Posted on by Fraser Cain

Spirit Steering Problem Returns

A problem that affects the steering on NASA’s Mars Exploration Rover Spirit has recurred after disappearing for nearly two weeks.

Engineers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., are working to fully understand the intermittent problem and then implement operational work-arounds. Meanwhile, Spirit successfully steered and drove 3.67 meters (12 feet) on Oct. 17.

Rover engineers are also analyzing a positive development on Spirit’s twin, Opportunity: a sustained boost in power generation by Opportunity’s solar panels.

Both rovers have successfully completed their three-month primary missions and their first mission extensions. They began second extensions of their missions on Oct. 1.

Rover engineers refrained from driving Spirit for five days after an Oct. 1 malfunction of a system that prevents wheels from being jostled in unwanted directions while driving. Each of the front and rear wheels of the rover has a motor called a steering actuator. It sets the direction in which the wheel is headed. The steering actuators are different from the motors that make the wheels roll, and hold the wheel in a specific direction while driving. A relay used in turning these steering actuators on and off is the likely cause of the intermittent nature of the anomaly.

The relay operates Spirit’s right-front and left-rear wheels concurrently, and did not operate as commanded on Oct. 1. Subsequent testing showed no trace of the problem, and on Oct. 7, the rover steered successfully and drove about 2 meters (7 feet), putting it in position to examine a layered rock called “Tetl” for several days. However, the anomaly occurred again on Oct. 13, and the problem appeared intermittently in tests later last week.

“We are continuing tests on Spirit and in our testbed here at JPL,” said Jim Erickson, Mars Exploration Rover project manager at JPL. One possible work-around would be to deliberately blow a fuse controlling the relay, disabling the brake action of the steering actuators. The rovers could be operated without that feature. “The only change might be driving in shorter steps when the rover is in rugged terrain,” Erickson said.

Spirit has driven a total of 3,647 meters (2.27 miles) since landing, more than six times the distance set as a goal for the mission. Its current target is a layered rock called “Uchben” in the “Columbia Hills.” Opportunity has driven 1,619 meters (just over a mile). Its latest stop is a lumpy boulder dubbed “Wopmay” inside “Endurance Crater.”

The daily power supply for each rover comes from 1.3 square meters (14 square feet) of solar panels converting sunlight into electricity. Just after the landings in January, the output was about 900 watt-hours per day for each rover — enough to run a 100-watt bulb for nine hours. As anticipated, output gradually declined due to dust buildup and the martian seasonal change with fewer hours of sunlight and a lower angle of the Sun in the sky. By July, Spirit’s daily output had declined to about 400 watt-hours per day. It has been between 400 and 500 watt-hours per day for most of the past two months.

Opportunity, closer to Mars’ equator and with the advantage of a sunward-facing tilt as it explored inside the southern half of a crater, maintained an output level between 500 and 600 watt-hours per day in June, July and August. Since early September, the amount of electricity from Opportunity’s solar panels has increased markedly and unexpectedly, to more than 700 watt-hours per day, a level not seen since the first 10 weeks of the mission.

“We’ve been surprised but pleased to see this increase,” said Erickson, “The team is evaluating ways to determine which of a few different theories is the best explanation.”

Possible explanations under consideration include the action of wind removing some dust from the solar panels or the action of frost causing dust to clump. “We seem to have had several substantial cleanings of the solar panels,” Erickson said.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Science Mission Directorate, Washington. Additional information about the project is available from JPL at http://marsrovers.jpl.nasa.gov/ and from Cornell University, Ithaca, N.Y., at http://athena.cornell.edu.

Original Source: NASA/JPL News Release

Posted on by Fraser Cain

Frame Dragging Confirmed

An international team of NASA and university researchers has found the first direct evidence the Earth is dragging space and time around itself as it rotates.

The researchers believe they have measured the effect, first predicted in 1918 by using Einstein’s theory of general relativity, by precisely observing shifts in the orbits of two Earth-orbiting laser-ranging satellites. The researchers observed the orbits of the Laser Geodynamics Satellite I (LAGEOS I), a NASA spacecraft, and LAGEOS II, a joint NASA/Italian Space Agency (ASI) spacecraft.

The research, reported in the journal Nature, is the first accurate measurement of a bizarre effect that predicts a rotating mass will drag space around it. The Lense-Thirring Effect is also known as frame dragging.

The team was led by Dr. Ignazio Ciufolini of the University of Lecce, Italy, and Dr. Erricos C. Pavlis of the Joint Center for Earth System Technology, a research collaboration between NASA’s Goddard Space Flight Center, Greenbelt, Md., and the University of Maryland Baltimore County.

“General relativity predicts massive rotating objects should drag space-time around themselves as they rotate,” Pavlis said. “Frame dragging is like what happens if a bowling ball spins in a thick fluid such as molasses. As the ball spins, it pulls the molasses around itself. Anything stuck in the molasses will also move around the ball. Similarly, as the Earth rotates, it pulls space-time in its vicinity around itself. This will shift the orbits of satellites near Earth.” The study is a follow-up to earlier work in 1998 where the authors’ team reported the first direct detection of the effect.

