Posted on by Fraser Cain

New Type of Star Discovered

An artist’s impression of a neutron star with its magnetic field lines showing. Image credit: Russell Kightly Media. Click to enlarge
Astronomers of the University of Manchester’s Jodrell Bank Observatory (UK) have led an international team which used the Parkes radio telescope in Australia to find a new kind of cosmic object which sends out radio flashes. These flashes are very short and very rare: one hundredth of a second long, the total time the objects are visible amounts to only about one tenth of a second per day.

The discovery will be published in this week’s issue of the journal Nature.

Eleven sources of flashes have been found in different parts of the plane of the Milky Way in a survey for radio pulsars, which are small, compressed, highly-magnetised, neutron stars that produce regular pulses as they rotate, like cosmic light-houses. While that survey found over 800 pulsars and is the most successful in history, it also uncovered this new type of star. Rather than searching only for the periodic trains of pulses, the astronomers developed new techniques for detecting single short bursts of radiation.

Dr Maura McLaughlin explained: “It was difficult to believe that the flashes we saw came from outer space, because they looked very much like man-made interference”. The isolated flashes last for between 2 and 30 milliseconds. In between, for times ranging from 4 minutes to 3 hours, the new stars are silent.

After confirmation of their celestial nature, studies over the next 3 years revealed that 10 of the 11 sources have underlying periods of between 0.4 seconds and seven seconds.

“The periodicities found suggest that these new sources are also rotating neutron stars, but different from radio pulsars”, says Professor Andrew Lyne. “It is for this reason that we call them Rotating Radio Transients or RRATs. It’s as if, following a flash, a RRAT has to gather its strength during perhaps a thousand rotations before it can do it again !”.

RRATs are a new flavour of neutron stars in addition to the conventional radio pulsars and to the magnetars, which are also believed to be rotating neutron stars and are known to give off powerful X-ray and gamma-ray bursts. It is possible that RRATs represent a different evolutionary phase of neutron stars to or from magnetars.

The new objects probably far outnumber both their cousins. “Because of their ephemeral nature, RRATs are extremely difficult to find and so we believe that there are about 4 RRATs for every pulsar” says Dr Richard Manchester of the Australia Telescope National Facility. He is part of the team which also includes astronomers from the US, Canada and Italy.

Original Source: Jodrell Bank Observatory

Posted on by Fraser Cain

Southern Enceladus Covered in Fresh Snow

Saturn’s moon Enceladus. Image credit: NASA/JPL/SSI Click to enlarge
A false color look reveals subtle details on Enceladus that are not visible in natural color views.

The now-familiar bluish appearance (in false color views) of the southern “tiger stripe” features and other relatively youthful fractures is almost certainly attributable to larger grain sizes of relatively pure ice, compared to most surface materials.

On the “tiger stripes,” this coarse-grained ice is seen in the colored deposits flanking the fractures as well as inside the fractures. On older fractures on other areas of Enceladus, the blue ice mostly occurs on the exposed wall scarps.

The color difference across the moon’s surface (a subtle gradation from upper left to lower right) could indicate broad-scale compositional differences across the moon’s surface. It is also possible that the gradation in color is due to differences in the way the brightness of Enceladus changes toward the limb, a characteristic which is highly dependent on wavelength and viewing geometry.

See PIA07709 for a monochrome version of this view.

Terrain on the trailing hemisphere of Enceladus (505 kilometers, or 314 miles across) is seen here. North is up.

The view was created by combining images taken using ultraviolet, green and infrared spectral filters, and then was processed to accentuate subtle color differences. The images were taken with the Cassini spacecraft narrow-angle camera on Jan. 17, 2006 at a distance of approximately 153,000 kilometers (95,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 29 degrees. Image scale is 912 meters (2,994 feet) per pixel.

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

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

Original Source: NASA/JPL/SSI News Release

Posted on by Fraser Cain

Gemini Counts Up the Dark Matter in NGC 3379

NGC 3379. Image credit: NASA/University of Michigan. Click to enlarge
Using Gemini observations of globular clusters in NGC 3379 (M105), a team led by PhD student Michael Pierce and Prof. Duncan Forbes of Swinburne University in Australia, have found evidence for normal quantities of dark matter in the galaxy??bf?s dark halo. This is contrary to previous observations of planetary nebulae that indicated a paucity of dark matter in the galaxy.

The observations of 22 globular clusters in the Leo Group elliptical galaxy were made using the Gemini Multi-Object Spectrograph (GMOS) on Gemini North in early 2003. The data were obtained in the GMOS multi-slit mode with exposures of 10 hours on-source at a spectral resolution of FWHM ~4Aa over an effective wavelength range of 3800A-6660A. The final spectra have a signal-to-noise ratio of 18-58/A at 5000 A. The spectroscopic data allowed the team to derive ages, metallicities and α-element abundance ratios for the sample of globular clusters. All of the globular clusters were found to be >~ 10 Gyr, with a wide range of metallicities. A trend of decreasing α-element abundance ratio with increasing metallicity is also identified.

