Smallest Extrasolar Planet Found

A European team of astronomers [1] has discovered the lightest known planet orbiting a star other than the sun (an “exoplanet”).

The new exoplanet orbits the bright star mu Arae located in the southern Altar constellation. It is the second planet discovered around this star and completes a full revolution in 9.5 days.

With a mass of only 14 times the mass of the Earth, the new planet lies at the threshold of the largest possible rocky planets, making it a possible super Earth-like object. Uranus, the smallest of the giant planets of the Solar System has a similar mass. However Uranus and the new exoplanet differ so much by their distance from the host star that their formation and structure are likely to be very different.

This discovery was made possible by the unprecedented accuracy of the HARPS spectrograph on ESO’s 3.6-m telescope at La Silla, which allows radial velocities to be measured with a precision better than 1 m/s. It is another clear demonstration of the European leadership in the field of exoplanet research.

A unique planet hunting machine
Since the first detection in 1995 of a planet around the star 51 Peg by Michel Mayor and Didier Queloz from the Geneva Observatory (Switzerland), astronomers have learned that our Solar System is not unique, as more than 120 giant planets orbiting other stars were discovered mostly by radial-velocity surveys (cf. ESO PR 13/00, ESO PR 07/01, and ESO PR 03/03).

This fundamental observational method is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. The evaluation of the measured velocity variations allows to deduce the planet’s orbit, in particular the period and the distance from the star, as well as a minimum mass [2].

The continued quest for exoplanets requires better and better instrumentation. In this context, ESO undoubtedly took the leadership with the new HARPS spectrograph (High Accuracy Radial Velocity Planet Searcher) of the 3.6-m telescope at the ESO La Silla Observatory (see ESO PR 06/03). Offered in October 2003 to the research community in the ESO member countries, this unique instrument is optimized to detect planets in orbit around other stars (“exoplanets”) by means of accurate (radial) velocity measurements with an unequalled precision of 1 metre per second.

HARPS was built by a European Consortium [3] in collaboration with ESO. Already from the beginning of its operation, it has demonstrated its very high efficiency. By comparison with CORALIE, another well known planet-hunting optimized spectrograph installed on the Swiss-Euler 1.2-m telescope at La Silla (cf ESO PR 18/98, 12/99, 13/00), the typical observation times have been reduced by a factor one hundred and the accuracy of the measurements has been increased by a factor ten.

These improvements have opened new perspectives in the search for extra-solar planets and have set new standards in terms of instrumental precision.

The planetary system around mu Arae
The star mu Arae is about 50 light years away. This solar-like star is located in the southern constellation Ara (the Altar) and is bright enough (5th magnitude) to be observed with the unaided eye.

Mu Arae was already known to harbour a Jupiter-sized planet with a 650 days orbital period. Previous observations also hinted at the presence of another companion (a planet or a star) much further away.

The new measurements obtained by the astronomers on this object, combined with data from other teams confirm this picture. But as Fran?ois Bouchy, member of the team, states: “Not only did the new HARPS measurements confirm what we previously believed to know about this star but they also showed that an additional planet on short orbit was present. And this new planet appears to be the smallest yet discovered around a star other than the sun. This makes mu Arae a very exciting planetary system.”

During 8 nights in June 2004, mu Arae was repeatedly observed and its radial velocity measured by HARPS to obtain information on the interior of the star. This so-called astero-seismology technique (see ESO PR 15/01) studies the small acoustic waves which make the surface of the star periodically pulsate in and out. By knowing the internal structure of the star, the astronomers aimed at understanding the origin of the unusual amount of heavy elements observed in its stellar atmosphere. This unusual chemical composition could provide unique information to the planet formation history.

Says Nuno Santos, another member of the team: “To our surprise, the analysis of the new measurements revealed a radial velocity variation with a period of 9.5 days on top of the acoustic oscillation signal!”

This discovery has been made possible thanks to the large number of measurements obtained during the astero-seimology campaign.

From this date, the star, that was also part of the HARPS consortium survey programme, was regularly monitored with a careful observation strategy to reduce the “seismic noise” of the star.

These new data confirmed both the amplitude and the periodicity of the radial velocity variations found during the 8 nights in June. The astronomers were left with only one convincing explanation to this periodic signal: a second planet orbits mu Arae and accomplishes a full revolution in 9.5 days.

But this was not the only surprise: from the radial velocity amplitude, that is the size of the wobble induced by the gravitational pull of the planet on the star, the astronomers derived a mass for the planet of only 14 times the mass of the Earth! This is about the mass of Uranus, the smallest of the giant planets in the solar system.

The newly found exoplanet therefore sets a new record in the smallest planet discovered around a solar type star.

At the boundary
The mass of this planet places it at the boundary between the very large earth-like (rocky) planets and giant planets.