The previous measurement was much less accurate than the current work, due to inaccuracies in the gravitational model available at the time. Data from NASA’s GRACE mission allowed for a vast improvement in the accuracy of new models, which made this new result possible.

“We found the plane of the orbits of LAGEOS I and II were shifted about six feet (two meters) per year in the direction of the Earth’s rotation,” Pavlis said. “Our measurement agrees 99 percent with what is predicted by general relativity, which is within our margin of error of plus or minus five percent. Even if the gravitational model errors are off by two or three times the officially quoted values, our measurement is still accurate to 10 percent or better.” Future measurements by Gravity Probe B, a NASA spacecraft launched in 2004, should reduce this error margin to less than one percent. This promises to tell researchers much more about the physics involved.

Ciufolini’s team, using the LAGEOS satellites, previously observed the Lense-Thirring effect. It has recently been observed around distant celestial objects with intense gravitational fields, such as black holes and neutron stars. The new research around Earth is the first direct, precise measurement of this phenomenon at the five to 10 percent level. The team analyzed an 11-year period of laser ranging data from the LAGEOS satellites from 1993 to 2003, using a method devised by Ciufolini a decade ago.

The measurements required the use of an extremely accurate model of the Earth’s gravitational field, called EIGEN-GRACE02S, which became available only recently, based on an analysis of GRACE data. The model was developed at the GeoForschungs Zentrum Potsdam, Germany, by a group who are co-principal investigators of the GRACE mission along with the Center for Space Research of the University of Texas at Austin.

LAGEOS II, launched in 1992, and its predecessor, LAGEOS I, launched in 1976, are passive satellites dedicated exclusively to laser ranging. The process entails sending laser pulses to the satellite from ranging stations on Earth and then recording the round-trip travel time. Given the known value for the speed of light, this measurement enables scientists to precisely determine the distances between laser ranging stations on Earth and the satellite.

NASA and Stanford University, Palo Alto, Calif. developed Gravity Probe B. It will precisely check tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting 400-miles directly over the poles. The experiment will test two theories relating to Einstein’s Theory of General Relativity, including the Lense-Thirring Effect. These effects, though small for Earth, have far-reaching implications for the nature of matter and the structure of the universe.

Original Source: NASA News Release

Posted on by Fraser Cain

The Virgo Galaxy Cluster is Still Being Formed

An international team of astronomers [2] has succeeded in measuring with high precision the velocities of a large number of planetary nebulae [3] in the intergalactic space within the Virgo Cluster of galaxies. For this they used the highly efficient FLAMES spectrograph [4] on the ESO Very Large Telescope at the Paranal Observatory (Chile).

These planetary nebulae stars free floating in the otherwise seemingly empty space between the galaxies of large clusters can be used as “probes” of the gravitational forces acting within these clusters. They trace the masses, visible as well as invisible, within these regions. This, in turn, allows astronomers to study the formation history of these large bound structures in the universe.

The accurate velocity measurements of 40 of these stars confirm the view that Virgo is a highly non-uniform galaxy cluster, consisting of several subunits that have not yet had time to come to equilibrium. These new data clearly show that the Virgo Cluster of galaxies is still in its making.

They also prove for the first time that one of the bright galaxies in the region scrutinized, Messier 87, has a very extended halo of stars, reaching out to at least 65 kpc. This is more than twice the size of our own galaxy, the Milky Way.

A young cluster
At a distance of approximately 50 million light-years, the Virgo Cluster is the nearest galaxy cluster. It is located in the zodiacal constellation Virgo (The Virgin) and contains many hundreds of galaxies, ranging from giant and massive elliptical galaxies and spirals like our own Milky Way, to dwarf galaxies, hundreds of times smaller than their big brethren. French astronomer Charles Messier entered 16 members of the Virgo cluster in his famous catalogue of nebulae. An image of the core of the cluster obtained with the Wide Field Imager camera at the ESO La Silla Observatory was published last year as PR Photo 04a/03.

Clusters of galaxies are believed to have formed over a long period of time by the assembly of smaller entities, through the strong gravitational pull from dark and luminous matter. The Virgo cluster is considered to be a relatively young cluster because previous studies have revealed small “sub-clusters of galaxies” around the major galaxies Messier 87, Messier 86 and Messier 49. These sub-clusters have yet to merge to form a denser and smoother galaxy cluster.

Recent observations have shown that the so-called “intracluster” space, the region between galaxies in a cluster, is permeated by a sparse “intracluster population of stars”, which can be used to study in detail the structure of the cluster.

Cosmic wanderers
The first discoveries of intracluster stars in the Virgo cluster were made serendipitously by Italian astronomer, Magda Arnaboldi (Torino Observatory, Italy) and her colleagues, in 1996. In order to study the extended halos of galaxies in the Virgo cluster, with the ESO New Technology Telescope at La Silla, they searched for objects known as “planetary nebulae” [3].

