Posted on by Fraser Cain

Nicholson Crater on Mars

Perspective view of Nicholson Crater central peak. Image credit: ESA. Click to enlarge
This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA?s Mars Express spacecraft, shows Nicholson Crater, located at the southern edge of Amazonis Planitia on Mars.

The HRSC obtained this image during orbit 1104 with a ground resolution of approximately 15.3 metres per pixel. The scene shows the region around Nicholson Crater, at approximately 0.0? South and 195.5? East.

Nicholson Crater, measuring approximately 100 kilometres wide, is located at the southern edge of Amazonis Planitia, north-west of a region called Medusae Fossae.

Located in the centre of this crater is a raised feature, about 55 kilometres long and 37 kilometres wide, which extends to a maximum height of roughly 3.5 kilometres above the floor of the crater.

At present, it is still unclear how this central feature was shaped and what kind of processes led to its formation. It is thought that the remnant hill could be composed of material from underground or was built as a result of atmospheric deposition.

The tall feature in the centre of this hill is the central peak of the crater, which forms when the surface material ?rebounds? after being compressed during the formation of an impact crater.

However, it is clear that this feature has been heavily sculpted after its creation, by the action of wind or even water.

Original Source: ESA Mars Express

Posted on by Fraser Cain

Martian Dust Devils Will Plague Astronauts

Dust devil tracks. Image credit: NASA/JPL. Click to enlarge
Ah, Martian summer! Finally, the days are long, just like on dear old Earth. And daytime highs rocket all the way up to a balmy 20?C (68?F) from the summer nighttime low of -90?C (-130?F), meaning you and your fellow astronauts can warm up your machinery earlier to get a good start on mining operations.

Dust devils on Mars form the same way they do in deserts on Earth. “You need strong surface heating, so the ground can get hotter than the air above it,” explains Lemmon. Heated less-dense air close to the ground rises, punching through the layer of cooler denser air above; rising plumes of hot air and falling plumes of cool air begin circulating vertically in convection cells. Now, if a horizontal gust of wind blows through, “it turns the convection cells on their sides, so they begin spinning horizontally, forming vertical columns–and starting a dust devil.”

Hot air rising through the center of the column powers the whirling air ever faster–fast enough to begin picking up sand. Sand scouring the ground then dislodges flour-fine dust, and the central column of hot rising air buoys that dust high aloft. Once prevailing horizontal winds begin pushing the dust devil across the ground, look out!

“If you were standing next to the Spirit rover right now [in Gusev Crater] in the middle of the day, you might see half a dozen dust devils,” says Lemmon. Each Martian spring or summer day, dust devils begin appearing about 10 AM as the ground heats, and start abating about 3 PM as the ground cools (Mars’s solar day of 24 hours 39 minutes is only 39 minutes longer than Earth?s). Although the exact frequency and duration of Martian dust devils is unknown, photographs from Mars Global Surveyor in orbit reveal innumerable wandering tracks at all latitudes on the planet. These tracks crisscross the surface where dust devils have scoured away loose surface material to reveal different-colored soil beneath.

Moreover, actual dust devils have been photographed from orbit–some of them as large as 1 to 2 kilometers across at their base and (from their shadows) clearly towering 8 to 10 km high.

What intrigues Farrell from having chased dust devils in the Arizona desert, however, is the strange fact that terrestrial dust devils are electrically charged–and Martian dust devils might be, too.

Dust devils get their charge from grains of sand and dust rubbing together in the whirlwind. When certain pairs of unlike materials rub together, one material gives up some of its electrons (negative charges) to the other material. Such separation of electric charges is called triboelectric charging, the prefix “tribo” (pronounced TRY-bo) meaning “rubbing.” Triboelectric charging makes your hair stand on end when you rub a balloon against your head. Dust and sand, like plastic and hair, form a tribolelectric pair. (Dust and sand aren’t necessarily made of the same stuff, notes Lemmon, because “dust can be blown in from anywhere.”) Smaller dust particles tend to charge negative, taking away electrons from the larger sand grains.

Because the rising central column of hot air that powers the dust devil carries the negatively-charged dust upward and leaves the heavier positively-charged sand swirling near the base, the charges get separated, creating an electric field. “On Earth, with instruments we’ve measured electric fields on the order of 20 thousand volts per meter (20 kV/m),” Farrell says. That’s peanuts compared to the electric fields in terrestrial thunderstorms, where lightning doesn’t flash until electric fields get 100 times greater–enough to ionize (break apart) air molecules.

