Posted on by Fraser Cain

Redesigning Universe Today

You might have noticed, I’m starting to implement my new design for Universe Today into the website – folks reading the newsletter have seen this for a few weeks already. What I’m hoping is that this new design is simpler and cleaner, and lets you get to the news with less distractions. I’ve made the text a little larger to go with the bigger pictures, and put a big list of the last 30 articles over onto the right-hand side of the page, so you can see what’s on the site at a glance. It has less advertising… for now. It’s also much easier for me to maintain. Most of the site has adopted this new look, but I still have lots of copy-pasting to do to get everything fully going, so you’ll see the old site peeking through here and there. I’m also going to be tweaking it endlessly, so things will continue to shift and change.

Please give me any feedback, suggestions or let me know if you find any bugs. You can always email me at [email protected]

Fraser Cain
Publisher, Universe Today

Posted on by Fraser Cain

A Star in the Making

Examples of Bok globules. Image credit: SAAO. Click to enlarge.
Our Sun has been around for almost five billion years. Throughout most of its history the Sun has pretty much appeared the way it does today – a vast sphere of radiant gas and dust lit to incandescence by heat liberated through hydrogen fusion near its core. But before our Sun took form, matter had to be drawn together from the interstellar medium (ISM) and compacted in a small enough region of space to pass a critical balance between further condensation and stability. For this to occur, a delicate balance between outwardly exerted internal pressure and inward moving gravitational influence had to be overcome.

In 1947, Harvard observational astronomer Bart Jan Bok announced the result of years of study of an important subset of cold gases and dust often associated with extended nebulosity. Bok suggested that certain isolated and distinct globules obscuring background light in space were in fact evidence of an important preliminary stage in the formation of protostellar disks leading to the birth of stars such as our sun.

Subsequent to Bok’s announcement, many physical models emerged to explain how Bok globules could come to form stars. Typically, such models begin with the notion that matter comes together in regions of space where the interstellar medium is especially dense (in the form of nebulosity), cold, and subject to radiation pressure from neighboring stars. At some point enough matter may condense into a small enough region that gravitation overcomes gas pressure and the balance tips in favor of star formation.

According to the paper “Near Infrared Imaging Survey of Bok Globules: Density Structure”, published June 10, 2005 Ryo Kandori and a team of fourteen other investigators “suggest that a nearly critical Bonner-Ebert sphere characterizes the critical density of starless globules.”

The concept of a Bonner-Ebert sphere originates with the idea that a balance of forces can exist within an idealized cloud of gas and dust. Such a sphere is held to have a constant internal density while maintaining equilibrium between the expansionary pressure caused by gases of a given temperature and density and the gravitational influence of its total mass assisted by any gas or radiation pressure exerted from neighboring stars. This critical state relates to the diameter of the sphere, its total mass, and the amount of pressure generated by latent heat within it.

Most astronomers have assumed that the Bonner-Ebert model – or some variation thereof – would ultimately prove accurate in describing the point when a particular Bok globule crosses the line to become a protostellar disk. Today, Ryo Kandori et al have gathered enough evidence from a variety of Bok globules to strongly suggest that this notion is correct.

The team started by selecting ten Bok globules for observation based on small apparent size, near-circular shape, distance from neighboring nebulosity, proximity to the Earth (less than 1700 LYs away), and accessibility to near-infrared and radio wave collecting instruments located in both the northern and southern hemispheres. From a list of nearly 250 such globules, only those meeting the above criteria were included. Among those selected only one showed evidence of a protostellar disk. This one disk took the form of a point source of infrared light detected during an all-sky survey performed by IRAS (Infrared Astronomy Satellite – a joint project of the US, UK, and Netherlands). All ten globules were located in star and nebulosity rich regions of the Milky Way.

Once candidate Bok globules were selected, the team subjected each of them to a battery of observations designed to determine their mass, density, temperature, size, and if possible, the amount of pressure applied on them by the ISM and neighboring starlight. One important consideration was to get a sense if there were any variations in density throughout the globule. The presence of uniform pressure is particularly important when it comes to determining which of a variety of theoretical models best mapped against the constitution of the modules themselves.

Using a ground-based instrument (the 1.4 meter IRSF at the South African Astronomical Observatory) in 2002 and 2003, near-infrared light in three different bands (J, H, & K) was collected from each globule to magnitude 17 plus. The images were then integrated and compared to light originating from the background star region. This data was subjected to several analysis methods to allow the team to derive the density of gas and dust across each globule down to the level of resolution supported by seeing conditions (roughly one arc second). That work basically determined that each globule showed a uniform density gradient based on its projected three-dimensional distribution. The Bonner-Ebert sphere model looked like a very good match.