As current planetary formation models are still far from being able to account for all the amazing diversity observed amongst the extrasolar planets discovered, astronomers can only speculate on the true nature of the present object. In the current paradigm of giant planet formation, a core is formed first through the accretion of solid “planetesimals”. Once this core reaches a critical mass, gas accumulates in a “runaway” fashion and the mass of the planet increases rapidly. In the present case, this later phase is unlikely to have happened for otherwise the planet would have become much more massive. Furthermore, recent models having shown that migration shortens the formation time, it is unlikely that the present object has migrated over large distances and remained of such small mass.

This object is therefore likely to be a planet with a rocky (not an icy) core surrounded by a small (of the order of a tenth of the total mass) gaseous envelope and would therefore qualify as a “super-Earth”.

Further Prospects
The HARPS consortium, led by Michel Mayor (Geneva Observatory, Switzerland), has been granted 100 observing nights per year during a 5-year period at the ESO 3.6-m telescope to perform one of the most ambitious systematic searches for exoplanets so far implemented worldwide. To this aim, the consortium repeatedly measures velocities of hundreds of stars that may harbour planetary systems.

The detection of this new light planet after less than 1 year of operation demonstrates the outstanding potential of HARPS for detecting rocky planets on short orbits. Further analysis shows that performances achieved with HARPS make possible the detection of big “telluric” planets with only a few times the mass of the Earth. Such a capability is a major improvement compared to past planet surveys. Detection of such rocky objects strengthens the interest of future transit detections from space with missions like COROT, Eddington and KEPLER that shall be able to measure their radius.

More information
The research described in this Press release has been submitted for publication to the leading astrophysical journal “Astronomy and Astrophysics”. A preprint is available as a postscript file at http://www.oal.ul.pt/~nuno/.

Notes
[1]: The team is composed of Nuno Santos (Centro de Astronomia e Astrofisica da Universidade de Lisboa, Portugal), Fran?ois Bouchy and Jean-Pierre Sivan (Laboratoire d’astrophysique de Marseille, France), Michel Mayor, Francesco Pepe, Didier Queloz, St?phane Udry, and Christophe Lovis (Observatoire de l’Universit? de Gen?ve, Switzerland), Sylvie Vauclair, Michael Bazot (Toulouse, France), Gaspare Lo Curto and Dominique Naef (ESO), Xavier Delfosse (LAOG, Grenoble, France), Willy Benz and Christoph Mordasini (Physikalisches Institut der Universit?t Bern, Switzerland), and Jean-Louis Bertaux (Service d’A?ronomie de Verri?re-le-Buisson, Paris, France).

[2] A fundamental limitation of the radial-velocity method is the unknown of the inclination of the planetary orbit that only allows the determination of a lower mass limit for the planet. However, statistical considerations indicate that in most cases, the true mass will not be much higher than this value. The mass units for the exoplanets used in this text are 1 Jupiter mass = 22 Uranus masses = 318 Earth masses; 1 Uranus mass = 14.5 Earth masses.

[3] HARPS has been designed and built by an international consortium of research institutes, led by the Observatoire de Gen?ve (Switzerland) and including Observatoire de Haute-Provence (France), Physikalisches Institut der Universit?t Bern (Switzerland), the Service d’Aeronomie (CNRS, France), as well as ESO La Silla and ESO Garching.

Original Source: ESO News Release

Meteorites Could Have Supplied the Earth with Phosphorus

Image credit: University of Arizona
University of Arizona scientists have discovered that meteorites, particularly iron meteorites, may have been critical to the evolution of life on Earth.

Their research shows that meteorites easily could have provided more phosphorus than naturally occurs on Earth — enough phosphorus to give rise to biomolecules which eventually assembled into living, replicating organisms.

Phosphorus is central to life. It forms the backbone of DNA and RNA because it connects these molecules’ genetic bases into long chains. It is vital to metabolism because it is linked with life’s fundamental fuel, adenosine triphosphate (ATP), the energy that powers growth and movement. And phosphorus is part of living architecture ? it is in the phospholipids that make up cell walls and in the bones of vertebrates.

“In terms of mass, phosphorus is the fifth most important biologic element, after carbon, hydrogen, oxygen, and nitrogen,” said Matthew A. Pasek, a doctoral candidate in UA’s planetary sciences department and Lunar and Planetary Laboratory.

But where terrestrial life got its phosphorus has been a mystery, he added.

Phosphorus is much rarer in nature than are hydrogen, oxygen, carbon, and nitrogen.

