Posted on by Fraser Cain

Nearest Brown Dwarf Found

Image credit: ESO

A team of European astronomers have located the closest brown dwarf star ever discovered. Epsilon Indi, located only 12 light-years from the Earth, was thought to be a single star, but the ESO team spotted its companion. Epsilon Indi B is 45 times the mass of Jupiter and takes 400 years to orbit the main star.

A team of European astronomers [2] has discovered a Brown Dwarf object (a ‘failed’ star) less than 12 light-years from the Sun. It is the nearest yet known.

Now designated Epsilon Indi B, it is a companion to a well-known bright star in the southern sky, Epsilon Indi (now “Epsilon Indi A”), previously thought to be single. The binary system is one of the twenty nearest stellar systems to the Sun.

The brown dwarf was discovered from the comparatively rapid motion across the sky which it shares with its brighter companion : the pair move a full lunar diameter in less than 400 years. It was first identified using digitised archival photographic plates from the SuperCOSMOS Sky Surveys (SSS) and confirmed using data from the Two Micron All Sky Survey (2MASS). Follow-up observations with the near-infrared sensitive SOFI instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory confirmed its nature and has allowed measurements of its physical properties.

Epsilon Indi B has a mass just 45 times that of Jupiter, the largest planet in the Solar System, and a surface temperature of only 1000 ?C. It belongs to the so-called ‘T dwarf’ category of objects which straddle the domain between stars and giant planets.

Epsilon Indi B is the nearest and brightest T dwarf known. Future studies of the new object promise to provide astronomers with important new clues as to the formation and evolution of these exotic celestial bodies, at the same time yielding interesting insights into the border zone between planets and stars.

Tiny moving needles in giant haystacks
Imagine you are a professional ornithologist, recently returned home from an expedition to the jungles of South America, where you spent long weeks using your high-powered telephoto lenses searching for rare species of birds. Relaxing, you take a couple of wide-angle snapshots of the blooming flowers in your back garden, undistracted by the common blackbird flying across your viewfinder. Only later, when carefully comparing those snaps, you notice something tiny and unusually coloured, flittering close behind the blackbird: you’ve discovered an exotic, rare bird, right there at home.

In much the same way, a team of astronomers [2] has just found one of the closest neighbours to the Sun, an exotic ‘failed star’ known as a ‘brown dwarf’, moving rapidly across the sky in the southern constellation Indus (The Indian). Interestingly, at a time when telescopes are growing larger and are equipped with ever more sophisticated electronic detectors, there is still much to be learned by combining old photographic plates with this modern technology.

Photographic plates taken by wide-field (“Schmidt”) telescopes over the past decades have been given a new lease on life through being digitised by automated measuring machines, allowing computers to trawl effectively through huge and invaluable data archives that are by far not yet fully exploited [3]. For the Southern Sky, the Institute for Astronomy in Edinburgh (Scotland, UK) has recently released scans made by the SuperCOSMOS machine of plates spanning several decades in three optical passbands. These data are perfectly suited to the search for objects with large proper motions and extreme colours, such as brown dwarfs in the Solar vicinity.
Everything is moving – a question of perspective

In astronomy, the `proper motion’ of a star signifies its apparent motion on the celestial sphere; it is usually expressed in arcseconds per year [4]. The corresponding, real velocity of a star (in kilometres per second) can only be estimated if the distance is known.

A star with a large proper motion may indicate a real large velocity or simply that the star is close to us. By analogy, an airplane just after takeoff has a much lower true speed than when it’s cruising at high altitude, but to an observer watching near an airport, the departing airplane seems to be moving much more quickly across the sky.

Proxima Centauri, our nearest stellar neighbour, is just 4.2 light-years away (cf. ESO PR 22/02) and has a proper motion of 3.8 arcsec/year (corresponding to 23 km/sec relative to the Sun, in the direction perpendicular to the line-of-sight). The highest known proper motion star is Barnard’s Star at 6 light-years distance and moving 10 arcsec/year (87 km/sec relative to the Sun). All known stars within 30 light-years are high-proper-motion objects and move at least 0.2 arcsec/year.

Trawling for fast moving objects
For some time, astronomers at the Astrophysical Institute in Potsdam have been making a systematic computerised search for high-proper-motion objects which appear on red photographic sky plates, but not on the equivalent blue plates. Their goal is to identify hitherto unknown cool objects in the Solar neighbourhood.

They had previously found a handful of new objects within 30 light-years in this way, but nothing as red or moving remotely as fast as the one they have now snared in the constellation of Indus in the southern sky. This object was only seen on the very longest-wavelength plates in the SuperCOSMOS Sky Survey database. It was moving so quickly that on plates taken just two years apart in the 1990s, it had moved almost 10 arcseconds on the sky, giving a proper motion of 4.7 arcsec/year. It was also very faint at optical wavelengths, the reason why it had never been spotted before. However, when confirmed in data from the digital Two Micron All Sky Survey (2MASS), it was seen to be much brighter in the infrared, with the typical colour signature of a cool brown dwarf.