Planetary nebulae (PNe) can be detected out to large distances from their strong emission lines. These narrow emission lines also allow for a precise measure of their radial velocities. Planetary Nebulae can thus serve to investigate the motions of stars in the halo regions of distant galaxies.

In their study, the astronomers found several planetary nebulae apparently not related to any galaxies but moving in the gravity field of the whole cluster. These “wanderers” belonged to a newly discovered intracluster population of stars.

Since these first observations, several hundreds of these wanderers have been discovered. They must represent the tip of the iceberg of a huge population of stars swarming among the galaxies in these enormous clusters. Indeed, as planetary nebulae are the final stage of common low mass stars – like our Sun – they are representative of the stellar population in general. And as planetary nebulae are rather short-lived (a few tens of thousand years – a blitz on astronomical timescales), astronomers can estimate that one star in about 8,000 million of solar-type stars is visible as a planetary nebula at any given moment. There must thus be a comparable number of stars in between galaxies as in the galaxies themselves. But because they are diluted in such a huge volume, they are barely detectable.

Because these stars are predominantly old, the most likely explanation for their presence in the intracluster space is that they formed within individual galaxies, which were subsequently stripped of many of their stars during close encounters with other galaxies during the initial stages of cluster formation. These “lost” stars were then dispersed into intracluster space where we now find them.

Thus planetary nebulae can provide a unique handle on the number, type of stars and motions in regions that may harbour a substantial amount of mass. Their motions contain the fossil record of the history of galaxy interaction and the formation of the galaxy cluster.

Measuring the speed of dying stars
The international team of astronomers [2] went on further to make a detailed study of the motions of the planetary nebulae in the Virgo cluster in order to determine its dynamical structure and compare it with numerical simulations. To this aim, they carried out a challenging research programme, aimed at confirming intracluster planetary nebula candidates they found earlier and measuring their radial velocities in three different regions (“survey fields”) in the Virgo cluster core.

This is far from an easy task. The emission in the main Oxygen emission line from a planetary nebula in Virgo is comparable to that of a 60-Watt light bulb at a distance of about 6.6 million kilometres, about 17 times the average distance to the Moon. Furthermore intracluster planetary nebula samples are sparse, with only a few tens of planetary nebulae in a quarter of a degree square sky field – about the size of the Moon. Spectroscopic observations thus require 8 metre class telescopes and spectrographs with a large field of view. The astronomers had therefore to rely on the FLAMES-GIRAFFE spectrograph on the VLT [4], with its relatively high spectral resolution, its field of view of 25 arcmin and the possibility to take up to 130 spectra at a time.

The astronomers studied a total of 107 stars, among which 71 were believed to be genuine intracluster planetary candidates. They observed between 21 and 49 objects simultaneously for about 2 hours per field. The three parts of the Virgo core surveyed contain several bright galaxies (Messier 84, 86, 87, and NGC 4388) and a large number of smaller galaxies. They were chosen to represent different entities of the cluster.

The spectroscopic measurements could confirm the intracluster nature of 40 of the planetary nebulae studied. They also provided a wealth of knowledge on the structure of this part of the Virgo cluster.

In The Making
In the first field near Messier 87 (M87), the astronomers measured a mean velocity close to 1250 km/s and a rather small dispersion around this value. Most stars in this field are thus physically bound to the bright galaxy M87, in the same way as the Earth is bound to the Sun. Magda Arnaboldi explains: “This study has led to the remarkable discovery that Messier 87 has a stellar halo in approximate dynamical equilibrium out to at least 65 kpc, or more than 200,000 light-years. This is more than twice the size of our own galaxy, the Milky Way, and was not known before.”

The velocity dispersion observed in the second field, which is far away from bright galaxies, is larger than in the first one by a factor four. This very large dispersion, indicating stars moving in very disparate directions at different speeds, also tells us that this field most probably contains many intracluster stars whose motions are barely influenced by large galaxies. The new data suggest as a tantalizing possibility that this intracluster population of stars could be the leftover from the disruption of small galaxies as they orbit M87.

The velocity distribution in the third field, as deduced from FLAMES spectra, is again different. The velocities show substructures related to the large galaxies Messier 86, Messier 84 and NGC 4388. Most likely, the large majority of all these planetary nebulae belong to a very extended halo around Messier 84.

Ortwin Gerhard (University of Basel, Switzerland), member of the team, is thrilled: “Taken together these velocity measurements confirm the view that the Virgo Cluster is a highly non-uniform and unrelaxed galaxy cluster, consisting of several subunits. With the FLAMES spectrograph, we have thus been able to watch the motions in the Virgo Cluster, at a moment when its subunits are still coming together. And it is certainly a view worth seeing!”

More information
The results presented in this ESO Press Release are based on a research paper (“The Line-of-Sight Velocity Distributions of Intracluster Planetary Nebulae in the Virgo Cluster Core” by M. Arnaboldi et al.) that has just appeared in the research journal Astrophysical Journal Letters Vol. 614, p. 33.

