Posted on by Fraser Cain

A SWIFT Response to Gamma Ray Bursts


An artist’s impression of merging neutron stars, one of the theoretical progenitors of gamma-ray bursts. Image credit: NASA E/PO, Sonoma State University, Aurore Simonnet. Click to enlarge.
Gamma Ray bursters (GRBs) are almost a daily occurrence – so you’d think follow-up on such things would be routine by now – but that’s just not the case. Imagine a fire department having to respond to a new fire every day: they’d still have to pull on hats and heavy raincoats, slide down shiny metallic poles, and jump onto their fire engine as fast as possible.

And on Monday, May 9th, 2005 there were two fires; one reported earlier in the day by NASA’s HETE-2, and then another by its even more sophisticated associate SWIFT.

So even as we were working on a previous story for Universe Today readers about a dark Gamma Ray Burster detected by HETE-2 in August 2002, two new bursts occurred overhead. Both events sounded the alarm and astronomers worldwide scrambled to capture the rapidly diminishing optical afterglow (OAs) that might help explain one of the deepest mysteries in the Universe: how can so much energy be packed into those tiny, massless photons?

GRB events themselves are of two types. Some are “hard and fast” while others are “soft and slow”. When a “hard-fast” event occurs, astronomical fire fighters have to work quickly.

It all begins when HETE-2 or SWIFT detects an outburst from their lonely perches in low Earth orbit. Once a burst is detected, instruments aboard the craft swing around to make a determination of just where in space that event has occurred and capture whatever lingering x-ray data may still be available. Here SWIFT has the advantage over HETE-2 due to its smaller “error circle” – the satellite’s best guess as to the location of the event in the heavens. Data related to location, burst strength, and duration is then beamed to NASA instrument teams on Earth where the data is integrated and advisories are published to enlist available astronomers and instruments.

All this is comparable to an “all points bulletin” going out so astronomers anywhere can scramble to capture what is now the rapidly diminishing afterglow of the main event. Typically only small instruments associated with major observatories respond first, since larger instruments are scheduled months in advance for other projects. You’ll never see the mighty Hubble Space Telescope swing around for one of these events.

Even as available scopes turn to the sky, astronomers look for detailed survey charts of the region associated with the error circle. Why? Because images and data may already be available to simplify afterglow identification along with baseline spectra, and recessionary distances of host galaxies to assist their analysis.

As time passes, larger and larger instruments are made available for use. This is essential since dark GRBs fade quickly and more and more optical depth is needed to pick up the trail. In the case of GRB020819 detected by HETE-2 in 2002 not even the 10-meter Keck ESI instrument (capturing 26th magnitude light) was able to image an afterglow even though it swung around within 15 days of the initial high energy burst. But with SWIFT’s rapid response and tighter error circles its now becoming possible to catch a dark GRB in the act of disappearing for good.

Of the two GRB events of the day, GRB050509B is most promising because its optical light afterglow is relatively dim (fainter than the 20th magnitude) and galaxy is relatively bright (the 15th). And it is because roughly 1 in 10 GRBs are optically impoverished that makes them specially interesting to astrophysicists. Basically current models used to explain dark GRB events predict that a broad range of photon-energy levels should be seen to accompany any gamma-ray outburst. The fact that some GRBs don’t happen to map well against theory is troublesome, and therein lies the itch behind GRB020819’s (and now GRB050509B’s) scratch.

One theory of GRBs is that gamma rays somehow “muscle their way” through intervening matter in space while optical light – the “afterglow” of such an event – does not. This optical extinction scenario has yet to be demonstrated and several dark GRBs show no sign of the kind of massive clouds of intervening matter needed to support it.

Meanwhile there are three theories of the fireball-shock type postulated by astrophysicists to account for all rapidly diminishing short-time scale GRBs. The fireball scenario typically involves an explosion that hurls extremely hot gases at exceedingly high speeds into space after some kind of a cataclysmic event. These gases then interact with other material already present in the interstellar medium (ISM) or material previously ejected into space by the same object at lower velocities. One theory postulates a “relativistic jet” of hot gases penetrating either a stratified “onion” of other slower moving gases or a simple homogeneously filled-“bubble” of gases. The others assume either a rapidly expanding sphere of hot gases into the same type “bubble” or “onion”.

According to an international team of astronomers, data analyzed across the EM spectrum from GRB020819 supports the expanding sphere into homogeneous medium fireball-shock model. Those findings have been documented in a paper entitled “The Radio Afterglow and Host Galaxy of the Dark GRB020819” published May 2, 2005. The related Universe Today article is an online companion to this article entitled “Shedding Light on Dark Gamma Ray Bursters“.

