Posted on by Fraser Cain

Saturn’s Bands Becoming Clearer

Image credit: NASA/JPL/Space Science Institute
As Cassini nears its rendezvous with Saturn, new detail in the banded clouds of the planet’s atmosphere are becoming visible. Cassini took this narrow angle camera image on April 16, 2004 when it was 38.5 million kilometers (23.9 million miles) from Saturn. The image scale is approximately 231 kilometers (144 miles) per pixel. Contrast has been enhanced to aid visibility of features in the atmosphere.

This image was taken using a filter sensitive to light near 727 nanometers, which is one of the near-infrared absorption bands of methane gas, one of the constituents of Saturn’s atmosphere. Dark locales are generally areas of strong methane absorption, relatively free of high clouds. The bright areas are places with high, thick clouds which shield the methane below.

The clouded bands follow lines of constant latitude, and reflect the dominant effect of the planet’s rotation on the dynamics of its atmosphere. Bands move at different speeds, and the irregularities at their edges may be due to either the differential motion between them or to disturbances originating below the visible cloud layer. Such disturbances might be powered by the planet’s internal heat: Saturn radiates more energy than it receives from the Sun.

The dark spot at the south pole is remarkable because it is so small and well-centered. The spot could be affected by Saturn’s magnetic field, which is nearly aligned with the planet’s rotation axis, unlike the magnetic fields of Jupiter and Earth. From south to north, other notable features are the two white spots at roughly the same longitude but different latitudes, and the large dark oblong-shaped feature that extends into the bright equatorial band. The darker band beneath the bright equatorial region has begun to show a lacy pattern of lighter-colored, high altitude clouds, indicative of turbulent atmospheric conditions.

The moon Mimas (396 kilometers, 245 miles across) is visible to the left of the south pole. Saturn currently has 31 known moons, and Cassini scientists hope to discover new ones, perhaps embedded within the planet’s magnificent rings.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The Cassini imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

Posted on by Fraser Cain

Searching for a Way to Test String Theory

Image credit: Hubble
Scientists studying the Big Bang say that it is possible that string theory may one day be tested experimentally via measurements of the Big Bang’s afterglow.

Richard Easther, assistant professor of physics at Yale University will discuss the possibility at a meeting at Stanford University Wednesday, May 12, titled “Beyond Einstein: From the Big Bang to Black Holes.” Easther’s colleagues are Brian Greene of Columbia University, William Kinney of the University at Buffalo, SUNY, Hiranya Peiris of Princeton University and Gary Shiu of the University of Wisconsin.

String theory attempts to unify the physics of the large (gravity) and the small (the atom). These are now described by two theories, general relativity and quantum theory, both of which are likely to be incomplete.

Critics have disdained string theory as a “philosophy” that cannot be tested. However, the results of Easther and his colleagues suggest that observational evidence supporting string theory may be found in careful measurements of the Cosmic Microwave Background (CMB), the first light to emerge after the Big Bang.

“In the Big Bang, the most powerful event in the history of the Universe, we see the energies needed to reveal the subtle signs of string theory,” said Easther.

String theory reveals itself only over extreme small distances and at high energies. The Planck scale measures 10-35 meters, the theoretical shortest distance that can be defined. In comparison, a tiny hydrogen atom, 10-10 meters across, is ten trillion trillion times as wide. Similarly, the largest particle accelerators generate energies of 1015 electron volts by colliding sub-atomic particles. This energy level can reveal the physics of quantum theory, but is still roughly a trillion times lower than the energy required to test string theory.

Scientists say that the fundamental forces of the Universe — gravity (defined by general relativity), electromagnetism, “weak” radioactive forces and “strong” nuclear forces (all defined by quantum theory) — were united in the high-energy flash of the Big Bang, when all matter and energy was confined within a sub-atomic scale. Although the Big Bang occurred nearly 14 billion years ago its afterglow, the CMB, still blankets the entire universe and contains a fossilized record of the first moments of time.

The Wilkinson Microwave Anisotropy Probe (WMAP) studies the CMB and detects subtle temperature differences, within this largely uniform radiation, glowing at only 2.73 degrees Celsius above absolute zero. The uniformity is evidence of “inflation,” a period when the expansion of the Universe accelerated rapidly, around 10-33 seconds after the Big Bang. During inflation, the Universe grew from an atomic scale to a cosmic scale, increasing its size a hundred trillion trillion times over. The energy field that drove inflation, like all quantum fields, contained fluctuations. These fluctuations, locked into the cosmic microwave background like waves on a frozen pond, may contain evidence for string theory.