Pasek cites recent studies that show there’s approximately one phosphorus atom for every 2.8 million hydrogen atoms in the cosmos, every 49 million hydrogen atoms in the oceans, and every 203 hydrogen atoms in bacteria. Similarly, there’s a single phosphorus atom for every 1,400 oxygen atoms in the cosmos, every 25 million oxygen atoms in the oceans, and 72 oxygen atoms in bacteria. The numbers for carbon atoms and nitrogen atoms, respectively, per single phosphorus atom are 680 and 230 in the cosmos, 974 and 633 in the oceans, and 116 and 15 in bacteria.

“Because phosphorus is much rarer in the environment than in life, understanding the behavior of phosphorus on the early Earth gives clues to life’s orgin,” Pasek said.

The most common terrestrial form of the element is a mineral called apatite. When mixed with water, apatite releases only very small amounts of phosphate. Scientists have tried heating apatite to high temperatures, combining it with various strange, super-energetic compounds, even experimenting with phosphorous compounds unknown on Earth. This research hasn’t explained where life’s phosphorus comes from, Pasek noted.

Pasek began working with Dante Lauretta, UA assistant professor of planetary sciences, on the idea that meteorites are the source of living Earth’s phosphorus. The work was inspired by Lauretta’s earlier experiments that showed that phosphorus became concentrated at metal surfaces that corroded in the early solar system.

“This natural mechanism of phosphorus concentration in the presence of a known organic catalyst (such as iron-based metal) made me think that aqueous corrosion of meteoritic minerals could lead to the formation of important phosphorus-bearing biomolecules,” Lauretta said.

“Meteorites have several different minerals that contain phosphorus,” Pasek said. “The most important one, which we’ve worked with most recently, is iron-nickel phosphide, known as schreibersite.”

Schreibersite is a metallic compound that is extremely rare on Earth. But it is ubiquitous in meteorites, especially iron meteorites, which are peppered with schreibersite grains or slivered with pinkish-colored schreibersite veins.

Last April, Pasek, UA undergraduate Virginia Smith, and Lauretta mixed schriebersite with room-temperature, fresh, de-ionized water. They then analyzed the liquid mixture using NMR, nuclear magnetic resonance.

“We saw a whole slew of different phosphorus compounds being formed,” Pasek said. “One of the most interesting ones we found was P2-O7 (two phorphorus atoms with seven oxygen atoms), one of the more biochemically useful forms of phosphate, similar to what’s found in ATP.”

Previous experiments have formed P2-07, but at high temperature or under other extreme conditions, not by simply dissolving a mineral in room-temperature water, Pasek said.

“This allows us to somewhat constrain where the origins of life may have occurred,” he said. “If you are going to have phosphate-based life, it likely would have had to occur near a freshwater region where a meteorite had recently fallen. We can go so far, maybe, as to say it was an iron meteorite. Iron meteorites have from about 10 to 100 times as much schreibersite as do other meteorites.

“I think meteorites were critical for the evolution of life because of some of the minerals, especially the P2-07 compound, which is used in ATP, in photosynthesis, in forming new phosphate bonds with organics (carbon-containing compounds), and in a variety of other biochemical processes,” Pasek said.

“I think one of the most exciting aspects of this discovery is the fact that iron meteorites form by the process of planetesimal differentiation,” Lauretta said. That is, the building-blocks of planets, called planestesmals, form both a metallic core and a silicate mantle. Iron meteorites represent the metallic core, and other types of meteorites, called achondrites, represent the mantle.

“No one ever realized that such a critical stage in planetary evolution could be coupled to the origin of life,” he added. “This result constrains where, in our solar system and others, life could originate. It requires an asteroid belt where planetesimals can grow to a critical size ? around 500 kilometers in diameter ? and a mechanism to disrupt these bodies and deliver them to the inner solar system.”

Jupiter drives the delivery of planetesimals to our inner solar system, Lauretta said, thereby limiting the chances that outer solar system planets and moons will be supplied with the reactive forms of phosphorus used by biomolecules essential to terrestrial life.

Solar systems that lack a Jupiter-sized object that can perturb mineral-rich asteroids inward toward terrestrial planets also have dim prospects for developing life, Lauretta added.

Pasek is talking about the research today (Aug. 24) at the 228th American Chemical Society national meeting in Philadelphia. The work is funded by the NASA program, Astrobiology: Exobiology and Evolutionary Biology.

Original Source: UA News Release

Cassini Completes Orbital Maneuver

The Cassini spacecraft successfully completed a 51-minute engine burn that will raise its next closest approach distance to Saturn by nearly 300,000 kilometers (186,000 miles). The maneuver was necessary to keep the spacecraft from passing through the rings and to put it on target for its first close encounter with Saturn’s moon Titan on Oct. 26.