At this point, the object was thought to be an isolated traveller. However, a search through available online catalogues quickly revealed that just 7 arcminutes away was a well-known star, Epsilon Indi. The two share exactly the same very large proper motion, and thus it was immediately clear the two must be related, forming a wide binary system separated by more than 1500 times the distance between the Sun and the Earth.

Epsilon Indi is one of the 20 nearest stars to the Sun at just 11.8 light years [5]. It is a dwarf star (of spectral type K5) and with a surface temperature of about 4000 ?C, somewhat cooler than the Sun. As such, it often appears in science fiction as the home of a habitable planetary system [6]. That all remains firmly in the realm of speculation, but nevertheless, we now know that it most certainly has a very interesting companion.

This is a remarkable discovery: Epsilon Indi B is the nearest star-like source to the Sun found in 15 years, the highest proper motion source found in over 70 years, and with a total luminosity just 0.002% that of the Sun, one of the intrinsically faintest sources ever seen outside the Solar System!

After Proxima and Alpha Centauri, the Epsilon Indi system is also just the second known wide binary system within 15 light years. However, unlike Proxima Centauri, Epsilon Indi B is no ordinary star.

Brown dwarfs: cooling, cooling, cooling …
Within days of its discovery in the database, the astronomers managed to secure an infrared spectrum of Epsilon Indi B using the SOFI instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile). The spectrum showed the broad absorption features due to methane and water steam in its upper atmosphere, indicating a temperature of ‘only’ 1000 ?C. Ordinary stars are never this cool – Epsilon Indi B was confirmed as a brown dwarf.

Brown dwarfs are thought to form in much the same way as stars, by the gravitational collapse of clumps of cold gas and dust in dense molecular clouds. However, for reasons not yet entirely clear, some clumps end up with masses less than about 7.5% of that of our Sun, or 75 times the mass of planet Jupiter. Below that boundary, there is not enough pressure in the core to initiate nuclear hydrogen fusion, the long-lasting and stable source of power for ordinary stars like the Sun. Except for a brief early phase where some deuterium is burned, these low-mass objects simply continue to cool and fade slowly away while releasing the heat left-over from their birth.

Theoretical discussions of such objects began some 40 years ago. They were first named ‘black dwarfs’ and later ‘brown dwarfs’, in recognition of their predicted very cool temperatures. However, they were also predicted to be very faint and very red, and it was only in 1995 that such objects began to be detected.

The first were seen as faint companions to nearby stars, and then later, some were found floating freely in the Solar neighbourhood. Most brown dwarfs belong to the recently classified spectral types L and T, below the long-known cool dwarfs of type M. These are very red to human eyes, but L and T dwarfs are cooler still, so much so that they are almost invisible at optical wavelengths, with most of their emission coming out in the infrared. [7].
How massive is Epsilon Indi B?

The age of most brown dwarfs detected to date is unknown and thus it is hard to estimate their masses. However, it may be assumed that the age of Epsilon Indi B is the same as that of Epsilon Indi A, whose age is estimated to be 1.3 billion years based on its rotational speed. Combining this information with the measured temperature, brightness, and distance, it is then possible to determine the mass of Epsilon Indi B using theoretical models of brown dwarfs.

Two independent sets of models yield the same result: Epsilon Indi B must have a mass somewhere between 4-6% of that of the Sun, or 40-60 Jupiter masses. The most likely value is around 45 Jupiter masses, i.e. well below the hydrogen fusion limit, and definitively confirming this new discovery as a bona-fide brown dwarf.

The importance of Epsilon Indi B
PR Photo 03c/03 shows the current census of the stars in the solar neighbourhood. All these stars have been known for many years, including GJ1061, which, however, only had its distance firmly established in 1997. The discovery of Epsilon Indi B, however, is an extreme case, never before catalogued, and the first brown dwarf to be found within the 12.5 light year horizon.

If current predictions are correct, there should be twice as many brown dwarfs as main sequence stars. Consequently, Epsilon Indi B may be the first of perhaps 100 brown dwarfs within this distance, still waiting to be discovered!

Epsilon Indi B is an important catch well beyond the cataloguing the Solar neighbourhood. As the nearest and brightest known brown dwarf and with a very accurately measured distance, it can be subjected to a wide variety of detailed observational studies. It may thus serve as a template for more distant members of its class.

With the help of Epsilon Indi B, astronomers should now be able to see further into the mysteries surrounding the formation and evolution of the exotic objects known as brown dwarfs, halfway between stars and giant planets, the physics of their inner cores, and the weather and chemistry of their atmospheres.

An historical note – the southern constellation Indus
The constellation Indus lies deep in the southern sky, nestled between three birds, Grus (The Crane), Tucana (The Toucan) and Pavo (The Peacock), cf. PR Photo 03d/03.

First catalogued in 1595-1597 by the Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman, this constellation was added to the southern sky by Johann Bayer in his book ‘Uranometria’ (1603) to honour the Native Americans that European explorers had encountered on their travels.