Easther and his colleagues compare the rapid cosmic expansion that occurred just after the Big Bang to enlarging a photograph to reveal individual pixels. While physics at the Planck scale made a “ripple” 10-35 meters across, thanks to the expansion of the Universe the fluctuation might now span many light years.

Easther stressed it is a long shot that string theory might leave measurable effects on the microwave background by subtly changing the pattern of hot and cold spots. However, string theory is so hard to test experimentally that any chance is worth trying. Successors to WMAP, such as CMBPol and the European mission, Planck, will measure the CMB with unprecedented accuracy.

The modifications to the CMB arising from string theory could deviate from the standard prediction for the temperature differences in the cosmic microwave background by as much as 1%. However, finding a small deviation from a dominant theory is not without precedent. As an example, the measured orbit of Mercury differed from what was predicted by Isaac Newton’s law of gravity by around seventy miles per year. General relativity, Albert Einstein’s law of gravity, could account for the discrepancy caused by a subtle warp in spacetime from the Sun’s gravity speeding Mercury’s orbit.

Refer to http://www-conf.slac.stanford.edu/einstein/ for more information on the “Beyond Einstein” meeting.

Original Source: Yale University News Release

Posted on by Fraser Cain

Great Wall From Space

Image credit: ESA
ESA’s Proba satellite here shows a winding segment of the 7240-km long Great Wall of China situated just northeast of Beijing. The Great Wall’s relative visibility or otherwise from orbit has inspired much recent debate.

The 21 hours spent in space last October by Yang Liwei – China’s first ever space traveller – were a proud achievement for his nation. The only disappointment came as Liwei informed his countrymen he had not spotted their single greatest national symbol from orbit.

“The Earth looked very beautiful from space, but I did not see our Great Wall,” Liwei told reporters after his return.

China has cherished for decades the idea that the Wall was just about the only manmade object visible to astronauts from space, and the news disappointed many. A suggestion was made that the Wall be lit up at night so it can definitely be seen in future, while others called for school textbooks to be revised to take account of Liwei’s finding.

However such revisions may be unnecessary, according to American astronaut Eugene Cernan, speaking during a visit to Singapore: “In Earth’s orbit at a height of 160 to 320 kilometres, the Great Wall of China is indeed visible to the naked eye.”

Liwei may well have been unlucky with the weather and local atmospheric or light conditions ? with sufficiently low-angled sunlight the Wall’s shadow if not the Wall itself could indeed be visible from orbit.

What is for sure is that what the human eye may not be able to see, satellites certainly can. Proba’s High Resolution Camera (HRC) acquired this image of the Wall from 600 km away in space. The HRC is a black and white camera that incorporates a miniature Cassegrain telescope, giving it far superior spatial resolution to the human eye.

So while the HRC resolves mad-made objects down to five square metres, astronauts in low Earth orbit looking with the naked eye can only just make out such large-scale artificial features as field boundaries between different types of crops or the grid shape formed by city streets. They require binoculars or a zoom lens to make out individual roads or large buildings.

China’s Great Wall
Proba (Project for On Board Autonomy) is an ESA micro-satellite built by an industrial consortium led by the Belgian company Verhaert, launched in October 2001 and operated from ESA’s Redu Ground Station (Belgium).

Orbiting 600 km above the Earth?s surface, Proba was designed to be a one-year technology demonstration mission of the Agency but has since had its lifetime extended as an Earth Observation mission. It now routinely provides scientists with detailed environmental images thanks to CHRIS – a Compact High Resolution Imaging Spectrometer developed by UK-based Sira Electro-Optics Ltd – one of the main payloads on the 100 kg spacecraft.

Also aboard is the HRC, a small-scale monochromatic camera made up of a miniature Cassegrain telescope and a 1024 x 1024 pixel Charge-Coupled Device (CCD), as used in ordinary digital cameras, taking 25-km square images to a resolution of five metres. Proba boasts an ‘intelligent’ payload and has the ability to observe the same spot on Earth from a number of different angles and different combinations of optical and infra-red spectral bands. A follow-on mission, Proba-2, is due to be deployed by ESA around 2005.

Original Source: ESA News Release

Posted on by Fraser Cain

Powerful Flare Seen on a Distant Star

Image credit: ESA
For years, astronomers have wondered whether stars similar to the Sun go through periodic cycles of enhanced X-ray activity, like those often causing troubles to telephone and power lines here on Earth.

