the mass of the Earth) is ejected into space at speeds of several thousand km per second.

Five explosions such as this per century can only be explained if the white dwarf is near the maximum mass it could have without collapsing to become an even denser neutron star.

What is also very unusual in RS Oph is that the red giant is losing enormous amounts of gas in a wind that envelops the whole system. As a result, the explosion on the white dwarf occurs “inside” its companion’s extended atmosphere and the ejected gas then slams into it at very high speed.

Within hours of notification of the latest outburst of RS Oph being relayed to the international astronomical community, telescopes both on the ground and in space swung into action. Among these is NASA’s Swift satellite which, as its name suggests, can be used to react rapidly to things that change in the sky. Included in its armoury of instruments is an X-ray Telescope (XRT), designed and built by the University of Leicester.

“We realised from the few X-ray measurements taken late in the 1985 outburst that this was an important part of the spectrum in which to observe RS Oph as soon as possible,” said Professor Mike Bode of Liverpool John Moores University, who led the observing campaign for the 1985 outburst and now heads the Swift follow-up team on the current explosion.

“The expectation was that shocks would be set up both in the ejected material and in the red giant’s wind, with temperatures initially of up to around 100 million degrees Celsius – nearly 10 times that in the core of the Sun. We have not been disappointed!”

The first observations by Swift, only three days after the outburst began, revealed a very bright X-ray source. Over the initial few weeks, it became even brighter and then began to fade, with the spectrum suggesting that the gas was cooling down, although still at a temperature of tens of millions of degrees. This was exactly what was expected as the shock pushed into the red giant’s wind and slowed down. Then something remarkable and unexpected happened to the X-ray emission.

“About a month after the outburst, the X-ray brightness of RS Oph increased very dramatically,” explained Dr. Julian Osborne of the University of Leicester. “This was presumably because the hot white dwarf, which is still burning nuclear fuel, then became visible through the red giant’s wind.

“This new X-ray flux was extremely variable, and we were able to see pulsations which repeat every 35 seconds or so. Although it is very early days, and data are still being taken, one possibility for the variability is that this is due to instability in the nuclear burning rate on the white dwarf.”

Meanwhile, observatories working at other wavelengths changed their programmes to observe the event. Dr. Tim O’Brien of Jodrell Bank Observatory, who did his PhD thesis work on the 1985 explosion, and Dr. Stewart Eyres of the University of Central Lancashire, lead the team that is securing the most detailed radio observations to date of such an event.

“In 1985, we were not able to begin observing RS Oph until nearly three weeks after the outburst, and then with facilities that were far less capable than those available to us today,” said Dr. O’Brien.

“Both the radio and X-ray observations from the last outburst gave us tantalising glimpses of what was happening as the outburst evolved. In addition, this time, we have developed very much more advanced computer models. The combination of the two now will undoubtedly lead to a greater understanding of the circumstances and consequences of the explosion.

“In 2006, our first observations with the UK’s MERLIN system were made only four days after the outburst and showed the radio emission to be much brighter than expected,” added Dr. Eyres. “Since then it has brightened, faded, then brightened again. With radio telescopes in Europe, North America and Asia now monitoring the event very closely, this is our best chance yet of understanding what is truly going on.”

Optical observations are also being obtained by many observatories around the globe, including the robotic Liverpool Telescope on La Palma. Observations are also being conducted at the longer wavelengths of the infrared part of the spectrum.

“For the first time we are able to see the effects of the explosion and its aftermath at infrared wavelengths from space, with NASA’s Spitzer Space Telescope,” said Professor Nye Evans of Keele University, who heads the infrared follow-up team.

“Meanwhile, the observations we have already obtained from the ground, from the United Kingdom Infrared Telescope on the summit of Mauna Kea in Hawaii, already far surpass the data we had during the 1985 eruption.

“The shocked red giant wind and the material ejected in the explosion give rise to emission not only at X-ray, optical and radio wavelengths, but also in the infrared, via coronal lines (so-called because they are prominent in the Sun’s very hot corona). These will be crucial in determining the abundances of the elements in the material ejected in the explosion and in confirming the temperature of the hot gas.”