Notes
[1]: The University of Basel Press Release on this topic is available at http://www.zuv.unibas.ch/uni_media/2004/20041022virgo.html.

[2]: The members of the team are Magda Arnaboldi (INAF, Osservatorio di Pino Torinese, Italy), Ortwin Gerhard (Astronomisches Institut, Universit?t Basel, Switzerland), Alfonso Aguerri (Instituto de Astrofisica de Canarias, Spain), Kenneth C. Freeman (Mount Stromlo Observatory, ACT, Australia), Nicola Napolitano (Kapteyn Astronomical Institute, The Netherlands), Sadanori Okamura (Dept. of Astronomy, University of Tokyo, Japan), and Naoki Yasuda (Institute for Cosmic Ray Research, University of Tokyo, Japan).

[3]: Planetary nebulae are Sun-like stars in their final dying phase during which they eject their outer layers into surrounding space. At the same time, they unveil their small and hot stellar core which appears as a “white dwarf star”. The ejected envelope is illuminated and heated by the stellar core and emits strongly in characteristic emission lines of several elements, notably oxygen (at wavelengths 495.9 and 500.7 nm). Their name stems from the fact that some of these nearby objects, such as the “Dumbbell Nebula” (see ESO PR Photo 38a/98) resemble the discs of the giant planets in the solar system when viewed with small telescopes.

[4]: FLAMES, the Fibre Large Array Multi-Element Spectrograph, is installed at the 8.2-m VLT KUEYEN Unit Telescope. It is able to observe the spectra of a large number of individual, faint objects (or small sky areas) simultaneously and covers a sky field of no less than 25 arcmin in diameter, i.e., almost as large as the full Moon. It is the result of a collaboration between ESO, the Observatoire de Paris-Meudon, the Observatoire de Gen?ve-Lausanne, and the Anglo Australian Observatory (AAO).

Original Source: ESO News Release

Posted on by Mark Mortimer

Book Review: Moonrush

The main doomsday premise is the exhaustion of the supply of high density, easily transportable energy (read oil and gas). Not only is this supply nearing exhaustion, but the overall population of human beings is still climbing. Using a number of case studies, the reader is shown that the Earth, as a closed system, can’t support the status quo. We either need less people, a lower quality of life or more Earths. The last option, crazy as it sounds, is exactly what Wingo is proposing. Within our Solar System, there are bodies that contain many of the elements that are mined on Earth. These include the rare and valuable platinum group metals, especially palladium, which play a key role in today’s economy and would do so even more in a future hydrogen based economy. Thus we have a proposed solution to the envisioned energy doomsday; that is, to mine for the required minerals on asteroids, comets and moons.

Wingo takes the reader on a whirlwind tour of the history of lunar exploration and present day space flight capability (there’s plenty of wailing and gnashing of teeth about the unproductive Apollo missions and the total lack of interest in lunar exploration). By using the results from the Apollo missions and the Clementine and Lunar Prospector missions, Wingo makes a strong case for lunar mining. As a response to the doomsday premise and using the data gathered by these spacecraft, we’re presented with plans to use existing technology to get mining on the Moon. A detailed $16 billion list of components and techniques follows to explain exactly what would get done. Wingo thinks that governments need to provide incentives, minimize obstacles and encourage private enterprise to get mining.

The title is well suited. Like the earlier gold rushes in North America that did so much to open up tracts of land, a Moon rush, with people headed to the Moon to bring minerals back to Earth can also lead to all kinds of innovations. Further, by extracting, smelting and refining off-Earth, we can keep the harmful waste away too. This would be another benefit to life on Earth, as the subtitle states.

The book’s prose lacks a bit. It’s kind of repetitive and I got the impression that it’s a cleaned up version of someone’s class notes. There’s quite a lot of extraneous information, like completely describing the Otto cycle internal combustion engine, and a lengthy study of the stock prices of Boeing and Microsoft. I get how they’re relevant, but I’m not sure it was the best use of space and focus. Still, the chapters are clear and well laid out.

I liked Moonrush. It’s not too technical, and there isn’t a lot of hand waving. The premise is clear and well supported. The historical perspective lends credence and vision. Finally, Wingo does a great job of describing vehicles and methodology that ring true to me (as an armchair Moon miner).

Although Moonrush – Improving Life on Earth with the Moon’s Resources starts on a sour note – you know, the impending doom of the human race – it’s really a positive book that shows how Dennis Wingo has enthusiasm and faith that private enterprise will help get us back to the Moon with 21st century pickaxes and shovels to get the minerals we need without having to wreck our own environment. Maybe doom won’t be around the corner after all. If Paul Allen’s got some pocket change left over, he’d be well advised to kick some cash to help harvest the Moon’s resources.

To read more reviews, or order the book online, visit Amazon.com.