Mission controllers received confirmation of a successful burn at 11:15 a.m. Pacific Time today. The spacecraft is approaching the highest point in its first and largest orbit about Saturn. Its distance from the center of Saturn is about 9 million kilometers (5.6 million miles), and its speed just prior to today’s burn was 325 meters per second (727 miles per hour) relative to Saturn. That means it is nearly at a standstill compared to its speed of about 30,000 meters per second (67,000 miles per hour) at the completion of its orbit insertion burn on June 30.

“Saturn orbit insertion got us into orbit and this maneuver sets us up for the tour,” said Joel Signorelli, spacecraft system engineer for the Cassini-Huygens mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

The maneuver was the third longest engine burn for the Cassini spacecraft and the last planned pressurized burn in the four-year tour. The Saturn obit insertion burn was 97 minutes long, and the deep space maneuver in Dec. 1998 was 88 minutes long.

“The October 26 Titan encounter will be much closer than our last one. We’ll fly by Titan at an altitude of 1,200 kilometers (746 miles), ‘dipping our toe’ into its atmosphere,” said Signorelli. Cassini’s first Titan flyby on July 2 was from 340,000 kilometers (211,000 miles) away.

Over the next four years, the Cassini orbiter will execute 45 Titan flybys as close as approximately 950 kilometers (590 miles) from the moon. In January 2005, the European-built Huygens probe that is attached to Cassini will descend through Titan’s atmosphere to the surface.

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 Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter.

For the latest images and more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

Original Source: NASA/JPL News Release

Martian Crater With Dunes

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows a Martian crater with a dune field on its floor.

The image was taken during orbit 427 in May 2004, and shows the crater with a dune field located in the north-western part of the Argyre Planitia crater basin.

The image is centred at Mars longitude 303? East and latitude 43? South. The image resolution is approximately 16.2 metres per pixel.

The crater is about 45 kilometres wide and 2 kilometres deep. In the north-eastern part of this crater, the complex dune field is 7 kilometres wide by 12 kilometres long.

In arid zones on Earth, these features are called ?barchanes?, which are dunes having an asymmetrical profile, with a gentle slope on the wind-facing side and a steep slope on the lee-side.

The dune field shown here suggests an easterly wind direction with its steeper western part. The composition of the dune material is not certain, but the dark sands could be of basaltic origin.

Original Source: ESA News Release

Small Telescope Finds a Huge Planet

Fifteen years ago, the largest telescopes in the world had yet to locate a planet orbiting another star. Today telescopes no larger than those available in department stores are proving capable of spotting previously unknown worlds. A newfound planet detected by a small, 4-inch-diameter telescope demonstrates that we are at the cusp of a new age of planet discovery. Soon, new worlds may be located at an accelerating pace, bringing the detection of the first Earth-sized world one step closer.

“This discovery demonstrates that even humble telescopes can make huge contributions to planet searches,” says Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics (CfA), a co-author on the study.

This research study will be posted online at http://arxiv.org/abs/astro-ph/0408421 and will appear in an upcoming issue of The Astrophysical Journal Letters.

This is the very first extrasolar planet discovery made by a dedicated survey of many thousands of relatively bright stars in large regions of the sky. It was made using the Trans-Atlantic Exoplanet Survey (TrES), a network of small, relatively inexpensive telescopes designed to look specifically for planets orbiting bright stars. A team of scientists co-led by David Charbonneau (CfA/Caltech), Timothy Brown of the National Center for Atmospheric Research (NCAR) and Edward Dunham of Lowell Observatory developed the TrES network. Initial support for the TrES network came from NASA’s Jet Propulsion Laboratory and the California Institute of Technology.

“It took several Ph.D. scientists working full-time to develop the data analysis methods for this search program, but the equipment itself uses simple, off-the-shelf components,” says Charbonneau.

Although the small telescopes of the TrES network made the initial discovery, follow-up observations at other facilities were required. Observations at the W.M. Keck Observatory which, for the University of California, Caltech, and NASA, operates the world’s two largest telescopes in Hawaii, were particularly crucial in confirming the planet’s existence.

Planet Shadows
The newfound planet is a Jupiter-sized gas giant orbiting a star located about 500 light-years from the Earth in the constellation Lyra. This world circles its star every 3.03 days at a distance of only 4 million miles, much closer and faster than the planet Mercury in our solar system.

Astronomers used an innovative technique to discover this new world. It was found by the “transit method,” which looks for a dip in a star’s brightness when a planet crosses directly in front of the star and casts a shadow. A Jupiter-sized planet blocks only about 1/100th of the light from a Sun-like star, but that is enough to make it detectable.

To be successful, transit searches must examine many stars because we only see a transit if a planetary system is located nearly edge-on to our line of sight. A number of different transit searches currently are underway. Most examine limited areas of the sky and focus on fainter stars because they are more common, thereby increasing the chances of finding a transiting system. However the TrES network concentrates on searching brighter stars in larger swaths of the sky because planets orbiting bright stars are easier to study directly.