But a mere 20 kV/m “is very close to the breakdown of the thin Martian atmosphere,” Farrell points out. More significantly, Martian dust devils are so much bigger than their terrestrial counterparts that their stored electrical energy may be much higher. “How would those fields discharge?” he asks. “Would you have Martian lightning inside the dust devils?” Even if lightning wouldn’t ordinarily occur naturally, the presence of an astronaut or rover or habitat might induce filamentary discharges, or local arcing. “The thing you’d really have to watch out for is corners, where electric fields can get very strong,” he adds. “You might want to make your vehicle or habitat rounded.”

Another consideration for astronauts on Mars would be “radio static as charged grains hit bare-wire antennas,” Farrell warns. And after the dust devil passed over and was gone, a lasting souvenir of its passage would be an increased adhesion of dust to spacesuits, vehicles, and habitats via electrostatic cling–the same phenomenon that causes socks to stick together when pulled out of a clothes dryer–making cleanup difficult before reentering a habitat.

Because Martian dust devils can tower 8 to 10 kilometers high, planetary meteorologists now think the devils may be responsible for throwing so much dust high into the Martian atmosphere. Importantly for astronauts, that dust may be carrying negative charges high into the atmosphere as well. Charge building up at the storm top could pose a hazard to a rocket taking off from Mars, as happened to Apollo 12 in November 1969 when it lifted off from Florida during a thunderstorm: the rocket exhaust ionized or broke down the air molecules, leaving a trail of charged molecules all the way down to the ground, triggering a lightning bolt that struck the spacecraft.

“Early sea navigators, like Columbus, understood that their ships had to be designed for extreme weather conditions,” Farrell points out. “To design a mission to Mars, we need to know the extremes of Martian weather–and those extremes appear to be in the form of dust storms and devils.”

Original Source: NASA News Release

Posted on by Fraser Cain

Discovery Won’t Launch Before Sunday

Space Shuttle Discovery on the launch pad. Image credit: NASA. Click to enlarge
NASA announced the earliest the Return to Flight Space Shuttle mission (STS-114) could launch is 2:14 p.m. EDT, Sunday, July 17. Mission Management Team and engineering meetings took place last night and today at NASA’s Kennedy Space Center.

Team members reviewed data and possible troubleshooting plans for the liquid hydrogen tank low-level fuel cut-off sensor. The sensor failed a routine pre-launch check during the launch countdown Wednesday, causing mission managers to scrub Discovery’s first launch attempt.

The sensor protects the Shuttle’s main engines by triggering shutdown if fuel runs unexpectedly low. The sensor is one of four inside the liquid hydrogen section of the External Tank (ET).

A new official launch date will be scheduled once a troubleshooting plan is complete and engineers are working on a solution. Space Shuttle Program managers plan meetings tomorrow to discuss the problem and finalize the troubleshooting plan.

The launch control team began troubleshooting while the liquid oxygen and liquid hydrogen was drained from the ET last night. The No. 2 liquid hydrogen sensor in the ET’s liquid hydrogen tank continued to read ‘wet’ and did not transition to a ‘dry’ indication once the tank was completely drained.

Following de-tanking operations, the same commands that were sent during the launch countdown were repeated while draining. While going through commands, sensor No. 2 continued to show ‘wet’ instead of ‘dry.’ The firing room reissued commands, and the sensor went to ‘dry’ as it should. Another round of commands was sent and sensor No. 2 performed as expected, with all sensors in the ‘dry’ state. Space Shuttle Discovery remains at Launch Pad 39B. The Rotating Service Structure was put back around the vehicle last night.

The STS-114 crew, led by Commander Eileen Collins, remains at Kennedy Space Center while engineers assess the problem. During their 12-day Return to Flight mission to the International Space Station, Discovery’s seven crew members will test new techniques and equipment designed to make Space Shuttle missions safer. They’ll also deliver supplies and make repairs to the Space Station.

For the latest information about the STS-114 mission, visit: http://www.nasa.gov/returntoflight

Original Source: NASA News Release

Posted on by Fraser Cain

Satellite Can Tell When Ice is Melting

Resolute Bay seen by the Hyperion instrument aboard Earth Observing-1. Image credit: NASA. Click to enlarge
Spring thaw in the Northern Hemisphere was monitored by a new set of eyes this year — an Earth-orbiting NASA spacecraft carrying a new version of software trained to recognize and distinguish snow, ice, and water from space.