Review by Mark Mortimer

Posted on by Fraser Cain

Huygens Will Listen For Thunderstorms

Image credit: ESA
The sound of alien thunder, the patter of methane rain and the crunch (or splash) of a landing, all might be heard as Huygens descends to the surface of Titan on 14 January 2005.

What?s more, they will be recorded by a microphone on the probe and relayed back so that everyone on Earth can hear the sounds of Titan. Although the Russians took a microphone to Venus in the 1970s, few scientific results came out if that endeavour. A similar microphone for Mars was destroyed when NASA?s Mars Polar Lander crashed a few years ago.

The new microphone is part of the Huygens Atmospheric Structure Instrument (HASI), one of six multi-functional experiments carried on the Huygens probe. It is designed to help track down lightning by listening for the clap of thunder usually associated with such an event.

Although there is only a small chance that the spacecraft will pass near a thunderstorm, it is an extremely important investigation to carry out. It may help us to understand if thunderstorms are an important energy source for organic chemistry on Titan.

This may hold clues about how life began on Earth. Titan?s atmosphere is laced with chemicals and many scientists think these are the same as those that formed the building blocks of life on Earth, 4000 million years ago. But how did they join together on Earth to ultimately become DNA?

One possibility is that sudden discharges of energy, as occur in lightning, could have forced the simple chemicals together, making more complicated ones. So Huygens will listen for thunder and ?sniff? for chemicals that might have been produced in lightning strikes.

In fact, a second microphone experiment can also be found on Huygens. It is part of the Surface Science Package (SSP) and contributes to an experiment to measure the speed of sound in Titan?s atmosphere.

These results present an exciting possibility because if the HASI microphone does hear thunder, electrodes on the same instrument will register the lightning?s electrical discharge and scientists will be able to calculate how close Huygens passed to the storm.

If Huygens actually passes through a storm, the microphone will detect the splash of the rain onto the spacecraft casing. Unlike on Earth, this rain will not be water but probably liquid methane.

Marcello Fulchignoni, of the Universit? Denis Diderot, Paris, is the principal investigator of HASI. He says, ?Combined with the camera images, temperature and pressure profiles, and altitude data, the ?soundtrack? will provide a fascinating look at the details of the mission?s descent. We will be working hard to bring the voice of Huygens to the public as soon as we can after the descent.?

Original Source: ESA News Release

Posted on by Fraser Cain

Gmail Invites

I made a mention in yesterday’s newsletter that I had a few Gmail invites left over. You know, this is Google’s competitor to Hotmail and Yahoo that gives you a free email address with one GB of space. It’s still in beta, but I’m really impressed with it so far. I made a small mention down at the bottom, but I was still deluged with email requests for a Gmail invite. I had posted 6 invites in the Universe Today forum, and they were snapped up in a few minutes.

Now, I know there are hundreds of you reading this newsletter with some Gmail invites to spare, so I was wondering if you could help out. Visit the forum, head down to the bottom and post any spare invite links that you have. I’ve posted instructions in the forum on how to do this. Do not email me directly asking for an invite.

Here’s a link to the thread in the forum where everyone is posting their invites. Please help out if you can.

Thanks!

Fraser Cain
Publisher
Universe Today

P.S. The Universe Today forum has nearly 3,000 members now from all around the world. Come, hang out, and chat with other space enthusiasts!

Posted on by Fraser Cain

Arizona Telescope Turned Into a Robot

Today, the world of astronomy meets the science fiction world of Isaac Asimov’s “I, Robot” with the commissioning of a new robotic telescope. While it lacks the humanoid qualities of the movie version, this robot will aid in humanity’s quest to understand the early universe by observing the most distant and powerful explosions known.

Located at the Fred L. Whipple Observatory on Mt. Hopkins, Arizona, the Peters Automated Infrared Imaging Telescope (PAIRITEL) is the first fully “robotic” infrared telescope in North America dedicated to observing transient astronomical events. The telescope, used for several years in a major all-sky survey (2MASS), has been refurbished to work autonomously. It will operate in tandem with NASA’s new gamma-ray burst satellite “Swift,” to be launched on November 8 from Kennedy Space Center.

With PAIRITEL, a team of astronomers led by Dr. Joshua Bloom of the Harvard Society of Fellows, Harvard-Smithsonian Center for Astrophysics (CfA) and UC Berkeley, hopes to pinpoint the gamma-ray burst explosions from the first and most distant stars in the universe. A gamma ray burst (GRB) is a quick flash of gamma-ray radiation lasting about a minute, accompanied by an afterglow emission of X-rays, visible, infrared, and radio light. The afterglow may be observable for days to weeks afterward. The majority of GRBs are believed to be due to massive stars that explode violently and release tremendous blasts of energy.

“Innovatively exploring the night sky in the time domain – seeing how things change from night to night, and even from minute to minute – is the next big frontier in astronomy,” said Bloom. “PAIRITEL was optimized to study cosmic events like GRBs that are here today and gone tomorrow.”

