Ancient Habitat for Life

By The Daily Galaxy

Wide view of sunset over Gusev Crater taken by NASA’s Spirit Rover in 2005. Both blue aureole and pink sky are seen. Because of the fine nature of Martian dust, it can scatter blue light coming from the Sun forward towards the observer.

The “Pot of Gold” rock outcrop inGusev Crater that Spirit Mars Rover examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic; hence, it was favorable as a habitat for life.”This is one of the most significant findings by the rovers,” said Steve Squyres of Cornell University a principal investigator for the Mars twin rovers, Spirit and Opportunity. “A substantial carbonate deposit in a Mars outcrop tells us that conditions that could have been quite favorable for life were present at one time in that place.”

Spirit inspected rock outcrops, striking a bonanza at one the NASA scientists named Comanche, along the rover’s route from the top of Husband Hill to the vicinity of the Home Plate plateau. Magnesium iron carbonate makes up about one-fourth of the measured volume in Comanche. That is a tenfold higher concentration than any previously identified for carbonate in a Martian rock.

“We used detective work combining results from three spectrometers to lock this down,” said Dick Morris, a member of a rover science team at NASA’s Johnson Space Center in Houston.”The instruments gave us multiple, interlocking ways of confirming the magnesium iron carbonate, with a good handle on how much there is.”

Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now.

 

Gusev_homeplate_fumerols_20081001_12_1024

 

Shown above is a National Geographic artist’s concept of how Gusev Crater might have appeared billions of years ago. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere. It is important to determine where most of the carbon dioxide went. Some theorize it departed to space.

Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.

Spirit’s Alpha Particle X-ray Spectrometer instrument detected a high concentration of light elements, a group including carbon and oxygen, that helped quantify the carbonate content.

Extremely Rare

By The Daily Galaxy

Oxygen is the third most common element in the universe, after hydrogen and helium, and in the 1970s astronomers predicted that molecular oxygen would be the third most common interstellar molecule, after molecular hydrogen (H2) and carbon monoxide (CO). In fact, astronomers have detected interstellar molecular oxygen in only two places: the Orion Nebula and the Rho Ophiuchi cloud (above). But even there the molecule is much rarer than theory predicts. For example, hydrogen molecules in the Orion Nebula outnumber oxygen molecules a million to one.

In 1998, NASA even launched a satellite that was supposed to find lots of molecular oxygen but never did—except when scientists, worried that the instrument was faulty, aimed it at Earth. Now, a ground-based experiment has revealed why this life-giving molecule is so rare in the cosmos: because oxygen atoms cling tightly tostardust, preventing them from joining together to form oxygen molecules. The discovery should yield insight into the chemical conditions that prevail when stars and planets arise.To explain the scarcity, astronomers recently proposed that oxygen atoms bind tightly to the dust particles that pepper space clouds. “Everybody knows that the binding energy of atomic oxygen is very important,” says Jiao He, an experimental astrophysicist at Syracuse University in New York. “But there was no experimental measurement of this parameter.”

Now, He and his colleagues have measured this number. The scientists heated two types of solids that make up interstellar dust grains—water ice and silicate—to see how readily oxygen atoms escape. As they recently reported in The Astrophysical Journal, the binding energy of oxygen is more than twice what scientists had calculated decades ago: 0.14 electron volts for water ice and 0.16 electron volts for silicate. That’s high enough to keep oxygen atoms stuck to stardust without the minimal heat of cold interstellar clouds dislodging them. The Orion Nebula may owe its small quantity of molecular oxygen to a shock wave that ripped atoms from the dust grains; Earth’s air abounds with oxygen because trees and other plants put it there.

“It’s a very valuable measurement,” says Gary Melnick, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who recently predicted a binding energy about that high. “It explains a lot.”

Oxygen atoms that float away from interstellar dust grains can join to make molecular oxygen. But when they stay stuck to the grains, hydrogen atoms combine with the oxygen to create water ice (H2O) instead. The water can then become part of asteroids, comets, and planets, setting the stage for the creation of life.

Paul Goldsmith, an astronomer at the Jet Propulsion Laboratory in Pasadena, California, spent more than a quarter-century seeking interstellar molecular oxygen before finally succeeding when Europe’s Herschel Space Observatory examined the Orion Nebula in 2010 and detected the elusive molecule. “I may have been misguided in spending so many years searching for it, but in a way, with this laboratory data and all the Herschel data, we can really say well, we do understand it now.”