Meanwhile – at this very moment – astronomical “firefighters and fire marshals” are gathering data associated with SWIFT’s detection of GRB 050509B. This process may continue in one form or another for as long as six months. Several years hence a team of investigators – such as that associated with GRB020819 – may attempt to make sense of how a little understood paroxysm of matter and energy occuring some 2.5 billion years ago in the direction of the springtime constellation Coma Berenices could ever have happened in the first place.

To make all this possible numerous and ever larger “eyes on the skies” will have to collect and focus radio, near-infrared, optical, and near-ultraviolet light. All of that information will be sifted through with infinite patience in an effort to forensically determine not “who done it” but “what”.

Written by Jeff Barbour

Posted on by Fraser Cain

New Moon for Saturn Makes Waves in the Rings

Newly discovered moon S/2005 S1 and its effect on Saturn’s rings. Image credit: NASA/JPL/SSI. Click to enlarge.
In a spectacular kick-off to its first season of prime ring viewing, which began last month, the Cassini spacecraft has confirmed earlier suspicions of an unseen moon hidden in a gap in Saturn’s outer A ring. A new image and movie show the new moon and the waves it raises in the surrounding ring material.

The moon, provisionally named S/2005 S1, was first seen in a time- lapse sequence of images taken on May 1, 2005, as Cassini began its climb to higher inclinations in orbit around Saturn. A day later, an even closer view was obtained, which has allowed a measure of the moon’s size and brightness.

The new images can be seen at http://saturn.jpl.nasa.gov, http://www.nasa.gov/cassini and http://ciclops.org.

The images show the tiny object in the center of the Keeler gap and the wavy patterns in the gap edges that are generated by the moon’s gravitational influence. The Keeler gap is located about 250 kilometers (155 miles) inside the outer edge of the A ring, which is also the outer edge of the bright main rings. The new object is about 7 kilometers (4 miles) across and reflects about half the light falling on it — a brightness that is typical of the particles in the nearby rings.

“It’s too early to make out the shape of the orbit, but what we’ve seen so far of its motion suggests that it is very near the exact center of the gap, just as we had surmised,” said Dr. Joseph Spitale, imaging team associate and planetary scientist at the Space Science Institute in Boulder, Colo. The new moonlet orbits approximately 136,505 kilometers (84,820 miles) from the center of Saturn. More Cassini observations will be needed to determine whether the moon’s orbit around Saturn is circular or eccentric.

S/2005 S1 is the second known moon to exist within Saturn’s rings. The other is Pan, 25 kilometers (16 miles) across, which orbits in the Encke gap. Atlas and other moons exist outside the main ring system, as do the two F ring shepherd moons, Prometheus and Pandora.

Imaging scientists had predicted the new moon’s presence and its orbital distance from Saturn after last July’s sighting of a set of peculiar spiky and wispy features in the Keeler gap’s outer edge. The similarities of the Keeler gap features to those noted in Saturn’s F ring and the Encke gap led imaging scientists to conclude that a small body, a few kilometers across, was lurking in the center of the Keeler gap, awaiting discovery.

“The obvious effect of this moon on the surrounding ring material will allow us to determine its mass and test our understanding of how rings and moons affect one another,” said Dr. Carl Murray, imaging team member from Queen Mary, University of London. An estimate of the moon’s mass, along with a measure of its size, yields information on its physical makeup. For instance, the new moonlet might be quite porous, like an orbiting icy rubble pile. Other moons near the outer edge of Saturn’s rings – like Atlas, Prometheus and Pandora – are also porous. Whether a moon is porous or dense says something about how it was formed and its subsequent collision history.

The Keeler gap edges also bear similarities to the scalloped edges of the 322-kilometer-wide (200-mile) Encke gap, where the small moon Pan (25 kilometers, or 16 miles across) resides. From the size of the waves seen in the Encke gap, imaging scientists were able to estimate the mass of Pan. They expect to do the same eventually with this new moon.

“Some of the most illuminating dynamical systems we might hope to study with Cassini are those involving moons embedded in gaps,” said Dr. Carolyn Porco, imaging team leader at the Space Science Institute. “By examining how such a body interacts with its companion ring material, we can learn something about how the planets in our solar system might have formed out of the nebula of material that surrounded the Sun long ago. We anticipate that many of the gaps in Saturn’s rings have embedded moons, and we’ll be in search of them from here on.”