The team also observed each globule using the 45 meter radio telescope of the Nobeyama Radio Observatory in Minamisaku, Nagano, Japan. The idea here was to collect specific radio frequencies associated with excited N2H+ and C18O. By looking at the amount of blur in these frequencies the team was able to determine the internal temperature of each globule which, along with the density of the gas, can be used to approximate the gas pressure internal to each globule.

After gathering the data, subjecting it to analysis, and quantifying the results, the team “found that more then half of the starless globules (7 out of 11 sources) are located near the (Bonner-Ebert) critical state. Thus we suggest that a nearly critical Bonner-Ebert sphere characterizes the typical density structure of starless globules.” In addition the team determined that three Bok globules (Coalsack II, CB87 & Lynds 498) are stable and clearly not in process of star formation, four (Barnard 66, Lynds 495, CB 161 & CB 184) are poised near the stable Bonner-Ebert state but tending toward star formation based on that model. Finally the remaining six (FeSt 1-457, Barnard 335, CB 188, CB 131, CB 134) are clearly moving toward gravitation collapse. Those six “stars in the making” include globules CB 188 and Barnard 335 already known to possess protostellar disks.

On any relatively cloudless day it doesn’t take much in the way of instrumentation to prove that one very unique and important ‘Bok globule’ existing some 5 billion years ago did manage to tip the scales and become a star in the making. Our Sun is firey proof that matter – once adequately condensed – can begin a process that leads to some extraordinary new possibilities.

Written by Jeff Barbour

Posted on by Fraser Cain

Early Black Holes Grew Up Quickly

Illustration of the early Universe. Image credit: NASA. Click to enlarge.
It all began a long time ago while the universe was very young. The earliest massive breeder stars frolicked in their youth – spinning and cavorting among rich green grasses of virgin matter. As their allotted time played out, nuclear engines boiled off expansive streams of hot hydrogen and helium gas – enrichening the interstellar media. During this phase, supermassive star clusters formed in small pockets near nascent galactic cores – each cluster a swim in small regions of primordial mini-halo matter.

Completing their cycle, the earliest breeder stars exploded, spewing forth heavy atoms. But before too much heavy matter accumulated in the Universe, the earliest black holes formed, grew rapidly through mutual assimilation, and accumulated enough gravitational influence to draw “Goldilocks” gases of precise temperatures and composition into large wide accretion disks. This supercritical phase of growth matured the earliest massive black holes (MBHs) rapidly to supermassive black hole (SMBH) status. Out of this the earliest quasars took residence within the fused mini-haloes of numerous protogalaxies.

This picture of early quasar formation emerged from a recent paper (published June 2, 2005) entitled “Rapid Growth of High Redshift Black Holes” written by Cambridge UK Cosmologists Martin J. Rees and Marta Volonteri. That study treats the possibility that a brief window of rapid SMBH formation opened after the time of universal transparency but before gases in the interstellar media fully re-ionized through stellar radiation and seeded with heavy metals by supernovae. The Rees-Volonteri model attempts to explain facts coming out of the Sloan Digital Sky Survey (SDSS) dataset. By 1 billion years after the Big Bang, many highly radiant quasars had already formed. Each with SMBHs having masses exceeding 1 billion suns. These had arisen out of “seed black holes” – gravitational cinders left behind after the earliest cycle of supernovae collapse among the first massive galactic clusters. By one billion years post Big Bang, it was all but over. How could so much mass condense so quickly into such small regions of space?

According to Volontari and Rees, “To grow such seeds up to 1 billion solar masses requires an almost continuous accretion of gas…” Working against such a high accretion rate, is the fact that radiation from matter falling into a black hole typically offsets rapid “weight gain”. Most models of SMBH growth show that about 30% of the mass falling toward an intermediate (massive – not supermassive) black hole is converted to radiation. The effect of this is two-fold: Matter that would otherwise feed the MBH is lost to radiation, and outward radiation pressure stifles the march of additional matter inward to feed rapid growth.

The key to understanding rapid SMBH formation lies in the possibility that early accretion disks around MBH’s were not as optically dense as they are today – but “fat” with tenuously distributed matter. Under such conditions, radiation has a wider mean free path and can escape beyond disks without impeding inward motion of matter. Fuel driving the entire SMBH growth process is delivered copiously into the black hole event horizon. Meanwhile, the type matter present in the earliest epoch was mainly monatomic hydrogen and helium – not the kind of heavy metal rich accretion disks of a later era. All of this suggests that early MBH’s grew up in a hurry, ultimately accounting for the many fully mature quasars seen in the SDSS dataset. Such early MBHs must have had mass-energy conversion ratios more typical of fully mature SMBH’s than the MBH’s of today.