“All that we have to work with is the light that comes from the star,” says Brown. “It’s much harder to learn anything when the stars are faint.”

“It’s almost paradoxical that small telescopes are more efficient than the largest ones if you use the transit method, since we live in a time when astronomers already are planning 100-meter-diameter telescopes,” says lead author Roi Alonso of the Astrophysical Institute of the Canaries (IAC), who discovered the new planet.

Most known extrasolar planets were found using the “Doppler method,” which detects a planet’s gravitational effect on its star spectroscopically by breaking the star’s light into its component colors. However, the information that can be gleaned about a planet using the Doppler method is limited. For example, only a lower limit to the mass can be determined because the angle at which we view the system is unknown. A high-mass brown dwarf whose orbit is highly inclined to our line of sight produces the same signal as a low-mass planet that is nearly edge-on.

“When astronomers find a transiting planet, we know that its orbit is essentially edge-on, so we can calculate its exact mass. From the amount of light it blocks, we learn its physical size. In one instance, we’ve even been able to detect and study a giant planet’s atmosphere,” says Charbonneau.

Sorting Suspects
The TrES survey examined approximately 12,000 stars in 36 square degrees of the sky (an area half the size of the bowl of the Big Dipper). Roi Alonso, a graduate student of Brown’s, identified 16 possible candidates for planet transits. “The TrES survey gave us our initial line-up of suspects. Then, we had to make a lot of follow-up observations to eliminate the imposters,” says co-author Alessandro Sozzetti (University of Pittsburgh/CfA).

After compiling the list of candidates in late April, the researchers used telescopes at CfA’s Whipple Observatory in Arizona and Oak Ridge Observatory in Massachusetts to obtain additional photometric (brightness) observations, as well as spectroscopic observations that eliminated eclipsing binary stars.

In a matter of two month’s time, the team had zeroed in on the most promising candidate. High-resolution spectroscopic observations by Torres and Sozzetti using time provided by NASA on the 10-meter-diameter Keck I telescope in Hawaii clinched the case.

“Without this follow-up work the photometric surveys can’t tell which of their candidates are actually planets. The proof of the pudding is an orbit for the parent star, and we got that using the Doppler method. That’s why the Keck observations of this star were so important in proving that we had found a true planetary system,” says co-author David Latham (CfA).

Remarkably Normal
The planet, called TrES-1, is much like Jupiter in mass and size (diameter). It is likely to be a gas giant composed primarily of hydrogen and helium, the most common elements in the Universe. But unlike Jupiter, it orbits very close to its star, giving it a temperature of around 1500 degrees F.

Astronomers are particularly interested in TrES-1 because its structure agrees so well with theory, in contrast to the first discovered transiting planet, HD 209458b. The latter world contains about the same mass as TrES-1, yet is around 30% larger in size. Even its proximity to its star and the accompanying heat don’t explain such a large size.

“Finding TrES-1 and seeing how normal it is makes us suspect that HD 209458b is an `oddball’ planet,” says Charbonneau.

TrES-1 orbits its star every 72 hours, placing it among a group of similar planets known as “hot Jupiters.” Such worlds likely formed much further away from their stars and then migrated inward, sweeping away any other planets in the process. The many planetary systems found to contain hot Jupiters indicate that our solar system may be unusual for its relatively quiet history.

Both the close orbit of TrES-1 and its migration history make it unlikely to possess any moons or rings. Nevertheless, astronomers will continue to examine this system closely because precise photometric observations may detect moons or rings if they exist. In addition, detailed spectroscopic observations may give clues to the presence and composition of the planet’s atmosphere.

The paper describing these results is authored by: Roi Alonso (IAC); Timothy M. Brown (NCAR); Guillermo Torres and David W. Latham (CfA); Alessandro Sozzetti (University of Pittsburgh/CfA); Georgi Mandushev (Lowell), Juan A. Belmonte (IAC); David Charbonneau (CfA/Caltech); Hans J. Deeg (IAC); Edward W. Dunham (Lowell); Francis T. O’Donovan (Caltech); and Robert Stefanik (CfA).

This joint announcement is being issued simultaneously by CfA, IAC, NCAR, the University of Pittsburgh, and Lowell Observatory.

The W.M. Keck Observatory is operated by the California Association for Research in Astronomy, a scientific partnership of the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

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

Double Jets Around Exploded Star

The spectacular NASA’s Chandra X-ray Observatory image of Cassiopeia A released today has nearly 200 times more data than the “First Light” Chandra image of this object made five years ago. The new image reveals clues that the initial explosion was far more complicated than suspected.