Using this software, the Space Technology 6 Autonomous Sciencecraft Experiment autonomously tracked changes in the cryosphere, the section of Earth that is frozen, and relayed the information and images back to scientists.

The software, developed by engineers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., controls the Earth Observing-1 spacecraft. NASA’s Goddard Space Flight Center, Greenbelt, Md, manages the satellite. The software has taken more than 1,500 images of frozen lakes in Minnesota, Wisconsin, Quebec, Tibet and the Italian Alps, along with sea ice in Arctic and Antarctic bays.

While other spacecraft only capture images when they receive explicit commands to do so, for the last year Earth Observing-1 has been making its own decisions. Based on general guidelines from scientists, the spacecraft automatically tracks events such as volcano eruptions, floods and ice formation. The most recent software upgrade allows the spacecraft to accurately recognize cryosphere changes such as ice melting.

Previously, scientists spent several months developing software for Earth Observing-1 to detect changes in snow, water and ice. The new software is capable of learning by itself, and it took only a few hours for scientists to train it to recognize cryosphere changes. In fact, the new software has learned to classify the images so well that scientists plan to use it for the remainder of the mission.

“This new software is capable of a rudimentary form of learning, much the way a child learns the names of new objects,” said Dominic Mazzoni, the JPL computer scientist who developed the software. “Instead of programming the software using a complicated series of commands and mathematical equations, scientists play the role of a teacher, repeatedly showing the computer different images and giving feedback until it has correctly learned to tell them apart.”

On Earth Observing-1, the software searches for specific cryospheric events and reprograms the spacecraft to capture additional images of the event.

“The software has exceeded all of our expectations,” said Dr. Steve Chien, JPL principal investigator for the Autonomous Sciencecraft Experiment. “We have demonstrated that a spacecraft can operate autonomously, and the software has taken literally hundreds of images without ground intervention.”

Similar software has been used to distinguish between different types of clouds in images captured by JPL’s Multi-angle Imaging SpectroRadiometer, an instrument on NASA’s Terra spacecraft. Automatically identifying types of clouds from space will help scientists better understand Earth’s global energy balance and predict future climate trends.

Future versions of the software also might be used to track dust storms on Mars, search for ice volcanoes on Jupiter?s moon Europa, and monitor activity on Jupiter’s volcanically active moon Io. NASA’s New Millennium Program developed both the satellite and the software. The program is responsible for testing new technologies in space.

For more information on the Autonomous Sciencecraft Experiment on the Internet, visit: http://ase.jpl.nasa.gov .

For more information on the New Millennium Program on the Internet, visit: http://nmp.jpl.nasa.gov .

For information about the Earth Observing-1 spacecraft on the Internet, visit: http://eo1.gsfc.nasa.gov .

Original Source: NASA News Release

Posted on by Fraser Cain

Planet Found in Triple Star System

Artist’s animation shows the view from a hypothetical moon in orbit around the planet. Image credit: NASA. Click to enlarge
A NASA-funded astronomer has discovered a world where the sun sets over the horizon, followed by a second sun and then a third. The new planet, called HD 188753 Ab, is the first known to reside in a classic triple-star system.

“The sky view from this planet would be spectacular, with an occasional triple sunset,” said Dr. Maciej Konacki (MATCH-ee Konn-ATZ-kee) of the California Institute of Technology, Pasadena, Calif., who found the planet using the Keck I telescope atop Mauna Kea mountain in Hawaii. “Before now, we had no clues about whether planets could form in such gravitationally complex systems.”

The finding, reported in this week’s issue of Nature, suggests that planets are more robust than previously believed.

“This is good news for planets,” said Dr. Shri Kulkarni, who oversees Konacki’s research at Caltech. “Planets may live in all sorts of interesting neighborhoods that, until now, have gone largely unexplored.” Kulkarni is the interdisciplinary scientist for NASA’s planned SIM PlanetQuest mission, which will search for signs of Earth-like worlds.

Systems with multiple stars are widespread throughout the universe, accounting for more than half of all stars. Our Sun’s closest star, Alpha Centauri, is a member of a trio.