Most significantly, including 14 extra globular clusters from Puzia, et al. (2004), the projected velocity dispersion of the globular cluster system was found to be constant with radius from the galaxy center, indicating significant dark matter at large radii in its halo. This result is in stark contrast to the ??bf?No/Low Dark Matter??bf? interpretation by Romanowsky, et al. (2003) in the journal Science using observations of planetary nebula that indicated a decrease in the velocity dispersion profile with radius.

Reconciling the two velocity dispersion profiles is possible. Dekel, et al. (2005) recently showed that stellar orbits in the outer regions of merger-remnant elliptical galaxies are elongated and that declining planetary nebula velocity dispersions do not necessarily imply a dearth of dark matter.

Another possibility the authors suggest is that NGC 3379 could be a face-on S0 galaxy (as originally suggested by Capaccioli, et al. 1991). If a significant fraction of the planetary nebulae belong to the disk, this could suppress the line-of-sight velocity dispersion of the planetary nebulae relative to that of the globular clusters that lie in a more spherical halo.

Original Source: Gemini Observatory

Posted on by Fraser Cain

NASA Builds a Stardust Factory

The Cat’s Eye nebula taken by the Hubble Space Telescope. Image credit: NASA./ESA Click to enlarge
Researchers using a “stardust factory” at NASA’s Goddard Space Flight Center, Greenbelt, Md., have solved a mystery of how dying stars make silicate dust at high temperatures. Understanding this process helps us understand our origin, because this dust will become part of another generation of stars and planets, just as previous generations of stars contributed dust grains into our solar system that at least on one planet led to life.

Dying stars heat up internally while expelling their outer layers of gas into space. The gas expands and cools, allowing some matter in it to condense into dust grains. Observations over the last quarter century show dust grains made of silicon and oxygen (SiO or amorphous silicate grains) condensing at 1,300 degrees Fahrenheit (more than 700 degrees Celsius) in the billowing clouds of gas (nebulae) surrounding old stars. The prevailing theory said that this temperature was too high to condense solid silicate grains – the silicon and oxygen should have remained in the gas.

“Even though theory said it was impossible, stars made dust grains at high temperatures anyway — it was happening right before our eyes,” said Dr. Joseph Nuth of Goddard, lead author of a paper on this research recently submitted to the Astrophysical Journal. “So we went to our laboratory at Goddard where we vaporize material in a vacuum and observe how it condenses to see what we were missing.”

The experiment revealed that the “vapor pressure” at which the dust grains condense was too high in the theory. Just as fog (water vapor) condenses out of the air when the temperature drops or the humidity rises, SiO will condense out of nebular gas at certain temperatures and pressures. Warm air holds more water as gas than cold air, which is why 100 percent humidity — the amount of water gas required to completely saturate the air — feels so much more uncomfortable on a hot summer day. Similarly, at high temperatures, it takes more SiO gas in the circumstellar outflow before it will become completely saturated and condense into dust grains.

The pressure at which the SiO gas starts to condense is called its saturated vapor pressure — 100 percent humidity for SiO gas. The experiment revealed that the actual value at 1,300 degrees F was about 100,000 times lower than what was predicted by the theory. The lower actual value means that SiO gas can form dust grains in a 1,300 degree-nebula at concentrations about 100,000 times lower than previously believed. “If weather forecasters had made a similar prediction about the vapor pressure for water, they would say rain was impossible — they would think there was never enough water in the air to make it rain,” said Nuth.

“We plugged the actual, lower saturated vapor pressure values from our experiment into the theory, and it was almost good enough. The modified theory predicted that the SiO gas was very close to condensing into dust grains, but there was still some factor missing,” said Dr. Frank Ferguson of the Catholic University of America, Washington, Co-author of the paper.

According to the researchers, the missing factor was that the SiO molecules can lose energy by radiating it out into space. Molecules can vibrate at different levels, each with more energy than the one below, until, at the highest vibrational levels, they have so much energy that they just break apart. If nothing excites a molecule, giving it energy by hitting it for example, the molecule will spontaneously lose energy by dropping to a lower-energy vibrational level, and will continue to do this until it reaches the ??bf?ground state??bf? or lowest level possible. Since the pressure is low in the outflowing nebular gas, a SiO molecule there does not often collide with another gas molecule. It is also unlikely to be excited by light from the dying star, since the nebula is expanding into the darkness of deep space and only part of its field of view includes the star itself. Under these circumstances a large population of ground-state SiO molecules develops that contain minimal vibrational energy.

