Supernova Origins

In 1572, people on Earth saw the bright light of a supernova. Now, by combining different intensities of x-ray data, scientists using NASA’s Chandra X-ray Observatory have created a new image of the debris left from that explosion, which hints at the origins of the cosmic blast.

Known as Tycho’s supernova remnant, the space puffball includes a cloud of expanding debris (yellow) enveloped by a high-energy blast wave (blue). The latest image also shows an arc of high-energy x-rays (bottom left) that seems to be coming from a faster moving ball of material.

Astronomers think that the supernova happened when a white dwarf star siphoned so much material from a companion star that it exploded. The blast blew material off the sunlike companion, and that debris is now emitting the arc of x-rays.

NASA’s Mars Reconnaissance Orbiter has discovered the total amount of atmosphere on Mars changes dramatically as the tilt of the planet’s axis varies. This process can affect the stability of liquid water, if it exists on the Martian surface, and increase the frequency and severity of Martian dust storms.

The moon’s orbit about the Earth is not a perfect circle—it is slightly eccentric. As a result, during part of its orbit it is a little closer to us than at other times.

The closest approach is called perigee, while the greatest separation is called apogee.

On average, the moon’s distance from Earth is 239,228 miles (385,000 kilometers).

A galaxy’s core is a busy place, crowded with stars swarming around an enormous black hole. When galaxies collide, it gets even messier as the two black holes spiral toward each other, merging to make an even bigger gravitational monster.

Once it is created, the monster goes on a rampage. The merger kicks the black hole into surrounding stars. There it finds a hearty meal, shredding and swallowing stars at a rapid clip. According to new research by Nick Stone and Avi Loeb (Harvard-Smithsonian Center for Astrophysics), upcoming sky surveys might offer astronomers a way to catch a gorging black hole “in the act.”

Comet Encounter

Like a potato emerging from the shadows, the icy core of comet Tempel 1 looms into view in a new picture from NASA’s Stardust spacecraft released Tuesday.

The image was snapped at 11:39 p.m. ET during a close flyby that brought the office desk-size craft within 110 miles (178 kilometers) of the 3.7-mile-wide (6-kilometer-wide) comet. Stardust took 72 high-resolution pictures during the encounter, 60 of which had been successfully beamed back to Earth as of Tuesday afternoon ET.

The comet and spacecraft are both seasoned pros when it comes to NASA missions. In 2005 Tempel 1 was visited by a NASA probe called Deep Impact, which smashed an 800-pound (363-kilogram) metal slug into the comet’s core, or nucleus (see pictures of the comet impact). And in 2004 Stardust collected samples from the comet Wild 2 (pronounced “Vilt 2″).

The Stardust-NExT mission involved retargeting Stardust for a Valentine’s Day rendezvous with Tempel 1 after the comet had made a complete trip around the sun.

“This is the first time we’ve ever had the opportunity to visit a comet twice,” Stardust-NExT project manager Tim Larson said today during a press briefing.

Tempel 1, he added, “comes as close to the sun as the orbit of Mars, and that’s about where we met it last night with the spacecraft.”

Tempel 1′s Close-up

Proposed in 2006, the Stardust-NExT mission had three main science objectives that involved taking pictures, according to Joe Veverka, the Stardust-NExT principal investigator, based at Cornell University in Ithaca, New York.

“First of all, we wanted to look again at areas on Tempel 1 that we had seen before with Deep Impact and, for the first time, see what changes that occur on a comet when it gets close to the sun,” Veverka said during the briefing.

“We also wanted the opportunity to look at the Deep Impact impact site, and we wanted to take the opportunity to extend our exploration and see areas on Tempel 1 not seen before.”

Based on the images that scientists have seen so far—such the one above taken at 11:39 p.m. ET Monday—the mission hit the mark: “Was this mission 100 percent successful?” Veverka asked. “I’d have to say no, it was 1,000 percent successful!”