Volontari and Rees say that earlier investigators have shown that fully developed “quasars have a mass-energy conversion efficiency of roughly 10%…” The pair cautions however that this mass-energy conversion value comes out of studies of quasars from a later period in Universal expansion and that “nothing is known about the radiative efficiency of pregalactic quasars in the early Universe.” For this reason “the picture we have of the low redshift Universe may not apply at earlier times.” Clearly the early Universe was more densely packed with matter, that matter was at a higher temperature, and there was a higher ratio of non-metals to metals. All these factors say that it?s almost anyone’s best guess as to the mass-energy conversion efficiencies of early MBHs. Since we now must account for why so many SMBHs exist among early quasars, it makes sense that Volontari and Rees use what they know of today’s accretion disks as a means to explain how they such disks may have been different in the past.

And it is the earliest times – before radiation from numerous stars re-ionized gases within the inter-stellar media – that offered conditions ripe for rapid SMBH formation. Such conditions may well have lasted less than 100 million years and required an adept balance in the temperature, density, distribution, and composition of matter in the Universe.

To get the complete picture (as painted in the paper), we start with the idea that the early universe was populated by innumerable mini-halos comprised of dark and baryonic matter with highly massive but exceedingly dense star clusters in their midst. Due to the density of these clusters – and the massiveness of the stars comprising them – supernovae quickly developed to spawn numerous “seed black holes”. These seed BHs coalesced into massive black holes. Meanwhile gravitational forces and real motions rapidly brought the various mini-halos together. This created ever more massive halos capable of feeding MBHs.

In the early Universe, matter surrounding MBHs took the form of huge metal-poor spheroids of hydrogen and helium averaging some 8,000 degrees Kelvin in temperature. At such high temperatures, atoms remain ionized. Due to ionization, there were few electrons associated with atoms to act as photon traps. The effects of radiation pressure diminished to the point where matter fell more readily into a black holes event horizon. Meanwhile free electrons themselves scatter light. Some of that light actually re-radiates back toward the accretion disk and another source of mass – in the form of energy – feeds the system. Finally a dearth of heavy metals – such as oxygen, carbon, and nitrogen – means that monotomic atoms remain hot. For as temperatures fall below 4,000 degrees K, atoms de-ionize and again become subject to radiation pressure reducing the flux of fresh matter falling into the BH event horizon. All these purely physical properties tended to push mass-energy efficiency ratios down – allowing MBHs to put on weight rapidly.

Meanwhile as mini-halos coalesced, hot baryonic matter condensed into huge “thick” disks – not the thin rings seen around the SMBH’s today. This came about because halo matter itself completely surrounded the rapidly growing MBHs. This spheroidal distribution of matter provided a constant source of fresh, hot, virgin matter to feed the accretion disk from a variety of angles. Thick disks meant greater amounts of matter at lower optical density. Once again, matter managed to avoid being “solar-sailed” outward away from the looming maw of the MBH and mass-energy conversion ratios fell.

Both factors – fat disks and ionized, low mass atoms – say that during the golden age of an early green Universe, MBHs grew up fast. Within one billion years of the Big Bang they had settled down into a relatively quiet maturity efficiently converting matter into light and casting that light across vast reaches of time and space into a potentially ever-expanding Universe.

Written by Jeff Barbour

Posted on by Fraser Cain

Foton-M2 Mission Returns to Earth

Computer illustration of the Foton-M2 satellite. Image credit: ESA. Click to enlarge.
The re-entry module of the Foton-M2 spacecraft, which has been in low-Earth orbit for the last 16 days made a successful landing today in an uninhabited area 140 km south-east of the town of Kostanay in Kazakhstan, close to the Russian border at 09:37 Central European Time, 13:37 local time.

The unmanned Foton-M spacecraft, which was launched on 31 May from the Baikonur Cosmodrome in Kazakhstan, carried a European payload of 385 kg covering 39 experiments in fluid physics, biology, crystal growth, meteoritics, radiation dosimetry and exobiology.

All de-orbit to landing procedures went according to plan beginning with the jettison of the Foton-M2 battery module three hours prior to landing. At an altitude of about 300 kilometres, travelling at 7.8 km/s and 30 minutes prior to landing, the retro-rocket situated on the Foton service module was fired for 45 seconds slowing the spacecraft down to reduce its altitude. The Foton-M2 service module was hereafter separated from the re-entry module and, as planned, burnt up in Earth?s atmosphere.

