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Does The Asteroid Belt Hold Key To The Building Blocks Of Planets

September 27, 2017 by  
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The asteroid belt may have started out empty, later becoming a “cosmic refugee camp” taking on leftovers of planetary formation from across the solar system, a new study finds.

The main asteroid belt, located between the orbits of Mars and Jupiter, makes up 0.05 percent the mass of Earth. The asteroids there can range greatly in mass, with the four largest ones — Ceres, Vesta, Pallas and Hygiea — holding more than half the belt’s mass.

To explain the dramatic range of sizes in the asteroid belt, previous models suggested that the primordial asteroid belt originally possessed a mass equal to at least that of Earth, and that its members had less disparity in mass. The gravitational pulls of the planets later helped whittle down this primordial belt, depleting asteroids of certain sizes more than others.  

However, these prior models of asteroid formation raised a question: how the belt could have lost more than 99.9 percent of its mass without losing all of it, said study lead author Sean Raymond, an astronomer at the University of Bordeaux in France.

“Our approach is the opposite. We asked the question, ‘Could the asteroid belt have been born empty?’,” Raymond told “The answer is yes, effortlessly.”

The scientists developed computer models of an empty primordial asteroid belt to see whether leftovers from planetary formation could explain the belt’s current composition. The inner belt is dominated by dry S-type, or silicaceous, asteroids, which appear to be made of silicate materials and nickel iron and account for about 17 percent of known asteroids. The outer belt is dominated by water-rich C-type, or carbonaceous, asteroids, which consist of clay and stony silicate rocks and make up more than 75 percent of known asteroids.

The researchers found that an empty primordial asteroid belt could explain the mass and compositions of the current members of the asteroid belt. This model suggests that this zone between Mars and Jupiter is a repository of planetary leftovers, “a refugee camp housing objects that were kicked out of their homes and left to brave interplanetary space, finally settling onto stable orbits in the asteroid belt,” Raymond told 

In this new model, the inner belt consists largely of rocky leftovers from the formation of the terrestrial planets — Earth, Mars, Venus and Mercury. In contrast, the outer belt is made up of remnants of the formation of the gas giant planets, such as Jupiter and Saturn.

“In terms of composition, Jupiter and Saturn grew in a region that was much colder than where the rocky planets grew,” Raymond said. “Being colder, their cores could incorporate ice and other volatiles. The C-types are about 10 percent water, whereas the S-types are much drier, having started off in the much hotter terrestrial planet zone.”

These findings suggest that the asteroid belt “is a treasure trove — it must contain relics of the building blocks of all the planets,” Raymond said. “There must be pieces of terrestrial building blocks out in the asteroid belt, as well as leftovers from building the giant planets’ cores.”

Future research can further test how well the various models of asteroid-belt formation match reality. Raymond hopes the team’s new concept “will help keep people’s minds open to potentially drastically different origins stories for the solar system, and for extra-solar planets, too.”

Raymond and his colleague Andre Izidoro at the University of Bordeaux detailed their findings online Sept. 13 in the journal Science Advances.


Astronomer Solved Nebula Mystery

May 10, 2017 by  
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It turns out the iconic Ring Nebula was actually discovered by 18th century comet-hunter Charles Messier, a new study shows. 

Until now, history has credited the discovery of this well-known nebula, also known as Messier 57 or NGC 6720, to 18th-century French astronomer Antoine Darquier. However, astronomers Donald Olson, a physics professor at Texas State University, and Giovanni Maria Caglieris of Italy re-evaluated the observation notes taken by Messier and Darquier, revealing a small discrepancy 238 years later. 

The researchers found that Messier’s observation notes from Jan. 31, 1779, said that he spotted a “small patch of light” near the path of Bode’s comet, according to a statement from Texas State.

“In comparing the comet to β Lyrae on this morning, I observed in the telescope a small patch of light … this patch of light was round and was located between γ & β Lyrae,” Messier wrote in his notes, according to the statement. This patch of light was the same nebula Darquier later observed in February 1779. 

Although Messier was the first to detect the Ring Nebula, history has credited Darquier as the founder, since Messier’s Catalogue states, “Darquier in Toulouse discovered this nebula, while observing the same comet,” in the description of M57, according to the statement. This description is what caused the discrepancy over who first discovered the Ring Nebula, researchers said. 

“The confusion stems from language creep and lack of context,” Texas State representatives said in the statement. “Messier’s statement appears to be an endorsement of Darquier being the first person to spot the Ring Nebula. In the 18th century, however, ‘discover’ more commonly meant to simply discern something, a use that is almost obsolete today.” 

“Alternatively, Messier could have used ‘discover’ to qualify Darquier’s observations as a later, independent discovery,” they added.

Darquier’s observation notes, along with a letter sent to Messier in September 1779, confirm that he was not the first to observe and record M57, as he wrote to Messier saying “he did not begin to observe the sky near the path of Bode’s comet until the second week of February,” according to the statement. Darquier began observing the region between stars β & γ Lyrae only after reading about Messier’s comet observations, the statement said. 

The Ring Nebula is among Messier’s list of 110 deep-sky objects, which at the time was used to provide a list of objects for 18th century comet hunters to avoid. This nebula is located just over 2,000 light-years from Earth in the Lyra constellation and measures 1 light-year (about 6 trillion miles, or 10 trillion kilometers) across. 

The researchers were able to determine who exactly discovered the iconic Ring Nebula using historical documents that only recently became widely available online. Their findings were published in the June 2017 issue of Sky & Telescope magazine.


Astronomers Find Black Hole In The Early Universe

July 19, 2016 by  
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A bright galaxy in the early universe likely contains a mysterious kind of black hole that had previously existed only in theory, a new study suggests.

This probable “direct-collapse” black hole may help explain how supermassive black holes — the light-gobbling behemoths that lurk at the hearts of most, if not all, galaxies — got their start, researchers said.

“The special aspect of this [direct-collapse] process is that it leads to the formation of a very massive ‘seed’ black hole in one go,” study co-author Avi Loeb, chair of the astronomy department at Harvard University, told via email. “It is difficult to make such a giant black hole over such a short time if they start from low-mass seeds

When a massive star reaches the end of its lifetime, it can collapse inward on itself to form a black hole. These dense objects then grow by feeding on surrounding gas and dust, but the process can take time.