Valentine’s Visit

Two small, circular craters—visible in a picture taken by the Stardust craft Monday night—flank the region of comet Tempel 1 that was hit during the 2005 Deep Impact mission. The cosmic smashup had sent up a bright spray of ice and dirt, obscuring the crater site in pictures taken at the time.

“That created a lot of mystery, but it also helped create this mission,” said Pete Schultz, a Stardust-NExT co-investigator at Brown University in Providence, Rhode Island.

The path and timing of the Stardust-NExT flyby was carefully calculated so that scientists could get a look at the impact site. The new pictures prove that Deep Impact made a crater, about 492 feet (150 meters) wide—too small to be seen in this picture. The pit is not very sharply defined, though, with a small mound in its center.

“The bottom-line message is that the surface of the comet at the impact site is very weak, so the crater partly healed itself,” Schultz said.

Target Sighted

From thousands of miles away, Tempel 1 looks like no more than a mote of dust in a picture taken by the Stardust spacecraft as it approached the comet Monday night. Not visible in the new pictures is the larger halo of ice grains and dust that surrounds the comet’s nucleus.

When a comet gets close to the sun—as Tempel 1 was during the flyby—ices on its surface sublimate, or turn directly from solid to gas. As this happens, “comets send out clouds of dust and ice and rock that come apart,” said Stardust-NExT co-investigator Don Brownlee of the University of Washington in Seattle.

“It’s a very dramatic environment.” (Also see “Comet Is Cosmic Snow Globe, NASA Flyby Shows.”)

In fact, Stardust recorded thousands of impacts with dust and ice grains as it swooped close to Tempel 1. Even so, the spacecraft emerged healthy, and mission managers plan to collect more data and pictures of the comet over the next few weeks as Stardust bids Tempel 1 adieu.

Surreal Sunrise

Clouds flow like a river over the lights of Swiss villages as the rising sun crowns the Alps with morning gold in a January 30 picture. To the right, a crescent moon and the bright dot of Venus decorate the paling sky.

Venus is closer to the sun than Earth, so—like a car going around a racetrack—Venus periodically overtakes Earth as it orbits. This means Venus changes from the evening star, visible after sunset, to the morning star, visible before sunrise, every 584 days.

Star-Struck Aurora

Stars wheeling across the sky seem to cut through a fiery aurora in a recently released long-exposure picture taken in western Sweden.

Auroras can appear in different colors depending on the types of gases in the atmosphere and where these gases are. Auroras happen when energized particles form the sun interact with air molecules and give them extra charge. These “excited” molecules then emit light. Oxygen, for example, can create auroras in yellow-green to red, while nitrogen emits light in blues and purples.

Aft View of Earth

An astronaut aboard the International Space Station snapped this recently released shot of the station’s rear end with Earth in the distance from aboard the ISS Progress 40 supply vehicle.

The unpiloted Progress 40 craft has since undocked from the station carrying waste items. The craft will be used for scientific experiments until it is burned up in Earth’s atmosphere.

Double Trouble

An arch of plasma called a solar filament erupts from the sun on January 28 in a video still from NASA’s Solar Dynamics Observatory spacecraft.

The craft caught the sun producing two events at once: At the same time the filament erupted, a coronal mass ejection on the opposite side of the solar disk (not pictured) blasted a huge spray of particles into space.

Have a Nice Day?

People with coulrophobia might want to avoid the south pole of Mars: Seasonal carbon dioxide frost has given rise to a pit that bears an eerie resemblance to a deranged clown face.

Scientists compared this newly released picture from the Mars Reconnaissance Orbiter with another taken in 2007 to see how the pit has changed over time. The team saw signs of growth inside the “happy face,” which they think is caused by frost that sublimates—turns directly from solid to gas—from the pit walls and then recondenses on its surfaces.