“Multiple-star systems have not been popular planet-hunting grounds,” said Konacki. “They are difficult to observe and were believed to be inhospitable to planets.”

The new planet belongs to a common class of extrasolar planets called “hot Jupiters,” which are gas giants that zip closely around their parent stars. In this case, the planet whips every 3.3 days around a star that is circled every 25.7 years by a pirouetting pair of stars locked in a 156-day orbit.

The circus-like trio of stars is a cramped bunch, fitting into the same amount of space as the distance between Saturn and our Sun. Such tight living quarters throw theories of hot Jupiter formation into question. Astronomers had thought that hot Jupiters formed far away from their parent stars, before migrating inward.

“In this close-knit system, there would be no room at the outskirts of the parent star system for a planet to grow,” said Konacki.

Previously, astronomers had identified planets around about 20 binary stars and one set of triple stars. But the stars in those systems had a lot of space between them. Most multiple-star arrangements are crowded together and difficult to study.

Konacki overcame this challenge using a modified version of the radial velocity, or “wobble,” planet-hunting technique. In the traditional wobble method, a planet’s presence is inferred by the gravitational tug, or wobble, it induces in its parent star. The strategy works well for single stars or far-apart binary and triple stars, but could not be applied to close-star systems because the stars’ light blends together.

By developing detailed models of close-star systems, Konacki was able to tease apart the tangled starlight. This allowed him to pinpoint, for the first time, the tug of a planet on a star snuggled next to other stars. Of 20 systems examined so far, HD 188753, located 149 light-years away, was the only one found to harbor a planet.

Hot Jupiters are believed to form out of thick disks, or “doughnuts,” of material that swirl around the outer fringes of young stars. The disk material clumps together to form a solid core, then pulls gas onto it. Eventually, the gas giant drifts inward. The discovery of a world under three suns contradicts this scenario. HD 188753 would have sported a truncated disk in its youth, due to the disruptive presence of its stellar companions. That leaves no room for HD 188753’s planet to form, and raises a host of new questions.

The masses of the three stars in HD 188753 system range from two-thirds to about the same mass as our Sun. The planet is slightly more massive than Jupiter.

For artist’s concepts and other graphics, visit http://planetquest.jpl.nasa.gov/ . For information about NASA and agency programs on the Web, visit http://www.nasa.gov/home/index.html .

Original Source: NASA News Release

Posted on by Fraser Cain

Superwinds Seen in Distant Galaxies

An artist’s impression of a Superwind in a young massive galaxy. Image credit: PPARC/David Hardy. Click to enlarge
A team of astronomers, led by the University of Durham, has discovered the aftermath of a spectacular explosion in a galaxy 11.5 billion light years away. Their observations, reported today (14th July 2005) in the journal Nature provide the most direct evidence yet of a galaxy being almost torn apart by explosions that produce a stream of high-speed material known as “Superwinds”. The observations were made using the 4.2 metre William Herschel Telescope on La Palma in which the UK is a major stakeholder.

Through Superwinds, galaxies are thought to blast a significant part of their gas into intergalactic space at speeds of up to several hundred miles per second. The driving force behind them is the explosion of many massive stars during an intense burst of star formation early in the galaxy’s life, possibly assisted by energy from a super massive black hole growing at its heart.

Superwinds are vital to the theory of galaxy formation for several reasons: firstly, they limit the sizes of galaxies by preventing further star formation – without them theoretical models indicate far more very bright galaxies than are actually seen in the Universe today. Secondly, they carry heavy elements – Star dust – far from their production sites in stars out into intergalactic space, providing raw material for planets and life across the Universe. Whilst the theories predicted Superwinds of this kind existed, previously observed examples were much smaller phenomena in nearby galaxies. These observations provide some of the most direct evidence yet for the existence of large-scale, galaxy-wide superwinds so far back in the history of the Universe.

The discovery of the Superwind was made by observing the gas in the halo of a galaxy (known as “LAB-2”), which at over 300,000 light years across is about three times larger than the disk of our own Milky Way galaxy. The astronomers discovered that light from hot glowing hydrogen gas is dimmed in a very specific way across the entire galaxy.