Additional closer observations of the new body may take place in the next several months, as Cassini continues its intensive survey of Saturn’s beautiful and mysterious rings.

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 Cassini-Huygens 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 team is based at the Space Science Institute, Boulder, Colo.

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Shedding Light on Dark Gamma Ray Bursters

Dark gamma ray burst GRB020819. Image credit: Keck. Click to enlarge.
Virtually everything we know about the Universe comes to us through the agency of light. Unlike matter, light is uniquely suited to travel the vast distances across space to our instruments. Most astronomical phenomena however are persistent and repeatable – we can rely on them to “hang around” for long-term observation or “come back around” on a regular basis. But this isn’t so for gamma ray bursts (GRB’s) – those mysterious cosmological events that supercharge photons (and sub-atomic particles) with absurdly high energy levels.

The first detected celestial GRB occurred during nuclear arms treaty monitoring in 1967. That event required years of analysis before its extraterrestrial origin was confirmed. After this discovery, primitive triangulation methods were put in place using detectors located on various space probes within the Interplanetary Network (IPN). Such methods required a great deal of number crunching and made instant follow-up using Earth-based instruments impossible. Despite the delays involved, hundreds of gamma ray sources were catalogued. Today – even using the Internet – it would still require several days to respond using an IPN-type detection approach.

All this began to change in 1991 when NASA put the Compton Gamma Ray Observatory (CGRO) into space using space shuttle Atlantis as part of its “Great Observatories” program. Within four months of scanning the sky, CGRO made it clear to astronomers that the Universe underwent sporadic and widely distributed gamma ray paroxysms on an almost daily basis – paroxysms caused by cataclysmic events that hurl vast quantities of gamma and other high-energy radiation across the abyss of space-time.

But CGRO had one main limitation – although it could detect gamma rays and alert astronomers quickly, it wasn’t particularly accurate as to where such events happened in space. Because of this large “error circle”, astronomers were unable to locate the visible light “afterglow” of such events. Despite this limitation, CGRO went on to detect hundreds of continuous, periodic, and episodic gamma ray sources – including supernovae, pulsars, black holes, quasars, and even the Earth itself! Meanwhile CGRO also discovered something unsuspected – certain pulsars acted as narrow band transmitters of gamma rays without accompanying visible light – and therein lay astronomer?s first sense of “dark” GRBs.

Today we know that “dark pulsars” are not the only “dark” sources of gamma rays in the Universe. Astronomers have determined that some small portion of episodic (one-time-only) GRBs are also low in visible light, and they – like anyone tickled by the unusual and inexplicable – want to know why. In fact GRB’s are so unique that aficionados may often be heard saying “When you’ve seen one GRB, you’ve seen one GRB”.

The first satellite to simplify optical detection of GRB afterglows was BeppoSAX. Developed by the Italian Space Agency in the mid 1990’s, BeppoSAX launched April 30, 1996 from Cape Canaveral and continued to detect and pinpoint X-ray emission sources until 2002. BeppoSax’s error circle was small enough to enable optical astronomers to rapidly track down many GRB afterglows for detailed study in visible light using earth-based instruments.

BeppoSAX re-entered the Earth’s atmosphere April 29, 2003, but by this time NASA’s replacement (HETE-2 the High Energy Transient Explorer-2) was already several years on station in low-earth orbit. Instrument’s on HETE-2 (its first incarnation HETE failed to separate from the third stage of its Pegasus rocket in 1996) expanded the range of X-ray detection and provided even tighter error circles – just the thing astronomers needed to improve their response time in locating GRB afterglows.

Two years and a few months later (Monday, August 19, 2002) HETE-2 set off the bells and whistles as a strong gamma ray source was detected somewhere near the head of the constellation Pisces the Fishes. That event (designated GRB 020819) caused a series of astronomical observatories to begin capturing radio-frequency, near-infrared, and visible light photons in an effort to determine just where the event occurred and help make sense of the phenomenon driving it.

According to the paper “The Radio Afterglow and Host Galaxy of the Dark GRB 020819” published May 2, 2005 by an international team of investigators (including Pall Jakobsson of the Niels Bohr Institute, Copenhagen Denmark who proofed this article), within 4 hrs of detection the 1 meter Siding Spring Observatory (SSO) telescope in Australia was turned to a region of space less than 1/7th the apparent diameter of the Moon. 13 hours later, a second, slightly larger instrument – the 1.5 meter P60 unit at Mt. Palomar – also joined the chase. Neither instrument – despite capturing light as faint as magnitude 22 – caught anything unusual for that region of space. However a large and extremely photogenic 19.5 magnitude face-on barred spiral galaxy fell nicely within the grasp of their instruments.