Snowy Berlin

Bright white snow and dark vegetation create a crystalline patchwork over the urban landscape of Berlin in a recently released satellite image of the German capital. Home to 3.4 million people, Berlin has the second largest population, within city limits, of any city in the European Union after London.

The picture was taken by the Japanese ALOS satellite and processed by theEuropean Space Agency. ALOS was designed to chart land cover in visible and near-infrared light.

WISE Comets

After a year of mapping the sky in infrared, NASA’s Wide-field Infrared Survey Explorer, or WISE, space telescope discovered 20 comets, seen above in a mosaic of false-color pictures. The backgrounds appear fuzzy because WISE also captured the faint heat signatures of dust in our solar system.

In addition to comets, WISE discovered more than 33,000 asteroids in the main belt, between the orbits of Mars and Jupiter, and 134 near-Earth objects—asteroids and comets that come within 28 million miles (45 million kilometers) of Earth’s orbit around the sun.

New research has settled decades of scientific debate about a puzzling aspect of space weather. Researchers from the University of California (UCLA) and British Antarctic Survey (BAS) have found the final link between electrons trapped in space and the glow of light from the upper atmosphere known as the diffuse aurora.

The research, published in the latest issue of the journal Nature, promises to further understanding of space weather, with benefits for the satellite, power grid and aviation industries, and how space storms affect the Earth’s atmosphere from the top down.

Scientists have long understood that the ‘diffuse aurora’ is caused by electrons striking the upper atmosphere. However, the electrons are normally trapped much higher up in the Earth’s magnetic field through a long chain of events starting with the Sun. The problem is to understand how these electrons reach the atmosphere.

Since the 1970s scientists have debated whether very low frequency (VLF) radio waves could scatter the trapped electrons into the atmosphere. Two types of VLF waves were identified in space as the possible cause of the ‘diffuse aurora’, but despite years of argument and research no conclusive result had been possible. The new research shows, without doubt, that VLF waves known as ‘chorus’ are responsible; so-called since the signals detected by ground-based recording equipment sound like the bird’s dawn chorus when played back through a loud speaker.

Through detailed analysis of satellite data the authors were able to calculate the effects on the trapped electrons and identify which radio waves were causing the scattering.

Lead author Professor Richard Thorne from UCLA says: "The breakthrough came when we realised that the electrons being lost from space to the Earth’s atmosphere were leaving a signature, effectively telling a story about how they were being scattered. We could then analyse our satellite data on the two types of VLF waves and by running calculations on them — including the rate at which the electrons were being lost to the Earth’s atmosphere — we could clearly see that chorus waves were the cause of the scattering."

Professor Richard Horne from British Antarctic Survey says: "Our finding is an important one because it will help scientists to understand how the diffuse aurora leads to changes in the chemistry of the Earth’s upper atmosphere, including effects on ozone at high altitude, which may affect temperature right through the atmosphere.

"We are also including the VLF waves into computer models to help predict ‘space weather’ which not only affects satellites and power grids, but also the accuracy of GPS navigation and high frequency radio communications with aircraft on polar routes."

The ‘diffuse aurora’, is not the same as the ‘discrete aurora’ known as the northern and southern lights. ‘Discrete aurora’ look like fiery moving curtains of colourful light and can be seen by the naked eye, whereas the diffuse aurora is much fainter but more extensive. The ‘diffuse aurora’, which typically accounts for three-quarters of the energy input into the upper atmosphere at night, varies according to the season and the 11 year solar cycle.

Notes:

*Chorus waves: Very low frequency radio waves coming from space and first detected on the ground. So-called because when played back through a loud speaker they sound like the bird’s dawn chorus.

*Diffuse aurora: caused when electrons that are trapped in the Earth’s magnetic field are funnelled towards the polar atmosphere. Light is emitted when the electrons collide with neutral atoms in the upper atmosphere. The diffuse aurora is not generally visible to the naked eye but is well captured in satellite images.