To begin forming a silicate dust grain, two SiO molecules have to stick together (condense). This releases energy. That energy has to go somewhere ??bf? likely into more energetic vibrational levels. Two molecules already in high-energy states are more likely to gain too much energy from the condensation reaction, so they would simply split apart again. On the other hand, two low-energy SiO molecules are more likely to remain stuck together with the reaction energy going temporarily into higher-level vibrational states until the larger molecule can radiate this energy into space. Therefore when many of the SiO molecules in the nebula are in low-energy vibrational states, they can condense at a slightly higher temperature than their vapor pressure alone indicates because these molecules are cooler than the surrounding gas.

“When we use the new vapor pressure and account for the vibrational levels of the SiO molecules in the expanding gas, silicate dust condenses easily,” said Nuth. “This result shows how experiment, observation, and theory all complement each other in the search to understand what really happens in nature.” The research was funded by NASA??bf?s Cosmochemistry Research and Analysis Program, NASA Headquarters.

Original Source: NASA News Release

Posted on by Fraser Cain

So, Is Pluto a Planet or Not?

Hubble photograph of Pluto and its three moons. Image credit: Hubble. Click to enlarge.
Unfortunately, the Solar System isn’t so simple. The case for Pluto’s planethood status has gotten a little eroded since its discovery, and there are further challenges facing it into the future.

The four gas giants are clearly planets. They dominate their respective orbits, and have clusters of moons, rings and all sorts of features that separate them from the rock and rubble of asteroids, comets, and other icy objects. Pluto, on the other hand, is nestled inside the Kuiper Belt; a vast population of ice bodies extending beyond the orbit of Neptune. There are an estimated 70,000 objects in the belt larger than 100 km (62 miles) across, and Pluto appears to just be a particularly large example.

As powerful observatories and space-based telescopes push out our understanding of the Kuiper Belt, many new objects have been discovered; several are close in size to Pluto. For every scientific measurement you can give Pluto: size, mass, moons, orbit, it ends up being a large Kuiper Belt Object. The brave members of the Bad Astronomy/Universe Today forum are giving this challenge their best attempt to define a planet.

And this controversy has been expanded with the discovery of 2003UB313 by the team of Michael Brown, Chad Trujillo, and David Rabinowitz. Also part of the Kuiper Belt, this object – code named Xena for now – is about 3000 km across. That makes it 700 km (430 miles) larger than Pluto! Its 557-year orbit is highly eccentric, varying between 38 and 98 astronomical units (the distance of the Earth to the Sun). Pluto, on the other hand, has an orbit that varies between 29 and 49 AU, and Neptune is 30 AU.

So there are times when Xena gets closer to the Sun than Pluto… and it’s bigger. Oh, and it probably has a moon too (code named Gabrielle). Is Xena a planet? If not, why does Pluto get to remain a planet, since it’s smaller, and sometimes orbits further from the Sun.

Objects have been unplaneted already. Before astronomers realized there were thousands of asteroids in the main asteroid belt, the first 4 discovered were considered planets for several decades: Ceres, Pallas, Juno and Vesta.

What’s a planet then? The International Astronomical Union has developed some definitions in 2001 for extrasolar planets, and modified them as recently as 2003, so we can start there.

Under their definition, planets are any objects orbiting stars or stellar remnants (like pulsars) which are below the limiting mass for thermonuclear fusion of deuterium. This sets an upper limit at about 13 times the mass of Jupiter.

What about a lower limit? Well, the IAU goes on to state that the minimum size/mass for an extrasolar planet should be under the same criteria for what’s used to define planets in the Solar System. This brings us right back to the beginning. When super powerful telescopes are developed that can detect objects as small as Pluto around other stars, whether or not they’re planets depends on Pluto’s planetary status.

Back to the beginning, then.

Mike Brown, one of the astronomers who original discovered Xena, has heard rumours that the International Astronomical Union is going to be discussing this dilemma at their upcoming meeting in Prague in August 2006. We could wind up with 8 planets (sorry Pluto), 9 planets (nothing changes), or 10 planets (welcome Xena and all future super-Plutos). And if the IAU extends this to 10 planets, will 11 be around the corner? Are you ready to memorize the 30 planets?

Brown states on his website:

  • A special committee of the International Astronomical Union (IAU) was charged with determining “what is a planet.”
  • Sometime around the end of 2005, this committee voted by a narrow margin for the “pluto and everything bigger” definition, or something close to it.
  • The executive committee of the IAU then decided to ask the Division of Planetary Sciences (DPS) of the American Astronomical Society to make a recommendation.
  • The DPS asked their committee to look in to it.
  • The DPS committee decided to form a special committee.
  • Rumor has emerged that when the IAU general assembly meets in August in Prauge they will make a decision on how to make a final decision!

Whatever they decide, NASA is going to see Pluto up close. New Horizons just launched earlier this year, and it will take 9 years to reach Pluto in 2015. Its Pluto/Charon encounter will begin in July, and last for more than 100 days, giving us our first close up look at this planet/big Kuiper Belt Object. By the time it arrives, we can only hope the IAU has made up their minds.