Indeed, it probably takes quite a while for such a small seed to grow into a supermassive black hole, which can contain billions of times more mass than the sun, scientists say. This poses a puzzle: Where, then, did the supermassive black holes in the early universe come from?

Some of these monsters existed only 750 million years after the Big Bang that created the universe, Loeb said. (Scientists know this because they have spotted quasars — incredibly bright galactic cores powered by supermassive black holes — of this vintage.)

“It is difficult to make such a giant black hole over such a short time if they start from low-mass seeds,” Loeb said.

In 2003, Loeb and Volker Bromm of the University of Texas at Austin (UT Austin) — also a co-author of the new study — theorized that clouds of dust and gas in the early universe were so hot that they failed to fragment into multiple clumps of thousands of stars. Instead, such clouds likely created just a single massive star at the center, roughly 1 million times larger than “normal” stars, Loeb said.

Such gigantic stars would quickly consume all of the nearby gas and dust. Overeating would lead to a rapid demise; these stars would last only a few million years before collapsing into midsized black holes that could continue to feed, ultimately growing into the giants that lie at the centers of galaxies.

To stay so superhot, the gas at the heart of this process would need to be almost purely hydrogen and helium, without “heavier” elements to help cool it down. Since heavy elements are produced in the hearts of stars and then released during a supernova, such “direct-collapse black holes” could only form in the early universe, the researchers said. [The Universe: Big Bang to Now in 10 Easy Steps]

But there hadn’t been much evidence for this idea — until now.

From prediction to reality

Last year, astronomers spotted a strange signal from a galaxy known as CR7, one of the most luminous objects in the early universe. Although the galaxy showed signs of temperatures greater than 180,000 degrees Fahrenheit (100,000 degrees Celsius) and signatures of helium atoms gaining and losing electrons — a process known as ionization — there were no signs of other elements.

“That makes the galaxy that we have discovered really unique, and ticks all the boxes for predictions for both first-generation stars or a direct-collapse black hole,” David Sobral, an astrophysicist at the University of Lisbon in Portugal, told

Sobral led the team of astronomers that identified irregularities in CR7 last year and other similar galaxiesmore recently. In their paper, they argued that, while CR7 could contain a direct-collapse black hole, the unusual signal favored a cluster of the universe’s first stars.

“Regardless, the actual material — pristine gas — to make either first-generation stars or a direct-collapse black hole is essentially the same, and it is extremely exciting to finally start asking actual physical questions about the nature of the very early galaxies,” Sobral said. “This goes way beyond the traditional approach of simply counting distant galaxies.”



Astronomers Catch Slow Motion Black Hole

July 15, 2016 by  
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After zooming in on a star being consumed by a supermassive black hole, scientists have discovered that a jet emanating from the system is moving much more slowly than expected. The team suggests that instead of wiggling around, the jet stays superstable because of the way the gas interacts with the surrounding environment.

The new research shows that when the gas from the jet hits the interstellar medium (the dust, gas and other small particles in between stars), the jet’s gas decelerates quickly. It’s a new insight into how these jets behave in space, the team said.

“We were able to measure the jet’s position to a precision of 10 microarcseconds … These are some of the sharpest measurements ever made by [a] radio telescope,” lead author Jun Yang, of the Onsala Space Observatory and the Chalmers University of Technology in Sweden, said in a statement

The jet comes from a source known as Swift J1644+57, a black hole swallowing a star 3.9 billion light-years from Earth that was discovered in 2011 with NASA’s Swift space telescope.

When a supermassive black hole consumes a star, roughly half of the gas goes toward the black hole and creates a disk around it. Some of this material is then ejected into jets — narrow beams of particles that fly out at nearly the speed of light. The jets shine brightly in radio wavelengths, while the disk of gas is bright in many different wavelengths of light.

The researchers scrutinized Swift J1644+57 using the European Very Large Baseline Interferometry Network, a telescope network that spans multiple continents. Interferometry involves linking two or more telescopes so they act as one receiver. This allows for more sensitive measurements than would be possible with a single telescope. In the case of the European network, the interferometer is the size of Earth, allowing for extremely precise measurements.

For three years, the researchers examined the jet for motion close to the speed of light, called superluminal motion, which happens when the jet moves. The telescope network was sensitive enough to see this motion, but none was detected — the jet was strangely slow.

“Earlier studies suggest we may be seeing the jet at a very small angle,” team member Zsolt Paragi, head of user support at the Joint Institute for VLBI ERIC in the Netherlands, said in the same statement. “That could contribute to the apparent compactness.”

The results were presented Friday (July 8) at the European Week of Astronomy and Space Science in Athens, Greece, and they were also published in May in the journal Monthly Notices of the Royal Astronomical Society.



Astronomers Go Deep Into Nebulas

July 11, 2016 by  
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Glittering, glamorous, graceful. The latest red-carpet fashion statement? No, of course not. I’m talking about nebulas, the wispy clouds of gas and dust scattered through each galaxy. Earthly fabrics can’t come close to the heavenly, tenuous beauty of these objects.

Peppered throughout the Milky Way, they provide amateur astronomers an eyeful of delight and give professional astronomers plenty to ponder. We see these objects in all sorts of shapes, sizes, colors and configurations, from almost-perfect spheres and shells to dazzlingly complex helices to tangled wrecks. But where exactly do they come from? And, perhaps more importantly, where are they going?

To get a good look at nebulas, let’s first look at the stars. Tiny, compact and dense — at least, astronomically speaking — a star is pretty much the opposite of a nebula. The power of a star comes from nuclear fusion, which occurs because of the intense pressures shoving elements together way past their personal comfort zones. That fusion creates heavier elements and a tiny bit of leftover energy, which is enough to maintain the star for millions (in the case of huge stars) to trillions (in the case of teensy-tiny-barely-above-brown-dwarf stars) of years. [50 Fabulous Deep-Space Nebula Photos]

No matter how long they last, stars are finite creatures. Thus, they must have come from somewhere and will end up going to somewhere else. Presumably, they didn’t start life as tiny, dense balls and they won’t end life the same way either. So where do stars come from, and where are they going?

Based on this article’s topic, you can probably guess what the answer is: nebulas. Stars come from nebulas and end up turning into nebulas. Likewise, nebulas can generally be classified into two categories: about-to-be-stars and used-to-be-stars.