The image at the top of the page shows Rho Ophiuchi, the bright triple star at the right of this image that is surrounded by the blue reflection nebula, IC 4604. At the bottom of the image, the blue star Sigma Scorpii is surrounded by an intense red hydrogen emission nebula. To the upper left of Sigma Scorpii is the large globular cluster M4. To the upper left is the brightest star in the image, the red supergiant Antares, which means “rival of Mars”.

If Antares were at the center of our solar system, its outer atmosphere would reach to the orbit of Jupiter. Antares’ strong stellar wind has created the relatively cool yellow nebula IC 4606 that appears to engulf the star. The field of view is punctuated by part of the the dark nebula B44, known as The Dark River, created from dust that is in front of the surrounding nebula.

Diamond Planet

By The Daily Galaxy

Astronomers have detected wildly changing temperatures on a super Earth – the first time any atmospheric variability has been observed on a rocky planet outside the solar system – and believe it could be due to huge amounts of volcanic activity, further adding to the mystery of what had been nicknamed the ‘diamond planet’.

“This is the first time we’ve seen such drastic changes in light emitted from an exoplanet, which is particularly remarkable for a super Earth,” said Dr Nikku Madhusudhan of Cambridge’s Institute of Astronomy, a co-author on the new study. “No signature of thermal emissions or surface activity has ever been detected for any other super Earth to date.”For the first time, researchers led by the University of Cambridge have detected atmospheric variability on a rocky planet outside the solar system, and observed a nearly threefold change in temperature over a two year period. Although the researchers are quick to point out that the cause of the variability is still under investigation, they believe the readings could be due to massive amounts of volcanic activity on the surface. The ability to peek into the atmospheres of rocky ‘super Earths’ and observe conditions on their surfaces marks an important milestone towards identifying habitable planets outside the solar system.

Using NASA’s Spitzer Space Telescope, the researchers observed thermal emissions coming from the planet, called 55 Cancri e – orbiting a sun-like star located 40 light years away in the Cancer constellation – and for the first time found rapidly changing conditions, with temperatures on the hot ‘day’ side of the planet swinging between 1000 and 2700 degrees Celsius.

 

4-astronomersf

 

Although the interpretations of the new data are still preliminary, the researchers believe the variability in temperature could be due to huge plumes of gas and dust which occasionally blanket the surface, which may be partially molten. The plumes could be caused by exceptionally high rates of volcanic activity, higher than what has been observed on Io, one of Jupiter’s moons and the most geologically active body in the solar system.

“We saw a 300 percent change in the signal coming from this planet, which is the first time we’ve seen such a huge level of variability in an exoplanet,” said Dr Brice-Olivier Demory of the University’s Cavendish Laboratory, lead author of the new study. “While we can’t be entirely sure, we think a likely explanation for this variability is large-scale surface activity, possibly volcanism, on the surface is spewing out massive volumes of gas and dust, which sometimes blanket the thermal emission from the planet so it is not seen from Earth.”

55 Cancri e is a ‘super Earth’: a rocky exoplanet about twice the size and eight times the mass of Earth. It is one of five planets orbiting a sun-like star in the Cancer constellation, and resides so close to its parent star that a year lasts just 18 hours. The planet is also tidally locked, meaning that it doesn’t rotate like the Earth does – instead there is a permanent ‘day’ side and a ‘night’ side. Since it is the nearest super Earth whose atmosphere can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets.

Most of the early research on exoplanets has been on gas giants similar to Jupiter and Saturn, since their enormous size makes them easier to find. In recent years, astronomers have been able to map the conditions on many of these gas giants, but it is much more difficult to do so for super Earths: exoplanets with masses between one and ten times the mass of Earth.

Earlier observations of 55 Cancri e pointed to an abundance of carbon, suggesting that the planet was composed of diamond. However, these new results have muddied those earlier observations considerably and opened up new questions. THe planet 40 light years from our solar system, is believed to be the first-ever discovered planet to consist largely of diamond.