Twenty minutes prior to landing the spherical re-entry module entered the stratosphere, experiencing temperatures up to 2000?C and an acceleration of up to 9g. At 8.5 minutes before landing, the drogue parachute was deployed, which in turn opened the brake parachute, reducing the descent speed from supersonic to subsonic. The main parachute was deployed thirty seconds later, at an altitude of 2.5 km, reducing the speed of the re-entry module to 10 m/s. Brake rockets finally reduced the speed of the re-entry module to 3 m/s, 0.35 seconds before landing impact.

ESA representatives were on hand at the landing site to undertake initial procedures related to European experiments. This included immediate retrieval of the Biopan, Stone and Autonomous Experiments. The same team removed the FluidPac experiment facility?s digital tape recorder and configured FluidPac for safe transport to the TsSKB-Progress factory in Samara. The Foton capsule is currently being transported to Samara where the FluidPac facility and the Telescience Support Unit will be removed from the capsule and shipped to ESA/ESTEC in Noordwijk, the Netherlands.

?I am extremely pleased that the majority of experiments have performed well.? said ESA?s Project Manager for Foton missions, Antonio Verga. ?My thanks to the ESA Operations Team who has closely followed the mission from the Payload Operations Centre at Esrange in Kiruna, Sweden and our Russian counterparts at Roskosmos, TsSKB-Progress and the Barmin Design Bureau for General Engineering. The hard work and dedication of everyone involved has been crucial in making this mission a success and optimising the scientific returns from the mission?.

The Foton-M2 staff at Esrange, consisted of a team of 30 scientists, engineers and operators who worked in close coordination with the Mission Operation Centre at TsSKB, Samara, and with the Flight Control Centre in Moscow, which continuously reported and informed about the orbital phases of Foton-M2, via a powerful and effective data network operated and maintained by ESA?s European Space Operations Centre (ESOC) in Darmstadt, Germany.

Fluid physics experiments were conducted in the FluidPac and SCCO experiment facilities. The data return from these was nearly complete and most of the scientific objectives were achieved. The BAMBI experiment produced some excellent images, a substantial role in which was played by the on-line processing capability of TeleSupport Unit.

The Agat furnace performed flawlessly as well. The processed samples should provide the material science community with good specimens to analyse. Unfortunately, the Russian Polizon furnace suffered a failure due to as yet unknown reasons, which prevented the processing of the semiconductor alloys stored in its drum at the required high temperatures.

The very successful technology experiment MiniTherm was performed during the mission, which deals with the performance of a new design of heat pipes. This experiment was controlled from Esrange, during its 5 days-long execution.

Also numerous experiments attached to the outside of the Foton satellite were performed, which deal with space exposure and technology aspects.

The European Space Agency has been participating in this type of scientific mission for 18 years and with a total of 385 kg of European experiments and equipment, this mission constituted the largest European payload that has been put into orbit.

“The Foton-M2 mission has been a resounding success and I look forward to seeing the positive impact the results of the experiments will have in the future,? said Daniel Sacotte, ESA?s Director of Human Spaceflight, Microgravity and Exploration Programmes. ?I also look forward to building on this success with the Foton-M3 mission, which is planned to be launched in 2007.?

For more information on the Foton-M2 mission and the status of the ESA experiments: http://www.spaceflight.esa.int/foton

Original Source: ESA News Release

Posted on by Fraser Cain

Second MARSIS Boom Deployed

Artist illustration of Mars Express deploying its MARSIS boom. Image credit: ESA. Click to enlarge.
The second 20-metre antenna boom of the MARSIS instrument on board Mars Express was successfully ? and smoothly ? deployed, confirmed today by the ground team at ESA?s European Space Operations Centre.

The command to deploy the second MARSIS boom was given to the spacecraft at 13:30 CEST on 13 June 2005.

Shortly before the deployment started, Mars Express was set into a slow rotation to last 30 minutes during and after the boom extension. This rotation allowed all the boom?s hinges to be properly heated by the Sun.

Just after, an autonomous manoeuvre oriented the spacecraft towards the Sun, to have the spacecraft recharge its batteries and for a further heating of the hinges.

A first positive sign reached ground in the afternoon of 14 June, at 16:20 CEST, when Mars Express was able to properly re-orient itself and point towards Earth to transmit data.

The data received in the following hours confirmed that the initial spacecraft behaviour was consistent with two fully and correctly deployed booms and that the deployment had not induced disturbance frequencies that may have been dangerous for the spacecraft.

A series of tests during the following 48 hours was necessary to verify that the long boom was successfully locked and that the deployment did not affect the integrity of the spacecraft systems.

The complete success of the operation was announced today at 14:00 CEST, when the ground team had completed all tests on the spacecraft systems. This confirmed that the spacecraft is in optimal shape and under control, with the second MARSIS boom straight and locked into the correct position.