In particular, it has been suggested that it is specifically the native peoples of Tierra del Fuego and Patagonia that are represented in Indus, just over two thousand kilometres south of La Silla where the first spectroscopic observations of Epsilon Indi B were made some 400 years later.

In the later drawing by Bode shown here, Epsilon Indi, the fifth brightest star in Indus, is associated with one of the arrows in the Indian’s hand.

Original Source: ESO News Release

Posted on by Fraser Cain

Supernova Won’t Destroy the World

Image credit: Hubble

Just in case you were worried, it appears that a supernova would have to be really really close to the Earth before it could cause massive damage to our environment. Scientists at NASA and Kansas University used data from a recent exploding star to determine that a supernova would have to be only 26 light-years away in order to strip away the ozone layer – an encounter that only happens once every 670 million years.

We have one less thing to worry about. While the cosmic debris from a nearby massive star explosion, called a supernova, could destroy the Earth’s protective ozone layer and cause mass extinction, such an explosion would have to be much closer than previously thought, new calculations show.

Scientists at NASA and Kansas University have determined that the supernova would need to be within 26 light years from Earth to significantly damage the ozone layer and allow cancer-causing ultraviolet radiation to saturate the Earth’s surface.

An encounter with a supernova that close only happens at a rate of about once in 670 million years, according to Dr. Neil Gehrels of NASA’s Goddard Space Flight Center in Greenbelt, Md., who presents these findings today at the American Astronomical Society meeting in Seattle.

“Perhaps a nearby supernova has bombarded Earth once during the history of multicellular life with its punishing gamma rays and cosmic rays,” said Gehrels. “The possibility for mass extinction is indeed real, yet the risk seems much lower than we have thought.”

The new calculations are based largely on advances in atmospheric modeling, analysis of gamma rays produced by a supernova in 1987 called SN1987a, and a better understanding of galactic supernova locations and rates. A supernova is an explosion of a star at least twice as massive as our Sun.

Previous estimates from the 1970s stated that supernovae as far as 55 light years from Earth could wipe out up to 90 percent of the atmosphere for hundreds of years. The damage would be from gamma rays and cosmic rays, both prodigiously emitted by supernovae. Gamma rays are the most energetic form of light. Cosmic rays are atomic particles, the fastest-moving matter in the Universe, produced when the expanding shell of gas from the exploded star runs into surrounding dust and gas in the region. Gamma rays, moving at light speed, would hit the Earth’s atmosphere first, followed closely by the cosmic rays moving at close to light speed.

Gamma-ray light particles (called photons) and the cosmic-ray particles can wreak havoc in the upper atmosphere, according to Dr. Charles Jackman of NASA Goddard, who provided the atmospheric analysis needed for the new calculation.

The particles collide with nitrogen gas (N2) and break the molecule into highly-reactive nitrogen atoms (N). The nitrogen atoms then react fairly quickly with oxygen gas (O2) to form nitric oxide (NO) and, subsequently, other nitrogen oxides (NOx). The nitrogen oxide molecules can then destroy ozone (O3) through a catalytic process. This means that a single NOx molecule can destroy an ozone molecule and remain intact to destroy hundreds of more ozone molecules.

The new calculations — based on the NASA Goddard two-dimensional photochemical transport model — show that a supernova within 26 light years from Earth could wipe out 47 percent of the ozone layer, allowing approximately twice the amount of cancer-causing ultraviolet radiation to reach the Earth’s surface. Excessive UV radiation is harmful to both plants and animals, thus a doubling of UV levels would be a significant problem to life on Earth.

The gamma-ray irradiation would last 300 to 500 days. The ozone layer would then repair itself, but only to endure cosmic-ray bombardment shortly after, lasting at least 10 years. (Cosmic rays are electrically charged particles whose paths are influenced by magnetic fields, and the extent of such fields in the interstellar medium is not well understood.)

The calculations simultaneously point to the resilience of the ozone layer as well as its fragility in a violent Universe, said Dr. Claude Laird of the University of Kansas, who developed the gamma-ray and cosmic ray input code and performed the atmospheric model simulations. Although the ozone layer should recover relatively rapidly once the particle influx tapers off — within about one to two years, the Goddard models show — even this short period of time is sufficient to cause significant and lasting damage to the biosphere.

“The atmosphere usually protects us from gamma rays, cosmic rays, and ultraviolet radiation, but there’s only so much hammering it can take before Earth’s biological defenses break down,” he said.

Dr. John Cannizzo of NASA Goddard and University of Maryland, Baltimore Country, initiated and coordinated the new calculations. “I’ve long been fascinated by the possibility of extinction from something as remote as a star explosion,” he said. “With this updated calculation, we essentially worked backwards to determine what level of ozone damage would be needed to double the level of ultraviolet radiation reaching the Earth’s surface and then determined how close a supernova would need to be to cause that kind of damage.”