“We believe that the dimming is caused by a shell of cooled material which has been swept-up from the surroundings by a galaxy-wide Superwind explosion,” said Dr. Richard Wilman of the University of Durham. “Based on the uniformity of the absorption across the galaxy, it appears that the explosion was triggered several hundred million years earlier. This allows time for the gas to cool and to slow down from its high ejection speed, and thus to produce the absorption. As we see it, the shell is probably a few hundred thousand light years in front of its parent galaxy,” added Dr. Wilman.

Astronomers have long been puzzled about why key elements for the formation of planets and ultimately life (such as carbon, oxygen and iron) are so widely distributed throughout the Universe; only 2 billion years after the Big Bang, the remotest regions of intergalactic space have been enriched with them. The Superwind observed in this galaxy shows how such blast waves can travel through space carrying the elements formed deep within galaxies.

Crucial to the discovery and its interpretation was the ability to obtain detailed information on the gas in two-dimensions across the whole galaxy. This was made possible by a technique known as integral field spectroscopy, which is only just reaching maturity on the world’s largest telescopes.

Dr Joris Gerssen, a key member of the Durham team, explains, “Most astronomical spectroscopy is performed by placing a small aperture, or a narrow slit on the target, which for complex, extended sources such as this galaxy gives a rather incomplete picture”.

To overcome this the astronomers used an integral field spectrograph called ‘Sauron’ for a large survey of nearby galaxies, built at the Observatoire de Lyon by a collaboration of French, Dutch and UK astronomers.

Dr Gerssen added,” “Sauron is truly unique and its high efficiency means that it can more than hold its own against instruments on the world’s largest telescopes, some twice the size of the William Herschel Telescope. Nevertheless, the sheer distance of our target galaxy meant that Sauron had to stare at it for over 15 hours in order to make this discovery”.

“Sauron has provided us with the best evidence so far for an extensive outflow from a galaxy undergoing a huge starburst. These measurements are among the first steps towards understanding the physics of galaxy formation.,” commented Prof. Roger Davies, University of Oxford, one of the institutes involved on Sauron,” and we look forward to using similar two-dimensional spectrographs being built for 8m telescopes; these will probe the galaxy formation process to even earlier times.”

To date, observational evidence for Superwinds in young galaxies in the distant Universe has been largely indirect and circumstantial; efforts have focussed on searching for their subtle statistical signatures in large surveys of galaxies and intergalactic gas.

According to Prof. Richard Bower, from the University of Durham’s Institute of Computational Cosmology who initiated the research, “Astronomers have observed high-speed outflows in distant star-forming galaxies for several years, but never before have we been able to gauge their true scale from observations of a single galaxy. By taking advantage of the highly extended emission source of this galaxy, we can see the outflow as a kind of silhouette against the whole galaxy. This suggests that Superwinds are truly galaxy-wide in scale, and that they really are as important as our theories require.”

Original Source: PPARC News Release

Posted on by Fraser Cain

Malfunctioning Fuel Gauge Delays Shuttle

The Space Shuttle sits on the Mobile Launcher Platform (MLP). Image credit: NASA/KSC. Click to enlarge
The launch of NASA’s Space Shuttle Return to Flight mission, STS-114, will take place no earlier than Saturday, July 16 at 2:40 p.m. EDT. Space Shuttle Discovery’s liftoff today from NASA’s Kennedy Space Center, Fla., was postponed at 1:30 p.m. EDT.

During countdown activities, a low-level fuel cut-off sensor located inside the External Tank failed a routine prelaunch check. The sensor protects a Shuttle’s main engines by triggering their shut down in the event fuel runs unexpectedly low. The sensor is one of four inside the liquid hydrogen section of the External Tank.

The External Tank’s liquid oxygen and liquid hydrogen were drained this evening. While the tank was being emptied, engineers monitored and collected data on the liquid hydrogen sensor that failed. They will continue to collect and analyze data overnight.

Space Shuttle Program managers plan a series of meetings tomorrow to discuss the problem and determine the steps necessary to get back into the launch countdown.

The STS-114 crew will remain at Kennedy Space Center for now while engineers work on the problem.

During their 12-day Return to Flight mission to the International Space Station, Discovery’s seven crew members will test new techniques and equipment designed to make Space Shuttles safer. They’ll also deliver supplies and make repairs to the Space Station.