ESA’s X-ray observatory XMM-Newton has now revealed for the first time a cyclic behaviour in the X-ray radiation emitted by a star similar to the Sun. This discovery may help scientists to understand how stars affect the development of life on their planets.

Since the time Galileo discovered sunspots, in 1610, astronomers have measured their number, size and location on the disc of the Sun. Sunspots are relatively cooler areas on the Sun that are observed as dark patches. Their number rises and falls with the level of activity of the Sun in a cycle of about 11 years.

When the Sun is very active, large-scale phenomena take place, such as the flares and coronal mass ejections observed by the ESA/NASA solar observatory SOHO. These events release a large amount of energy and charged particles that hit the Earth and can cause powerful magnetic storms, affecting radio communications, power distribution lines and even our weather and climate.

During the solar cycle, the X-ray emission from the Sun varies by a large amount (about a factor of 100) and is strongest when the cycle is at its peak and the surface of the Sun is covered by the largest number of spots.

ESA’s X-ray observatory, XMM-Newton, has now shown for the first time that this cyclic X-ray behaviour is common to other stars as well. A team of astronomers, led by Fabio Favata, from ESA’s European Space Research and Technology Centre, The Netherlands, has monitored a small number of solar-type stars since the beginning of the XMM-Newton mission in 2000. The X-ray brightness of HD 81809, a star located 90 light years away in the constellation Hydra (the water snake), has varied by more than 10 times over the past two and a half years, reaching a well defined peak in mid 2002.

The star has shown the characteristic X-ray modulation (brightening and dimming) typical of the solar cycle. “This is the first clear sign of a cyclic pattern in the X-ray emission of stars other than the Sun,” said Favata. Furthermore, the data show that these variations are synchronised with the starspot cycle. If HD 81809 behaves like the Sun, its X-ray brightness can vary by a factor of one hundred over a few years. “We might well have caught HD 81809 at the beginning of an X-ray activity cycle,” added Favata.

The existence of starspot cycles on other stars had already been established long ago, thanks to observations that began in the 1950s. However, scientists did not know whether the X-ray radiation would also vary with the number of starspots. ESA’s XMM-Newton has now shown that this is indeed the case and that this cyclic X-ray pattern is not typical of the Sun alone. “This suggests that our Sun’s behaviour is probably nothing exceptional,” said Favata.

Besides its interest for scientists, the Sun’s cyclical behaviour can have an influence on everyone on Earth. Our climate is known to be significantly affected by the high-energy radiation emitted by the Sun. For instance, a temporary disappearance of the solar cycle in the 18th century corresponded with an exceptionally cold period on Earth. Similarly, in the early phases of the lifetime of a planet, this high-energy radiation has a strong influence on the conditions of the atmosphere, and thus potentially on the development of life.

Finding out whether the Sun’s X-ray cycle is common among other solar-type stars, and in particular among those hosting potential rocky planets, can give scientists much needed clues on whether and where other forms of life might exist outside the Solar System. At the same time, understanding how typical and long-lasting is the solar behaviour will tell us more about the evolution of the climate on Earth.

Further observations of HD 81809 and other similar stars are already planned with XMM-Newton. They will allow astronomers to study whether the large modulations in X-ray brightness observed in the Sun are indeed the norm for stars of its type. Understanding how other solar-like stars behave in general will give scientists better insight into the past and future of our own Sun.

Original Source: ESA News Release

Posted on by Fraser Cain

Chandra Sees Violent M87 Galaxy

Image credit: Chandra
Two observations by NASA’s Chandra X-ray Observatory of the giant elliptical galaxy M87 were combined to make this long-exposure image. A central jet is surrounded by nearby bright arcs and dark cavities in the multimillion degree Celsius atmosphere of M87. Much further out, at a distance of about fifty thousand light years from the galaxy’s center, faint rings can be seen and two spectacular plumes extend beyond the rings. These features, together with radio observations, are dramatic evidence that repetitive outbursts from the central supermassive black hole have been affecting the entire galaxy for a hundred million years or more. The faint horizontal streaks are instrumental artifacts that occur for bright sources.

The accompanying close-up shows the region surrounding the jet of high-energy particles in more detail. The jet is thought to be pointed at a small angle to the line of sight, out of the plane of the image. This jet may be only the latest in a series of jets that have been produced as magnetized gas spirals in a disk toward the supermassive black hole.