26 February 2006 was a highlight of the observational campaign. In what must surely be a unique event, four space satellites, plus radio observatories around the globe, observed RS Oph on the same day.

“This star could not have exploded at a better time for international ground and space based studies of an event which has been changing every time we look at it,” said Professor Sumner Starrfield of Arizona State University, who heads the U.S. side of the collaboration. “We are all very excited and exchanging many emails every day trying to understand what is happening on that day and then predict the behaviour on the next.”

What is apparent is that RS Oph is behaving like a “Type II” supernova remnant. Type II supernovae represent the catastrophic death of a star at least 8 times the mass of the Sun. They also eject very high velocity material which interacts with their surroundings. However, the full evolution of a supernova remnant takes tens of thousands of years. In RS Oph, this evolution is literally occurring before our eyes, around 100,000 times faster.

“In the 2006 outburst of RS Oph, we have a unique opportunity of understanding much more fully such things as runaway thermonuclear explosions and the end-points of the evolution of stars,” said Professor Bode.

“With the observational tools now at our disposal, our efforts 21 years ago look rather primitive by comparison.”

Original Source: RAS News Release

Posted on by Fraser Cain

Swirling Feature on the Moon

Reiner Gamma Formation. Image credit: ESA/Space-X. Click to enlarge
This image was taken by ESA’s SMART-1 spacecraft, and shows a bright feature on the surface of the Moon called the Reiner Gamma Formation. This is a bright spot on the Moon which is totally flat, and surrounded by much darker “mare”. Ground observations originally misidentified it as a crater, but when US and Russian spacecraft visited the Moon, they revealed this strange swirling morphology.

These images taken by the Advanced Moon Imaging Experiment (AMIE) on board ESA’s SMART-1 spacecraft, shows a feature characterised by bright albedo, and called Reiner Gamma Formation.

The Reiner Gamma Formation, a totally flat area consisting of much brighter material than the surrounding dark ‘mare’, is centred on an area located at 57.8 degrees West, 8.1 degrees North, in the Oceanus Procellarum on the near (visible) side of the Moon, and has an extension of approximately 30 by 60 kilometres.

The AMIE camera obtained the images on 14 January 2006, from a distance between 1599 and 1688 kilometres and with a ground resolution between 144 and 153 metres per pixel.

From early ground-based observations, this feature was initially misidentified as a crater. Only later detailed observations from orbit (such as those performed by USSR’s Zond-6, and NASA’s Lunar Orbiter, Apollo and Clementine missions) revealed its true nature: a very unusual morphology, consisting of swirl-like patterns that do not correspond to any topographic features.

Its main part consists of a bright pattern of elliptical shape, located to the west of Reiner crater. Bright elongated patches extend to the northeast in the Marius Hills region and small swirls extend to the southwest. The origin of the Reiner Gamma Formation and other swirls occurring on the lunar surface is still unclear.

Lunar swirls are associated with magnetic anomalies and some of these swirls – such as Mare Ingenii and Mare Marginis – are ‘antipodal’ to large impact structures (that is they are located right into opposite regions of the Moon globe).

So, it was suggested that the Reiner Gamma swirls correspond to magnetised materials in the crust or iron-rich ejecta materials able to deflect the solar wind (constant flow of charged particles coming from the Sun). This would prevent surface materials to undergo maturation processes, and so produce an optical anomaly.

However, Reiner Gamma Formation still stands as a particular case. In fact, the magnetic anomaly does not correlate with the scale of the lunar crust structure and large-scale anomalies seen on the far side. Furthermore, the anomaly is not associated with any obvious antipodal basin structure, and the surface material related to Reiner Gamma appears optically very immature (the age for its emplacement could be quite recent).

The analysis of NASA’s Clementine imaging data showed that the optical and spectroscopic properties of the local regolithic surface layer are close to those of immature mare crater-like soils. This is consistent with the properties of a shallow subsurface mare soil layer.

Considerations from works on impact cratering support the hypothesis that the uppermost part of the regolith could have been modified through an interaction with falling fragments of a low-density comet nucleus, previously broken by tidal forces and having ploughed the regolith.