For the latest information about the STS-114 mission, visit:
http://www.nasa.gov/returntoflight

Original Source: NASA News Release

Posted on by Fraser Cain

Cluster Spacecraft Give Each Other Some Room

An artist’s impression of the Cluster quartet. Image credit: ESA. Click to enlarge
The four spacecraft of ESA?s Cluster fleet have reached their greatest distance from each other in the course of their mission to study Earth?s magnetosphere in three dimensions.

This operation, marking the fifth anniversary of Cluster in space, transforms Cluster in the first ?multi-scale? mission ever.
In one of the most complex manoeuvres ever conducted by ESA spacecraft, three of the spacecraft were separated to 10 000 kilometres from each other, with the fourth spacecraft at 1000 kilometres from the third one.

This new fleet formation for Cluster was achieved in two months of operations. The repositioning of the satellites was started by mission controllers at ESA’s European Space Operations Centre (ESOC), in Darmstadt, Germany, on 26 May, and was run until 14 July.

During the course of the mission, the distance between the Cluster satellites had already changed five times, in a range between 100 and 5000 kilometres. Varying the size – but not the shape – of the Cluster ?constellation? had allowed Cluster to examine Earth?s magnetosphere at different scales.

But now this new ?asymmetric? flying formation is allowing the Cluster spacecraft to make measurements of medium- and large-scale phenomena simultaneously, transforming Cluster in the first ever ?multi-scale? mission.

With this, it is possible to study at the same time the link between small-scale kinetic processes of the plasma around Earth and the large-scale morphology of the magnetosphere.

The knowledge gained by Cluster about the magnetosphere ? the natural magnetic shield that surrounds and protects our planet ? has already helped advance our understanding of how the solar wind affects Earth?s natural space environment.

This is also important in our daily life as, for instance, intense solar activity can disrupt terrestrial communication networks, power grids and data lines.

Original Source: ESA Portal

Posted on by Fraser Cain

Will We Find Super Earths?


An extrasolar planet with hypothetical (possible but unproven) water-bearing moons. Image credit: NASA/IPAC/R. Hurt. Click to enlarge
Over the past decade, astronomers using a planet-hunting technique that measures small changes in a star’s speed relative to Earth, have discovered more than 130 extrasolar planets. The first such planets were gas giants, the mass of Jupiter or larger. After several years, the scientists began to detect Saturn-mass planets. And last August, they announced the discovery of a handful of Neptune-mass planets. Could these be super-Earths?

In a recent talk at a symposium on extrasolar planets, Carnegie Institution of Washington astronomer Alan Boss explained the possibilities.

Radial-velocity planet-hunting techniques recently have pushed our discovery capability below the Saturn-mass limit down into what we would call the ice-giant limit.

So we are now able to find planets, close to their host stars, with masses comparable to that of Uranus and Neptune (14 to 17 times the mass of Earth).

In large part this is due to Michel Mayor and his colleagues having a new spectrometer in La Silla, which has unprecedented spectral resolution down to about 1 meter per second or so. And I think Geoff Marcy and Paul Butler’s group are quite close behind that as well.

The interesting question, though, is: What are these things? Are they ice giants that formed several AUs out and migrated in, or are they something else? Unfortunately, we don’t know exactly what their masses are. Even more importantly, we don’t really know what their density is. So they could be 15-Earth-mass rocks, or they could be 15-Earth-mass ice giants.

What we really need to do is to have folks go out and discover another 7 or so. We’ve got 3 so far. If we had 10 altogether, then we’ll have enough that 1 of them, at least, should transit its star and then we’ll be able to get some idea of what its density is.

I think, though, that there’s a good chance that these might actually be a new class of planet altogether: super-Earths. The reason I would argue that is that, at least in 2 of the systems where they’ve been found, these “hot Neptunes” are accompanied by a larger Jupiter-mass planet with a longer-period orbit.

If the lower-mass planets are ice giants that formed far from their stars, unless you have some highly contrived scenario, you wouldn’t imagine them to end up migrating inward, past the larger guys. These systems look more like our own solar system, where you have the low-mass fellows inside of the gas giants.

The planets in a system like our system presumably did not undergo very much migration. So I would claim that perhaps these guys are objects which formed inside the gas giants and only migrated in a little bit, ending up where we can detect them with the short-period spectroscopy surveys.