These results will appear in the Astrophysical Journal 2003, March 10, vol. 585. Co-authors include Barbara Mattson of NASA Goddard (via L3 Com Analytics Corporation) and Wan Chen of Sprint IP Design in Reston, Virginia.

Original Source: NASA News Release

Posted on by Fraser Cain

Rosetta Launch Postponed Indefinitely

Just a day after they announced that Rosetta could be flying by the end of the month, the European Space Agency decided to put the mission on hold indefinitely because of their concerns with the Ariane-5 rocket. Unfortunately, since Rosetta won’t be launching by the end of the month, it won’t be able to meet up with Comet Wirtanen. by 2011, so the entire mission will need to be redesigned to seek a new target.

Posted on by Fraser Cain

Three new moons discovered for Neptune

Image credit: NASA

A team of astronomers from the Harvard-Smithsonian Center for Astrophysics have discovered three previously unknown moons orbiting the planet Neptune. Since they’re only 30-40km across, the moons were a challenge to spot. The team had to digitally merge multiple exposures of the planet moving across a background of stars. Over time, the planets and their motions were picked up as points of light. This brings the gas giant’s total to 11 known moons.

A team of astronomers led by Matthew Holman (Harvard-Smithsonian Center for Astrophysics) and JJ Kavelaars (National Research Council of Canada) has discovered three previously unknown moons of Neptune. This boosts the number of known satellites of the gas giant to eleven. These moons are the first to be discovered orbiting Neptune since the Voyager II flyby in 1989, and the first discovered from a ground-based telescope since 1949.

It now appears that each giant planet’s irregular satellite population is the result of an ancient collision between a former moon and a passing comet or asteroid. “These collisional encounters result in the ejection of parts of the original parent moon and the production of families of satellites. Those families are exactly what we’re finding,” said Kavelaars.

The team that discovered these new satellites of Neptune includes Holman and Kavelaars, graduate student Tommy Grav (University of Oslo & Harvard-Smithsonian Center for Astrophysics), and undergraduate students Wesley Fraser and Dan Milisavljevic (McMaster University, Hamilton, Ontario, Canada).

Needle in a Haystack

The new satellites were a challenge to detect because they are only about 30-40 kilometers (18-24 miles) in size. Their small size and distance from the Sun prevent the satellites from shining any brighter than 25th magnitude, about 100 million times fainter than can be seen with the unaided eye.

To locate these new moons, Holman and Kavelaars utilized an innovative technique. Using the 4.0-meter Blanco telescope at the Cerro Tololo Inter-American Observatory, Chile, and the 3.6-meter Canada-France-Hawaii Telescope, Hawaii, they took multiple exposures of the sky surrounding the planet Neptune. After digitally tracking the motion of the planet as it moved across the sky, they then added many frames together to boost the signal of any faint objects. Since they tracked the planet’s motion, stars showed up in the final combined image as streaks of light, while the moons accompanying the planet appeared as points of light.

Prior to this find, two irregular satellites and six regular satellites of Neptune were known. The two irregular satellites are Triton, discovered in 1846 by William Lassell, and Nereid, discovered in 1949 by Gerard Kuiper. Triton is considered irregular because it orbits the planet in a direction opposite to the planet’s rotation, indicating that Triton is likely a captured Kuiper Belt Object. (The Kuiper Belt is a disk-shaped collection of icy objects that circle the Sun beyond the orbit of Neptune.) Nereid is considered irregular because it has a highly elliptical orbit around Neptune. In fact, its orbit is the most elliptical of any satellite in the solar system. Many scientists believe that Nereid once was a regular satellite whose orbit was disrupted when Triton was gravitationally captured. The six regular satellites were discovered by the Voyager probe during its encounter with Neptune. The three new satellites were missed by Voyager II because of their faintness and great distance from Neptune. According to Holman, “The discovery of these moons has opened a window through which we can observe the conditions in the solar system at the time the planets were forming.”

Tracking Faint Blips

The researchers are currently conducting follow-up observations to better define the orbits of the newfound moons using orbital predictions supplied by Brian Marsden (Director of the Minor Planet Center in Cambridge, Mass.) and Robert Jacobson (Jet Propulsion Laboratory).

To follow up the initial find, team members Brett Gladman (University of British Columbia, Canada); Jean-Marc Petit, Philippe Rousselot, and Olivier Mousis (Observatoire de Besancon, France); and Philip Nicholson and Valerio Carruba (Cornell University) conducted additional observations using the Hale 5-meter telescope on Mount Palomar and one of the four 8.2-meter telescopes of the European Southern Observatory’s Very Large Telescope at Paranal Observatory, Chile. Grav made additional tracking observations using the 2.6-meter Nordic Optical Telescope on La Palma, Spain.

Holman says, “Tracking these moons is an enormous, international undertaking involving the efforts of many people. Without teamwork, such faint objects could be easily lost.”

Based in La Serena, Chile, the Cerro Tololo Inter-American Observatory is part of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation.