*Discrete aurora: known as the Aurora Borealis at the North Pole (above the Arctic circle) and Aurora Australis at the South Pole (above Antarctica). They look like fiery, moving curtains of colourful light and can be seen by the naked eye whereas the diffuse aurora is much fainter but is more extensive and can cover the whole sky.

A group of international astronomers in the UK, France and the USA, led by the University of Leicester, have found proof to confirm the distance and brightness of the most extreme ultra-luminous X-ray source, which may herald a new type of Black Hole.

The X-ray source, HLX-1, is the most extreme member of an extraordinary class of objects — the ultra-luminous X-ray sources — and is located in the galaxy ESO 243-49 at a distance of ~300 million light years from the Earth.

The astronomers’ findings confirm that the extreme luminosity (which is a factor of ~100 above most other objects in its class, and a factor of ~10 higher than the next brightest ultra-luminous X-ray source) is correct.

This is forcing scientists to rethink their theories on the maximum brightness of ultra-luminous X-ray sources, and provides support to the idea that HLX-1 may contain an intermediate mass black hole.

This latest result will be reported September 8 in the scientific journal, The Astrophysical Journal.

Using the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT) in Chile, the team have obtained an optical spectrum of their record breaking ultra-luminous X-ray source (HLX-1) in the distant galaxy ESO 243-49.

Their findings enable them to show conclusively that HLX-1 is indeed located within this galaxy, and is neither a foreground star nor a background galaxy. The main implication of this discovery is that ultra-luminous X-ray sources such as HLX-1 can be brighter than was originally thought, which is consistent with at least the brightest of them hosting intermediate mass black holes.

A black hole is an ultra-dense object with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

While astrophysicists have suspected that an intermediate class of black hole might exist, with masses between a hundred and several hundred thousand times that of the Sun, such black holes had not previously been reliably detected and their existence has been fiercely debated among the astronomical community.

The VLT enabled the team of researchers to confirm the detection of HLX-1 in optical wavelengths and to measure a precise distance to it.

The lead author of the paper reporting this result, Dr Klaas Wiersema of Leicester’s Department of Physics and Astronomy, commented: "After our earlier discovery of the very bright X-ray source, we were very keen to find out just how far away it really is, so that we can work out how much radiation this black hole produces.

"We could see on images taken with big telescopes that a faint optical source was present at the location of the X-ray source, located near the core of a large and bright galaxy.

"We suspected that this faint optical source was directly associated with the X-ray source, but to be sure we had to study the light of this source in detail, using the Very Large Telescope in Chile.

"The data we got from the VLT were of a very high quality, and allowed us to separate the light of the big, bright galaxy from that of the faint optical source.

"Much to our delight we saw in the resulting measurements exactly what we were hoping for: the characteristic light of hydrogen atoms was detected allowing us to accurately measure the distance to this object. This provided conclusive proof that the black hole was indeed located inside the big, bright galaxy, and that HLX-1 is the brightest ultra-luminous X-ray source known.

"Now that we have established the distance to this black hole and now we know where it lives, we would like to find out what makes this source so bright, and how it ended up in this big galaxy."

This is a very important result as it is consistent with the idea that HLX-1 contains an intermediate mass black hole. Ultra-luminous X-ray sources are among the most promising candidates for intermediate mass black holes, with masses between stellar mass black holes (around ~3-20 times the mass of the Sun) and the super-massive black holes found in the centres of most galaxies (around 1 million — 1 billion times the mass of the Sun).

The research team can now conclusively prove that HLX-1 is not in our own Galaxy, nor is it a super-massive black hole in the centre of a distant background galaxy. This result also confirms that it really is as bright as they thought it was.

Dr Didier Barret, of the Centre d’Etude Spatiale des Rayonnements in France, commented: "The XMM-Newton and Swift X-ray observatories are keeping a close eye on this source. The latest data, which was obtained while HLX-1 was very faint, indicates that it is behaving in a very similar way to stellar mass black holes in our own Galaxy, but at a level ~100 — 1,000 times brighter."