About to be stars

One could argue that the natural state of matter is clouds of stuff. In fact, I’m about to make just that argument. Stars depend on a specific process, nuclear fusion, to survive, and once that process ends, they quit being stars. The objects known as stars are altogether temporary. But a cloud of gas and dust? It can just hang out being a cloud of gas and dust for as long as it wants. If no forces nudge it one way or the other, it’s perfectly happy just being what it is.

That will change only when a nebula does get nudged, say by a chance gravitational interaction with a neighbor, or by being too close to a nearby supernova (you gotta hate it when that happens). Once nudged, the nebula can become unstable, its natural self-gravitational pull overwhelming its equally natural gas pressure (an event marked by reaching a threshold dubbed the “Jeans instability”). Very quickly, pieces of the nebula branch and break off, smashing down in on themselves to get the fusion party started and make some stars.

The smashed-down bits turn into “dark nebulas” (hint: they’re kind of black) as their high densities shroud the light coming from any newly forming stars. Fortunately, radio and infrared radiation penetrate even the densest of these nebulas, allowing astronomers to peer into these clouds’ stellar wombs.

A typical cloud of gas, once unsettled, might make hundreds or even thousands of stars in a single batch. The largest and brightest of those stars will spew out tons of hot, heavy, high-energy radiation, exciting the molecules in the remaining nebula and causing it to glow rosy red.

Called “emission nebulas” — because their material is, well, emitting light — they won’t last long. Those big, bright stars spewing radiation are sure to go supernova, ripping apart the already-tenuous veils of dust and gas and spreading this material so thin even the keenest observers are unable to distinguish it from the general spacey background.

And that brings us to where nebulas come from in the first place. The answer, of course, is stars. When stars die, it’s not pretty — or it’s very pretty, depending on your point of view. [Supernova Photos: Great Images of Star Explosions]

The largest stars go off in spectacular fashion, unleashing almost all their unspent energy in a blast that can outshine entire galaxies (to be fair, the blast will last only a few days or weeks, while galaxies keep on shining for trillions of years). That blast naturally carries a lot of “stuff” far from the original star; basically, the whole star is turned inside out and goes from point-like to cloud-like in one fantastic event.

The ejected material rides the shockwaves at a healthy fraction of the speed of light, so it doesn’t take long for a decent-size nebula to form. Even supernovas that occurred only hundreds of years ago (which in astronomical terms might as well be yesterday) have already become beautiful artistic displays. One such example is the Crab nebula, which is itself lit by the intense radiation still pouring out of the hot, left-over core of its dead star.

Stars like Earth’s sun don’t go off as intensely, but that doesn’t mean they don’t get to create their own masterpieces. Near the ends of these stars’ lives, the switchover from hydrogen- to helium-based fusion in the cores leads to complex interplay in the stellar interiors. This causes the outmost layers to swell, expand and eventually slough off. The erratic nature of the star during this time pushes the outward-moving gas in weird directions.

The result: planetary nebulas, which unfortunately have absolutely nothing to do with planets. They come in a wild variety of shapes and patterns. They don’t last long. Like their supernova cousins, they’re lit by the remaining core of the star, and once that peters out after a few thousand years, the fireworks show is over.

But since stars like the Earth’s sun are so common, this galaxy continues to produce new planetary nebulas, decorating the galactic disk like Christmas ornaments.

So that’s it: Nebulas turn into stars, and stars turn into nebulas. It’s a cycle that has persisted for over 13 billion years, starting when the first nebula scrunched down into a star. And it will continue to last for trillions more. Eventually, though, the nebulas will win: You need to pack enough stuff into a small enough space to make a star, and once you run out of opportunities you run out of stars, and the universe will return to its natural, long-term state: a bunch of gas and dust floating around.




Astronomers Get A Picture of The Milky Way’s Galactic Neighborhood

September 8, 2014 by  
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A new cosmic map is giving scientists an unprecedented look at the boundaries for the giant supercluster that is home to Earth’s own Milky Way galaxy and many others. Scientists even have a name for the colossal galactic group: Laniakea, Hawaiian for “immeasurable heaven.”

The scientists responsible for the new 3D map suggest that the newfound Laniakea supercluster of galaxies may even be part of a still-larger structure they have not fully defined yet.

“We live in something called ‘the cosmic web,’ where galaxies are connected in tendrils separated by giant voids,” said lead study author Brent Tully, an astronomer at the University of Hawaii at Honolulu.

Galactic structures in space

Galaxies are not spread randomly throughout the universe. Instead, they clump in groups, such as the one Earth is in, the Local Group, which contains dozens of galaxies. In turn, these groups are part of massive clusters made up of hundreds of galaxies, all interconnected in a web of filaments in which galaxies are strung like pearls. The colossalstructures known as superclusters form at the intersections of filaments.

The giant structures making up the universe often have unclear boundaries. To better define these structures, astronomers examined Cosmicflows-2, the largest-ever catalog of the motions of galaxies, reasoning that each galaxy belongs to the structure whose gravity is making it flow toward.

“We have a new way of defining large-scale structures from the velocities of galaxies rather than just  looking at their distribution in the sky,” Tully said.

Laniakea, our home in the universe

The new 3D map developed by Tully and colleagues shows that the Milky Way galaxy resides in the outskirts of the Laniakea Supercluster, which is about 520 million light-years wide. The supercluster is made up of about 100,000 galaxies with a total mass about 100 million billion times that of the sun.

The name Laniakea was suggested by Nawa’a Napoleon, who teaches Hawaiian language at Kapiolani Community College in Hawaii. The name is meant to honor Polynesian navigators who used their knowledge of the heavens to make long voyages across the immensity of the Pacific Ocean.

“We live in the Local Group, which is part of the Local Sheet next to the Local Void — we wanted to come up with something a little more exciting than ‘Local,'” Tully told

This supercluster also includes the Virgo cluster and Norma-Hydra-Centaurus, otherwise known as the Great Attractor. These new findings help clear up the role of the Great Attractor, which is a problem that has kept astronomers busy for 30 years. Within the Laniakea Supercluster, the motions of galaxies are directed inward, as water flows in descending paths down a valley, and the Great Attractor acts like a large flat-bottomed gravitational valley with a sphere of attraction that extends across the Laniakea Supercluster.

Tully noted Laniakea could be part of an even larger structure.

“We probably need to measure to another factor of three in distance to explain our local motion,” Tully said. “We might find that we have to come up with another name for something larger than we’re a part of — we’re entertaining that as a real possibility.”