When a jet plows into the surrounding gas, a buoyant, magnetized bubble of high-energy particles is created, and an intense sound wave rushes ahead of the expanding bubble. These bubbles, which rise like hot air from a fire or explosion in the atmosphere, show up as bright regions in radio images and dark cavities in X-ray images. Bright X-ray arcs surrounding the cavities appear to be gas that has been swept up on rising, buoyant bubbles. An alternative interpretation is that the arcs are shock waves that surround the jet and are seen in projection.

A version of this long-exposure image that has been specially processed to bring out faint features in the outer region of the galaxy reveals two circular rings with radii of 45 thousand and 55 thousand light years, respectively. These features are likely sound waves produced by earlier explosions about 10 million and 14 million years ago, respectively in M87-time. M87 is 50 million light years from Earth.

The spectacular, curved X-ray plumes extending from the upper left to the lower right are thought to be gas carried out from the center of the galaxy on buoyant bubbles created by previous outbursts. A very faint arc at an even larger distance at the bottom of the image has a probable age of 100 million years.

X-ray features similar to those seen in M87 have been observed in other large galaxies in the centers of galaxy clusters (see, e.g., Perseus A). This suggests that episodic outbursts from supermassive black holes in giant galaxies may be common phenomena that determine how fast giant galaxies and their central black holes grow. As gas in the galaxy cools, it would flow inward to feed the black hole, producing an outburst which shuts down the inflow for a few million years, at which point the cycle would begin again. (NASA/CXC)

Original Source: Chandra News Release

Posted on by Fraser Cain

Wallpaper: Dying Star Spins a Spiderweb

Image credit: Hubble
Astronomers may not have observed the fabled “Stairway to Heaven,” but they have photographed something almost as intriguing: ladder-like structures surrounding a dying star.

A new image, taken with NASA’s Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our Milky Way. Cataloged as HD 44179, this nebula is more commonly called the “Red Rectangle” because of its unique shape and color as seen with ground-based telescopes.

Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen with ground-based telescopes looking through the Earth’s turbulent atmosphere. Details of the Hubble study were published in the April 2004 issue of The Astronomical Journal.

Hubble’s sharp pictures show that the Red Rectangle is not really rectangular, but has an overall X-shaped structure, which the astronomers involved in the study interpret as arising from outflows of gas and dust from the star in the center. The outflows are ejected from the star in two opposing directions, producing a shape like two ice-cream cones touching at their tips. Also remarkable are straight features that appear like rungs on a ladder, making the Red Rectangle look similar to a spider web, a shape unlike that of any other known nebula in the sky. These rungs may have arisen in episodes of mass ejection from the star occurring every few hundred years. They could represent a series of nested, expanding structures similar in shape to wine glasses, seen exactly edge-on so that their rims appear as straight lines from our vantage point.

The star in the center of the Red Rectangle is one that began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula. The shedding of the outer layers began about 14,000 years ago. In a few thousand years, the star will have become smaller and hotter, and will begin to release a flood of ultraviolet light into the surrounding nebula; at that time, gas in the nebula will begin to fluoresce, producing what astronomers call a planetary nebula.

At the present time, however, the star is still so cool that atoms in the surrounding gas do not glow, and the surrounding dust particles can only be seen because they are reflecting the starlight from the central star. In addition, there are molecules mixed in with the dust, which emit light in the red portion of the spectrum. Astronomers are not yet certain which types of molecules are producing the red color that is so striking in the Red Rectangle, but suspect that they are hydrocarbons that form in the cool outflow from the central star.

Another remarkable feature of the Red Rectangle, visible only with the superb resolution of the Hubble telescope, is the dark band passing across the central star. This dark band is the shadow of a dense disk of dust that surrounds the star. In fact, the star itself cannot be seen directly, due to the thickness of the dust disk. All we can see is light that streams out perpendicularly to the disk, and then scatters off of dust particles toward our direction. Astronomers found that the star in the center is actually a close pair of stars that orbit each other with a period of about 10 1/2 months. Interactions between these stars have probably caused the ejection of the thick dust disk that obscures our view of the binary. The disk has funneled subsequent outflows in the directions perpendicular to the disk, forming the bizarre bi- conical structure we see as the Red Rectangle. The reasons for the periodic ejections of more gas and dust, which are producing the “rungs” revealed in the Hubble image, remain unknown.

The Red Rectangle was first discovered during a rocket flight in the early 1970s, in which astronomers were searching for strong sources of infrared radiation. This infrared source lies about 2,300 light-years from Earth in the direction of the constellation Monoceros. Stars surrounded by clouds of dust are often strong infrared sources because the dust is heated by the starlight and radiates long-wavelength light. Studies of HD 44179 with ground-based telescopes revealed a rectangular shape in the dust surrounding the star in the center, leading to the name Red Rectangle which was coined in 1973 by astronomers Martin Cohen and Mike Merrill.