The Canada-France-Hawaii Telescope is operated by the CFHT Corporation under a joint agreement between the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

The European Southern Observatory is an intergovernmental, European organization for astronomical research. It has ten member countries. ESO operates astronomical observatories in Chile and has its headquarters in Garching, near Munich, Germany.

Headquartered in Cambridge, Massachusetts, 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: CfA News Release

Posted on by Fraser Cain

Rosetta Due for Late January Launch

Image credit: ESA

The European Space Agency’s Rosetta mission will be the first spacecraft to ever orbit and then land on a distant comet. Scheduled for launch on board an Ariane-5 rocket as early as January 22, the spacecraft will rendezvous with Comet Wirtanen in 2011. There is some uncertainty about the launch, however, because of a booster accident with an enhanced Ariane-5 last month. The spacecraft must launch by the end of January if it’s to meet up with Wirtanen; otherwise, a new objective will have to be selected.

ESA’s Rosetta will be the first mission to orbit and land on a comet. Comets are icy bodies that travel throughout the Solar System and develop a characteristic tail when they approach the Sun. Rosetta is scheduled to be launched on-board an Ariane-5 rocket in January 2003 from Kourou, French Guiana.

The decision on the launch date will be taken by Tuesday 14 January 2003 (See Arianspace’s press release number 03/02 of 7 January 2003 or look at the web site http://www.arianespace.com). The mission target is Comet Wirtanen and the encounter will occur in 2011. Rosetta’s name comes from the famous Rosetta Stone that, almost 200 years ago, led to the deciphering of Egyptian hieroglyphics. In a similar way, scientists hope that the Rosetta spacecraft will unlock the mysteries of the Solar System.

Comets are very interesting objects for scientists since their composition reflects how the Solar System was when it was very young and still ‘unfinished’, more than 4600 million years ago. Comets have not changed much since then. By orbiting Comet Wirtanen and landing on it, Rosetta will collect essential information to understand the origin and evolution of our Solar System. It will also help discover whether comets contributed to the beginnings of life on Earth. Comets are carriers of complex organic molecules that, when delivered to Earth through impacts, perhaps played a role in the origin of living forms. Furthermore, ‘volatile’ light elements carried by comets may have also played an important role in forming the Earth’s oceans and atmosphere.

“Rosetta is one of the most challenging missions ever undertaken so far,” says Prof. David Southwood, ESA Director of Science. “No one before has attempted a simular mission, unique for its scientific implications as well as for its complex and spectacular interplanetary space manoeuvres.” Before reaching its target in 2011, Rosetta will circle the Sun almost four times on wide loops in the inner Solar System. During its long trek, the spacecraft will have to endure some extreme thermal conditions. Once it is close to Comet Wirtanen, scientists will take it through a delicate braking manoeuvre; then the spacecraft will closely orbit the comet, and gently drop a lander on it. It will be like landing on a small, fast-moving cosmic bullet that has, at present, an almost unknown ‘geography’.

An amazing 8-year interplanetary trek
Rosetta is a 3-tonne box-type spacecraft about 3 metres high, with two 14-metre long solar panels. It consists of an orbiter and a lander. The lander is approximately 1 metre across and 80 centimetres high. It will be attached to the side of the Rosetta orbiter during the journey to Comet Wirtanen. Rosetta carries 21 experiments in total, 10 of them on the lander. They will be kept in hibernation during most of its 8-year trek towards Wirtanen.

What makes Rosetta’s cruise so long? At the time of the rendezvous, Comet Wirtanen will be as far from the Sun as Jupiter is. No launcher could possibly get Rosetta there directly. ESA’s spacecraft will gather speed from gravitational ‘kicks’ provided by three planetary fly-bys: one of Mars in 2005 and two of Earth in 2005 and 2007. During the trip, Rosetta will also visit two asteroids, Otawara (in 2006) and Siwa (in 2008). During these encounters, scientists will switch on Rosetta’s instruments for calibration and scientific studies.

Long trips in deep space include many hazards, such as extreme changes in temperature. Rosetta will leave the benign environment of near-Earth space for the dark, frigid regions beyond the asteroid belt. To manage these thermal loads, experts have done very tough pre-launch tests to study Rosetta’s endurance. For example, they have heated its external surfaces to more than 150 degrees Celsius, then quickly cooled it to -180 degrees Celsius in the next test.

Scientists will fully reactivate the spacecraft prior to the comet rendezvous manoeuvre in 2011. Then, Rosetta will orbit the comet, an object only 1.2 kilometres wide, while it cruises through the inner Solar System at 135 000 kilometres per hour. At the time of the rendezvous, around 675 million kilometres from the Sun, Wirtanen will hardly show any surface activity. The characteristic coma (the comet’s ‘atmosphere’) and the tail will not yet have formed because of the large distance from the Sun. The comet’s tail is made up of dust grains and frozen gases from the comet’s surface that vapourise because of the Sun’s heat.