If the decision were up to me, I’d say Pluto is a planet. For starters we wouldn’t have to go back and edit all those astronomy textbooks, websites, sculptures, museum exhibits and PBS documentaries. Our Solar System just isn’t so simple; objects scale from the tiny to the huge, with all sizes in between. Any decision on Pluto’s planethood will be an arbitrary one, and the arbitrary decision I like is… Pluto’s a planet.

Written by Fraser Cain

Posted on by Mark Mortimer

Book Review: Getting Off the Planet

Before the U.S.’s Mercury mission placed people in orbit, the U.S. sent chimpanzees to test the physiological impact of space travel. Before either of these, people and animals were subject to simulations of the high acceleration of lift off as well as the micro-gravity of space. Of course, as the rockets weren’t ready, other test devices were needed. Thus, using ingenuity, trial and perseverance, people gathered the background knowledge for putting a human into space and having them undertake a useful role during their voyage.

Dr. Chambers was the head of the Human Engineering Division of the Aviation Medical Acceleration Laboratory. In this role, he prepared experiments and trials that built confidence in the success of human space flight. Extreme experiments included a 24 hour exposure to a 2G force that simulated a mission to Mars and bungee cords placed along a wall to simulate bouncing along in the lighter Moon gravity. With human space flight just beginning, almost everything undertaken was original but all had role in preparing the astronauts. In keeping with standard research and development, a prescriptive series of steps were used to resolve each increment of research. And Dr. Chambers was at the centre of the action, though it is Mary Chambers who wrote this book.

Mary Chambers is Dr. Chambers’ wife and thus she had a ring-side view of the experiments, experimenters and subjects. From this perspective, she provides a charming and witty account of the goings-on of her husband and cohorts. In a more familial than technical narrative, she discuses how her husband developed a research methodology and then she discusses many of the experiments themselves. Often Dr. Chambers was the test subject in these original trials which of course brings in many spousal concerns. She continues on to present a more emotional aspect of the training; the fears and uncertainties of the subjects, the boundless curiosity of the testers and their unifying desire for success. Her view is warmly candid and evocative of the time.

This book is a short, well illustrated memorial to the Chambers family and the work accomplished by Dr. Chambers. Many references to the Mercury astronauts and even Ham the chimpanzee show how closely the family was integrated into the space program. There is a certain lack of technical issues or contributions to science. A simple statement of the establishment of principles and standards of human capabilities and limitations’ is made without more detail. In spite of this, Mrs. Chambers does provide a nice tie-in between this space research and today’s physiological understanding such as the detrimental effects of extensive bed rest. However, this book isn’t a technical reference; rather it’s a folksy memorial to a vibrant time and one family’s contribution.

Travelling into the unknown is fun but also scary. Simulations and training can reduce the fear so that people can continue making contributions, even while experiencing new environments. Mary Jane Chambers and Dr. Randall Chambers in their book Getting Off the Planet show the depth of research needed to prepare humans for space flight. With such effort, astronauts were able to navigate in space, perform orbital rendezvous and competently travel on the Moon’s surface.

Review by Mark Mortimer

Read more reviews online or purchase a copy from Amazon.com

Posted on by Fraser Cain

What’s Up This Week – February 20 – February 26, 2006

What's Up 2006

Download our free “What’s Up 2006” ebook, with entries like this for every day of the year.

M41. Image credit: NOAO/AURA/NSF. Click to enlarge.
Monday, February 20 – Today in 1962, John Glenn was onboard Friendship 7 and became the first American to orbit the Earth. As Colonel Glenn looked out the window, he reported seeing “fireflies” glittering outside his Mercury space capsule. Let’s see if we can find some…

The open cluster M41 in Canis Major is just a quick drift south of the brightest star in the northern sky – Sirius. Even the smallest scopes and binoculars will reveal this rich group of mixed magnitude stars and fill the imagination with strange notions of reality. Through larger scopes, many faint groupings emerge as the star count rises to well over 100 members. Several stars of color – orange in particular – are also seen along with a number of doubles.

First noted telescopically by Giovanni Batista Hodierna in the mid-1500s, ancient texts indicate that Aristotle saw this naked-eye cluster some 1800 years earlier. Like other Hodierna discoveries, M41 was included on Messier’s list – along with even brighter clusters of antiquity such as Praesepe in Cancer and the Pleiades in Taurus.
Open cluster M41 is located 2300 light years away and recedes from us at 34km/sec – about the speed Venus moves around the Sun. M41 is a mature cluster, around 200 million years old and 25 light years in diameter. Remember M41…Fireflies in night skies.

Tuesday, February 21 – Be sure to have a look at the Moon this morning before dawn, because Jupiter will be joining it!

Tonight Luna will rise well after midnight, so let’s return to look at two of the few globular clusters of the season. Starting with M79 in Lepus, head due south around 15 degrees into Columba – the Dove. There you’ll find a second winter cluster almost a full magnitude brighter than M79 – NGC 1851. Give it a try!