Fifteen days later, the 10 meter Keck ESI instrument on Mauna Kea, Hawaii imaged the same region in blue and red light down to magnitude 26.9. At this optical depth, a distinct 24th magnitude “blob” (suspected to be an HII star-formation region) could be seen 3 arc seconds north of the spiral galaxy. A final attempt to detect anything further was made January 1, 2003 – again using the Keck 10 meter. No change was seen in optical light emanating from the region of GRB 020819. All this confirmed that no visible afterglow accompanied the gamma ray outburst detected by HETE-2 some 134 days earlier. The investigating team had their “dark gamma ray burster”. Later would come the task of figuring out just what the heck it was – or at least was not…

Periodically throughout the cycle of optical and near-infrared inspection, the region of the burst was monitored in radio-wave frequencies. Using the VLA (Very Large Array – consisting of 27 Y-configured 25 meter dishes located fifty miles west of Socorro, New Mexico) the team succeeded in capturing a dwindling trail of 8.48 Ghz radiation and identified its locale.

First radio waves from GRB 020819 were collected 1.75 days after the HETE-2 alert. By day 157, rf energy levels flattened to the point where the source could no longer be seen with confidence. However by this time, its location had been pinpointed to the “blob” three arc-seconds north of the core of the previously uncharted spiral galaxy. Unfortunately – due to its faintness – the distance to the blob itself could not be determined spectrographically – however the galaxy was found to lie some 6.2 BLY away and enjoys “high-confidence” in terms of having a relationship with the source.

As a result of such investigations astronomers are now learning more and more about a class of cataclysmic events that results in massive fluxes of high and low energy photons while almost completely skipping intermediate frequencies – such as ultraviolet, visible, and near-infrared of light. Is there anything that could account for this?

Based on learning from GRB 020819, the team explored three fireball-shock models of how dark GRBs might occur. Of the three (an even expansion of high energy gases into a homogenous medium, even expansion into a stratified medium, and a collimated jet penetrating either type medium), the best fit against GRB 020819 behaviors was that of an even expansion of high energy gases into a homogenous medium of other gases (a model first proposed by the astrophysicist R. Sari et al in 1998). The virtue of this isotropic-expansion model being (in the words of the investigating team) that “only a modest amount of extinction must be invoked” to account for the absence of visible light.

In addition to narrowing the range of possible scenarios associated with dark GRBs, the team concluded that “GRB 020819, a relatively nearby burst, is only one of two of the 14 GRB’s localized to within (2 arc minutes using) HETE-2 that does not have a reported OA. This lends support to the recent proposition that the dark burst fraction is far lower than previously suggested, perhaps as small as 10%.”

Written by Jeff Barbour

Posted on by Fraser Cain

Superflares Might Have Protected the Early Earth

Artist illustration of a superflare on a young star. Image credit: NASA. Click to enlarge.
New results from NASA’s Chandra X-ray Observatory imply that X-ray super-flares torched the young Solar System. Such flares likely affected the planet-forming disk around the early Sun, and may have enhanced the survival chances of Earth.

By focusing on the Orion Nebula almost continuously for 13 days, a team of scientists used Chandra to obtain the deepest X-ray observation ever taken of this or any star cluster. The Orion Nebula is the nearest rich stellar nursery, located just 1,500 light years away.

These data provide an unparalleled view of 1400 young stars, 30 of which are prototypes of the early Sun. The scientists discovered that these young suns erupt in enormous flares that dwarf – in energy, size, and frequency — anything seen from the Sun today.

“We don’t have a time machine to see how the young Sun behaved, but the next best thing is to observe Sun-like stars in Orion,” said Scott Wolk of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “We are getting a unique look at stars between one and 10 million years old – a time when planets form.”

A key result is that the more violent stars produce flares that are a hundred times as energetic as the more docile ones. This difference may specifically affect the fate of planets that are relatively small and rocky, like the Earth.

“Big X-ray flares could lead to planetary systems like ours where Earth is a safe distance from the Sun,” said Eric Feigelson of Penn State University in University Park, and principal investigator for the international Chandra Orion Ultradeep Project. “Stars with smaller flares, on the other hand, might end up with Earth-like planets plummeting into the star.”