Peering back to a time when the universe was less than 1 billion years old is the holy grail of observational astronomy. So far, only energetic galaxy cores known as quasars have been used to probe the early universe. But gamma-ray burst afterglows, if astronomers are able to image them quickly, hold clear advantages over quasars. For up to one hour after the burst, afterglow brightnesses can reach up to 1000 times that of the brightest known quasar in the universe.

Also, explained Bloom, “The stars that create GRBs likely formed before the black holes that create quasars. So by looking for the youngest and most distant GRBs, we can study the earliest epochs of the universe.”

A key feature of PAIRITEL that will allow the location of distant GRBs is its rapid response time. PAIRITEL will receive signals from Swift and automatically move, in under 2 minutes, to the part of the sky where a GRB has appeared.

“My ultimate vision is to have astronomy robots talking to robots, deciding what to observe and how, with no human intervention,” said Bloom. “As it is, PAIRITEL only e-mails us when it’s found a particularly interesting source, or when something goes wrong and it needs help!”

Another key feature of PAIRITEL is its sensitivity at infrared wavelengths, setting this system apart from the bevy of visible-light robotic telescopes already in existence. Images taken with infrared filters (about twice the wavelength of visible light) are indispensable: visible light emitted from more than 12 billion light-years away is completely extinguished for observers on Earth. Bloom explained, “Forget about the dimming due to the extreme distances: the hydrogen gas between us and the explosions makes it like searching for a firefly behind a thick London fog. In the infrared we can peer through the shroud to the good stuff.” In addition, the unique camera on PAIRITEL takes pictures simultaneously at three different wavelengths of light, allowing for instantaneous full-color snapshots.

The Swift spacecraft will find GRBs at a rate 10 to 20 times higher than currently feasible, and should find more bursts in 6 months than all well-studied bursts to date. Bloom said he is most excited about using Swift and PAIRITEL “together to find the golden needle in the haystack – a high-redshift GRB that’s farther away than the most distant known galaxy or quasar.”

When PAIRITEL is not chasing down GRBs, it will be used to make precision measurements of supernovae to help determine the few fundamental parameters that dictate the expansion of the universe. Among other projects, Dr. Michael Pahre (CfA) will use PAIRITEL to study the near-infrared light of nearby galaxies to compare it with mid-infrared light in images obtained with NASA’s Spitzer Space Telescope. Harvard graduate student Cullen Blake, who has written software for the project, will also use PAIRITEL to try to find Earth-mass planets around brown dwarfs. Other PAIRITEL team members include: Prof. Mike Skrutskie (Univ. of Virginia), Dr. Andrew Szentgyorgyi (CfA), Prof. Robert Kirshner (Harvard University/CfA), Dr. Emilio Falco (CfA), Dr. Thomas Matheson (NOAO), and Dan Starr (Gemini Observatory, Hawaii). The staff of Mt. Hopkins-Wayne Peters, Bob Hutchins, and Ted Groner-worked on the automation of the telescope.

PAIRITEL, nearly 2 years after the inception of the project, is being dedicated today to the late Jim Peters, who worked for the Smithsonian Astrophysical Observatory, first on satellite tracking and then as a telescope operator on Mt. Hopkins for 25 years. His widow and son will be in attendance at the ceremony.

The project was funded by a grant from the Harvard Milton Fund. The telescope is owned by the Smithsonian Astrophysical Observatory and the infrared camera is on loan from the University of Virginia.

Additional information about Swift and PAIRITEL is available online at:

http://swift.gsfc.nasa.gov/docs/swift/swiftsc.html
http://pairitel.org/

Original Source: CfA News Release

Posted on by Fraser Cain

Mystery Object in the Milky Way’s Halo

Most of the stars in our Milky Way galaxy lie in a very flat, pinwheel-shaped disk. Although this disk is prominent in images of galaxies similar to the Milky Way, there is also a very diffuse spherical “halo” of stars surrounding and enclosing the disks of such galaxies.

Recent discoveries have shown that this outer halo of the Milky Way is probably composed of small companion galaxies ripped to shreds as they orbited the Milky Way.

A discovery announced today by the Sloan Digital Sky Survey (SDSS) reveals a clump of stars unlike any seen before. The findings may shed light on how the Milky Way’s stellar halo formed.

This clump of newly discovered stars, called SDSSJ1049+5103 or Willman 1, is so faint that it could only be found as a slight increase in the number of faint stars in a small region of the sky.

“We discovered this object in a search for extremely dim companion galaxies to the Milky Way,” explains Beth Willman of New York University’s Center for Cosmology and Particle Physics. “However, it is 200 times less luminous than any galaxy previously seen.”

Another possibility, adds Michael Blanton, an SDSS colleague of Willman’s at New York University, is that Willman 1 is an unusual type of globular cluster, a spherical agglomeration of thousands to millions of old stars.”

“Its properties are rather unusual for a globular cluster. It is dimmer than all but three known globular clusters. Moreover, these dim globular clusters are all much more compact than Willman 1”, explains Blanton. “If it’s a globular cluster, it is probably being torn to shreds by the gravitational tides of the Milky Way.”