This image was made from observations taken on March 17-18, 1999 with Hubble’s Wide Field Planetary Camera 2.

Original Source: Hubble News Release

Posted on by Fraser Cain

13 Advocacy Groups Ally Together

Image credit: NASA
In an unprecedented show of unity, thirteen of the nation’s premier space advocacy groups, industry associations and space policy organizations have teamed up to support the effort to refocus NASA’s human space activities toward exploration, including a return to the Moon and moving on to Mars and beyond.

The organizations involved include: Aerospace Industries Association, Aerospace States Association, American Astronautical Society, American Institute of Aeronautics and Astronautics, California Space Authority, Florida Space Authority, The Mars Society, National Coalition of Spaceport States, National Space Society, The Planetary Society, ProSpace, Space Access Society and Space Frontier Foundation.

Collectively these groups can count almost one million Americans as members or as employees of member companies. Their first goal as a group is to work for broad Congressional support of the new national vision for space exploration outside of low earth orbit, which they refer to as Moon, Mars and Beyond. To begin they will work to secure first year funding for the initiative, which they view as a necessary first step for in-depth planning of the exploration program to commence in earnest.

In addition they intend to aggressively refute the false impression that Moon, Mars and Beyond is too expensive for this country to take on. They will demonstrate how modest but steady growth in our national expenditures on space can move the nation toward these important goals, and the benefits those expenditures will provide.

As space activity becomes increasingly integrated with every aspect of life here on earth, this new focus on exploration will provide myriad advances in science and technology, untold economic opportunity and serve as an inspiration to our nation’s youth. Given those benefits and the many more that lie in store, this new program of human space exploration beyond low earth orbit is a vital link to the future of the United States and the world.

Original Source: NSS News Release

Posted on by Fraser Cain

2004 Astronaut Class Named

Image credit: NASA
Eleven new astronaut candidates are joining the ranks of space explorers. NASA introduced the new class during a Space Day celebration today at the National Air and Space Museum’s Steven F. Udvar-Hazy Center in Chantilly, Va. The class of 2004 will be the first focused from the very beginning on realizing the new Vision for Space Exploration.

NASA Administrator Sean O’Keefe called members of the new astronaut class, “our next generation of explorers, who’ll help blaze a galactic trail through the solar system.

“We are indeed living in an age of heroic potential, as we move forward in the Solar System to explore mysterious new worlds, make important new discoveries and help to expand the sense of possibility for all humans on his planet,” O’Keefe said.

Former Astronaut and U.S. Sen. John Glenn, who introduced O’Keefe, looked back, and ahead. “How far we’ve come in the past few years,” he said, “how far we yet have to go, and how much we have yet to learn. I’m envious of the young people just coming into the space program now for the opportunities that they have.”

The class includes pilots, mission specialists (MS) and three new mission specialist-educator (MS-E) astronauts, teachers who will help ensure there’s always a next generation primed to explore.

The astronaut candidates:

# Mission Specialist-Educator Joe Acaba: A 36-year-old teacher at Dunnellon Middle School in Florida and a former Peace Corps volunteer in the Dominican Republic.

# Mission Specialist-Educator Ricky Arnold: A 40-year-old math and science teacher at the American International School of Bucharest, Romania; he’s also taught in Morocco, Indonesia, and Saudi Arabia.

# Pilot Randy Bresnik: A 36-year-old Marine Corps major, F/A-18 pilot and experimental test pilot who’s getting married this month in a Scottish castle.

# Mission Specialist Chris Cassidy: A 34-year old Navy Seal who has done two tours of duty in Afghanistan.

# Pilot Jim Dutton: A 35-year-old U.S. Air Force major and F/A-22 test pilot who flew combat air patrols over northern Iraq in the 1990s.

# Mission Specialist Jose Hernandez: A 41-year-old engineer at NASA’s Johnson Space Center in Houston; grew up as a migrant farm worker before settling in Stockton, Calif.

# Mission Specialist Shane Kimbrough : A 36-year-old U.S. Army major and flight simulation engineer at NASA’s Johnson Space Center in Houston; served as a platoon leader in an Apache helicopter company during Desert Storm.

# Mission Specialist Tom Marshburn: A 43-year-old flight surgeon at NASA’s Johnson Space Center in Houston; also an avid mountain climber and a private pilot.