According to recent theoretical work, X-ray flares can create turbulence when they strike planet-forming disks, and this affects the position of rocky planets as they form. Specifically, this turbulence can help prevent planets from rapidly migrating towards the young star.

“Although these flares may be creating havoc in the disks, they ultimately could do more good than harm,” said Feigelson. “These flares may be acting like a planetary protection program.”

About half of the young suns in Orion show evidence for disks, likely sites for current planet formation, including four lying at the center of proplyds (proto-planetary disks) imaged by Hubble Space Telescope. X-ray flares bombard these planet-forming disks, likely giving them an electric charge. This charge, combined with motion of the disk and the effects of magnetic fields should create turbulence in the disk.

The numerous results from the Chandra Orion Ultradeep Project will appear in a dedicated issue of The Astrophysical Journal Supplement in October, 2005. The team contains 37 scientists from institutions across the world including the US, Italy, France, Germany, Taiwan, Japan and the Netherlands.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release

Posted on by Fraser Cain

Spinning Hyperion

Saturn’s chaotically tumbling moon, Hyperion. Image credit: NASA/JPL/SSI. Click to enlarge.
Saturn’s chaotically tumbling moon Hyperion is captured in this view. At the top is a 130-kilometer-wide (80-mile) crater seen in some NASA Voyager spacecraft images. Detecting specific features is the first step in trying to understand the current rotation state of Hyperion, compared to that at the time of Voyager. Hyperion is 266 kilometers (165 miles) across.

This is the second-closest view of Hyperion obtained by Cassini so far. The closest view was included in a previously released montage of Hyperion images.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 19, 2005, at a distance of approximately 1.3 million kilometers (824,000 miles) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 63 degrees. Resolution in the original image was 8 kilometers (5 miles) per pixel. The image has been contrast-enhanced and magnified by a factor of three to aid visibility.

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 team is based at the Space Science Institute, Boulder, Colo.

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

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

What’s Up This Week – May 9 – May 15, 2005

Photo of galaxy NGC 2903. Image credit: Zsolt Frei and James E. Gunn. Click to enlarge.
Monday, May 9 – Can you spot the very slender crescent Moon tonight? Look for it just after sunset low on the western horizon. Both bright Venus and the Plieades are to its west and will present a delightful challenge.

Before the Moon steals our early dark skies, let’s begin the week by studying a galaxy very similar to our own Milky Way – NGC 2903. Located less than two degrees south of Lambda Leonis, this magnificent 9.7 magnitude barred spiral can be spotted with binoculars from a dark location, and will be an easy small scope object. While the NGC 2903’s size and central bar closely resembles our own galaxy’s structure, the Hubble Space Telescope crossed the 25 million light year gap and found evidence of young globular clusters in its galactic halo – unlike our own old structures. This widespread star forming region is believed to be attributed to the gravity of the central bar. Small telescopes will show it as a lateral concentration across the central structure, while larger aperture will reveal spiral arms and concentrations of stars.

Tuesday, May 10 – Tonight give the Moon time to set and the constellation of Canes Venatici to rise as we go hunting the “Sunflower Galaxy” – M63. Located about a fist width southwest of the M51, you can normally spot it easily by scanning the area midway between Alkaid and Cor Caroli.

Originally discovered in 1779 by my hero Mechain, this bright galaxy is located about 37 million light years away and is believed to be part of a group of galaxies that includes M51. To binoculars it will appear as a faint misty oval, but larger scopes with optimal sky conditions will reveal the galaxy’s spiral arms as a grainy background that brightens considerably towards its center. Perhaps the most interesting feature of the M63 is its spiral arms. Most typical spiral galaxies contain two or three distinct spiral arms, yet this one’s structure is multiple short spiral arcs that remind many observers of a “celestial flower”. Scientific study of the M63 reveals that the galactic material at the edges of these arms is moving much faster than normal. Given the gravity of visible matter, this indicates the existence of dark matter within its structure.

Wednesday, May 11 – For viewers in south/central Australia and New Zealand, the Moon will occult Beta Taurii on this universal date. Please check IOTA webpages for details and times in your area.

So how about if we wait until the Moon sets and do a little comet hunting tonight? Let’s start with a familiar face – the “Magnificent Macholz”. Now faded to a soft magnitude 9, it can still be found with larger binoculars from a dark sky location. This evening will put the comet about equo-distant between Epsilon and Gamma Ursae Majoris and in the same field as star 73. Telescope users should still be able to see remnants of Macholz’ tail. For a little more challenge, locate 9/P Tempel 1 about 2 degrees southwest of Epsilon Virginis. At an estimated magnitude 10, Tempel 1 will be a bit fainter than Macholz, but far brighter than 13.5 magnitude NGC 4779 in the same lower power field.