“Although this young supernova remnant has been intensely studied for years, this deep observation is the most detailed ever made of the remains of an exploded star,” said Martin Laming of the Naval Research Laboratory in Washington, D.C. Laming is part of a team of scientists led by Una Hwang of the Goddard Space Flight Center in Greenbelt, Maryland. “It is a gold mine of data that astronomers will be panning through for years to come.”

The one-million-second observation of Cassiopeia A uncovered two large, opposed jet-like structures that extend to about 10 light years from the center of the remnant. Clouds of iron that have remained nearly pure for the approximately 340 years since the explosion were also detected.

“The presence of the bipolar jets suggests that jets could be more common in relatively normal supernova explosions than supposed,” said Hwang. A paper by Hwang, Laming and others on the Cassiopeia A observation will appear in an upcoming issue of The Astrophysical Journal Letters.

X-ray spectra show that the jets are rich in silicon atoms and relatively poor in iron atoms. In contrast, fingers of almost pure iron gas extend in a direction nearly perpendicular to the jets. This iron was produced in the central, hottest regions of the star. The high silicon and low iron abundances in the jets indicate that massive, matter-dominated jets were not the immediate cause of the explosion, as these should have carried out large quantities of iron from the central regions of the star.

A working hypothesis is that the explosion produced high-speed jets similar to those in hypernovae that produce gamma-ray bursts, but in this case, with much lower energies. The explosion also left a faint neutron star at the center of the remnant. Unlike the rapidly rotating neutron stars in the Crab Nebula and Vela supernova remnants that are surrounded by dynamic magnetized clouds of electrons, this neutron star is quiet and faint. Nor has pulsed radiation been detected from it. It may have a very strong magnetic field generated during the explosion that helped to accelerate the jets, and today resembles other strong-field neutron stars (a.k.a. “magnetars”) in lacking a wind nebula.

Chandra was launched aboard the Space Shuttle Columbia on July 23, 1999. Less than a month later, it was able to start taking science measurements along with its calibration data. The original Cassiopeia A observation was taken on August 19, 1999, and then released to the scientific community and the public one week later on August 26. At launch, Chandra’s original mission was intended to be five years. Having successfully completed that objective, NASA announced last August that the mission would be extended for another five years.

The data for this new Cas A image were obtained by Chandra’s Advanced CCD Imaging Spectrometer (ACIS) instrument during the first half of 2004. Due to its value to the astronomical community, this rich dataset was made available immediately to the public.

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:

http://chandra.harvard.edu
and
http://chandra.nasa.gov

Original Source: Chandra News Release

Gone for a Week… Now I’m Back

In case you hadn’t noticed, I didn’t update Universe Today all last week. I was just in the process of working on Monday’s issue when I found out that my Grandma was very sick in the hospital, and probably wouldn’t last too much longer. I rushed back to Vancouver to see her, and she ended up passing away on Tuesday morning. She was 96, and had lived a long and happy life. I spent the rest of the week hanging out with my family, and attending the memorial – I didn’t really feel like working on the website. 🙁

Strangely, the news didn’t wait for me, so I’ve spent the weekend catching up. That’s why the next issue’s pretty big.

Thanks for all your support.

Fraser Cain
Publisher
Universe Today

More Evidence for Past Water on Mars

Now that NASA’s Mars Exploration Rover Spirit is finally examining bedrock in the “Columbia Hills,” it is finding evidence that water thoroughly altered some rocks in Mars’ Gusev Crater.

Spirit and its twin, Opportunity, completed successful three-month primary missions on Mars in April and are returning bonus results during extended missions. They remain in good health though beginning to show signs of wear.

On Opportunity, a tool for exposing the insides of rocks stopped working Sunday, but engineers are optimistic that the most likely diagnosis is a problem that can be fixed soon. “It looks like there’s a pebble trapped between the cutting heads of the rock abrasion tool,” said Chris Salvo, rover mission manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We think we can treat it by turning the heads in reverse, but we are still evaluating the best approach to remedy the situation. There are several options available to us.”

Opportunity originally landed right beside exposed bedrock and promptly found evidence there for an ancient body of saltwater. On the other hand, it took Spirit half a year of driving across a martian plain to reach bedrock in Gusev Crater. Now, Spirit’s initial inspection of an outcrop called “Clovis” on a hill about 9 meters (30 feet) above the plain suggests that water may once have been active at Gusev.

“We have evidence that interaction with liquid water changed the composition of this rock,” said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the science instruments on both rovers. “This is different from the rocks out on the plain, where we saw coatings and veins apparently due to effects of a small amount of water. Here, we have a more thorough, deeper alteration, suggesting much more water.”

Squyres said, “To really understand the conditions that altered Clovis, we’d like to know what it was like before the alteration. We have the ‘after.’ Now we want the ‘before.’ If we’re lucky, there may be rocks nearby that will give us that.”