# Mission Specialist-Educator Dottie Metcalf-Lindenburger: A 29-year-old science teacher at Hudson’s Bay High School in Vancouver, Wash.; she was a championship runner in college.

# Mission Specialist Bobby Satcher Jr.: A 38-year-old M.D. and orthopedic surgeon at Northwestern Memorial Hospital in Chicago; he’s done charity medical work overseas.

# Mission Specialist Shannon Walker: A 38-year-old Ph.D and manager at NASA’s Johnson Space Center in Houston; she’s lived and worked in Russia, and is an avid private pilot.

After their formal introduction, the new astronaut candidates joined students from NASA’s Earth Crew at an afternoon webcast from NASA Headquarters. The kids introduced the class and showered them with cheers and confetti.

Also at that event, NASA’s Deputy Administrator Fred Gregory read a special Space Day message from President Bush, congratulating the class and praising “America’s spirit of discovery and innovation.”

The candidates will report to NASA’s Johnson Space Center this summer. Once settled in Houston, they will begin the intensive training. Initially, they will undergo land survival training, T-38 jet ground and flight training, Shuttle orbiter systems training, Space Station systems training, science and engineering briefings, and orientation tours at all NASA centers, including the Kennedy Space Center and Marshall Space Flight Center.

“These are the men and women who will help us ‘extend life to there,'” Readdy said. “Naming this new class is an important next step in our exploration goals.”

“Right now, tomorrow’s space explorers are seated in America’s classrooms. As NASA carries out the vision for space exploration, the Education Enterprise remains committed to working closely with our nation’s schools, fostering learning environments that will stimulate students to participate in the journey to go to the Moon, Mars and beyond,” said Dr. Adena Loston, NASA’s Associate Administrator for Education.

Original Source: NASA News Release

Posted on by Fraser Cain

Two Hot Planets Seen Orbiting Very Close to Parent Stars

Image credit: ESO
A European team of astronomers [1] are announcing the discovery and study of two new extra-solar planets (exoplanets). They belong to the OGLE transit candidate objects and could be characterized in detail. This trebles the number of exoplanets discovered by the transit method; three such objects are now known.

The observations were performed in March 2004 with the FLAMES multi-fiber spectrograph on the 8.2-m VLT Kueyen telescope at the ESO Paranal Observatory (Chile). They enabled the astronomers to measure accurate radial velocities for forty-one stars for which a temporary brightness “dip” had been detected by the OGLE survey. This effect might be the signature of the transit in front of the star of an orbiting planet, but may also be caused by a small stellar companion.

For two of the stars (OGLE-TR-113 and OGLE-TR-132), the measured velocity changes revealed the presence of planetary-mass companions in extremely short-period orbits.

This result confirms the existence of a new class of giant planets, designated “very hot Jupiters” because of their size and very high surface temperature. They are extremely close to their host stars, orbiting them in less than 2 (Earth) days.

The transit method for detecting exoplanets will be “demonstrated” for a wide public on June 8, 2004, when planet Venus passes in front of the solar disc, cf. the VT-2004 programme.

Discovering other Worlds
During the past decade, astronomers have learned that our Solar System is not unique, as more than 120 giant planets orbiting other stars were discovered by radial-velocity surveys (cf. ESO PR 13/00, ESO PR 07/01, and ESO PR 03/03).

However, the radial-velocity technique is not the only tool for the detection of exoplanets. When a planet happens to pass in front of its parent star (as seen from the Earth), it blocks a small fraction of the star’s light from our view. The larger the planet is, relative to the star, the larger is the fraction of the light that is blocked.

It is exactly the same effect when Venus transits the Solar disc on June 8, 2004, cf. ESO PR 03/04 and the VT-2004 programme website. In the past centuries such events were used to estimate the Sun-Earth distance, with extremely useful implications for astrophysics and celestial mechanics.

Nowadays, planetary transits are gaining renewed importance. Several surveys are attempting to find the faint signatures of other worlds, by means of stellar photometric measurements, searching for the periodic dimming of a star as a planet passes in front of its disc.

One of these, the OGLE survey, was originally devised to detect microlensing events by monitoring the brightness of a very large number of stars at regular intervals. For the past four years, it has also included a search for periodical shallow “dips” of the brightness of stars, caused by the regular transit of small orbiting objects (small stars, brown dwarfs or Jupiter-size planets). The OGLE team has since announced 137 “planetary transit candidates” from their survey of about 155,000 stars in two southern sky fields, one in the direction of the Galactic Centre, the other within the Carina constellation.