Then, the magnetic anomaly would not be the result of an antipodal crustal field generated in the formation process of large impact basins. It would rather arise from local effects during the interaction between the lunar surface and cometary physical environment, with the possibility that the solar wind is locally deflected and contributes to the unusual optical properties.

So, the Reiner Gamma Formation could be an interesting site for future human exploration because of the radiation deflected from the surface. Further testing of this hypothesis requires access to the physical properties of the surface to constrain the mechanisms of formation of the lunar swirls. This is an ongoing task for the AMIE camera, aimed at studying regolith photometric properties.

Original Source: ESA Portal

Posted on by Fraser Cain

First Colour Images from Mars Reconnaissance Orbiter

First colour images from MRO. Image credit: NASA/JPL-Caltech/University of Arizona. Click to enlarge.
The first full colour photographs are back from NASA’s Mars Reconnaissance Orbiter, and they’re big and beautiful. The photos were actually taken in the infrared spectrum, so this isn’t what the human eye would see – the colouring was done on computer. The spacecraft was 2,493 kilometers (1,549 miles) above the surface of Mars when it captured this image. It’ll be getting much closer in the coming months, so the photos are only going to get better.

This is the first color image of Mars from the High Resolution Imaging Science Experiment on NASA’s Mars Reconnaissance Orbiter. At the center portion of the camera’s array of light detectors there are extra detectors to image in green and near-infrared color bandpasses, to be combined with the black-and-white images (from red-bandpass detectors) to create color images. This is not natural color as seen by human eyes, but infrared color — shifted to longer wavelengths. This image also has been processed to enhance subtle color variations. The southern half of the scene is brighter and bluer than the northern half, perhaps due to early-morning fog in the atmosphere. Large-scale streaks in the northern half are due to the action of wind on surface materials. The blankets of material ejected from the many small fresh craters are generally brighter and redder than the surrounding surface, but a few are darker and less red. Two greenish spots in the middle right of the scene may have an unusual composition, and are good future targets for the Compact Reconnaissance Imaging Spectrometer for Mars, a mineral-identifying instrument on Mars Reconnaissance Orbiter ( http://crism.jhuapl.edu/). In the bottom half of the image we see a redder color in the rough areas, where wind and sublimation of water or carbon dioxide ice have partially eroded patches of smooth-textured deposits.

This image was taken by HiRISE on March 24, 2006. The image is centered at 33.65 degrees south latitude, 305.07 degrees east longitude. It is oriented such that north is 7 degrees to the left of up. The range to the target was 2,493 kilometers (1,549 miles). At this distance the image scale is 2.49 meters (8.17 feet) per pixel, so objects as small as 7.5 meters (24.6 feet) are resolved. In total this image is 49.92 kilometers (31.02 miles) or 20,081 pixels wide and 23.66 kilometers (14.70 miles) or 9,523 pixels long. The image was taken at a local Mars time of 07:33 and the scene is illuminated from the upper right with a solar incidence angle of 78 degrees, thus the sun was 12 degrees above the horizon. At an Ls of 29 degrees (with Ls an indicator of Mars’ position in its orbit around the sun), the season on Mars is southern autumn.

Images from the High Resolution Imaging Science Experiment and additional information about the Mars Reconnaissance Orbiter are available online at: http://www.nasa.gov/mro or http://HiRISE.lpl.arizona.edu. For information about NASA and agency programs on the Web, visit: http://www.nasa.gov.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Pulsars Form Planets Too

Artist illustration of a planetary disk forming around a pulsar. Image credit: NASA/JPL. Click to enlarge.
Think planets can only form around stars? Well, think again. NASA’s Spitzer Space Telescope has uncovered evidence for a potential planet-forming disk around a pulsar. In a former life, the pulsar would have been a large star 10-20 times bigger than the Sun that eventually consumed its fuel and exploded as a supernova. The remaining debris has started to collect again, and could eventually turn into new planets. This helps explain how planets were discovered around another pulsar in 1992, including one that’s Earth-sized.