The real distinction between the globular cluster and dwarf galaxy interpretations is that galaxies are usually accompanied by substantial quantities of dark matter, says Julianne Dalcanton, an SDSS researcher at the University of Washington. “Clearly the next step is to carry out additional measurements to determine whether there is any dark matter associated with Willman 1.”

SDSS consortium member Daniel Zucker of the Max Planck Institute for Astronomy in Heidelberg, Germany, says the Sloan Digital Sky Survey has proven to be “a veritable gold mine for studies of the outer parts of our galaxy and its neighbors, as shown by Dr. Willman’s discovery, and by our group’s earlier discovery of a giant stellar structure and a new satellite galaxy around the Andromeda Galaxy.”

If Willman 1 does turn out to be a dwarf galaxy, this discovery could shed light on a long-standing mystery.

The prevailing ‘Cold Dark Matter’ model predicts that our own Milky Way galaxy is surrounded by hundreds of dark matter clumps, each a few hundred light years in size and possibly populated by a dwarf galaxy.

However, only 11 dwarf galaxies have been discovered orbiting the Milky Way. Perhaps some of these clumps have very few embedded stars, making the galaxies particularly difficult to find.

“If this new object is in fact a dwarf galaxy, it may be the tip of the iceberg of a yet unseen population of ultra-faint dwarf galaxies,” suggests Willman.

The Milky Way has been an area of intense research by SDSS consortium members.

“The colors of the stars in Willman 1 are similar to those in the Sagittarius tidal stream, a former dwarf companion galaxy to the Milky Way now in the process of merging into the main body of our Galaxy,” explains Brian Yanny, an SDSS astrophysicist at The Department of Energy’s Fermi National Accelerator Laboratory, a leader in research on the Milky Way’s accretion of material.

Continues Yanny: “If Willman 1 is a globular cluster, then it may have piggybacked a ride into our Galaxy’s neighborhood on one of these dwarf companions, like a tiny mite riding in on a flea as it, in turn, latches onto a massive dog.”

“Whether it is a globular cluster or a dwarf galaxy, this very faint object appears to represent one of the building blocks of the Milky Way,” Willman said.

Original Source: SDSS News Release

Posted on by Fraser Cain

Orionid Meteor Shower, October 21

Would you like to see a piece of Halley’s Comet streak past a planet that looks like an exploding star? No problem. Just set your alarm.

It’s going to happen, in plain view–no telescope required, on Thursday morning, Oct. 21st.

Go outside before sunrise, around 5:30 a.m. is best, and look east. The brightest object in that direction is the planet Venus. It looks like a star going supernova. Above Venus lies Saturn, and below, near the horizon, is Jupiter. Every 10 minutes or so you’ll see a meteor streak among these planets. The meteors are pieces of Comet Halley.

“Every year around this time Earth glides through a cloud of dusty debris from Halley’s Comet,” explains Bill Cooke of the NASA Marshall Space Flight Center. “Bits of dust, most no larger than grains of sand, disintegrate in Earth’s atmosphere and become shooting stars.”

“It’s not an intense shower,” he says, “but it is a pretty one.”

Astronomers call it the “Orionid meteor shower,” because the meteors appear to stream out of a point (called “the radiant”) in the constellation Orion. The radiant is near Orion’s left shoulder. But don’t stare at that spot, advises Cooke. Meteors near the radiant seem short and stubby, a result of foreshortening. Instead, look toward any dark region of the sky about 90 degrees away. The vicinity of Venus or Jupiter is good. You’ll see just as many Orionids there, but they will seem longer and more dramatic.

Framing the scene are several bright stars: Sirius, Regulus, Procyon and others. Pay special attention to Castor and Pollux in Gemini. They’re arranged in an eye-catching line with Saturn.

To sum it up in one word: “sparkling.” Two more words: “early” and “cold.” Or how about “worth waking up for?” You decide.

More about the Orionids
The Orionids are related to the eta Aquarids, a southern hemisphere meteor shower in May. Both spring from Halley’s Comet.

Earth comes close to the orbit of Halley’s Comet twice a year, once in May and again in October,” explains Don Yeomans, manager of NASA’s Near-Earth Object Program at the Jet Propulsion Laboratory. Although the comet itself is rarely nearby–it’s near the orbit of Neptune now–Halley’s dusty debris constantly moves through the inner solar system and causes the two regular meteor showers.

In 1986, the last time Comet Halley swung past the Sun, solar heating evaporated about 6 meters of dust-laden ice from the comet’s nucleus. That’s typical, say researchers. The comet has been visiting the inner solar system every 76 years for millennia, shedding layers of dust each time.

At first, the bits of dust simply follow the comet, which means they can’t strike our planet. Earth’s orbit and Halley’s orbit, at their closest points, are separated by 22 million km (0.15 AU). Eventually, though, the dust spreads out and some of it migrates until it is on a collision course with Earth.