With the two MARSIS 20-metre radar booms fully deployed, Mars Express is already in principle capable of ?looking? beneath the Martian surface, and also studying its ionosphere (the upper atmosphere). The third 7-metre ?monopole? boom, to be deployed perpendicularly to the first two booms, will be used to correct some surface roughness effects on the radio waves emitted by MARSIS and reflected by the surface.

The third boom deployment, not considered critical because of its orientation and shorter length, will take place on 17 June 2005. It will be followed by further tests on the spacecraft and the MARSIS instrument for a few more days.

The radar, with its long booms, will allow Mars Express to continue its search for water on Mars. By night, it will be used to make soundings for water below the surface. By day, it will probe the structure of the ionosphere.

Jean-Jacques Dordain, ESA Director General, said: “This is a great success following some tense moments and careful judgements. The result shows the power of the teamwork between ESA, European industry and ESA’s partners in the scientific community in Europe and elsewhere.”

Original Source: ESA News Release

Posted on by Fraser Cain

Discovery Back on the Launch Pad

Space shuttle Discovery back on its launch pad. Image credit: NASA. Click to enlarge.
With new safety modifications, the Space Shuttle Discovery is back at Launch Pad 39B at NASA’s Kennedy Space Center, Fla. Carried by a giant Crawler Transporter, Discovery arrived at the pad at 12:17 p.m. EDT today in preparation for its historic Return to Flight mission (STS-114) planned for July.

“We’ve addressed some additional concerns about ice formation on the external fuel tank,” said NASA’s Deputy Associate Administrator for International Space Station and Space Shuttle Programs Michael Kostelnik. “This is an even safer vehicle for Commander Eileen Collins and her crew, and the new modifications will ensure this important mission to the International Space Station is successful.”

Discovery’s journey took a little longer than expected. It left the Vehicle Assembly Building about 2:00 a.m. EDT for its four-mile journey. The Crawler Transporter, which has a top speed of about one mph, traveled even slower than normal today. It stopped frequently, so engineers could address overheating bearings. But when Discovery finally rolled up to the pad around lunchtime, it was a satisfying sight for those who have been working more than two years to get the Shuttle back to space.

“Seeing Discovery back on the launch pad is a visible testament to the dedication of everyone involved in making sure STS-114 is the safest mission it can be,” said Space Shuttle Program Manager Bill Parsons. “We still have some work to do, but today is indicative that the hardware is getting ready for a launch in July.”

With Discovery at the pad, workers will begin final preparations for launch. They will close out, test, and install the payload, NASA’s Italian-built Multi-Purpose Logistics Module, Raffaello.

They will also load the hypergolic propellants for flight. The process includes adding the propellants, monomethyl hydrazine and nitrogen tetroxide, into the Orbiter Maneuvering System and the Forward Reaction Control System.

Discovery was de-mated from its previous External Tank (ET-120) and attached to a new External Tank (ET-121) on June 7. A new heater was added to ET-121 on the feedline bellows. The heater is designed to minimize potential ice and frost buildup on the bellows, a part of the pipeline that carries liquid oxygen to the Shuttle’s main engines. ET-121 was originally scheduled to fly with Atlantis on the second Return to Flight mission (STS-121).

The new tank was fitted with temperature sensors and accelerometers to gather information about the tank’s performance and measure vibration during flight.

“Returning Discovery to the launch pad is the last major processing milestone prior to launch,” said NASA Launch Director Mike Leinbach. “The launch team is completing the final procedures and documentation, and we are looking forward to beginning the launch countdown three days prior to liftoff.”

NASA plans to launch Discovery during a window from July 13 to 31. A launch date will be set during the Flight Readiness Review scheduled for June 29 and 30.

During their 12-day mission, Discovery’s seven crew members will test new hardware and techniques to improve Space Shuttle safety. They will also deliver supplies to the International Space Station.

Video from the rollout will feed on NASA TV available on the Web and via satellite in the continental U.S. on AMC-6, Transponder 9C, C-Band, at 72 degrees west longitude. The frequency is 3880.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz. In Alaska and Hawaii, it’s available on AMC-7, Transponder 18C, C-Band, at 137 degrees west longitude. The frequency is 4060.0 MHz. Polarization is vertical, and audio is monaural at 6.80 MHz.

Original Source: NASA News Release

Posted on by Fraser Cain

Earth Formed from Melted Asteroids

The image above is a false color view of the asteroid 951 Gaspra taken by the Galileo spacecraft. Image credit: NASA/JPL. Click to enlarge.
Important new research documenting how the Earth formed from melted asteroids 4.5 billion years ago is published in the 16 June issue of Nature. The paper was written by Dr Richard Greenwood and Dr Ian Franchi of the Open University?s Planetary and Space Sciences Research Institute (PSSRI).