Thursday, May 12 – For viewers in Florida, Bermuda and eastern Canada, the Moon will occult open cluster NGC 2331 on this universal date. Please check out this IOTA webpage for details. NGC 2331 is located roughly halfway between Beta and Epsilon Geminorum. At roughly magnitude 8, this scattered open cluster will be best detected with larger scopes during the occultation.

If you chose to view the Moon tonight, look for splendid dark crater Endymion on the terminator to the north. Normally its floor appears very smooth and very dark, but tonight it will seem to match its surroundings as the sunrise illuminates its west wall and the broad shadow of east wall defines its borders.

For viewers in western Europe, tonight would be a wonderful opportunity to spend some quality time with Jupiter. The great “Red Spot” will transit at 21:23 UT. Two of the galieans will add to the excitement as Europa’s shadow crosses the surface between 18:50 and 21:31 – followed by the ingress of Io’s shadow at 21:51.

Friday, May 13 – For viewers in Australia and New Zealand, the Moon will occult Iota Geminorum on the universal date. Please check IOTA webpages for further details.

If you are exploring the lunar surface tonight, be sure to look closely along the east boundary of Mare Nectaris. The bright cliff you see will be the Pyranees Mountains which holds crater Gutenburg in their grasp. This is a crater that has been filled with lava and terribly eroded over its lifetime. Its northeast wall has been broken by an impact known as Gutenburg E before the lava flood. The southern edge contains a very unusual mountain walled enclosure.

Saturday, May 14 – Tonight the Moon will be at apogee and will have reached its greatest distance of 404,600 km (251,407 miles). Let’s journey away to the lunar surface to view a very fine old crater – Theophilus. Slightly south of mid-point on the terminator, this crater contains an unusually large multiple peaked central mountain which can be spotted in binoculars. Theophilus is an odd crater, one that is a parabola – with no area on the floor being flat. Tonight it will appear dark, shadowed by its massive west wall, but look for sunrise on its summit!

Let’s turn our attention now to a splendid double star for the small telescope – Delta Corvi. Known as Algorab, this highly visible third magnitude star lies at the northeastern corner of the odd rectangle that forms the major pattern of Corvus. Its 9th magnitude companion is a wide split at 24 arcseconds away.

Sunday, May 15 – Would you like to see two planets in the same field of view? Then this morning would be well worth getting up early for as Mars and Uranus will only be about one degree apart. At +0.5 magnitude, reddish Mars will make a nice contrast with the 6th magnitude greenish Uranus. This will be very viewable in small binoculars and outstanding with the telescope.

Today is the birthday of Nicholas Louis de la Caille (or de Lacaille). Born in 1731, the French astronomer and mapmaker was the first to demonstrate Earth’s bulge at its equator. From 1751 to 1753, he had the great fortune to observe southern skies from the Cape of Good Hope. Putting his cartography skills to use, he mapped the southern skies and established the 14 constellations that remain in use to this day.

For lunar viewers tonight, enjoy the bright crests of the Caucasus Mountains with prominent craters Eudoxus and Aristoteles to the north.

Until next week? Ask for the Moon, but keep reaching for the stars! May all your journeys be at Light Speed… ~Tammy Plotner

Posted on by Fraser Cain

Crater Holden and Uzboi Vallis on Mars

140-km wide crater Holden, taken by Mars Express. Image credit: ESA. Click to enlarge.
This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows the outlet channel of the Uzboi Vallis system into Crater Holden on Mars.

The HRSC obtained this image during orbit 511 with a ground resolution of approximately 45 metres per pixel. The scene shows the region of Noachis Terra, over an area centred at about 26? South and 325? East.

The valley of Uzboi Vallis begins in the region of Argyre Planitia and crosses the southern highlands in the direction of the northern lowlands. It connects several large impact craters, such as the 140 kilometre-wide Crater Holden seen in the main image.

Due to a layer of haze close to the base of Holden, the area within the crater appears lighter coloured and slightly less detailed than the surrounding area.

A small, dark dune-field can be seen in the eastern half of the crater floor. It indicates the role of wind in the morphological evolution of Crater Holden.

The terrain within Crater Holden is the result of a long and varied evolution. The numerous smaller craters inside Holden indicate that the crater is old.

Many smaller craters on the floor of Holden are covered with sediments, which were deposited after the formation of these craters and indicate that they are older than the unfilled small craters.