Astronomers Develop New Theories On The Evolution Of Our Solar System

August 12, 2014 by  
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Astronomers have traced the growth of Earth’s solar system back to its cosmic womb, before the sun and planets were born.

The solar system coalesced from a huge cloud of dust and gas that was isolated from the rest of the Milky Way galaxy for up to 30 million years before the sun’s birth nearly 4.6 billion years ago, a new study published online today (Aug. 7) in the journal Science suggests. This cloud spawned perhaps tens of thousands of other stars as well, researchers said.

If further work confirms these findings, “we will have the proof that planetary systems can survive very well early interactions with many stellar siblings,” said lead author Maria Lugaro, of Monash University in Australia.

“In general, becoming more intimate with the stellar nursery where the sun was born can help us [set] the sun within the context of the other billions of stars that are born in our galaxy, and the solar system within the context of the large family of extrasolar planetary systems that are currently being discovered,” Lugaro told via email.

A star is born

Radiometric dating of meteorites has given scientists a precise age for the solar system — 4.57 billion years, give or take a few hundred thousand years. (The sun formed first, and the planets then coalesced from the disk of leftover material orbiting our star.)

But Lugaro and her colleagues wanted to go back even further in time, to better understand how and when the solar system started taking shape.

This can be done by estimating the isotope abundances of certain radioactive elements known to be present throughout the Milky Way when the solar system was forming, and then comparing those abundances to the ones seen in ancient meteorites. (Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei.)

Because radioactive materials decay from one isotope to another at precise rates, this information allows researchers to determine when the cloud that formed the solar system segregated out from the greater galaxy — that is, when it ceased absorbing newly produced material from the interstellar medium.

Estimating radioisotope abudances throughout the Milky Way long ago is a tall order and involves complex computer modeling of how stars evolve, generate heavy elements in their interiors and eventually eject these materials into space, Lugaro said.

But she and her team made a key breakthrough, coming up with a better understanding of the nuclear structure of one radioisotope known as hafnium-181. This advance led the researchers to a much improved picture of how hafnium-182 — a different isotope whose abundances in the early solar system are well known — is created inside stars.

“I think our main advantage has been to be a team of experts in different fields: stellar astrophysics, nuclear physics, and meteoritic and planetary science so we have managed to exchange information effectively,” Lugaro said.

A long-lasting stellar nursery

The team’s calculations suggest that the solar system’s raw materials were isolated for a long time before the sun formed — perhaps as long as 30 million years.

“Considering that it took less than 100 million years for the terrestrial planets to form, this incubation time seems astonishingly long,” Martin Bizzarro, of the University of Copenhagen in Denmark, wrote in an accompanying “Perspectives” piece in the same issue of Science.

Bizzarro, like Lugaro, thinks the new results could have application far beyond our neck of the cosmic woods.

“With the anticipated discovery of Earthlike planets in habitable zones, the development of a unified model for the formation and evolution of our solar system is timely,” Bizarro wrote. “The study of Lugaro et al. nicely illustrates that the integration of astrophysics, astronomy and cosmochemistry is the quickest route toward this challenging goal.”

The researchers plan to investigate other heavy radioactive elements to confirm and refine their timing estimates, Lugaro said.

The abstract of the new study can be found here, while this link leads to the abstract of Bizzarro’s companion piece.


Can A New Test Prove If Voyager Is In Interstellar Space?

July 29, 2014 by  
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A new test could determine once and for all whether NASA’s Voyager 1 probe has indeed entered interstellar space, some researchers say.

While mission team members declared last year that Voyager 1 reached interstellar space in August 2012, not all scientists are sold. Two researchers working with Voyager 1 have drawn up a test to show whether the spacecraft is inside or outside of the heliosphere — the bubble of solar particles and magnetic fields that the sun puffs around itself.

The scientists who came up with the test predict that Voyager 1 will cross the current sheet — a huge surface within the heliosphere — at some point within the next one to two years. When that happens, Voyager team members should see a reversal in the magnetic field surrounding the probe, proving that it is still within the heliosphere. If this change doesn’t occur in the next two years or so, then Voyager is almost certainly already in interstellar space, researchers said.

“The proof is in the pudding,” George Gloeckler of the University of Michigan, lead author of the new study detailing the test, said in a statement. “This controversy will continue until it is resolved by measurements.”

Scientists have recently made measurements that seem to bolster the belief that Voyager is in interstellar space. Researchers measuring data from a solar eruption that shook the particles around Voyager 1 found that the density of the probe’s surroundings was much higher than earlier measurements, when it was thought to be inside the heliosphere.

Because of this difference, some team members have come to the conclusion that Voyager 1 is, in fact, outside of the heliosphere. (While particle densities are higher in the inner solar system than they are in interstellar space, this is not the case at the extreme outer reaches of the heliosphere, scientists said.)

Voyager 1 has measured cosmic rays and other signs indicating that it may have passed into interstellar space, it still hasn’t detected the predicted magnetic field change, Gloeckler pointed out. He expects that the polarity reversal may happen in 2015.

“If that happens, I think if anyone still believes Voyager 1 is in the interstellar medium, they will really have something to explain,” Gloeckler said in the statement. “It is a signature that can’t be missed.”

The developers of the new test think Voyager 1 is moving faster than the solar wind, meaning that it will cross over parts of the current sheet where the magnetic field reversal will happen. This data could prove that the probe is inside the heliosphere, according to a statement from the University of Michigan and the American Geophysical Union.

Other scientists working with Voyager also welcome the test.

“It is the nature of the scientific process that alternative theories are developed in order to account for new observations,” Ed Stone, NASA’s Voyager project scientist, said in a statement. “This paper differs from other models of the solar wind and the heliosphere and is among the new models that the Voyager team will be studying as more data are acquired by Voyager.”

Voyager 1 and its twin Voyager 2 launched to space in 1977 to study the planets of the solar system. Voyager 2 is still in communication with Earth and is expected to continue on, potentially entering into interstellar space a few years from now.

The new test, detailed in a study by Gloeckler and his co-author Len Fisk of the University of Michigan, has been accepted for publication in the journal Geophysical Research Letters.



Voyager 1 Goes Intersellar

July 11, 2014 by  
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New data collected by NASA’s Voyager 1 spacecraft have helped scientists confirm that the far-flung probe is indeed cruising through interstellar space, the researchers say.