Want another challenge? Head for bright Alnitak – the easternmost star in Orion’s belt. Using medium to low power, carefully shift bright Alnitak out from the center of the field about a full moon’s width to the west. With dark skies, you will see a large, faint, tulip-shaped nebulosity broken by one or more dark lanes. This is the “Flame Nebula”
– NGC 2024. Congratulations. This one isn’t easy, but on the darkest of nights it may surprise you!

Wednesday, February 22 – If skies are clear this evening, all you need do is step outside as the last glow of the long-set Sun pales to the southwest. Prepare your eyes – and heart – to follow the great expanse of the many brilliant stars of the winter Milky Way. Arching from Puppis to Cassiopeia, you might also see a fading Deneb – crown star of the Northern Cross – descending west. If you live towards the southern hemisphere, you should see brilliant Canopus – second brightest star in the night sky high to the south. In honor of the many splendid lights of the winter Milky Way, take out your binoculars and explore the marvels that await you!

Did you find something in the binoculars that caught your eye? Why not get the scope out and see if you can track it down. Navigating with a scope can be a challenge. Things look differently by eye, binoculars, finderscope, and telescope, but that’s what learning the night sky is all about.

Thursday, February 23 – On this date in 1987, Ian Shelton made an astonishing discovery – a supernova. At 160,000 light years away, distant SN1987a was the brightest novae display seen in almost 400 years. More importantly, before it occurred, a blue star of roughly 20 solar masses was already known to exist in that same location within the Large Magellanic Cloud. Catalogued as Sanduleak -69?202, that star is now gone. With available data on the star, astronomers were able to get a “before and after” look at one of the most extraordinary events in the universe! Tonight, let’s have a look at a similar event known as “Tycho’s Supernova.”

Located northwest of Kappa Cassiopeia, SN1572 appeared so bright in that year that it could be seen with the unaided eye for six months. Since its appearance was contrary to Ptolemaic theory, this change in the night sky now supported Copernicus’ views and heliocentric theory gained credence. We now recognize it as a strong radio source, but can it still be seen? There is a remnant left of this supernova, and it is challenging even with a large telescope. Look for thin, faint filaments that form an incomplete ring around 8 arc minutes across.

Friday, February 24 – In 1968, during a radio-telescope search for quasars, Susan Jocelyn Bell discovered the first pulsar. At first the regularity of the pulses was so precise that Bell and her college advisor, D. A. Hewish, thought they might be receiving a signal from a distant civilization. It soon became clear as the number of these objects multiplied that all were natural – rather than artificial – phenomena. Two co-directors of the project, Hewish and Ryle, later matched Bell’s observations to the notion of a rotating neutron star. This won them the 1974 Physics Nobel Prize and proved a theory brought forward thirty years earlier by J. Robert Oppenheimer.
Tonight let’s take a journey just a breath above Zeta Tauri and spend some quality time with a pulsar embedded in the most famous supernova remnant of all. Factually, we know the Crab Nebula to be the remains of an exploded star recorded by the Chinese in 1054. We know it to be a rapid expanding cloud of gas moving outward at a rate of 1,000 km per second, just as we understand there is a pulsar in the center. We also know it as first recorded by John Bevis in 1758, and then later cataloged as the beginning Messier object – penned by Charles himself some 27 years later to avoid confusion while searching for comets. We see it revealed beautifully in timed exposure photographs, its glory captured forever through the eye of the camera — but have you ever really taken the time to truly study M1?

Then you just may surprise yourself…

In a small telescope, M1 might seem to be a disappointment – but do not just glance at it and move on. There is a very strange quality to the light which reaches your eye, even though initially it may just appear as a vague, misty patch. Allow your eyes to adjust and M1 will appear to have “living” qualities – a sense of movement in something that should be motionless. The “Crab” holds true to many other spectroscopic studies. The concept of differing light waves crossing over one another and canceling each other out – with each trough and crest revealing differing details to the eye – is never more apparent than during study. To observe M1 is to at one moment see a “cloud” of nebulosity, the next a broad ribbon or filament, and at another a dark patch. When skies are stable you may see an embedded star, and it is possible to see six such stars.

Many observers have the ability to see spectral qualities, but they need to be developed. From ionization to polarization – our eye and brain are capable of seeing to the edge of infra-red and ultra-violet. Even a novice can see the effects of magnetism in the solar “Wilson Effect.” But what of the spinning neutron star at M1’s heart? We’ve known since 1969 that M1 produces a “visual” pulsar effect. About once every five minutes, changes occurring in the neutron star’s pulsation affect the amount of polarization, causing the light waves to sweep around like a giant “cosmic lighthouse” and flash across our eyes. M1 is much more than just another Messier. Capture it tonight!!