Dr. Doug Ming, a rover science team member from NASA’s Johnson Space Center, Houston, said indications of water affecting Clovis come from analyzing the rock’s surface and interior with Spirit’s alpha particle X-ray spectrometer and finding relatively high levels of bromine, sulfur and chlorine inside the rock. He said, “This is also a very soft rock, not like the basaltic rocks seen back on the plains of Gusev Crater. It appears to be highly altered.”

Rover team members described the golf-cart-sized robots’ status and recent findings in a briefing at JPL today.

Opportunity has completed a transect through layers of rock exposed in the southern inner slope of stadium-sized “Endurance Crater.” The rocks examined range from outcrops near the rim down through progressively older and older layers to the lowest accessible outcrop, called “Axel Heiberg” after a Canadian Arctic island. “We found different compositions in different layers,” said Dr. Ralf Gellert, of Max-Planck-Institut fur Chemie, Mainz, Germany. Chlorine concentration increased up to threefold in middle layers. Magnesium and sulfur declined nearly in parallel with each other in older layers, suggesting those two elements may have been dissolved and removed by water.

Small, gray stone spheres nicknamed “blueberries” are plentiful in Endurance just as they were at Opportunity’s smaller landing-site crater, “Eagle.” Pictures from the rover’s microscopic imager show a new variation on the blueberries throughout a reddish-tan slab called “Bylot” in the Axel Heiberg outcrop. “They’re rougher textured, they vary more in size, and they’re the color of the rock, instead of gray,” said Zoe Learner, a science team collaborator from Cornell. “We’ve noticed that in some cases where these are eroding, you can see a regular blueberry or a berry fragment inside.” One possibility is that a water-related process has added a coarser outer layer to the blueberries, she said, adding, “It’s still really a mystery.”

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA’s Science Mission Directorate, Washington. 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

Ganymede’s Lumpy Interior

Scientists have discovered irregular lumps beneath the icy surface of Jupiter’s largest moon, Ganymede. These irregular masses may be rock formations, supported by Ganymede’s icy shell for billions of years. This discovery comes nearly a year after the orchestrated demise of NASA’s Galileo spacecraft into Jupiter’s atmosphere and more than seven years after the data were collected.

Researchers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Los Angeles, report their findings in a paper that will appear in the Aug. 13 issue of the journal Science.

The findings have caused scientists to rethink what the interior of Ganymede might contain. The reported bulges reside in the interior, and there are no visible surface features associated with them. This tells scientists that the ice is probably strong enough, at least near the surface, to support these possible rock masses from sinking to the bottom of the ice for billions of years. But this anomaly could also be caused by piles of rock at the bottom of the ice.

“The anomalies could be large concentrations of rock at or underneath the ice surface. They could also be in a layer of mixed ice and rock below the surface with variations in the amount of rock,” said Dr. John Anderson, a scientist and the paper’s lead author at JPL. “If there is a liquid water ocean inside Ganymede’s outer ice layer there might be variations in its depth with piles of rock at the ocean bottom. There could be topographic variations in a hidden rocky surface underlying a deep outer icy shell. There are many possibilities, and we need to do more studies.”

Dr. Gerald Schubert, co-author at UCLA, said “Although we don’t yet have anything definitive about the depth at this point, we did not expect Ganymede’s ice shell to be strong enough to support these lumpy mass concentrations. Thus, we expect that the irregularities would be close to the surface where the ice is coldest and strongest, or at the bottom of the thick ice shell resting on the underlying rock. It would really be a surprise if these masses were deep and in the middle of the ice shell.”

Ganymede has three main layers. A sphere of metallic iron at the center (the core), a spherical shell of rock (mantle) surrounding the core, and a spherical shell of mostly ice surrounding the rock shell and the core. The ice shell on the outside is very thick, maybe 800 kilometers (497 miles) thick. The surface is the very top of the ice shell. Though it is mostly ice, the ice shell might contain some rock mixed in. Scientists believe there must be a fair amount of rock in the ice near the surface. Variations in this amount of rock may be the source of these possible rock formations.

Scientists stumbled on the results by studying Doppler measurements of Ganymede’s gravity field during Galileo’s second flyby of the moon in 1996. Scientists were measuring the effect of the moon’s gravity on the spacecraft as it flew by. They found unexpected variations.

“Believe it or not, it took us this long to straighten out the anomaly question, mostly because we were analyzing all 31 close flybys for all four of Jupiter’s large moons,” said Anderson. “In the end, we concluded that there is only one flyby, the second flyby of Ganymede, where mass anomalies are evident.”