Voyager 1 made headlines around the world last year when mission scientists announced that the probe had apparently left the heliosphere — the huge bubble of charged particles and magnetic fields surrounding the sun — in August 2012.

They came to this conclusion after analyzing measurements Voyager 1 made in the wake of a powerful solar eruption known as a coronal mass ejection, or CME. The shock wave from this CME caused the particles around Voyager 1 to vibrate substantially, allowing mission scientists to calculate the density of the probe’s surroundings (because denser plasma oscillates faster.) [Photo Timeline: Voyager 1’s Trek to Interstellar Space]

This density was much higher than that observed in the outer layers of the heliosphere, allowing team members to conclude that Voyager 1 had entered a new cosmic realm. (Interstellar space is emptier than areas near Earth, but the solar system thins out dramatically near the heliosphere’s edge.)

The CME in question erupted in March 2012, and its shock wave reached Voyager 1 in April 2013. After these data came in, the team dug up another, much smaller CME-shock event from late 2012 that had initially gone unnoticed. By combining these separate measurements with knowledge of Voyager 1’s cruising speed, the researchers were able to trace the probe’s entry into interstellar space to August 2012.

And now mission scientists have confirmation, in the form of data from a third CME shock, which Voyager 1 observed in March of this year, NASA officials announced Monday (July 7).

“We’re excited to analyze these new data,” Don Gurnett of the University of Iowa, the principal investigator of Voyager 1’s plasma wave instrument, said in a statement. “So far, we can say that it confirms we are in interstellar space.”

Interstellar space begins where the heliosphere ends. But by some measures, Voyager 1 remains inside the solar system, which is surrounded by a shell of comets known as the Oort Cloud.

While it’s unclear exactly how far away from Earth the Oort Cloud lies, Voyager 1 won’t get there for quite a while. NASA scientists have estimated that Voyager 1 will emerge from the Oort Cloud in 14,000 to 28,000 years.

The craft launched in September 1977, about two weeks after its twin, Voyager 2. The probes embarked upon a “grand tour” of the outer solar system, giving the world some its first good looks at Jupiter, Saturn, Uranus, Neptune and the moons of these planets.

Like Voyager 1, Voyager 2 is still active and operational. It took a different route through the solar system and is expected to follow its twin into interstellar space a few years from now.


NASA’s Voyager Probes Still Ticking Away

June 3, 2014 by  
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NASA’s Voyager 1 and Voyager 2 spacecraft are still going strong after nearly 37 years in space.

“Both spacecraft are still operating, still very healthy. I guess as healthy as we are at the table right now,” Suzanne Dodd, the Voyager project manager at NASA’s Jet Propulsion Laboratory (JPL) said, drawing a big laugh from the audience at the SpaceFest VI conference in Pasadena, California, on May 11.

Dodd was fresh out of college in 1985 when JPL recruited her as it geared up for Voyager 2’s upcoming encounter with Uranus. Nearly 30 years later, she is project manager of the Voyager Interstellar Mission under which the two spacecraft continue to explore the vast expanse of space beyond the planets.

Voyagers of the solar system

Dodd was actually the youngster on the Voyager reunion panel. She was joined by Voyager Project Scientist Ed Stone and retired Voyager Mission Design Manager Charley Kohlhase, who were both on the project when it was in the planning stages in the early 1970s.

When the Voyagers were launched in 1977, NASA expected them to last four or five years, long enough to get them through close encounters with Jupiter and Saturn. But, they just kept going and going.

Voyager 2 went on to flybys of Uranus in 1986 and Neptune in 1989. It is now about 105 astronomical units from Earth. (One AU is the average distance between the Earth and sun, about 92 million miles.) Voyager 1, which flew out of the plane of the solar system after its 1980 flyby of Saturn, is in interstellar space at 127 AUs.

Stone and Kohlhase recalled their astonishment when an image showing two exploding volcanoes on Jupiter’s moon Io came into JPL late on a Friday afternoon in March 1979. The plumes went hundreds of miles above the surface, and the fallout covered an area the size of France.

“We had what I call a terracentric view, which was based on understanding Earth,” Stone said. “Before Voyager, the only known active volcanoes in the solar system were on Earth. Then we flew by Io, a little moon about the size of our moon, with 10 times the volcanic activity of Earth. And suddenly our terracentric extrapolation just was falling way short, and that was happening time after time after time.

“It was an incredible time where every day there were so many things we were discovering that we just moved on to the next one,” Stone added. “If we didn’t understand what we were seeing right away, we said, all right, let’s wait ’til tomorrow to see what else we get.”

A groundbreaking mission

The Voyager missions also forever changed the way spacecraft were built and operated.

“The key thing about Voyager that was a revolution was it was a totally computer-controlled spacecraft that flies itself and has fault protection on board so that if something goes wrong, it takes action,” he said. “Because now it takes us 17 and a half hours to get a command up there, and it’s 17 and a half hours before we know if anything has happened.” Before the spacecraft were launched, Kohlhase had the job of sorting through some 10,000 trajectories for projected launch windows in 1976 through 1978. He used computers to determine which ones would allow the spacecraft to make the best approaches to Jupiter, Saturn and their moons. Kohlhase and the scientists settled on 110 trajectories and ultimately used two of them.

Dodd says the Voyager mission continues to throw up challenges today. The spacecraft have 20-watt transmitters – the equivalent of a refrigerator light bulb – and signals are only 1 billionth of a billionth of a watt in strength by the time they reach Earth. JPL uses the powerful antennas of the Deep Space Network to communicate with the distant spacecraft.

“The engineering challenges are extremely unique to Voyager,” Dodd said. “You’re operating instruments below temperatures that we can’t even measure. Challenges of finding out if we turn on a component that’s next to a hydrazine line, would that hydrazine line freeze or not. We don’t know.

“Another unique challenge to it is that the engineers who built this are retired, some have passed away, you need to get people like Charley out of retirement to come and talk to us,” Dodd added. “It’s a challenge engineering-wise, it’s a challenge from a knowledge standpoint of what people know. And that’s what makes this project fun.”

The Voyagers still have a lot of life left in them even after nearly four decades on space.

“Looking forward, we expect to get 10 more years of scientific data out of the Voyager spacecraft,” Dodd said. “We basically turned off everything we can turn off to save power. Backup heaters are off, backup systems are off. We’re having some serious discussions about how to move forward, because we’re almost down to the scientific instruments now.”