The central mount of Holden is partly hidden, because it has also been covered by sediments. The rim of the crater has been cut by gullies, which sometimes form small valley networks.

In the southern part of Crater Holden, well-preserved ?alluvial fans? (fan-shaped deposits of water-transported material) are visible at the end of some gullies (see close-up left).

In other parts of the crater rim, the alluvial fans are less distinct and partly covered by younger ?talus? cones (cone-shaped piles of debris from rock falls at the base of slopes).

Uzboi Vallis enters Crater Holden from the south-west. Two distinct phases of its development can be seen. In the first phase, a valley was formed up to 20 kilometres wide.

Later, a smaller channel was cut into the valley floor. The end of the small channel has been blocked by a landslide from the crater rim (see close-up 2).

The deepest parts of the valley floor are more than 1600 metres below the surrounding area. The numerous valleys at the flanks of Uzboi Vallis indicate that water probably played a major role in the formation and evolution of this region. Most of the valleys have been covered by younger sediments, indicating they have been inactive in recent geological time.

Original Source: ESA News Release

Posted on by Fraser Cain

Deployment of Second MARSIS Boom Delayed

The MARSIS boom on Mars Express will help search for underground sources of water. Image credit: ESA. Click to enlarge.
The deployment of the second antenna boom of the Mars Express Sub-Surface Sounding Radar Altimeter (MARSIS) science experiment has been delayed pending investigation of an anomaly found during deployment of the first antenna boom.

The anomaly was discovered on 7 May towards the end of the first deployment operations. Deployment of the first boom started on Wednesday 4 May. The problem with the boom was confirmed by flight control engineers working at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, on 7 May, after which further activity was stopped pending a full assessment of the situation.

The decision to delay deployment of Boom 2 pending clarification of the situation and implications was made on 8 May.

Mission controllers were able to determine that 12 of the 13 boom segments of Boom 1 were correctly locked into position. However, one of the final segments, possibly No. 10, had deployed but was not positively locked into position.

It was determined that deployment of the second boom should be delayed in order to determine what implications the anomaly in the first boom may have on the conditions for deploying the second.

This decision is in line with initial plans which had allowed for a delay should any anomalous events occur during the first boom deployment.

Mission staff will now take the time necessary to investigate the boom situation. Foreseen outcomes include confirming that all segments of Boom 1 have been locked into place and determining how the deployment of Boom 1 may affect that of Boom 2.

All efforts will be made to ensure the safety of the spacecraft overall and to minimise any effects on the operations of ongoing science activity on board Mars Express.

The MARSIS experiment is to map the Martian sub-surface structure to a depth of a few kilometres. The instrument’s 40-metre long antenna booms will send low frequency radio waves towards the planet, which will be reflected from any surface they encounter.

MARSIS is one of seven science experiments carried on board Mars Express, one of the most successful missions ever flown to the Red Planet. Mars Express was launched on 2 June 2003 and entered Mars orbit in December 2003.

Original Source: ESA News Release

Posted on by Fraser Cain

Did Phoebe Come from the Outer Solar System?

Saturn’s moon Phoebe, imaged by Cassini when it first arrived. Image credit: NASA/JPL/SSI. Click to enlarge.
Saturn’s battered little moon Phoebe is an interloper to the Saturn system from the deep outer solar system, scientists have concluded. The new findings appear in the May 5 issue of the journal Nature.

“Phoebe was left behind from the solar nebula, the cloud of interstellar gas and dust from which the planets formed,” said Dr. Torrence Johnson, Cassini imaging team member at NASA?s Jet Propulsion Laboratory, Pasadena, Calif. “It did not form at Saturn. It was captured by Saturn’s gravitational field and has been waiting eons for Cassini to come along.”

Cassini flew by Phoebe on its way to Saturn on June 11, 2004. Little was known about Phoebe at that time. During the encounter, scientists got the first detailed look at Phoebe, which allowed them to determine its makeup and mass. With the new information they have concluded that it has an outer solar system origin, akin to Pluto and other members of the Kuiper Belt.

“Cassini is showing us that Phoebe is quite different from Saturn’s other icy satellites, not just in its orbit but in the relative proportions of rock and ice. It resembles Pluto in this regard much more than it does the other Saturnian satellites,” said Dr. Jonathan Lunine, Cassini interdisciplinary scientist from the University of Arizona, Tucson.