Scientists have seen mass concentration anomalies on one other moon before, Earth’s, during the first lunar orbiter missions in the 1960s. The lunar mass concentrations during the Apollo moon mission era were due to lava in flat basins. However, scientists cannot draw any similarities between these mass concentrations and what they see at Ganymede.

“The fact that these mass anomalies can be detected with just flybys is significant for future missions,” said Dr. Torrence Johnson, former Galileo project scientist. “With this type of information you could make detailed gravity and altitude maps that allow us to actually map structures within the ice crust or on the rocky surface. Knowing more about the interior of Ganymede raises the level of importance of looking for gravity anomalies around Jupiter’s moons and gives us something to look for. This might be something NASA’s proposed Jupiter Icy Moons Orbiter Mission could probe into deeper.”

The paper was co-authored by Dr. Robert A. Jacobson and Eunice L. Lau of JPL, with Dr. William B. Moore and Jennifer L. Palguta of UCLA. JPL is a division of the California Institute of Technology in Pasadena. JPL designed and built the Galileo orbiter, and operated the mission. For images and information about the Galileo mission, visit http://galileo.jpl.nasa.gov.

Helicopter Will Catch Samples from Genesis

In a dramatic ending that marks a beginning in scientific research, NASA’s Genesis spacecraft is set to swing by Earth and jettison a sample return capsule filled with particles of the Sun that may ultimately tell us more about the genesis of our solar system.

“The Genesis mission — to capture a piece of the Sun and return it to Earth — is truly in the NASA spirit: a bold, inspiring mission that makes a fundamental contribution to scientific knowledge,” said Steven Brody, NASA’s program executive for the Genesis mission, NASA Headquarters, Washington.

On September 8, 2004, the drama will unfold over the skies of central Utah when the spacecraft’s sample return capsule will be snagged in midair by helicopter. The rendezvous will occur at the Air Force’s Utah Test and Training Range, southwest of Salt Lake City.

“What a prize Genesis will be,” said Genesis Principal Investigator Dr. Don Burnett of the California Institute of Technology, Pasadena, Calif. “Our spacecraft has logged almost 27 months far beyond the moon’s orbit, collecting atoms from the Sun. With it, we should be able to say what the Sun is composed of, at a level of precision for planetary science purposes that has never been seen before.”

The prizes Burnett and company are waiting for are hexagonal wafers of pure silicon, gold, sapphire, diamond and other materials that have served as a celestial prison for their samples of solar wind particles. These wafers have weathered 26-plus months in deep space and are now safely stowed in the return capsule. If the capsule were to descend all the way to the ground, some might fracture or break away from their mountings; hence, the midair retrieval by helicopter, with crew members including some who have performed helicopter stunt work for Hollywood.

“These guys fly in some of Hollywood’s biggest movies,” said Don Sweetnam, Genesis project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “But this time, the Genesis capsule will be the star.”

The Genesis capsule — carrying the agency’s first sample return since the final Apollo lunar mission in 1972, and the first material collected beyond the Moon — will enter Earth’s atmosphere at 9:55 am Mountain Time. Two minutes and seven seconds after atmospheric entry, while still flying supersonically, the capsule will deploy a drogue parachute at 33 kilometers (108,000 feet) altitude. Six minutes after that, the main parachute, a parafoil, will deploy 6.1 kilometers (20,000 feet) up. Waiting below will be two helicopters and their flight crews looking for their chance to grab a piece of the Sun.

“Each helicopter will carry a crew of three,” said Roy Haggard, chief executive officer of Vertigo Inc. and director of flight operations for the lead helicopter. “The lead helicopter will deploy an eighteen-and-a-half foot long pole with what you could best describe as an oversized, Space-Age fishing hook on its end. When we make the approach we want the helicopter skids to be about eight feet above the top of the parafoil. If for some reason the capture is not successful, the second helicopter is 1,000 feet behind us and setting up for its approach. We estimate we will have five opportunities to achieve capture.”

The helicopter that does achieve capture will carry the sample canister to a clean room at the Michael Army Air Field at the U.S. Army Dugway Proving Ground, where scientists await their cosmic prize. The samples will then be moved to a special laboratory at NASA’s Johnson Space Center, Houston, where they will be preserved and studied by scientists for many years to come.

“I understand much of the interest is in how we retrieve Genesis,” added Burnett. “But to me the excitement really begins when scientists from around the world get hold of those samples for their research. That will be something.”

JPL, a division of the California Institute of Technology, manages the Genesis mission for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, developed and operates the spacecraft. Los Alamos National Laboratory and NASA’s Johnson Space Center contributed to Genesis payload development, and the Johnson Space Center will curate the sample and support analysis and sample allocation.

News and information are available at http://www.nasa.gov/genesis. More detailed background on the mission is available at http://genesismission.jpl.nasa.gov/.

Original Source: NASA News Release