Saturday, February 25 – Since we’ve studied the “death” of a star, why not take the time tonight to discover the “birth” of one? Our journey will start by identifying Aldeberan (Alpha Tauri) and move northwest to bright Epsilon. Hop 1.8 degrees west and slightly to the north for an incredibly unusual variable star – T Tauri.
Discovered by J.R. Hind in October 1852, T Tauri and its accompanying nebula, NGC 1555, set the stage for discovery with a pre-main sequence variable star. Hind reported the nebula, but also noted that no catalog listed such an object in that position. His observations also included a 10th magnitude uncharted star and he surmised that the star in question was a variable. On each count Hind was right, and both were followed by astronomers for several years until they began to fade in 1861. By 1868, neither could be seen and it wasn’t until 1890 that the pair was re-discovered by E.E. Barnard and S.W. Burnham. Five years later? They vanished again.

T Tauri is the prototype of this particular class of variable stars and is itself totally unpredictable. In a period as short as a few weeks, it might move from magnitude 9 to 13 and other times remain constant for months on end. It is about equal to our own Sun in temperature and mass
– and its spectral signature is very similar to Sol’s chromosphere – but the resemblance ends there. T Tauri is a star in the initial stages of birth!

T Tauri are all pre-main sequence and are considered “proto-stars”. In other words, they continuously contract and expand, shedding some of their mantle of gas and dust. This gas and dust is caught by the star’s rotation and spun into an accretion disc – which might be more properly referred to as a proto-planetary disc. By the time the jets have finished spewing and the material is pulled back to the star by gravity, the proto-star will have cooled enough to have reached main sequence and the pressure may have allowed planetoids to form from the accreted material.

Sunday, February 26 – Today is the birth date of Camille Flammarion. Born in 1842, he became a widely read author of astronomy and originated the idea that we were not alone – the notion of extraterrestrial intelligence. Yet, Flammarion was more than the great grandfather of SETI. In 1877, Flammarion found Charles Messier’s personal notes and catalog in an antiquarian book store. Based on those notes, he was able to identify M102 as Dreyer’s NGC 5866 and associate NGC 4594 with M104. Because of Flammarion’s hard work of scholarship and astronomical observation, two previously obscure references to faint studies in the Messier Catalogue were properly identified.

To locate these two studies, you’ll be waiting until around local midnight. Start at Iota Draconis and head about half a fistwidth in the direction of bright Arcturus to a solitary 5.2 magnitude star. Small, 10th magnitude M102 is about one degree due north toward Polaris. M104 – the “Sombrero Galaxy” – is just a bit more than a fistwidth west of Spica. At magnitude 8.3, it can be easily seen as a small faint glow in binoculars or finderscope. But it requires a telescope and a dark sky to hint at its namesake.

While you’re waiting for them to rise, relax and enjoy the Delta Leonid meteor shower. Entering our atmosphere at speeds of up to 24 kilometers per second, these slow travelers will seem to radiate from a point around the middle of Leo’s “back.” The fall rate is rather slow at 5 per hour, but any meteor trail is a delight to catch!

May all your journeys be at light speed… ~Tammy Plotner. With Jeff Barbour @astro.geekjoy.com

Posted on by Fraser Cain

Great Mercury Viewing This Week

Mercury on Feb. 13, 2006. Image credit: Jeffrey Beall. Click to enlarge
It’s not every day you get to see a shrinking planet. Today could be the day.

Step outside this evening at sunset and look west toward the glow of the setting sun. As the sky fades to black, a bright planet will emerge. It’s Mercury, first planet from the sun, also known as the “Incredible Shrinking Planet.”

“This is only the second time in my life I’ve seen Mercury,” says sky watcher Jeffrey Beall who snapped this picture looking west from his balcony in Denver, Colorado:

Mercury is the bright “star” just above the mountain ridge, rivaling the city lights.

Mercury is elusive because it spends most of its time hidden by the glare of the sun. This week is different. From now until about March 1st, Mercury moves out of the glare and into plain view. It’s not that Mercury is genuinely farther from the sun. It just looks that way because of the Earth-sun-Mercury geometry in late February. A picture is worth a thousand words: diagram.

Friday, Feb. 24th, is the best day to look (sky map); that’s the date of greatest elongation or separation from the sun. Other dates of note are Feb 28th (sky map) and March 1st (sky map) when the crescent moon glides by Mercury??bf?very pretty.

When you see Mercury popping out of the evening twilight, you’re looking at a very strange place. “Shrinking” is a good example:

In 1974, NASA’s Mariner 10 spacecraft flew by Mercury and, for the first time, photographed the planet from close range. Cameras revealed a densely cratered world??bf?with wrinkles. Planetary geologists call them “lobate scarps” and, like wrinkles on a raisin, they are thought to be a sign of shrinking. What would make a planet shrink? One possibility: Mercury’s oversized iron core has been cooling for billions of years, and its contraction may be the driving force behind the wrinkles. No one knows for sure.

No one knows because Mercury has hardly been explored. Only one spacecraft has ever been there, and during its oh-so-brief visit Mariner 10 managed to photograph less than half (45%) of Mercury’s surface: image. The majority is terra incognita.