Phoebe has a density consistent with that of the only Kuiper Belt objects for which densities are known. Phoebe?s mass, combined with an accurate volume estimate from images, yields a density of about 1.6 grams per cubic centimeter (100 pounds per cubic foot), much lighter than most rocks but heavier than pure ice, which is about 0.93 grams per cubic centimeter (58 pounds per cubic foot). This suggests a composition of ice and rock similar to that of Pluto and Neptune’s moon Triton. Whether the dark material on other moons of Saturn is the same primordial material as on Phoebe remains to be seen.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. For Phoebe images and more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Mars Polar Lander Found?

Is this the Mars Polar Lander? Image credit: NASA/JPL. Click to enlarge.
The loss of Mars Polar Lander in December 1999 was a traumatic experience not only for those of us intimately involved in the mission, but also for the U. S. Mars Exploration Program. Following the failure, exhaustive reviews of what happened and why led to major shifts in the way planetary exploration was implemented. Without telemetry, the cause of the failure could only be surmised. It would be extremely important if, through some observation, it were possible to confirm the failure mode.

Shortly after the loss of Mars Polar Lander (MPL), the Mars Global Surveyor MOC was employed to acquire dozens of 1.5 m/pixel images of the landing uncertainty ellipses, looking for any evidence of the lander and its fate. The criteria we used in searching for MPL required a bright feature of irregular or elongated shape (the parachute) within about 1 kilometer (0.62 miles) of a location that included a dark area (rocket-disturbed martian dirt) and a small, bright spot near its center (the lander). In 2000, we found one example (see figure) that met these criteria, but in the absence of any substantive, corroborating evidence, the interpretation that this was MPL and its parachute were considered to be extremely speculative.

Observations by MGS MOC in 2004 of the Mars Exploration Rover (MER) landing sites provided guidance for a re-examination of the previously identified MPL candidate. For example, the material from which the MPL and MER parachutes are made is similar, and its brightness in MOC images can be calculated, at least in a relative sense, as a function of sun angle. The brightness of the candidate “parachute” in the MPL candidate location image turns out to be consistent with it being the same material. The brightness difference of the ground disturbed by rocket blast at the MER sites is similar to the brightness difference seen in the MPL candidate image, again adjusted for the difference in illumination and viewing angles. These consistencies lend credibility to this tentative identification.

If these features really are related to the MPL landing, what can we surmise about that landing from the image? First, we can tell that MPL’s descent proceeded more-or-less successfully through parachute jettison and terminal rocket firing. The relative location of the candidate parachute and lander is consistent with the slight west-to-east wind seen in dust cloud motion in the area around the date of landing. The blast-disturbed area is consistent with the engines continuing to fire until the vehicle was close to the ground. How close is not known. The larger MER retrorockets fired at about 100 m altitude and continued firing until the engines were about 20-25 m above the surface; the candidate MPL disturbance is roughly the same size, but whether this means the engines were firing as close to the ground as the MER rockets cannot be determined. These interpretations are consistent with the proposed MPL mode of failure: the engines fired at the correct time and altitude and continued firing until the flight software checked to see if an electronic message indicated that the landing leg contact switch had been set. Since the initial leg deployment several kilometers above the surface apparently induced sufficient motion to trigger this message, the software stopped the engines as soon as the check was made, about 28-30 seconds into the 36-40 second burn. MPL was probably at an altitude of about 40 m, from which it freely fell. This is equivalent to a fall on Earth from a height of about 40 feet. The observation of a single, small “dot” at the center of the disturbed location would indicate that the vehicle remained more-or-less intact after its fall.

What is important about having a candidate for the Mars Polar Lander site? It gives the MOC team a place to target for a closer look, using the compensated pitch and roll technique known as “cPROTO.” Examples of cPROTO images and a description of this capability, developed by the MGS team in 2003 and 2004, were discussed in a MOC release on 27 September 2004. Without a candidate for targeting a cPROTO image, it would take more than 60 Earth years to cover the entire Mars Polar Lander landing ellipse with cPROTO images, because the region spends the better part of each Mars year covered with carbon dioxide frost, part of each winter is spent in darkness, and, because of several uncertainties involved with the technique, it often takes two, three, or more tries before a cPROTO image hits a specific target. Now that a candidate site for Mars Polar Lander has been identified, we have a cPROTO target, which may permit us to obtain an image of about 0.5 meters per pixel (allowing objects approximately 1.5-2.5 meters in size to be resolved) during southern summer this year. At the present time (May 2005), the landing site is just beginning to lose its cover of seasonal carbon dioxide frost.

Original Source: Malin News Release