Resolving the nature of the OGLE transits
The OGLE transit candidates were detected by the presence of a periodic decrease of a few percent in brightness of the observed stars. The radius of a Jupiter-size planet is about 10 times smaller than that of a solar-type star [2], i.e. it covers about 1/100 of the surface of that star and hence it blocks about 1 % of the stellar light during the transit.

The presence of a transit event alone, however, does not reveal the nature of the transiting body. This is because a low-mass star or a brown dwarf, as well as the variable brightness of a background eclipsing binary system seen in the same direction, may result in brightness variations that simulate the ones produced by an orbiting giant planet.

However, the nature of the transiting object may be established by radial-velocity observations of the parent star. The size of the velocity variations (the amplitude) are directly related to the mass of the companion object and therefore allow to discriminate between stars and planets as the cause of the observed brightness “dip”.

In this way, photometric transit searches and radial-velocity measurements combine to become a very powerful technique to detect new exoplanets. Moreover, it is particularly useful for elucidating their characteristics. While the detection of a planet by the radial velocity method only yields a lower estimate of its mass, the measurement of the transit makes it possible to determine the exact mass, radius, and density of the planet.

The follow-up radial-velocity observations of the 137 OGLE transit candidates is not an easy task as the stars are comparatively faint (visual magnitudes around 16). This can only be done by using a telescope in the 8-10m class with a high-resolution spectrograph.

The nature of the two new exoplanets
A European team of astronomers [1] therefore made use of the 8.2-m VLT Kueyen telescope. In March 2004, they followed 41 OGLE “top transit candidate stars” during 8 half-nights. They profited from the multiplex capacity of the FLAMES/UVES fiber link facility that permits to obtain high-resolution spectra of 8 objects simultaneously and measures stellar velocities with an accuracy of about 50 m/s.

While the vast majority of OGLE transit candidates turned out to be binary stars (mostly small, cool stars transiting in front of solar-type stars), two of the objects, known as OGLE-TR-113 and OGLE-TR-132, were found to exhibit small velocity variations. When all available observations – light variations, the stellar spectrum and radial-velocity changes – were combined, the astronomers were able to determine that for these two stars, the transiting objects have masses compatible with those of a giant planet like Jupiter.

Interestingly, both new planets were detected around rather remote stars in the Milky Way galaxy, in the direction of the southern constellation Carina. For OGLE-TR-113, the parent star is of F-type (slightly hotter and more massive than the Sun) and is located at a distance of about 6000 light-years. The orbiting planet is about 35% heavier and its diameter is 10% larger than that of Jupiter, the largest planet in the solar system. It orbits the star once every 1.43 days at a distance of only 3.4 million km (0.0228 AU). In the solar system, Mercury is 17 times farther away from the Sun. The surface temperature of that planet, which like Jupiter is a gaseous giant, is correspondingly higher, probably above 1800 ?C.

The distance to the OGLE-TR-132 system is about 1200 light-years. This planet is about as heavy as Jupiter and about 15% larger (its size is still somewhat uncertain). It orbits a K-dwarf star (cooler and less massive than the Sun) once every 1.69 days at a distance of 4.6 million km (0.0306 AU). Also this planet must be very hot.

A new class of exoplanets
With the previously found planetary transit object OGLE-TR-56 [3], the two new OGLE objects define a new class of exoplanets, still not detected by current radial velocity surveys: planets with extremely short periods and correspondingly small orbits. The distribution of orbital periods for “hot Jupiters” detected from radial velocity surveys seems to drop off below 3 days, and no planet had previously been found with an orbital period shorter than about 2.5 days.

The existence of the three OGLE planets now shows that “very hot Jupiters” do exist, even though they may be quite rare; probably about one such object for every 2500 to 7000 stars. Astronomers are truly puzzled how planetary objects manage to end up in such small orbits, so near their central stars.

Contrary to the radial velocity method which is responsible for the large majority of planet detections around normal stars, the combination of transit and radial-velocity observations makes it possible to determine the true mass, radius and thus the mean density of these planets.

Great expectations
The two new objects double the number of exoplanets with known mass and radius (the three OGLE objects plus HD209458b, which was detected by the radial velocity surveys but for which a photometric transit was later observed). The new information about the exact masses and radii is essential for understanding the internal physics of these planets.