For six months, Rosetta will extensively map the comet surface, prior to selecting a landing site. In July 2012, the lander will self-eject from the spacecraft from a height of just one kilometre. Touchdown will take place at walking speed – less than 1 metre per second. Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space. It has to do this because the comet’s extremely weak gravity alone will not hold onto the lander. Operation and scientific observations on the comet surface will last 65 hours as a minimum, but may continue for many months.

During and after the lander operations, Rosetta will continue orbiting and studying the comet. Rosetta will be the first spacecraft to witness at close quarters the changes taking place in a comet when the comet approaches the Sun and grows its coma and tail. The trip will end in July 2013, after 10.5 years of adventure, when the comet is closest to the Sun.

Studying a comet on the spot
Rosetta’s goal is to examine a comet in great detail. The instruments on Rosetta’s orbiter include several cameras, spectrometers, and experiments that work at different wavelengths – infrared, ultraviolet, microwave, radio – and a number of sensors. They will provide, among other things, very high-resolution images and information about the shape, density, temperature, and chemical composition of the comet. Rosetta’s instruments will analyse the gases and dust grains in the so-called coma that forms when the comet becomes active, as well as the interaction with the solar wind.

The 10 instruments on board the lander will do an on-the-spot analysis of the composition and structure of the comet’s surface and subsurface material. A drilling system will take samples down to 30 centimetres below the surface and will feed these to the ‘composition analysers’. Other instruments will measure properties such as the near-surface strength, density, texture, porosity, ice phases, and thermal properties. Microscopic studies of individual grains will tell us about the texture. In addition, instruments on the lander will study how the comet changes during the day-night cycle, and while it approaches the Sun.

Ground operations
Data from the lander are relayed to the orbiter, which stores them for downlink to Earth at the next ground station contact. ESA has installed a new deep-space antenna at New Norcia, near Perth in Western Australia, as the main communications link between the spacecraft and the ESOC Mission Control in Darmstadt, Germany. This 35-metre diameter parabolic antenna allows the radio signal to reach distances of more than 1 million kilometres from Earth. The radio signals, travelling at the speed of light, will take up to 50 minutes to cover the distance between the spacecraft and Earth.

Rosetta’s Science Operations Centre, which is responsible for collecting and distributing the scientific data, will share a location at ESOC and ESTEC in Noordwijk, The Netherlands. The Lander Control Centre is located in DLR in Cologne, Germany, and the Lander Science Centre in CNES in Toulouse, France.

Building Rosetta
Rosetta was selected as a mission in 1993. The spacecraft has been built by Astrium Germany as prime contractor. Major subcontractors are Astrium UK (spacecraft platform), Astrium France (spacecraft avionics), and Alenia Spazio (assembly, integration, and verification). Rosetta’s industrial team involves more than 50 contractors from 14 European countries and the United States.

Scientific consortia from institutes across Europe and the United States have provided the instruments on the orbiter. A European consortium under the leadership of the German Aerospace Research Institute (DLR) has provided the lander. Rosetta has cost ESA Euro 701 million at 2000 economic conditions. This amount includes the launch and the entire period of development and mission operations from 1996 to 2013. The lander and the experiments, the so-called ‘payload’, are not included since they are funded by the member states through the scientific institutes.

Posted on by Fraser Cain

Binary Star Ejected From its System

Astronomers from the University of Mexico have found a distant star system where a small, young star has been flung out of its binary star system by the gravitational interaction with its neighbours. The star, called T Tauri Component Sb, has 20% the mass of the Sun, and was part of a group of stars 450 light years from the Earth. The team has been tracking the path of the rogue star since 1983, and watched it slingshot past one star and head out into space.

Posted on by Fraser Cain

Columbia Countdown Gets Started

Under a cloak of high security, NASA began the launch countdown for the Space Shuttle Columbia on Monday. If all goes well, the shuttle will launch on Thursday at a secret time – the actual launch time will only be announced 24 hours beforehand. The 16-day microgravity science mission was supposed to launch last year, but cracks discovered in shuttle fuel lines kept the whole fleet grounded while a solution was found. Isreal’s first astronaut, Ilan Ramon, is also due to take part in this mission.

Posted on by Fraser Cain

ICESat Launches

Image credit: NASA

A satellite designed to track the changes in the Earth’s major ice sheets was launched on Sunday after experiencing a month of delays due to technical difficulties. ICESsat (Ice Cloud and Land Elevation
Satellite) was launched aboard a Boeing Delta rocket from the Vandenberg US Air Force Base in California. On board the rocket was another, smaller satellite called CHIPSat, which will help astronomers study the hot gas coming off of stars.

NASA?s Ice, Cloud and Land Elevation satellite (ICESat) and Cosmic Hot Interstellar Spectrometer (CHIPS) satellite lifted off from Vandenberg Air Force Base, Calif., at 4:45 p.m. PST aboard Boeing?s Delta II rocket. Separation of the ICESat spacecraft occurred 64 minutes after launch at 5:49 p.m. PST. Initial contact with ICESat was made 75 minutes after launch at 6 p.m. PST as the spacecraft passed over the Svalbard Ground Station in Norway.