“This research is important, Dr Greenwood says, ?because it demonstrates that events and processes on asteroids during the birth of the Solar System determined the present-day composition of our Earth.”

Immediately following the formation of our Solar System 4.5 billion years ago, small planetary bodies formed, with some melting to produce volcanic and related rocks. The OU researchers analysed meteorites to see how processes on asteroids may have contributed to the formation of Earth.

In their paper ?Widespread magma oceans on asteroidal bodies in the early Solar System? Drs Greenwood and Franchi show that some asteroids experienced large-scale melting, with the formation of deep magma oceans. Such melted asteroids would have become layered with lighter rock forming near the surface, while denser rocks were deeper in the interior. Since large bodies, such as Earth, grew by incorporation of many such smaller bodies these important results shed new light on the processes involved in building planets.

The researchers suggest that in the chaotic, impact-rich environment of the early Solar System, significant amounts of the outer layers of these melted asteroids would have been removed prior to becoming part of the growing Earth. This process is a better explanation for the composition of the Earth than earlier theories which called for large amounts of light elements in the Earth?s dense core, or unknown precursor materials. The Open University researchers point to recent astronomical observations which show that these processes are also important in other planetary systems, such as that around the star Beta Pictoris.

Original Source: Open University Press Release

Posted on by Fraser Cain

Just How Earthlike is this New Planet?

Artist illustration of the rocky planet around the M dwarf Gliese 876. Image credit: NSF. Click to enlarge.
In the land rush known as extrasolar planet hunting, the most prized real estate is advertised as “Earth-like.” On Monday, June 13, scientists raced to plant their flag on a burning hunk of rock orbiting a red star.

This newly discovered planet is about seven times the mass of Earth, and therefore the smallest extrasolar planet found to orbit a main sequence, or “dwarf” star (stars, like our sun, that burn hydrogen).

There are even smaller planets known to exist beyond our solar system, but they have the misfortune to encircle pulsars, those rapidly spinning husks of dying stars. Such planets aren’t thought to be remotely habitable, due to the intense radiation emitted by pulsars.

Planets that are ten Earth masses or less are thought to be rocky, while more massive planets are probably gaseous, since their stronger gravity means they collect and retain more gas during planetary formation. 155 extrasolar planets have been found so far, but most of them have masses that are more comparable to gaseous Jupiter than rocky Earth (Jupiter is 318 times the mass of Earth).

Although this new planet is advertised as Earth-like because of its relatively low mass, earthlings wouldn’t want to rent a house there any time soon. For one thing, the house would melt. The surface temperatures estimated for this planet – 200 to 400 degrees Celsius (400 to 750 degrees Fahrenheit) – are due to the planet’s kissing-close distance from its star.

The planet resides a mere 0.021 AU from the star Gliese 876 (1 AU is the distance between the Earth and the sun), and completes an orbit in less then two Earth days. The closest planet to the sun in our own solar system – blazing hot Mercury – is nearly 20 times further away, orbiting at about 0.4 AU.

“Because the planet is in a two-day orbit, it is heated to oven-like temperatures, so we do not expect life,” says science team member Paul Butler of the Carnegie Institution of Washington.

In our solar system, the habitable zone – the temperate region where water could exist as a liquid on a planet’s surface – is roughly 0.95 to 1.37 AU, or between the orbits of Venus and Mars. The star Gliese 876 is about 600 times less luminous than our sun, so the proposed habitable zone is much closer in, roughly between 0.06 and 0.22 AU.

At 0.021 AU, the new planet is too close to the star to be in the habitable zone, and it also is subjected to greater amounts of high energy radiation like ultraviolet light and X-rays. While red dwarfs like Gliese 876 emit lower levels of UV than stars like our sun, they do emit violent X-ray flares.

Another complication from such a close orbit is that the planet may be tidally locked, with the same side of the planet always facing the star. Unless there is a substantial atmosphere to distribute heat, one side of the planet will be overcooked while the other will remain cold.

Gliese 876 is thought to be about 11 billion years old, making it more than twice as old as our sun. But in a way, Gliese is a teenager to our sun’s middle-aged adult. G-class stars like our sun live about 10 billion years, while M-class red dwarfs are thought to live for 100 billion years (older than the age of the universe!).

Science team member Geoff Marcy of the University of California, Berkeley, says that M stars take a long time to cool off and shrink down to their main sequence size and luminosity. He says that if the planet migrated inwards to its present day close orbit, it probably made this move during the first few million years, and then was subjected to much more radiation than at present for hundreds of millions of years.