After that, the spacecraft could continue on for another five to seven years sending engineering signals to Earth. Engineers are already in discussions with the Deep Space Network about what experiments could be conducted with those signals before the spacecraft fall silent.



Astronomers Find Neptune’s Lost Moon

October 11, 2013 by  
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A tiny, mysterious moon orbiting Neptune has been spotted for the first time in more than 20 years.

By analyzing photos taken by the Hubble Space Telescope, scientists at the SETI Institute in Mountain View, Calif., have caught sight of Naiad, the innermost of Neptune’s moons. The 62-mile-wide (100 kilometers) moon has remained unseen since the cameras on NASA’s Voyager 2 spacecraft discovered it in 1989.

Scientists recently tracked Naiad across a series of eight archival images taken by Hubble in December 2004 after using a different technique to help cancel out Neptune’s glare. Neptune is 2 million times brighter than Naiad, so Naiad is difficult to see from Earth, SETI officials said. [See photos of Neptune, the mysterious blue planet]

“Naiad has been an elusive target ever since Voyager left the Neptune system,” SETI scientist Mark Showalter said in a statement. Showalter announced the new findings today (Oct. 8) during a session at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences, held in Denver.

Now that scientists have spotted the small moon again, there are other mysteries to be solved. Naiad seems to have drifted off course: The new observations show that the moon is now ahead of its predicted path in orbit around Neptune, SETI officials said.

Scientists expect that the new trajectory could have something to do with Naiad’s interaction with one of Neptune’s other moons that caused the innermost moon to speed up in its orbit. The exact cause of the moon’s new orbit won’t be known until researchers collect more data.

The images taken in 2004 also reveal something about the ring arcs surrounding Neptune. Voyager observed four arcs during its flyby of the system, but the newly processed images show that the two leading arcs are absent, while the two trailing arcs haven’t changed, SETI officials said. Scientists aren’t sure what is causing this change, but the arcs have been shifting since their discovery.

“It is always exciting to find new results in old data,” Showalter said. “We keep discovering new ways to push the limit of what information can be gleaned from Hubble’s vast collection of planetary images.”

The same images taken by Hubble also helped Showalter and his colleagues find another small moon orbiting Neptune — a discovery they announced in July. The newfound moon, called S/2004 N 1, is much smaller than Naiad, at 12 miles (20 km) across, but it was easier to spot in the images because its orbit takes it farther from Neptune than Naiad’s orbit takes it from the planet, SETI officials said.

S/2004 N 1 evaded Voyager 2’s cameras in 1989 because of its tiny size. During its flyby, Voyager revealed six previously unknown moons circling Neptune. Scientists have now discovered 14 moons in orbit around the blue planet.


Will Voyager I Send Any News From Interstellar Space?

September 17, 2013 by  
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NASA’s Voyager 1 probe won’t rest on its laurels after becoming the first manmade object ever to reach interstellar space.

Voyager 1 arrived in interstellar space in August 2012 after 35 years of spaceflight, researchers announced Thursday (Sept. 12). While this milestone is momentous enough in its own right, it also opens up a new science campaign whose potential already has scientists salivating.

“For the first time, we’re actually going to be able to put our hands in the interstellar medium and ask what it does and what characteristics it possesses,” Gary Zank, director of the Center for Space Plasma and Aeronomic Research at the University of Alabama in Huntsville, told reporters Thursday. “It’s a tremendous opportunity.”

Into the unknown

Voyager 1 and its twin, Voyager 2, launched a few weeks apart in 1977 to study Jupiter, Saturn, Uranus and Neptune, as well as the moons of these outer planets.

The probes completed this historic “grand tour” in 1989, then embarked on a quest to study the outer reaches of the solar system and beyond.

Voyager 1 finally popped free of the heliosphere — the huge bubble of charged particles and magnetic fields that the sun puffs out around itself — on or around Aug. 25, 2012, becoming humanity’s first envoy to the vast realms between the stars.

“This is truly a remarkable achievement,” Zank said. “We’ve exited the material that’s created by the sun, and we’re in a truly alien environment. The material in which Voyager finds itself is not created by the sun; it’s created, in fact, by our neighboring stars, supernova remnants and so forth.”

Many discoveries to come

This new vantage point should yield big scientific dividends, Zank added. For example, Voyager 1 should now help researchers get a much better look at galactic cosmic rays, charged particles accelerated to incredible speeds by far-off supernova explosions.

Observations of galactic cosmic rays made from within the heliosphere are not ideal, since the solar wind tends to affect these high-energy particles substantially.

“Being outside the heliosphere allows us an opportunity to, in a sense, look at the undiluted galactic cosmic ray spectrum,” Zank said. “That will tell us a great deal more about the interstellar medium at very distant locations. It’ll tell us about how the galactic cosmic rays propagate through this very complicated interstellar medium.”

Voyager 1 should also be able to shed light on the nature of the instellar medium, and how material from other stars flows around the heliosphere, researchers said.

“Now we will be able to understand and measure and observe that interaction, which is a very important part of how the sun interacts with what’s around it,” Voyager chief scientist Ed Stone, a physicist at the California Institute of Technology in Pasadena, told

In short, reaching interstellar space does not mark the end of the road for Voyager 1, which should be able to continue gathering data for a dozen more years as long as nothing too important breaks down. (The probe’s dwindling power supply will force the mission team to turn off the first instrument in 2020, and all of Voyager 1’s science gear will be shut down by 2025.)

“This mission is not over,” said Voyager project manager Suzanne Dodd, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Many, many more discoveries are out there, yet to come.”


Astronomers Find Mini-Neptune In Cluster

June 28, 2013 by  
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Alien planets are popping up in unexpected places.

Astronomers using the planet-hunting Kepler spacecraft have found two planets circling different stars in the violent environment of an ancient open star cluster called NGC 6811 located about 3,300 light-years from Earth. Until now, four of the more than 850 planets known outside the solar system were spotted in clusters.

The planets — Kepler-66b and Kepler-67b — are both smaller than the planets previously found in clusters. They are slightly smaller than Neptune, but larger than the Earth and circle sunlike stars. [The Strangest Alien Planets (Gallery)]

“We don’t have any planet that falls in that size bin or that mass bin between the Earth and Neptune, so we have to try to speculate about how they might be, structurally speaking,” lead study author Soren Meibom, of the Harvard-Smithsonian Center for Astrophysics, said. “It’s unlikely that they’re completely solid like the Earth because there is no precedence for that. If you have a planet this size, three-quarters the size of Neptune, about three Earth radii, it’s very likely to have a gaseous envelope, so it’s kind of in between a rocky planet like a Neptune … but we don’t have any analogue in the solar system, so we’re left guessing a little bit.”