The CHIPS spacecraft separated from the launch vehicle 83 minutes after launch at 6:08 p.m. PST. Initial contact with CHIPS was made 98 minutes after launch at 6:23 p.m. PST as the spacecraft passed over the University of California, Berkeley.

?The Delta vehicle gave us a great ride! The ICESat spacecraft was right where we expected and is performing great. The whole team is thrilled to be having such a wonderful start to our mission? said Jim Watzin, the ICESat Project Manager at NASA?s Goddard Space Flight Center in Greenbelt, Md.

Over the next few days the ICESat spacecraft will gradually be despun and placed into a safe stable attitude. Within two weeks the onboard propulsion system will gradually tune the orbit. Once in its final orbital position, ICESat will be approximately 373 miles (600 kilometers) above the Earth.

ICESat is the latest in a series of Earth Observing System spacecraft, following the Terra satellite launched in December 1999, and the Aqua satellite launched earlier in May of this year. The primary role of ICESat is to quantify ice sheet growth or retreat and to thereby answer questions concerning many related aspects of the Earth?s climate system, including global climate change and changes in sea level.

Ball Aerospace and Technologies Corporation (Ball) in Boulder, Colorado built the ICESat spacecraft. The Earth Science Data and Information System at NASA Goddard will provide space and ground network support and the University of Colorado?s Laboratory for Atmospheric and Space Physics will team with Ball to provide mission operations and flight dynamics support. The GLAS and ICESat data will be initially processed at the ICESat Investigator-led Processing System with support from the University of Texas, Center for Space Research. The mission data will be distributed and archived by the National Snow and Ice Data Center.

Original Source: NASA News Release

Posted on by Fraser Cain

Hubble Spots Earliest Bright Objects

Image credit: Hubble

The most recent photos released from the Hubble Space Telescope show objects so old they might be from a time when stars in the universe were just starting to shine in significant numbers – about 13 billion years ago. These objects are at the limit of Hubble’s resolving power, but the next generation James Webb Space Telescope is expected to see the entire group of proto-galaxies, and look back even further.

Researchers using NASA’s Hubble Space Telescope reported today they are seeing the conclusion of the cosmic epoch called the “Dark Ages,” a time about a billion years after the big bang when newly-formed stars and galaxies were just starting to become visible.

“With the Hubble Telescope, we can now see back to the epoch when stars in young galaxies began to shine in significant numbers, concluding the cosmic ‘dark ages’ about 13 billion years ago,” said Haojing Yan, a Ph.D. graduate student at Arizona State University (ASU). The results are being presented at the meeting of the American Astronomical Society in Seattle, WA.

Current theory holds that after the big bang that created the universe, there was a time of expansion and cooling that led to what is known as the “dark ages” in cosmic terms. The universe cooled sufficiently for protons and electrons to combine to form neutral hydrogen atoms and block the transmission of light. This epoch started about 300,000 years after the big bang, and may have ended about a billion years later. Stars and galaxies started to form at some point during this era, but the omni-present neutral hydrogen in the universe absorbed the ultraviolet light produced by stars and can not be seen by current telescopes.

The ASU team reports that Hubble’s Advanced Camera for Surveys (ACS) is revealing numerous faint objects that may be young star-forming galaxies seen when the universe was seven times smaller than it is today and less than a billion years old.

This was an important transition in the evolution of the universe. Because ionized hydrogen does not absorb ultraviolet light as easily as neutral hydrogen, the Dark Ages came to an end when enough hot stars had formed that their ultraviolet light pervaded the universe and re-ionized the neutral hydrogen. The shining stars opened a window for astronomers to look very far back into time.

“The objects we found are in the epoch when the universe started to produce stars in significant numbers ?- the hard-to-find young galaxies,” says Rogier Windhorst, professor of astronomy at ASU. “These galaxies are at the boundary of the directly observable universe.”

The ASU team found the objects while examining a small portion of the sky in the spring zodiacal constellation Virgo. This particular area of the sky contains no known bright galaxies, helping reduce light contamination in the observations. The entire ACS field of view shows about thirty such faint red objects. The distances to the suspected young galaxies are believed to be quite large, based on how red the observed objects are compared with nearby galaxies.

Based on this sample, the ASU researchers estimate that at least 400 million such objects filled in the entire universe at this cosmic epoch, to the limit of this Hubble image. And, they say they are able to see only the tip of the iceberg with current telescopes such as Hubble. NASA’s planned 7-meter James Webb Space Telescope is expected to see the entire population of these proto-galactic objects after it is launched in 2010.

Original Source: Hubble News Release

Posted on by Fraser Cain

Gravity Moves at the Speed of Light

Image credit: NRAO

Theorized by Einstein for almost a century, physicists have found evidence to support the theory that the force of gravity moves at the speed of light. The speed was measured by physicist Sergei Kopeikin by watching how light from a distant quasar was bent by Jupiter’s gravity. Variations in how the image of the quasar was bent accounted for this speed of gravity.