Another puzzle is the mystery-substance at Mercury’s poles. Radio astronomers have pinged Mercury from afar using radars on Earth, and they have found something very bright in Mercury’s polar craters. Again, no one knows what it is, although a favorite possibility is ice. Frozen water is a good reflector of radio waves and would explain the observations nicely.

How could frozen water exist on Mercury? The sun heats the planet’s surface to 400 ??bf?C (750 ??bf?F) or more, too hot for frozen anything. Yet deep down in some polar craters, researchers believe, the sun never shines. In permanent shadow, the temperature drops below -212??bf? C (-350??bf? F). Suppose a piece of an icy comet or meteorite landed in such a crater; some of the ice might survive.

Or it could be something else entirely.

What does the unknown half of Mercury look like? Is the planet really shrinking? Can ice stay frozen in an inferno? Mercury poses many questions: list. A new NASA probe named “MESSENGER” is en route to find some answers, but it will not reach Mercury until 2008.

For now, one can only peer into the twilight and wonder. Give it a try, this evening.

Original Source: NASA News Release

Posted on by Fraser Cain

Earth’s Iron Building Blocks

Artist’s conception shows Romulus and Remus orbiting the asteroid 87 Sylvia. Image credit: ESO Click to enlarge
Iron meteorites are probably the surviving fragments of the long-lost asteroid-like bodies that formed the Earth and other nearby rocky planets, according to researchers from Southwest Research Institute (SwRI) and Observatoire de la Cote d’Azur in Nice, France. Their findings are described in the Feb.16 issue of Nature.

Iron meteorites, which are composed of iron and nickel alloys, represent some of the earliest material formed in the solar system, with most coming from the cores of small asteroids. According to Dr. William Bottke, an SwRI research scientist and leader of the joint U.S.-French team, iron-meteorite parent bodies probably emerged from the same disk of planetary debris that produced the Earth and other inner solar system planets.

“Small bodies that form quickly in the inner solar system end up melting and differentiating from the decay of short-lived radioactive elements,” explains Bottke. “Iron meteorites came from the molten material that sinks to the center of these objects, cools and solidifies.”

For these meteorites to arrive on Earth, they must have been extracted from their parent bodies and kept around for billions of years. The team’s computer simulations found that any asteroids managing to avoid being gobbled up by the planets were quickly demolished by impacts. Each breakup, however, produces millions of fragments, many in the form of iron meteorites. These leftovers were scattered across the solar system by gravitational interactions with protoplanetary bodies, with some reaching the relative safety of the asteroid belt. Over billions of years, a few of the survivors escaped their captivity in the asteroid belt and were delivered to Earth.

“This means that certain iron meteorites may tell us what the precursor material for the primordial Earth was like, while also helping us unlock several fundamental questions about the Earth’s origins,” says Bottke. “There’s also the possibility that larger versions of this material may still be hiding among the asteroids. The hunt for them is on.”

A new way to look at iron meteorites

A potential problem in using meteorites to understand the formation of Earth and other terrestrial planets Mercury, Venus and Mars is that most come from the distant asteroid belt. This population of interplanetary bodies, ranging from tiny pebbles to Texas-sized objects, is located between the orbits of Mars and Jupiter about 140 million miles from Earth.

Most members of the asteroid belt are assumed to have formed there, so the vast majority of meteorite samples tell us about formation events in that region, not those that took place near Earth. Meteorite compositions are so diverse, however, that it is difficult to reconcile that all came from this one, fairly narrow region of space.

“While tens of thousands of stony meteorites have been collected, most can be traced back to perhaps a few tens of parent asteroids,” says Dr. Alessandro Morbidelli of the Observatorie de la Cote d’Azur. “What is strange is that the iron meteorites, despite their smaller numbers, represent almost two-thirds of all of the unique parent asteroids sampled to date.”

To explain this discrepancy, the team tracked the origin and evolution of iron-meteorite parent bodies using several computer models. They found that while many iron meteorites are likely residing in the asteroid belt today, their precursors probably did not form there. Instead, the simulations indicate that the precursors of most iron meteorites formed in the terrestrial planet region.

To investigate this hypothesis, the researchers first examined the constraints provided by the meteorites themselves. Iron meteorites are unusual in that most come from the disrupted cores of small melted (differentiated) asteroids that formed very early in solar system history. These are precisely the kinds of bodies that computer models predict should have formed near Earth.

“It is hard to produce small differentiated bodies in the asteroid belt without also melting lots of large asteroids,” explains Dr. Robert Grimm, assistant director of the SwRI Space Studies Department. “These events would produce a number of telltale signs that would be easily detected by observers.”

Using computer simulations, the team then tracked how a disk of asteroid-like bodies interacting with a host of protoplanetary objects in the terrestrial planet region might evolve. Simulations showed that some of these asteroid-like bodies could have scattered far enough to take up residence in the asteroid belt.