The new research is detailed in the June 27 issue of the journal Nature.

Forming in a cluster

Some scientists thought that it would be more difficult for exoplanets to survive in star clusters because of the turbulent environment that surrounds them. Supernova explosions and the movements of other stars in the cluster can change the orbits of planets that formed around relatively stable stars. [How Alien Planet Sizes Stack Up (Infographic)]

The orbits of Kepler-66b and Kepler-67b, however, do not seem to have been disturbed since their formation one billion years ago, Meibom said.

These planets are also unique because they are the first cluster-based planets to be discovered by transiting — passing between their star and the Earth. This allowed Meibom to measure their relatively small size.

“Big planets are easier to find, but if they are less common than small ones, we may not find them,” William Welsh, an astronomer at San Diego State University who is unaffiliated with the research, said. “Previous searches for transiting planets in clusters didn’t find any planets, but it’s not because planets are rare. It’s because 1) planets as small as the ones in this paper are extremely hard, if not impossible, to detect using a ground-based telescope; and (2) the large Jupiter-size planets that could have been found are less common than the harder-to-see and more common small planets.”

Just as common

Meibom and his team used data they collected from 377 stars in the cluster to understand the frequency of finding cluster-based planets versus planets circling stars in the open field. They found that astronomers can expect to detect a similar number of mini-Neptunes in both the field and in clusters.

These types of planets could be just as commonly found orbiting stars in clusters as they are around other kinds of stars.

“The two planets we found are going around their stars over a time of 15 and 17 days respectively and that is also a very typical orbital period for planets found outside of clusters,” Meibom said. “Both the frequency and the properties in terms of size and orbital period are consistent with what we see outside of clusters.”

This finding might also help scientists understand whether habitable alien planets could form in clusters, however, it is still unclear whether life could exist while a young star remains within a cluster.

“The sun was once part of a cluster, and our solar system planets formed while part of the cluster,” Welsh wrote in an email to “Life probably did not emerge while the sun was part of the cluster, though that depends on how long it took for the cluster to dissolve. But the reason for that may be more due to the bombardment of the very young Earth by proto-planetary debris than anything to do with the cluster environment … Life probably did not get a permanent foot-hold on Earth while we were part of a cluster, if the cluster dispersed in less than 700 million years.”

Future missions

It could also be possible to search for planets in closer star clusters like the Pleiades or the Hyades, but it might not happen for a while, Meibom said. Kepler cannot hunt for planets in those closer clusters because it is focused on only one part of the distant sky, and ground-based methods have not been powerful enough to detect any small planets as of yet.

Future missions, however, could help scientists investigate these closer clusters, Meibom said. NASA’s planned Transiting Exoplanet Survey Satellite, launching in 2017, will search for planets transiting in front of smaller and cooler stars — the most common in the galaxy.

This is the second bit of surprising exoplanet news in as many days. Scientists recently found three planets within the habitable zone of a star 22 light-years from Earth.


Astronomers May Begin Search For Mars Like Planets

May 30, 2013 by  
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NASA’s Spitzer Space Telescope could be used to find Mars-size alien planets orbiting strange “failed stars” known as brown dwarfs, according to a new proposal by a multinational astronomy team.

The group, led by a postdoctoral researcher at MIT, proposes to use the venerable observatory to find small, rocky exoplanets around brown dwarfs, which are larger than planets but too small to ignite the nuclear fusion reactions that power stars.

Astronomers will seek planets crossing the face of these brown dwarfs, in the hopes that some of them will end up being capable of supporting life as we know it. [9 Exoplanets That Could Host Alien Life]

The planets sought would orbit more closely than Mercury does to the sun, but the faint warmth of brown dwarfs could still make such inner regions habitable, researchers said.

“Our program represents an essential step towards the atmospheric characterization of terrestrial planets and carries the compelling promise of studying the concept of habitability beyond Earth-like conditions,” the team’s paper stated.

Spotting small planets around brown dwarfs

The team is aiming for Mars-size planets because of their importance in planetary formation models, lead author Armaury Triaud told

Models suggest our solar system emerged from a spinning disk of dust and gas, with planets slowly clumping together as particles collided, Triaud said, cautioning that we can’t be completely sure of what actually occurred.

Our nascent solar system crossed an important threshold when those protoplanets reached the size of Mars, he said.

“Eventually these planet embryos, the size of Mars, those would collide and form bigger rocky planets, or the core of [gas giant] planets such as Jupiter,” Triaud said.

It would be easier to spot such small, rocky worlds around a brown dwarf than a larger star, he added. Brown dwarfs are brighter in the infrared – the wavelength in which heat radiates – and those we can see are relatively close to Earth, making it easier to detect the effect of any planets on their motions.

Spitzer’s data on planets could then be used by the forthcoming James Webb Space Telescope. James Webb should be able to probe planetary atmospheres, possibly to search for “biomarker” molecules such as oxygen, Triaud noted, although the orbiting observatory would need to stare at the planet for a long time.

“Right now, there are no projects able to find an Earth-sized planet whose atmosphere can be studied with the James Webb,” he said. “Our project is the only path.”

Short orbits, lots of data

In a brown dwarf’s “habitable zone” — the range of distances in which liquid water could exist on a world’s surface — it’s possible that a planet could pass between the brown dwarf and Earth more than 50 times a year, providing ample opportunity for the science team to conduct observations.

“Our simulation shows that with only 50 occultations, you’ll be able to reliably detect the atmosphere of a planet. It’s 50 years, in a sense, of research.”

The same data, Triaud noted, would be useful for studying brown dwarfs themselves — specifically their rotations and what happens in their atmosphere.

The team’s paper, which is a portion of an observing proposal made for NASA, is available on the online preprint site

Triaud said the proposal is being considered, along with many others, as cases to further extend Spitzer’s mission. If the extension is accepted, his team’s proposal will compete against those of others for valuable telescope time.

Spitzer launched in August 2003. It ran out of coolant four years agobut is observing new targets (such as near-Earth objects) as part of an extended mission.