The complementarity of the transit and radial velocity techniques now opens the door towards a detailed study of the true characteristics of exoplanets. Space-based searches for planetary transits – like the COROT and KEPLER missions – together with ground-based radial velocity follow-up observations will in the future lead to the characterization of other worlds as small as our Earth.

Original Source: ESO News Release

Posted on by Fraser Cain

NASA Considers Risking Rover on Dangerous Descent

Image credit: NASA/JPL
Scientists and engineers celebrated when they saw the first pictures NASA’s Opportunity sent from the rim of a stadium- sized crater that the rover reached after a six-week trek across martian flatlands.

Multiple layers of exposed bedrock line much of the inner slope of the impact crater informally called “Endurance.” Such layers and their thicknesses may reveal what the environment on Mars was like before the salty standing body of water evaporated to produce the telltale rocks that were explored in the tiny “Eagle” Crater. That?s where Opportunity spent its first eight weeks on Mars.

“It’s the most spectacular view we’ve seen of the martian surface, for the scientific value of it but also for the sheer beauty of it,” Dr. Steve Squyres of Cornell University, Ithaca, N.Y., said about a color panorama of Endurance Crater released at a news conference today at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. He is the principal investigator for the science instruments on both Opportunity and its twin Mars Exploration Rover, Spirit.

In coming days, Opportunity will circle the rim of Endurance, observing the crater’s interior from various angles. Scientists and engineers have begun to identify interesting science targets and assess how difficult it would be for the rover to descend partway into the crater and climb back out. “We will need to decide whether the science is compelling enough to send the rover into a crater it might never leave, or whether to explore other sites first before entering Endurance,” said Orlando Figueroa, director of the Mars Exploration Program, NASA Headquarters, Washington.

At Eagle Crater, an outcrop of bedrock only about the height of a street curb yielded evidence that the site was once covered by a body of salty water deep enough to splash in. “That was the last dying gasp of a body of water,” Squyres said. “The question that has intrigued us since we left Eagle Crater is what preceded that. Was there a deep body of water for a long time? Was there a shallow, short-lived playa? We don’t know.”

The strategy for seeking answers is to examine older rocks from deeper layers, so Opportunity was sent on drives totaling about 800 meters (half a mile) to reach the deepest crater nearby, Endurance. This crater excavated by the impact of a tiny asteroid or a piece of a comet is about 130 meters (430 feet) wide and, from the highest point on the rim, more than 20 meters (66 feet) deep, 10 times as deep as Eagle. An exposure of outcrop in a cliff high on the inner wall across from the rover’s current position reveals a stack of layers 5 to 10 meters (16 to 33 feet) tall. Other exposures around the inner slope of the crater may be more accessible than the cliff, and chunks from the same layers may have been thrown out onto surrounding ground by the crater-forming impact.

“There is a rock unit below what we saw at Eagle Crater,” Squyres said. “It looks fundamentally different from anything we’ve seen before. It’s big. It’s massive. It has a story to tell us.”

Brian Cooper, leader of JPL’s squad of rover drivers for Spirit and Opportunity, said the initial view of the crater doesn’t settle accessibility questions yet. “The slope right in front of us averages 18 to 20 degrees. Getting into the crater is no problem, but we have a lot more work to do to assess whether we could get back out. That depends on soil properties and slippage, as well as slope.” The planned circuit around the rim will also require careful navigation. “If you don’t go close enough to the lip, you can’t look in, but if you go too far, you could fall in,” he said. “We’re going to have a very interesting few weeks.”

When NASA sent astronauts to the lunar surface more than 30 years ago, it was decided not to allow them to enter craters as fresh and steep as Endurance, but Opportunity may be able to do what no human has done before on another planet.

Scientists and engineers working with the other rover, Spirit, are also examining images of a destination area to identify possible targets of study and to assess how well the rover can get to them. However, that destination area, informally named “Columbia Hills,” still lies several weeks of travel ahead of Spirit. Images and surface-temperature information from the NASA orbiters Mars Global Surveyor and Mars Odyssey are supplementing Spirit’s own increasingly detailed pictures of the hills. Nighttime surface temperatures indicate that some areas within the hills are rockier than others, said Amy Knudson, a rover science team collaborator from Arizona State University, Tempe.

“The hills represent a different rock unit, likely older than the plains we’re on,” Knudson said. “There are intriguing features in the hills and we want to investigate the processes that formed them. We’re especially interested to see if water played any role.”

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C. Images and additional information about the project are available from JPL at http://marsrovers.jpl.nasa.gov and from Cornell University at http://athena.cornell.edu.

Original Source: NASA/JPL News Release