NASA’s Spitzer Space Telescope has uncovered new evidence that planets might rise up out of a dead star’s ashes.

The infrared telescope surveyed the scene around a pulsar, the remnant of an exploded star, and found a surrounding disk made up of debris shot out during the star’s death throes. The dusty rubble in this disk might ultimately stick together to form planets.

This is the first time scientists have detected planet-building materials around a star that died in a fiery blast.

“We’re amazed that the planet-formation process seems to be so universal,” said Dr. Deepto Chakrabarty of the Massachusetts Institute of Technology in Cambridge, principal investigator of the new research. “Pulsars emit a tremendous amount of high energy radiation, yet within this harsh environment we have a disk that looks a lot like those around young stars where planets are formed.”

A paper on the Spitzer finding appears in the April 6 issue of Nature. Other authors of the paper are lead author Zhongxiang Wang and co-author David Kaplan, both of the Massachusetts Institute of Technology.

The finding also represents the missing piece in a puzzle that arose in 1992, when Dr. Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12. Those pulsar planets, two the size of Earth, were the first planets of any type ever discovered outside our solar system. Astronomers have since found indirect evidence the pulsar planets were born out of a dusty debris disk, but nobody had directly detected this kind of disk until now.

The pulsar observed by Spitzer, named 4U 0142+61, is 13,000 light-years away in the Cassiopeia constellation. It was once a large, bright star with a mass between 10 and 20 times that of our sun. The star probably survived for about 10 million years, until it collapsed under its own weight about 100,000 years ago and blasted apart in a supernova explosion.

Some of the debris, or “fallback,” from that explosion eventually settled into a disk orbiting the shrunken remains of the star, or pulsar. Spitzer was able to spot the warm glow of the dusty disk with its heat-seeking infrared eyes. The disk orbits at a distance of about 1 million miles and probably contains about 10 Earth-masses of material.

Pulsars are a class of supernova remnants, called neutron stars, which are incredibly dense. They have masses about 1.4 times that of the sun squeezed into bodies only 10 miles wide. One teaspoon of a neutron star would weigh about 2 billion tons. Pulsar 4U 0142+61 is an X-ray pulsar, meaning that it spins and pulses with X-ray radiation.

Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992.

“I find it very exciting to see direct evidence that the debris around a pulsar is capable of forming itself into a disk. This might be the beginning of a second generation of planets,” Wolszczan said.

Pulsar planets would be bathed in intense radiation and would be quite different from those in our solar system. “These planets must be among the least hospitable places in the galaxy for the formation of life,” said Dr. Charles Beichman, an astronomer at NASA’s Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif.

The Jet Propulsion Laboratory manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. JPL is a division of Caltech. Spitzer’s infrared array camera, which made the pulsar observations, was built by NASA’s Goddard Space Flight Center, Greenbelt, Md. The instrument’s principal investigator is Dr. Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

For more information about Spitzer, visit:

http://www.spitzer.caltech.edu/spitzer/

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

How Prometheus Pulls on Saturn’s F Ring

Prometheus acting on Saturn’s F ring. Image credit: NASA/JPL/SSI. Click to enlarge
One of the most amazing images sent back by the Cassini spacecraft shows one of Saturn’s shepherd moons, Prometheus, tugging a stream of particles away from the F ring. Scientists from Queen Mary, University of London have developed a model that explains the forces at work in this dramatic interaction. It was originally believed that Prometheus steals ring particles, but it now appears that it just borrows them as it comes past, and they drift back into the ring system after the moon sweeps by.

Images from Saturn’s F ring region obtained by the Cassini Imaging Science Subsystem (ISS) cameras have revealed structure never seen before in a planetary ring.

The rings around all the giant planets in our Solar System are thought to be stabilised by small ‘shepherd moons’ that orbit in or near the rings and stabilize them by gravitational influences.

The narrow F ring of Saturn ? which lies just outside the spectacular main rings – is tended by two small shepherds. Prometheus (100 km in diameter) orbits just inside the F ring, while Pandora (85 km in diameter) moves around Saturn just outside the F ring.