Unique Technique Used To Find Rocky Alien Worlds

May 28, 2013 by  
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Numerous rocky, Earth-like worlds have been discovered by transit surveys such as NASA’s Kepler mission.

For those familiar with the transit of Venus last year, exoplanet transits are the same idea — an exoplanet crosses the face of its parent star as perceived by observers on or near Earth. By comparing the amount of starlight the transiting planet blocks and the total starlight emitted by the host star, astronomers can determine the radius of a transiting planet.

Recent surveys have hinted at the existence of exoplanets with rocky surfaces, making them similar to our own “terrestrial” planets Mercury, Venus, Earth and Mars. However, a number of the exoplanets thought to have rocky surfaces appear to not have any significant atmospheres. [The Strangest Alien Planets]

One such exoplanet is Corot-7b, which orbits very close to its parent star.  Exoplanet 55 Cancri e, estimated to have roughly twice Earth’s radius and eight times Earth’s mass, also may be a rocky planet, and perhaps even made of diamond.

The first rocky exoplanet discovered by the Kepler mission was Kepler-10b, with roughly 4 1/2 times Earth’s mass. The Kepler mission has since discovered numerous “super-Earth” type exoplanets, which have masses greater than Earth but less than planets such as Neptune. Due in part to their high mass, super-Earths could be rocky or have very thick gaseous atmospheres like Neptune.

In order to better understand the composition of terrestrial exoplanets, researchers from MIT and Caltech have proposed a method to identify unique chemical signatures from various surface materials by studying exoplanets in the infrared portion of the electromagnetic spectrum. A better understanding of exoplanet surface compositions will help researchers determine how prevalent Earth-like planets are in our galaxy, they say.

“Looking for Earth-like planets is one of key endeavors shared by many astronomers and a broader scientific community,” says lead author Renyu Hu of MIT.

Airless rocky planets

While the end goal would help researchers with the search for Earth-like exoplanets, the researchers’ methods are currently aimed at “airless” rocky worlds. Because there are similar objects in our solar system — notably our moon, Mars and Mercury — the team may be able to compare detected minerals in the solar system against signatures from rocky exoplanets.

The team proposes to analyze exoplanets in the infrared portion of the electromagnetic spectrum in order to determine the surface composition of exoplanets. Ideal exoplanets to study using the team’s method are those that transit their host star. With current technology however, the team cautions that determining surface composition of exoplanets is a very different process than studying their solar system counterparts. Due to the limits of technology, the team proposes to concentrate on the most prominent mineral signatures detected from exoplanets.

Mark Swain of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who is not on the research team, said, “We’re most likely to discover signs of life through atmospheric discoveries.”

By focusing their method on “airless” rocky exoplanets with surface temperatures under 3,140 degrees Fahrenheit (1,727 degrees Celsius), the team can analyze the unique chemical signatures of different materials.

Several exoplanets detected by the Kepler mission (Kepler-22b, Kepler-20f and Kepler-11b) may in fact have silicate (rocky) surfaces, making them ideal candidates for the team’s method. The team states that a large number of exoplanets detected by Kepler are the right distance from their host star to have rocky surfaces. [A World of Kepler Planets (Gallery)]

“We propose to determine whether an exoplanet has rocky surfaces by astronomical observations, via the unique thermal emission feature of silicate rocks,” Hu said. “By spectroscopy one may literally ‘see’ the rocks, or more precisely planetary regoliths.”

Different surface minerals provide unique signatures in different wavelengths. For example, in the visible and near-infrared, minerals such as pyroxene, olivine and hematite provide strong chemical signatures. Minerals such as hematite have prominent signals in the visible and ultraviolet wavelengths. Additionally, materials formed with water offer signals in the near-infrared.

“Several types of surfaces that can be distinguished by observing the reflection are ultramafic surfaces (indicating active volcanism on the planet), clay surfaces (indicating past or extant liquid water), and water ice,” Hu said. “Understanding the surface composition of a rocky exoplanet is one of the key steps to access the habitability and the availability of natural resources on the planet.”

Reading the rocks

Using infrared analysis techniques, the surface compositions of rocky objects in the solar system have been studied in detail.

On our moon, the basaltic nature of dark lunar regions, commonly referred to as “mare,” indicate they were formed by volcanic eruptions. Conversely, lunar highlands are bright, and their composition indicates the formation from a magma ocean.

Mars features strong iron signatures, which, combined with its red color, helped determine that a major component of the Martian surface is a mineral known as hematite. Additional surface signatures on Mars also indicate the presence of minerals such as pyroxene and olivine.

Observations of Mercury indicate similarities to the lunar highlands. However, recent observations by NASA’s Messenger spacecraft orbiting Mercury have challenged that view due to more precise surface composition readings.

The team asserts that rocky surfaces on exoplanets exhibit unique chemical signatures, along with volcanic surfaces, and surface water ice. If an exoplanet has a thin atmosphere, it may introduce additional signatures, especially if said atmosphere contains water vapor, carbon dioxide, methane, or ammonia. The team also stresses that without prior knowledge of a planet’s atmosphere, it can be difficult to determine exact surface compositions.

“Once you add an atmosphere, disentangling the signals becomes more work,” Swain said.  “Sorting out what’s present is non-trivial, and detecting these mineralogy features in the presence of molecular features from the planet’s atmosphere will be a challenge. More papers in the future will most likely explore how to separate atmospheric and surface signals.”

“The key to resolve this is broad wavelength coverage and sensitive measurements,” he added. “The team really did a good job of focusing on this.”

In contrast to an atmosphere’s effect on determining surface composition, space weathering may alter the surface chemistry on an airless planet. Constant bombardment of a surface by cosmic rays, the solar wind, and micrometeorites can darken and redden the surface.

While current space-based observatories do not possess the necessary instruments to identify exoplanet surfaces, space telescopes such as the upcoming James Webb Space Telescope are thought to have the capability to detect rocky surfaces on planets orbiting sun-like stars.

Eventually, direct imaging of exoplanets may be necessary to determine the exact surface composition. Determining the surface composition of an exoplanet will provide a better understanding of its geological history and its odds for hosting life, scientists say.

“In the more distant future, the detailed composition of rocky surfaces on an exoplanet can be investigated by observing the stellar light reflected by the planetary surfaces,” Hu said. “To do this, the rocky exoplanet needs to be directly imaged, which requires space-based telescopes with great power.”


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