“When we first identified this planet, the measurements supported a carbon-rich model,” said Madhusudhan, who along with Demory is a member of the Cambridge Exoplanet Research Centre. “But now we’re finding that those measurements are changing in time. The planet could still be carbon rich, but now we’re not so sure – earlier studies of this planet have even suggested that it could be a water world. The present variability is something we’ve never seen anywhere else, so there’s no robust conventional explanation. But that’s the fun in science – clues can come from unexpected quarters. The present observations open a new chapter in our ability to study the conditions on rocky exoplanets using current and upcoming large telescopes.”

Rippled Structure

By The Daily Galaxy

The Milky Way galaxy is at least 50 percent larger than is commonly estimated, according to new findings that reveal that the galactic disk is contoured into several concentric ripples. The research, conducted by an international team led by Rensselaer Polytechnic Institute Professor Heidi Jo Newberg, revisits astronomical data from the Sloan Digital Sky Survey which, in 2002, established the presence of a bulging ring of stars beyond the known plane of the Milky Way.

“In essence, what we found is that the disk of the Milky Way isn’t just a disk of stars in a flat plane—it’s corrugated,” said Heidi Newberg, professor of physics, applied physics, and astronomy in the Rensselaer School of Science. “As it radiates outward from the sun, we see at least four ripples in the disk of the Milky Way. While we can only look at part of the galaxy with this data, we assume that this pattern is going to be found throughout the disk.”

Importantly, the findings show that the features previously identified as rings are actually part of the galactic disk, extending the known width of the Milky Way from 100,000 light years across to 150,000 light years, said Yan Xu, a scientist at the National Astronomical Observatories of China (which is part of the Chinese Academy of Science in Beijing), former visiting scientist at Rensselaer, and lead author of the paper.

“Going into the research, astronomers had observed that the number of Milky Way stars diminishes rapidly about 50,000 light years from the center of the galaxy, and then a ring of stars appears at about 60,000 light years from the center,” said Xu. “What we see now is that this apparent ring is actually a ripple in the disk. And it may well be that there are more ripples further out which we have not yet seen.”

 

HNewbergApJRippledGalaxy4

 

 

The research, funded in part by the National Science Foundation and titled “Rings and Radial Waves in the Disk of the Milky Way,” was published today in the Astrophysical Journal. Newberg, Xu, and their collaborators used data from the Sloan Digital Sky Survey (SDSS) to show an oscillating asymmetry in the main sequence star counts on either side of the galactic plane, starting from the sun and looking outward from the galactic center. In other words, when we look outward from the sun, the mid-plane of the disk is perturbed up, then down, then up, and then down again.

“Extending our knowledge of our galaxy’s structure is fundamentally important,” said Glen Langston, NSF program manager. “The NSF is proud to support their effort to map the shape of our galaxy beyond previously unknown limits.”

The new research builds upon a 2002 finding in which Newberg established the existence of the “Monoceros Ring,” an “over-density” of stars at the outer edges of the galaxy that bulges above the galactic plane. At the time, Newberg noticed evidence of another over-density of stars, between the Monoceros Ring and the sun, but was unable to investigate further. With more data available from the SDSS, researchers recently returned to the mystery.

“I wanted to figure out what that other over-density was,” Newberg said. “These stars had previously been considered disk stars, but the stars don’t match the density distribution you would expect for disk stars, so I thought ‘well, maybe this could be another ring, or a highly disrupted dwarf galaxy.”

When they revisited the data, they found four anomalies: one north of the galactic plane at 2 kilo-parsecs (kpc) from the sun, one south of the plane at 4-6 kpc, a third to the north at 8-10 kpc, and evidence of a fourth to the south 12-16 kpc from the sun. The Monoceros Ring is associated with the third ripple. The researchers further found that the oscillations appear to line up with the locations of the galaxy’s spiral arms.

Newberg said the findings support other recent research, including a theoretical finding that a dwarf galaxy or dark matter lump passing through the Milky Way would produce a similar rippling effect. In fact, the ripples might ultimately be used to measure the lumpiness of dark matter in our galaxy.

“It’s very similar to what would happen if you throw a pebble into still water – the waves will radiate out from the point of impact,” said Newberg. “If a dwarf galaxy goes through the disk, it would gravitationally pull the disk up as it comes in, and pull the disk down as it goes through, and this will set up a wave pattern that propagates outward. If you view this in the context of other research that’s emerged in the past two to three years, you start to see a picture is forming.”