Gliese 876 is thought to be metal-poor (to an astronomer, any element heavier than hydrogen and helium is classified as a “metal”). The formation of planets may be related to the metallicity of the star, since both the star and the planets form from the same original material. So a rocky planet like the Earth, made out of elements such as silicates and iron, is expected to orbit a star that is metal-rich.

Despite being metal-poor, Gliese 876 is a multiple planet system. Two gas giant planets are known to orbit Gliese 876: the outermost planet is nearly twice the mass of Jupiter, and orbits at 0.21 AU; the middle planet is about half the mass of Jupiter, orbiting at 0.13 AU.

“The whole planetary system is sort of a miniature of our solar system,” says Marcy. “The star is small, the orbits are small, and in closer is the smallest of them, just as the architecture is in our own solar system, with the smallest planets orbiting inward of the giants.”

We have a lot more elbow room in our solar system. Mercury is further away from the sun than the distances of all these planets combined. The planets in the Gliese 876 system are so close together, they gravitationally interact with each other. This sort of gravitational tug of war was how the scientists were able to detect the planets in the first place.

Over the course of an orbit, planets will gravitationally pull on their star from different sides. Scientists measure the resulting shift in star light to determine the existence of orbiting planets.

To learn more about Gliese 876’s smallest planet, scientists would need to use another planet-hunting technique called transit photometry. This method looks at how a star’s light seems to dip when a planet passes in front of the star from our field of view. The eclipse of the orbiting planet allows astronomers to determine that planet’s mass and radius. Pinning down those numbers indicates the planet’s density, which then suggests what the planet is made of, and whether the planet is rocky or gaseous.

Transit photometry can’t be used to tell us anything about planets orbiting Gliese 876, however, because the system is inclined 50 degrees from our point of view. This angle means the planets won’t block any of the starlight that reaches Earth.

Red dwarfs are the most common type of star in our galaxy, comprising about 70 percent of all stars. Yet out of the 150 red dwarfs they have studied over the years, Marcy and Butler only have found planets orbiting two of them. Because most of the planets found so far are gas giants, this could mean that red dwarfs are less apt to harbor those kinds of worlds.

Marcy says they will continue to monitor Gliese 876 for any hints of a fourth or fifth planet. “This will definitely be one of our favorite stars from now on.”

A Race to the Finish Line
The research paper describing this discovery has been submitted to the Astrophysical Journal. The scientists say they received a favorable preliminary referee’s report, and they expect their paper will be accepted and then published in a few months. During Monday’s press conference, the scientists were asked why they decided to publicize their finding now, before the paper had been accepted for publication. Was it done to beat out other planet hunters who might be hot on their heels?

Marcy replied that they wanted to prevent news of their discovery from leaking out. “We knew about it three years ago, we’ve been following it quietly, carefully, guarding the secret while we double and triple checked. Then about a month ago I talked with Michael Turner here, people at NSF (National Science Foundation), and jointly we decided that this discovery was so extraordinary, maybe what you would call a milestone in planetary science, that it was difficult to imagine keeping the lid on this for very much longer. So we decided that rather than have it leak out to the news media, and be dribbled around, with one newspaper learning about it early and so on, that it would be better to quickly announce this.”

Marcy then launched into a defense for why he believed their finding is correct, and he was quickly backed by his fellow team members. However, the accuracy of their finding had not been questioned. Perhaps their early announcement, combined with the need for secrecy beforehand, is evidence of the intense competition that has marked planet hunting since the beginning.

The first extrasolar planet discovery was announced October 5, 1995 by Michel Mayor and Didier Queloz of the Geneva Observatory, and Marcy and Butler confirmed the observations the following week. A recent example of the competition to grab other extrasolar planet “firsts” occurred last summer, when on August 25, 2004, Mayor, Nuno Santos, and colleagues announced the discovery of the first extrasolar Neptune-mass planet — at the time the smallest extrasolar planet known to orbit a sun-like star. This announcement came less than a week before two other Neptune-mass planet discoveries were announced by Marcy and Butler.

Mayor and his colleagues also have studied Gliese 876. At an astronomy conference in June 1998, Mayor and Marcy each independently announced the detection of the more massive gas giant orbiting this star. Marcy and Butler were first to follow up on this finding, announcing the discovery of the star’s second gas giant planet in 2001.