In support of this idea, there’s some theoretical work from Carnegie’s George Wetherill from almost 10 years ago, now, where he had done some calculations of the accumulation process of rocky planets. He often found there was quite a spread in the masses of what you got out, because accumulation’s a very stochastic process. For the typical parameters he used, at the end of 100 million years or so, he would not only get objects of 1 Earth mass, but also objects ranging up to 3 Earth masses.

Well, at the time, he assumed for his calculations a fairly low surface density at 1 AU, where these planets were forming. Given what we know now, if you want to be able to make a Jupiter at 5 AU using the core-accretion model of planetary formation, you have to crank up the density in the protoplanetary disk by a factor of 7 or so over what Wetherill assumed.

That scales directly with the mass of the planets you’d expect to find as a result. So if you did these calculations over again, assuming this higher initial density, the upper limit on the mass of the inner planets would go from 3 Earth masses, which is what Wetherill got, up to say 21 Earth masses. That is in the range of what we are estimating for these newly discovered hot Neptune-mass objects.

So perhaps what we really are seeing is a new class of objects, super-Earths, rather than ice giants.

Original Source: NASA Astrobiology

Posted on by Fraser Cain

Three Space Telescopes Find a Neutron Star

Artist’s impression of neutron star IGR J16283-4838. Image Credit:NASA/Dana Berry. Click to enlarge
An international team of scientists has uncovered a rare type of neutron star so elusive that it took three satellites to identify it.

The findings, made with ESA?s Integral satellite and two NASA satellites, reveals new insights about star birth and death in our Galaxy. We report this discovery, highlighting the complementary nature of European and US spacecraft, on the day in which ESA?s Integral celebrates 1000 days in orbit.
The neutron star, called IGR J16283-4838, is an ultra-dense ?ember? of an exploded star and was first seen by Integral on 7 April 2005. This neutron star is about 20,000 light years away, in a ?double hiding place?. This means it is deep inside the spiral arm Norma of our Milky Way galaxy, obscured by dust, and then buried in a two-star system enshrouded by dense gas.

?We are always hunting for new sources,? said Simona Soldi, the scientist at the Integral Science Data Centre in Geneva, Switzerland, who first saw the neutron star. ?It is exciting to find something so elusive. How many more sources like this are out there??

Neutron stars are the core remains of ?supernovae?, exploded stars once about ten times as massive as our Sun. They contain about a Sun’s worth of mass compacted into a sphere about 20 kilometres across.

?Our Galaxy?s spiral arms are loaded with neutron stars, black holes and other exotic objects, but the problem is that the spiral arms are too dusty to see through,? said Dr Volker Beckmann at NASA Goddard Spaceflight Centre, lead author of the combined results.

?The right combination of X-ray and gamma-ray telescopes could reveal what is hiding there, and provide new clues about the true star formation rate in our Galaxy,? he added.

Because gamma rays are hard to focus into sharp images, the science team then used the X-ray telescope on Swift to determine a precise location. In mid April 2005, Swift confirmed that the light was ?highly absorbed?, which means the binary system was filled with dense gas from the stellar wind of the companion star.

Later the scientists used the Rossi Explorer to observe the source as it faded away. This observation revealed a familiar light signature, clinching the case for a fading high-mass X-ray binary with a neutron star.

IGR J16283-4838 is the seventh so-called ?highly absorbed?, or hidden neutron star to be identified. Neutron stars, created from fast-burning massive stars, are intrinsically tied to star formation rates. They are also energetic ?beacons? in regions too dusty to study in detail otherwise. As more and more are discovered, new insights about what is happening in the Galaxy’s spiral arms begin to emerge.

IGR J16283-4838 revealed itself with an ?outburst? on or near its surface. Neutron stars such as IGR J16283-4838 are often part of binary systems, orbiting a normal star. Occasionally, gas from the normal star, lured by gravity, crashes onto the surface of the neutron star and releases a great amount of energy. These outbursts can last for weeks before the system returns to dormancy for months or years.

Integral, the Rossi Explorer and Swift all detect X-rays and gamma rays, which are far more energetic than the visible light that our eyes detect. Yet each satellite has different capabilities. Integral has a large field of view, enabling it to scan our Milky Way galaxy for neutron stars and black hole activity.

Swift contains a high-resolution X-ray telescope, which allowed scientists to zoom in on IGR J16283-4838. The Rossi Explorer has a timing spectrometer, a device used to uncover properties of the light source, such as speed and rapid variations in the order of milliseconds.

Original Source: ESA Portal