Dr Sean Farrell, also in the Leicester Department of Physics and Astronomy, commented: "This is very difficult to explain without the presence of an intermediate mass black hole of between ~500 and 10,000 times the mass of the Sun. HLX-1 is therefore (so far!) weathering the scrutiny of the international astronomy community."

The centres of most galaxies are thought to contain super-massive black holes, and these powerhouses have an enormous impact on the surrounding galaxy. Super-massive black holes deposit an immense amount of energy into their host galaxies, which has dramatic consequences for the formation of stars and the growth of the galaxy as a whole. Intermediate mass black holes may be the building blocks of super-massive black holes.

"Understanding how super-massive black holes form and grow is thus crucial to our comprehension of the formation and evolution of galaxies, which in turn goes part of the way to answering one of the really big questions: How did our own Galaxy form and evolve?

"We are very pleased with this result, as it confirms our original discovery of the record breaking ultra-luminous X-ray source. In order to ensure the success of this project, we carefully prepared the VLT observations using data from the US-operated Magellan Telescopes. The VLT data analysis was especially complicated on this project, as it is very difficult to disentangle the signature in optical wavelengths of HLX-1 from the bright galaxy in which it lies.

"This work relied heavily on the expertise of researchers at the University of Leicester, and is testament to the high level of skills that are concentrated in our department, which works on some of the biggest questions in astronomy today. This is fitting as we are currently celebrating the 50th anniversary of the founding of the astronomy group here at Leicester."

Whether all ultra-luminous X-ray sources contain intermediate mass black holes is still quite uncertain. Dr Farrell’s research team will continue studying HLX-1 in order to understand how it formed, where it is located, and what is feeding it.

In order to do this they have been granted time on the Hubble Space Telescope to take the highest ever resolution images of this host galaxy, which will allow them to investigate in detail the nature of the environment around HLX-1 and the galaxy which hosts it. Once the Hubble observations are performed, most of the great observatories would have been used to study this source.

The next step will be to find out if there are more objects as extreme as this one, and to compare what they know about HLX-1 with the larger population of ultra-luminous X-ray sources. This will help them understand how many intermediate mass black holes might be out there, and where they are likely to find them.

New research challenges the controversial theory that an ancient comet impact devastated the Clovis people, one of the earliest known cultures to inhabit North America.

Writing in the October issue of Current Anthropology, archaeologists Vance Holliday (University of Arizona) and David Meltzer (Southern Methodist University) argue that there is nothing in the archaeological record to suggest an abrupt collapse of Clovis populations. "Whether or not the proposed extraterrestrial impact occurred is a matter for empirical testing in the geological record," the researchers write. "Insofar as concerns the archaeological record, an extraterrestrial impact is an unnecessary solution for an archaeological problem that does not exist."

The comet theory first emerged in 2007 when a team of scientists announced evidence of a large extraterrestrial impact that occurred about 12,900 years ago. The impact was said to have caused a sudden cooling of the North American climate, killing off mammoths and other megafauna. It could also explain the apparent disappearance of the Clovis people, whose characteristic spear points vanish from the archaeological record shortly after the supposed impact.

As evidence for the rapid Clovis depopulation, comet theorists point out that very few Clovis archaeological sites show evidence of human occupation after the Clovis. At the few sites that do, Clovis and post-Clovis artifacts are separated by archaeologically sterile layers of sediments, indicating a time gap between the civilizations. In fact, comet theorists argue, there seems to be a dead zone in the human archaeological record in North America beginning with the comet impact and lasting about 500 years.

But Holliday and Meltzer dispute those claims. They argue that a lack of later human occupation at Clovis sites is no reason to assume a population collapse. "Single-occupation Paleoindian sites — Clovis or post-Clovis — are the norm," Holliday said. That’s because many Paleoindian sites are hunting kill sites, and it would be highly unlikely for kills to be made repeatedly in the exact same spot.