Taking advantage of a rare cosmic alignment, scientists have made the first measurement of the speed at which the force of gravity propagates, giving a numerical value to one of the last unmeasured fundamental constants of physics.

“Newton thought that gravity’s force was instantaneous. Einstein assumed that it moved at the speed of light, but until now, no one had measured it,” said Sergei Kopeikin, a physicist at the University of Missouri-Columbia.

“We have determined that gravity’s propagation speed is equal to the speed of light within an accuracy of 20 percent,” said Ed Fomalont, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, VA. The scientists presented their findings to the American Astronomical Society’s meeting in Seattle, WA.

The landmark measurement is important to physicists working on unified field theories that attempt to combine particle physics with Einstein’s general theory of relativity and electromagnetic theory.

“Our measurement puts some strong limits on the theories that propose extra dimensions, such as superstring theory and brane theories,” Kopeikin said. “Knowing the speed of gravity can provide an important test of the existence and compactness of these extra dimensions,” he added.

Superstring theory proposes that the fundamental particles of nature are not pointlike, but rather incredibly small loops or strings, whose properties are determined by different modes of vibration. Branes (a word derived from membranes) are multidimensional surfaces, and some current physical theories propose space-time branes embedded to five dimensions.

The scientists used the National Science Foundation’s Very Long Baseline Array (VLBA), a continent-wide radio-telescope system, along with the 100-meter radio telescope in Effelsberg, Germany, to make an extremely precise observation when the planet Jupiter passed nearly in front of a bright quasar on September 8, 2002.

The observation recorded a very slight “bending” of the radio waves coming from the background quasar by the gravitational effect of Jupiter. The bending resulted in a small change in the quasar’s apparent position in the sky.

“Because Jupiter is moving around the Sun, the precise amount of the bending depends slightly on the speed at which gravity propagates from Jupiter,” Kopeikin said.

Jupiter, the largest planet in the Solar System, only passes closely enough to the path of radio waves from a suitably bright quasar about once a decade for such a measurement to be made, the scientists said.

The once-in-a-decade celestial alignment was the last in a chain of events that made measuring the speed of gravity possible. The others included a chance meeting of the two scientists in 1996, a breakthrough in theoretical physics and the development of specialized techniques that enabled the extremely precise measurement to be made.

“No one had tried to measure the speed of gravity before because most physicists had assumed that the only way to do so was to detect gravitational waves,” Kopeikin recalled. However, in 1999, Kopeikin extended Einstein’s theory to include the gravitational effects of a moving body on light and radio waves. The effects depended on the speed of gravity. He realized that if Jupiter moved nearly in front of a star or radio source, he could test his theory.

Kopeikin studied the predicted orbit of Jupiter for the next 30 years and discovered that the giant planet would pass closely enough in front of the quasar J0842+1835 in 2002. However, he quickly realized that the effect on the quasar’s apparent position in the sky attributable to the speed of gravity would be so small that the only observational technique capable of measuring it was Very Long Baseline Interferometry (VLBI), the technique embodied in the VLBA. Kopeikin then contacted Fomalont, a leading expert in VLBI and an experienced VLBA observer.

“I immediately realized the importance of an experiment that could make the first measurement of a fundamental constant of nature,” Fomalont said. “I decided that we had to give this our best shot,” he added.

To get the required level of precision, the two scientists added the Effelsberg telescope to their observation. The wider the separation between two radio-telescope antennas, the greater is the resolving power, or ability to see fine detail, achievable. The VLBA includes antennas on Hawaii, the continental United States, and St. Croix in the Caribbean. An antenna on the other side of the Atlantic added even more resolving power.

“We had to make a measurement with about three times more accuracy than anyone had ever done, but we knew, in principle, that it could be done,” Fomalont said. The scientists tested and refined their techniques in “dry runs,” then waited for Jupiter to make its pass in front of the quasar.

The wait included considerable nail-biting. Equipment failure, bad weather, or an electromagnetic storm on Jupiter itself could have sabotaged the observation. However, luck held out and the scientists’ observations at a radio frequency of 8 GigaHertz produced enough good data to make their measurement. They achieved a precision equal to the width of a human hair seen from 250 miles away.

“Our main goal was to rule out an infinite speed for gravity, and we did even better. We now know that the speed of gravity is probably equal to the speed of light, and we can confidently exclude any speed for gravity that is over twice that of light,” Fomalont said.

Most scientists, Kopeikin said, will be relieved that the speed of gravity is consistent with the speed of light. “I believe this experiment sheds new light on fundamentals of general relativity and represents the first of many more studies and observations of gravitation which are currently possible because of the enormously high precision of VLBI. We have a lot more to learn about this intriguing cosmic force and its relationship to the other forces in nature,” Kopeikin said.

This is not the first time that Jupiter has played a part in producing a measurement of a fundamental physical constant. In 1675, Olaf Roemer, a Danish astronomer working at the Paris Observatory, made the first reasonably accurate determination of the speed of light by observing eclipses of one of Jupiter’s moons.

Original Source: NRAO News Release