“While the amount of material reaching the asteroid belt was limited, much of it was placed in regions likely to produce meteorites,” says SwRI Research Scientist Dr. David Nesvorn??bf?. En route to the asteroid belt, the parent bodies of the iron meteorites were repeatedly bashed by other bodies, allowing core fragments from numerous bodies to escape.

“This could explain the many differences seen among iron meteorites,” says Dr. David O’Brien of the Observatoire de la Cote d’Azur.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Stardust’s Samples Under Analysis

Stardust’s aerogel sample. Image credit: NASA Click to enlarge
Scientists at the University of Chicago are among the first ever to analyze cometary dust delivered to Earth via spacecraft.

Scientists routinely examine extraterrestrial material that has fallen to Earth as meteorites, but never before NASA’s Stardust mission have they had access to verified samples of a comet. The leftover debris from the formation of the solar system 4.5 billion years ago, comets consist mostly of ice, dust and rock.

“We think comets make up a huge amount of stuff out in the solar system. We’d like to know the mineral composition of this big component of the solar system that we’ve never seen before for sure,” said Lawrence Grossman, Professor in Geophysical Sciences. “Various particles have been measured that have been inferred to be from comets, but nobody’s sure. This would finally provide some ground truth.”

Grossman and Steven Simon, Senior Research Associate in Geophysical Sciences, are members of the Stardust Preliminary Examination Team (PET). So are Andrew Davis, Senior Scientist in the Enrico Fermi Institute, and his colleagues Michael Pellin and Michael Savina of the U.S. Department of Energy’s Argonne National Laboratory. The role of PET is to describe the samples in a general way so that the scientists can propose more detailed studies based on that information.

Davis also is a member of the Stardust Sample Allocation Committee, which will decide how to distribute the samples for additional research once the preliminary examination period ends in mid-July.

The Stardust mission launched in February 1999, carrying a set of instruments that included one provided by the University of Chicago to monitor the impact of cometary dust. On Jan. 2, 2004, the spacecraft came within 150 miles of the comet and collected thousands of tiny dust particles streaming from its nucleus. The Stardust sample-return canister parachuted onto the desert salt flats of Utah on Jan. 15 following a journey of nearly three million miles.

During the 2004 cometary encounter, the University of Chicago’s Dust Flux Monitor Instrument successfully determined the flow and mass of the particles streaming from the comet’s nucleus. Based on data collected by the instrument, the University of Chicago’s Anthony Tuzzolino and Thanasis Economou estimated that the spacecraft had collected at least 2,300 particles measuring 15 micrometers (one-third the size of a human hair) or larger during the flyby.

“It will take the experts many, many months before they will determine the accurate number, but I am sure that in the end their number will be close to what we have predicted,” said Economou, who was at the Johnson Space Center in Houston when the samples were delivered from Utah. “Stardust was very successful beyond all expectation in all its phases.”

The comet dust is now available for comparison to tiny particles constantly raining down on Earth that scientists suspect come from comets. NASA routinely collects these stratospheric dust particles with high-altitude aircraft and maintains a collection of them, Simon said. Certain types of meteorites might also originate from comets, but without having cometary material to compare, “we don??bf?t know,” Grossman said.

Grossman and Simon received several samples on Feb. 7. The samples partly consist of several thin slices of one dust grain mounted in epoxy and held on a round copper grid covered by a thin film. They also received a bullet-shaped epoxy plug holding the remainder of the grain.

“They can make hundreds of slices of each individual grain,” Simon said. He and Grossman are studying their slices with an electron microprobe and a scanning electron microscope (SEM). The microprobe is capable of revealing the chemical composition of microscopically small patches of material, while the SEM provides highly magnified images.

The Stardust cometary materials now join a collection of charged particles from the sun gathered by NASA’s Genesis mission and returned to Earth in 2004. Davis serves as chair of the Genesis Oversight Committee, which guides the curation and analysis of that mission’s extraterrestrial materials.

“Cosmochemistry is a very exciting field these days,” Davis said, referring to research on the origin of the chemical elements and the chemistry of extraterrestrial materials. “It??bf?s an interesting time to get young people involved in the field.” In 2004, along with colleagues at Argonne and the Field Museum, Davis organized the Chicago Center for Cosmochemistry to promote education and research in cosmochemistry.

The Stardust spacecraft, meanwhile, may someday see further cometary action. “Stardust is still very healthy and has fuel left over,” Economou said. “After dropping the Space Return Canister, the spacecraft was diverted from entering the Earth’s atmosphere and placed in an orbit around the sun that could bring it to another comet in February 2011.”

The Stardust mission is managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif. Lockheed Martin Space Systems, Denver, developed and operated the spacecraft. For more information, see http://stardust.jpl.nasa.gov/home/index.html and http://cosmochemistry.uchicago.edu/.

Original Source: University of Chicago