The Kepler mission, due to launch in June 2008, will search for terrestrial planets orbiting distant stars. The mission defines an Earth-size planet as being between 0.5 and 2.0 Earth masses, or between 0.8 and 1.3 Earth’s diameter. Planets between 2 and 10 Earth masses, such as the planet announced on Monday, are defined as Large Terrestrial planets.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Staring into a Cosmic Jet

Herbig-Haro 211 consists of two jets of material, visible at lower right. Image credit: A.A. Muench-Nasrallah, CfA. Click to enlarge.
Astronomers find jets everywhere when they look into space. Small jets spout from newborn stars, while huge jets blast out of the centers of galaxies. Yet despite their commonness, the processes that drive them remain shrouded in mystery. Even relatively nearby stellar jets hide their origins behind almost impenetrable clouds of dust. All stars, including our sun, pass through a jet phase during their “childhood,” so astronomers are eager to understand how jets form and how they may influence star and planet formation.

At this week’s meeting on submillimeter astronomy in Cambridge, Mass., astronomers described the latest results from an international collaboration using the Submillimeter Array (SMA) atop Mauna Kea, Hawaii. The SMA has begun to peer through the dust and home in on the sources of nearby stellar jets.

“Using the SMA, we can stare into the throat of the jet,” said SMA project scientist Paul Ho of the Harvard-Smithsonian Center for Astrophysics (CfA). “We’re getting close to seeing its launching point.”

Astronomer Hsien Shang of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) and her colleagues have created a model of jet formation that calculates temperatures, densities and brightnesses within stellar jets. SMA observations of a young star system prosaically named Herbig-Haro (HH) 211 have confirmed the validity of the model.

“Our model predicts what we will see about 100 astronomical units from the star,” Shang said. (One astronomical unit is the average Earth-Sun distance of 93 million miles.) “With the SMA, we can begin to look at the HH 211 system at the scale of the model and test those predictions. So far, everything checks out.”

HH 211 is located about 1,000 light-years away in the constellation Perseus. Astronomers estimate that the small protostar hidden within HH 211 is less than 1,000 years old-a mere baby by astronomical standards, so young that it is still growing by accumulating matter from a surrounding disk of gas and dust. The protostar eventually will become a low-mass star similar to the sun.

Although most of the matter in the disk will flow onto the star, some must be ejected outward to carry away excess angular momentum. Complex physical processes funnel that ejected matter into dual jets that shoot outward in opposite directions.

“Jets form very close to a protostar, within about 5 million miles of its surface according to the model we applied” said researcher Naomi Hirano (ASIAA). “The SMA can help test the jet model on the youngest protostars using molecular tracers from within that innermost region.”

SMA’s successor, the planned ALMA project, should finally reveal the nature of the engine powering these jets by peering into the core where they form.

“The SMA has brought us tantalizingly close to our goal-the answer to the question of how jets form,” said Ho. “ALMA will take us those final few steps.”

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Posted on by Fraser Cain

Neutrino Evidence Confirms Big Bang Predictions

A cosmic view of neutrino ripples. Image credit: Oxford. Click to enlarge.
Astrophysicists from the Universities of Oxford and Rome have for the first time found evidence of ripples in the Universe?s primordial sea of neutrinos, confirming the predictions of both Big Bang theory and the Standard Model of particle physics.

Neutrinos are elementary particles with no charge and very little mass, which are extremely difficult to study due to their very weak interaction with matter. Yet pinning down the physical properties of neutrinos is of paramount importance to scientists attempting to understand the fundamental building blocks of Nature. According to the standard Big Bang model, neutrinos permeate the Universe at a density of about 150 per cubic centimetre. The Earth is therefore immersed in an ocean of neutrinos, without us ever noticing.

Although it is impossible to measure this ?Cosmic Neutrino Background? directly with present-day technology, physicists predict that ripples or waves in it have an impact on the growth of structures in the Universe.

In research to be published in the journal Physical Review Letters, Dr. Roberto Trotta, Lockyer Fellow of the Royal Astronomical Society at Oxford?s Department of Physics, and Dr. Alessandro Melchiorri of La Sapienza University in Rome were able to demonstrate for the first time the existence of ripples of primordial origin in the Cosmic Neutrino Background.

The discovery, made by combining data produced by the NASA WMAP (Wilkinson Microwave Anisotropy Probe) satellite and the Sloan Digital Sky Survey, confirms the predictions of both the Big Bang theory and the Standard Model of particle physics. The research has important implications for the study of neutrinos, showing that theories of the infinitely large (cosmology) and the infinitely small (particle physics) are in agreement.

Dr. Trotta said: ?This research provides important new evidence in favour of the current cosmological model, unifying it with fundamental physics theories. Cosmology is becoming a more and more powerful laboratory where physics not easily accessible on Earth can be tested and verified. The high quality of recent cosmological data allows us to investigate neutrinos in the cosmological framework, obtaining measurements which are competitive with ? if not superior to ? particle accelerator findings.?

Original Source: Oxford News Release