“Particles that leave the nucleus evolve away from the orbit of the comet for two main reasons,” explains Yeomans. “First, gravitational perturbations caused by encounters with planets are different [for the dust and for the comet]. Second, dust particles are affected by solar radiation pressure to a far greater extent than the comet itself.”

“The orbital evolution of Halley’s dust is a very complicated problem,” notes Cooke. No one knows exactly how long it takes for a dust-sized piece of Halley to move to an Earth-crossing orbit — perhaps centuries or even thousands of years. One thing is certain: “Orionid meteoroids are old.”

They’re also fast. “Orionid meteoroids strike Earth’s atmosphere traveling 66 km/s or 148,000 mph,” he continued. Only the November Leonids (72 km/s) are faster. Sometimes fast meteors explode, and they leave glowing “trains” (incandescent bits of debris in their wake) that last for several seconds to minutes. These trains, blown by upper atmospheric winds into twisted and convoluted shapes, can be even prettier than the meteors themselves.

You never know what you might see, before sunrise, on a magical Thursday morning.

Original Source: Science@NASA Story

Posted on by Fraser Cain

Some Stars Take an Erratic Journey

A team of European astronomers has discovered that many stars in the vicinity of the Sun have unusual motions caused by the spiral arms of our galaxy, the Milky Way. According to this research, based on data from ESA’s Hipparcos observatory, our stellar neighbourhood is the crossroads of streams of stars coming from several directions. Some of the stars hosting planetary systems could be immigrants from more central regions of the Milky Way.

The Sun and most stars near it follow an orderly, almost circular orbit around the centre of our galaxy, the Milky Way. Using data from ESA’s Hipparcos satellite, a team of European astronomers has now discovered several groups of ‘rebel’ stars that move in peculiar directions, mostly towards the galactic centre or away from it, running like the spokes of a wheel. These rebels account for about 20% of the stars within 1000 light-years of the Sun, itself located about 25 000 light-years away from the centre of the Milky Way.

The data show that rebels in the same group have little to do with each other. They have different ages so, according to scientists, they cannot have formed at the same time nor in the same place. Instead, they must have been forced together. “They resemble casual travel companions more than family members,” said Dr Benoit Famaey, Universit? Libre de Bruxelles, Belgium.

Famaey and his colleagues believe that the cause forcing the rebel stars together on their unusual trajectory is a ‘kick’ received from one of the Milky Way’s spiral arms. The spiral arms are not solid structures but rather regions of higher density of gas and stars, called ‘density waves’ and similar to traffic hot-spots along the motorway. An approaching density wave compresses the gas it encounters and favours the birth of new stars, but it can also affect pre-existing stars by deflecting their motion. After the wave has passed, many stars will thus travel together in a stream, all in the same direction, even though they were originally on different trajectories or not even born.

This research has shown that the neighbourhood of the Sun is a crossroads of many streams, made up of stars with different origins and chemical composition. These streams could also account for many of the stars with planetary systems recently discovered near the Sun.

Astronomers know that stars with planetary systems preferentially form in dense gas clouds with a high metal content, such as those located in the more central regions of the Milky Way. The streams discovered by Hipparcos could be the mechanism that brought them closer to the Sun. As Famaey explains, “If these stars are kicked by a spiral arm, they can be displaced thousands of light-years away from their birthplace.” These stars, together with their planets, can thus have migrated closer to the Sun.

To learn more about the structure of our Milky Way, an aggregate of thousands of millions of stars, astronomers look at the way in which stars stay together in a coherent way or move with respect to the Sun and relative to one another. During its four-year mission, ESA’s Hipparcos satellite has measured the distance and motion of more than a hundred thousand stars within a 1000 light-years of the Sun. However, while Hipparcos’s data show in which directions stars are moving on the sky, they cannot tell whether stars are coming towards us or going away from us.

By combining the Hipparcos data with ground-based measurements of their ?Doppler shift?, obtained with a Swiss telescope at the Observatoire de Haute-Provence, France, Famaey and his colleagues could add the missing third dimension, namely the speed with which stars approach us or recede from us. Because of the Doppler shift, the colour of a star appears to change when it travels towards us or away from us, becoming respectively bluer or redder and giving astronomers information about its motion. “By combining all these first-class data, we now have a comprehensive, three-dimensional view of how nearby stars move about us,” said Famaey.

Scientists now wonder how widespread are the streams discovered by Famaey’s team and what role they could play in the evolution of our galaxy. “This result opens up exciting new prospects for our understanding of the dynamics of the Milky Way,” said Dr Michael Perryman, ESA Hipparcos and Gaia project scientist. ESA’s forthcoming mission Gaia, scheduled for launch in 2011, will make it possible to extend this investigation over a much wider region of our galaxy. Gaia will observe more than a thousand million stars and will measure their motion in all three dimensions simultaneously, thanks to the on-board spectrograph providing information on their Doppler shift. “This will give us the clearest view ever of the structure and evolution of the Milky Way,” Perryman said.

Original Source: ESA News Release