Periodic structures such as azimuthal gaps ? ‘channels’ of low optical depth – and ‘streamers’ have been discovered. These features can be seen in Movie1. The origin of these features has been explored by a team at Queen Mary, University of London (QMUL) using numerical integrations.

On Tuesday 4 April, Carlos Chavez of QMUL will be explaining to the RAS National Astronomy Meeting in Leicester the results of their computer models, which explain the close and complex relationship between Prometheus and the tangled F ring.

“The models are in excellent agreement with structures observed in the Cassini images,” said Chavez.

“We have found that the gaps are not due to a lack of particles, but to a forced change in orbital elements by a close encounter with Prometheus,” he explained. “The moon’s gravity temporarily pulls some of the particles away from the main stream as it passes by.”

“It is like a crowd of people walking in a number of lines in the same direction down a street. Suddenly, someone else comes from the other side of the street and collides with a few of them. He then tells them to come with him, and walks away. Only people in the closest lines follow him, which produces gaps in the crowd. However, they return back to the main group shortly afterwards.”

The most dramatic case will happen in late 2009, when the F ring and Prometheus are anti-aligned. Once per orbit during this anti-alignment Prometheus will be at apoapsis (its furthest point from Saturn) and the nearby ring particles will be at periapsis (closest point to Saturn). At that time, Prometheus and the ring particles are at their closest to each other.

The QMUL team explored how these events will affect collisions between the ring particles and Prometheus. They found a low number of collisions – only 0.6% of the particles collided per orbit. This was unexpected, since it was originally thought that Prometheus is a ‘thieving moon’, stealing particles from the F ring. What actually happens is that the particles are only temporarily pulled away and then drift back into the ring.

The ring-moon interactions are also likely to have an effect on the surface of Prometheus. Like our Moon and most other planetary satellites, Prometheus has a synchronous rotation, always showing the same face to Saturn.

The team at QMUL investigated the location on Prometheus’ surface where the particles would be expected to collide. They found that, in the synchronous co-rotating reference frame, the collisions surprisingly occurred on the trailing face of Prometheus, and preferably in the equatorial region.

This scenario has important implications for the surface features of Prometheus, and the team expects to find differences in albedo (reflectivity) between the trailing and leading faces.

“It would be like a man colliding with other people while facing continuously in a particular direction and hitting them with only one side of his body,” said Chavez.

Other members of the QMUL team examining the links between Prometheus and the F ring are: Prof. Carl D. Murray, Dr. Kevin Beurle, Dr. Nicholas J. Cooper, and Dr. Michael W. Evans.

Original Soure: RAS News Release

Posted on by Fraser Cain

A Super Mercury was Smashed up 4.5 Billion Years Ago

Evolution of the impact three hours from the time of collision. Image credit: Horner et Al. Click to enlarge
According to current models of planetary formation, Mercury has too much mass. A new explanation proposes that Mercury was created from a much larger parent planet that collided with a giant asteroid 4.5 billion years ago. Astronomers from the University of Bern ran various scenarios modeling early versions of Mercury. This scenario of an early cataclysm best matched the current mass and composition of Mercury. Some of the ejected material would have made it all the way to Venus and even to the Earth.

A New computer simulations of Mercury’s formation show the fate of material blasted out into space when a large proto-planet collided with a giant asteroid 4.5 billion years ago. The simulations, which track the material over several million years, shed light on why Mercury is denser than expected and show that some of the ejected material would have found its way to the Earth and Venus.

“Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision, but until these simulations we were not sure why so little of the planet’s outer layers were reaccreted following the impact,” said Dr Jonti Horner, who is presenting results at the Royal Astronomical Society’s National Astronomy Meeting on 5th April.

To solve this problem, Dr Horner and his colleagues from the University of Bern ran two sets of large-scale computer simulations. The first examined the behaviour of the material in both the proto-planet and the incoming projectile; these simulations were among the most detailed to date, following a huge number of particles and realistically modelling the behaviour of different materials inside the two bodies. At the end of the first simulations, a dense Mercury-like body remained along with a large swathe of rapidly escaping debris. The trajectories of the ejected particles were then fed in to a second set of simulations that followed the motion of the debris for several million years. Ejected particles were tracked until either they landed on a planet, were thrown into interstellar space, or fell into the Sun. The results allowed the group to work out how much material would have fallen back onto Mercury and investigate other ways in which debris is cleared up in the Solar System.