"So there is nothing surprising about a Clovis occupation with no other Paleoindian zone above it, and it is no reason to infer a disaster," Holliday said.

In addition, Holliday and Meltzer compiled radiocarbon dates of 44 archaeological sites from across the U.S. and found no evidence of a post-comet gap. "Chronological gaps appear in the sequence only if one ignores standard deviations (a statistically inappropriate procedure), and doing so creates gaps not just around [12,900 years ago] but also at many later points in time," they write.

Sterile layers separating occupation zones at some sites are easily explained by shifting settlement patterns and local geological processes, the researchers say. The separation should not be taken as evidence of an actual time gap between Clovis and post-Clovis cultures.

Holliday and Meltzer believe that the disappearance of Clovis spear points is more likely the result of a cultural choice rather than a population collapse. "There is no compelling data to indicate that North American Paleoindians had to cope with or were affected by a catastrophe, extraterrestrial or otherwise, in the terminal Pleistocene," they conclude.

History of Clovis people:

The Clovis culture is a prehistoric Native American culture that first appears in the archaeological record of North America around 13,500 years ago, at the end of the last ice age.

The culture is named for artifacts found near Clovis, New Mexico, where the first evidence of this tool complex was excavated in 1932. Earlier evidence included a mammoth skeleton with a spear-point in its ribs, found by a cowboy in 1926 near Folsom, New Mexico. Clovis sites have since been identified throughout all of the contiguous United States, as well as Mexico and Central America.

The Clovis people, also known as Paleo-Indians, are generally regarded as the the first human inhabitants of the New World, and ancestors of all the indigenous cultures of North and South America. However, this view has been recently contested by various archaeological finds which are claimed to be much older.

There are a number of controversial sites vying for the position of the earliest site in the region. The best evidence, however, suggests that a society of hunters and gatherers known as Clovis People were the first to settle in the Southwest, probably sometime before 9,500 B.C. The Clovis People were so named after the New Mexico town, site of the first discovery in 1932, near Clovis, N.M.

Since the mid 20th century, the standard theory among archaeologists has been that the Clovis people were the first inhabitants of the Americas. The primary support of the theory was that no solid evidence of pre-Clovis human inhabitation has been found. According to the standard accepted theory, the Clovis people crossed the Beringia land bridge over the Bering Strait from Siberia to Alaska during the period of lowered sea levels during the ice age, then made their way southward through an ice-free corridor east of the Rocky Mountains in present-day western Canada as the glaciers retreated.

The culture lasted for about a half a millennium, from about 11,200 to 10,900 years ago. People of the Clovis culture were successful, efficient big-game hunters and foragers. Judging from sites on the North American Great Plains, the Clovis people were skilled hunters of huge animals, especially Ice Age mammoths and mastodons.

It is generally accepted that Clovis people hunted mammoth: sites abound where Clovis points are found mixed in with mammoth remains. Whether they drove the mammoth to extinction via overhunting them – the so-called Pleistocene overkill hypothesis – is still an open, and controversial, question, keeping in mind that Archaeology is purely a theoretical endeavor.

A 2008 Google Earth search led to the discovery of Kamil crater, one of the best-preserved meteorite impact sites ever found. Earlier this year, a gritty, sand-blown expedition reached the site deep in the Egyptian desert to collect iron debris and determine the crater’s age and origins.

One day within the last several thousand years, a rare metallic meteorite travelling over 12 000 km/hour smashed into Earth’s surface near what is today the trackless border region between Egypt, Sudan and Libya. The impact of the 1.3 m, 10-tonne chunk of iron generated a fireball and plume that would have been visible over 1000 km away, and drilled a hole 16 m deep and 45 m wide into the rocky terrain.

Since then, the crater had sat undisturbed by Earth’s geologic and climatic processes, which usually render all but the very largest terrestrial impact craters invisible. It was also, as far as is recorded, unseen by humans.