The research was funded by the NSF, as well as the Chinese National Science Foundation and the National Basic Research Program of China. Newberg currently researches the structure and evolution of our own galaxy, using stars as tracers of the galactic halo and disks. These stars in turn are used to trace the density distribution of dark matter in the Milky Way. She has been a participant of the Sloan Digital Sky Survey and is currently head of participants in LAMOST U.S., a partnership allowing U.S. astronomers to take part in a survey of more than 7 million stars by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope in China (LAMOST).

Mystery

By The Daily Galaxy

“We can see a completely new component of the center of our galaxy with NuSTAR’s images,” said Kerstin Perez of Columbia University in New York, lead author of a new report on the findings in the journal Nature. “We can’t definitively explain the X-ray signal yet — it’s a mystery. More work needs to be done.”

Peering into the heart of the Milky Way, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) has spotted a mysterious glow of high-energy X-rays that, according to scientists, could be the “howls” of dead stars as they feed on stellar companions.The center of our Milky Way galaxy is bustling with young and old stars, smaller black holes and other varieties of stellar corpses – all swarming around a supermassive black hole called Sagittarius A*. The image above reveals what cannot be seen in visible light: cooler stars (blue), heated dust (reddish hue), and Sgr A* supermassive black hole as bright white spot in the middle.

NuSTAR, launched into space in 2012, is the first telescope capable of capturing crisp images of this frenzied region in high-energy X-rays. The new images show a region around the supermassive black hole about 40 light-years across. Astronomers were surprised by the pictures, which reveal an unexpected haze of high-energy X-rays dominating the usual stellar activity.

“Almost anything that can emit X-rays is in the galactic center,” said Perez. “The area is crowded with low-energy X-ray sources, but their emission is very faint when you examine it at the energies that NuSTAR observes, so the new signal stands out.”

Astronomers have four potential theories to explain the baffling X-ray glow, three of which involve different classes of stellar corpses. When stars die, they don’t always go quietly into the night. Unlike stars like our sun, collapsed dead stars that belong to stellar pairs, or binaries, can siphon matter from their companions. This zombie-like “feeding” process differs depending on the nature of the normal star, but the result may be an eruption of X-rays.

 

High-energy-x-ray (1)

 

According to one theory, a type of stellar zombie called a pulsar could be at work. Pulsars are the collapsed remains of stars that exploded in supernova blasts. They can spin extremely fast and send out intense beams of radiation. As the pulsars spin, the beams sweep across the sky, sometimes intercepting the Earth, like lighthouse beacons.

“We may be witnessing the beacons of a hitherto hidden population of pulsars in the galactic center,” said co-author Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena, and principal investigator of NuSTAR. “This would mean there is something special about the environment in the very center of our galaxy.”

Other possible culprits include heavy-set stellar corpses called white dwarfs, which are the collapsed, burned-out remains of stars not massive enough to explode in supernovae. Our sun is such a star, and is destined to become a white dwarf in about five billion years. Because these white dwarfs are much denser than they were in their youth, they have stronger gravity and can produce higher-energy X-rays than normal. Another theory points to small black holes that slowly feed off their companion stars, radiating X-rays as material plummets down into their bottomless pits.

Alternatively, the source of the high-energy X-rays might not be stellar corpses at all, astronomers say, but rather a diffuse haze of charged particles, called cosmic rays. The cosmic rays might originate from the supermassive black hole at the center of the galaxy as it devours material. When the cosmic rays interact with surrounding, dense gas, they emit X-rays.

However, none of these theories match what is known from previous research, leaving the astronomers largely stumped.

“This new result just reminds us that the galactic center is a bizarre place,” said co-author Chuck Hailey of Columbia University. “In the same way people behave differently walking on the street instead of jammed on a crowded rush hour subway, stellar objects exhibit weird behavior when crammed in close quarters near the supermassive black hole.”

The team says more observations are planned. Until then, theorists will be busy exploring the above scenarios or coming up with new models to explain what could be giving off the puzzling high-energy X-ray glow.

“Every time that we build small telescopes like NuSTAR, which improve our view of the cosmos in a particular wavelength band, we can expect surprises like this,” said Paul Hertz, the astrophysics division director at NASA Headquarters in Washington.