The group found that the fate of the debris depended on whereabouts Mercury was hit, both in terms of its orbital position and in terms of the angle of the collision.

Whilst purely gravitational theory suggested that a large fraction of the debris would eventually fall back onto Mercury, the simulations showed that it would take up to 4 million years for 50% of the particles to land back on the planet and in this time many would be carried away by solar radiation. This explains why Mercury retained a much smaller proportion than expected of the material in its outer layers.

The simulations also showed that some of the ejected material made its way to Venus and the Earth. While this is only a small fraction, it illustrates that material can be transferred between the inner planets relatively easily. Given the amount of material that would have been ejected in such a catastrophe, it is likely that there is a reasonable amount (possibly as much as 16 million billion tonnes [1.65×10^19 kg]) of proto-Mercury in the Earth.

Original Source: RAS News Release

Posted on by Fraser Cain

Star Forming Dust Clouds Imaged by Hubble

NGC 281. Image credit: Hubble. Click to enlarge
The dark patch in this Hubble Space Telescope photograph is a “Bok globule” in the nearby star forming region, NGC 281. Astronomer Bart Bok first came up with the theory that dark globules like this are giant clouds of molecular gas, hundreds of light years across. Once perturbed, parts can collapse and become gravitationally bound; eventually forming stars and planets.

The yearly ritual of spring cleaning clears a house of dust as well as dust “bunnies,” those pesky dust balls that frolic under beds and behind furniture. NASA’s Hubble Space Telescope has photographed similar dense knots of dust and gas in our Milky Way Galaxy. This cosmic dust, however, is not a nuisance. It is a concentration of elements that are responsible for the formation of stars in our galaxy and throughout the universe.

These opaque, dark knots of gas and dust are called “Bok globules,” and they are absorbing light in the center of the nearby emission nebula and star-forming region, NGC 281. The globules are named after astronomer Bart Bok, who proposed their existence in the 1940’s.

Bok hypothesized that giant molecular clouds, on the order of hundreds of light-years in size, can become perturbed and form small pockets where the dust and gas are highly concentrated. These small pockets become gravitationally bound and accumulate dust and gas from the surrounding area. If they can capture enough mass, they have the potential of creating stars in their cores; however, not all Bok globules will form stars. Some will dissipate before they can collapse to form stars. That may be what’s happening to the globules seen here in NGC 281.

Near the globules are bright blue stars, members of the young open cluster IC 1590. The cluster is made up of a few hundred stars. The cluster’s core, off the image towards the top, is a tight grouping of extremely hot, massive stars with an immense stellar wind. The stars emit visible and ultraviolet light that energizes the surrounding hydrogen gas in NGC 281. This gas then becomes super heated in a process called ionization, and it glows pink in the image.

The Bok globules in NGC 281 are located very close to the center of the IC 1590 cluster. The exquisite resolution of these Hubble observations shows the jagged structure of the dust clouds as if they are being stripped apart from the outside. The heavy fracturing of the globules may appear beautifully serene but is in fact evident of the harsh, violent environment created by the nearby massive stars.

The Bok globules in NGC 281 are visually striking nonetheless. They are silhouetted against the luminous pink hydrogen gas of the emission nebula, creating a stark visual contrast. The dust knots are opaque in visual light. Conversely, the nebulous gas surrounding the globules is transparent and allows light from background stars and even background galaxies to shine through.

These images were taken with Hubble’s Advanced Camera for Surveys in October 2005. The hydrogen-emission image that clearly shows the outline of the dark globules was combined with images taken in red, blue, and green light in order to help establish the true color of the stars in the field. NGC 281 is located nearly 9,500 light-years away in the direction of the constellation Cassiopeia.

Original Source: HubbleSite News Release