The Astronomical Unit Gets Fixed
The Earth–Sun distance changes from slippery equation to single number.
(The new definitive value of the Astronomical Unit, in metres. Credit: Nature)
“Without fanfare, astronomers have redefined one of the most important distances in the Solar System. The astronomical unit (au) — the rough distance from the Earth to the Sun — has been transformed from a confusing calculation into a single number. The new standard, adopted in August by unanimous vote at the International Astronomical Union’s meeting in Beijing, China, is now 149,597,870,700 metres — no more, no less.”
“The effect on our planet’s inhabitants will be limited. The Earth will continue to twirl around the Sun, and in the Northern Hemisphere, autumn will soon arrive. But for astronomers, the change means more precise measurements and fewer headaches from explaining the au to their students.”
Viewing Alert: Jupiter Impacted by a Fireball
(George Hall, an amateur astronomer in Dallas Texas, captured the impact flash in his webcam on 10 September 2012. Credit)
“From astronomer Heidi Hammel of the Space Science Institute comes news about a potential new impact on Jupiter. She reports there has been a visual sighting of an apparent fireball on Jupiter earlier today (about 10 hours ago, as of this posting) so the impact site should be visible again over the next few hours. According to amateur astronomers discussing this on G+, the impact area on Jupiter won’t be visible again until about 05:00 UTC, (01:00 EDT). The amateur who observed the flash reported it to Richard Schmude of the Association of Lunar and Planetary Observers (ALPO). Hammel says the report sounds realistic, but obviously it needs confirmation if possible: a) by looking for any ‘impact scar’ tonight or over the next few days; b) by searching any webcam video that any observers might have been recording at the time. From the time and position given, the flash was on the North Equatorial Belt at approximately L1=335, L2=219, L3=257. ‘Let’s hope someone has a record of it!’ Hammel says.”
(UPDATE: Confirmation!)
This event is another example of something by now we’re familiar with: the impact of small comets and asteroids onto planets, happening right in front of us. The most famous example in modern times is the impact of Comet Shoemaker-Levy 9 onto Jupiter in 1994. As in that instance, we might expect evidence of the resulting fireball to persist for some number of rotations of Jupiter, perhaps visible as a dark splotch on its surface to keen observers. We’re reminded by this that even billions of years after it’s formation, the Solar System continues to be a violent place. -JCB
Too Much, Too Little: A Tale Of Cosmic Lithium
Two recent studies find more and less lithium than expected in very different places in the Universe.
(Solid metallic lithium floating in oil. Credit: Wikipedia)
Lithium is the lightest naturally-occurring element found in a metallic state on Earth; only hydrogen and helium are lighter, and both are gases at our temperatures and pressures. It’s a tiny constituent of our world, only 0.0017% by number. But it’s a chemical oddball in nature, even on as local a scale as the solar system. Astronomers studying the abundance of elements in the atmosphere of the Sun found it many times lower than the ‘primordial’ abundance in meteorites — thought to be the starting abundance of elements in the interstellar cloud out of which condensed the Sun and the planets. Later, we found that it’s oddly absent, or at least severely depleted in many stars. Recently, it was determined that stars known to host exoplanets are especially depleted in lithium, suggesting that the presence of lithium is some kind of indicator of the likelihood that a stellar system will form planets. The reason stars appear to “lose” their lithium is that under the right conditions it is destroyed by nuclear fusion, turned into heavier elements in the hot, deep interiors of young stars. However, this process is thought to occur only early in the lives of stars, setting their fraction of lithium at a fixed, permanent level.
Stars don’t really make much, if any, lithium. Instead, much of the lithium in the Universe was probably made in the Big Bang, which had just enough energy to create some of the lightest “metals” (to astronomers, elements heavier than helium). But we haven’t accounted for all of it. They key is which kind of lithium we’re talking about; that means which isotope. Kinds of atoms are defined by their atomic number, equal to the number of protons in the atom. Hydrogen has one, helium two, lithium three, and so on throughout the periodic table. The number of neutrons in an atom, however, doesn’t determine the kind of atom, just how heavy it is. The problem is with lithium-7, the most common form of lithium in the Universe: it has three protons and four neutrons. Some 30 years ago, researchers found apparently too little lithium-7 in the atmospheres of certain old stars, in contradiction to models of the amount of lithium made in the Big Bang; this became known as the “lithium problem”. The problem is sort of embarrassing for people who work on the abundances of elements in the Universe, because we seem to understand the other elements much better. Two new studies are further complicating the story.
(The Small Magellanic Cloud — the smaller of the two fuzzy dots to the right of the Milky Way’s dusty disk — is a dwarf galaxy currently orbiting the Milky Way. Credit: S&T Image Gallery: Luis Argerich)
Recent observations of stars in the Magellanic Clouds, small companion galaxies orbiting our Milky Way, shows the low abundance of lithium isn’t going away. J. C. Howk and co-workers used the high-resolution UVES spectrograph on the 8.2-meter Very Large Telescope in Chile to record the spectrum of a bright, young star in the Small Magellanic Cloud. They used it like a distant lightbulb to illuminate the gas and dust in the galaxy, allowing them to measure how many lithium atoms along the line of sight to the star were absorbing its light. They found that the amount of lithium is still less than what Big Bang models predict should have been around when the SMC formed. The problem is that some small amount of lithium is made inside stars, so the starting amount of lithium in the SMC had to be lower than it is today — in even greater disagreement with Big Bang predictions.
(The globular star cluster Messier 4. Credit: European Southern Observatory)
Sounds like Big Bang is doomed, right? One of its core predictions seems to not be verified by our observations of stars. It gets weirder. Another new paper claims to have found precisely the opposite — an old star in an ancient star cluster that seems to have way too much lithium. Observations of the globular star cluster Messier 4 show that at least one star — called by the designation “37934” — has far more lithium than both other stars in the cluster and the Big Bang prediction. The authors caution that this apparent overabundance may be the result of star 37934 happening to incorporate the lithium “pollution” of many earlier generations of stars by chance, but they cannot rule out the possibility that in fact the Big Bang lithium fraction was simply higher than the models predict. That may mean there’s something imperfect about our understanding of the physics of the Big Bang.
There’s a twist in this story, and it seems to back up the idea that we don’t really know as much about the Big Bang as we think. Remember the Small Magellanic Cloud? Howk’s team also may have seen the subtle fingerprints of a lighter, rarer isotope of lithium — lithium-6 — in their data. They’re not confident enough in the data to claim a detection, but if their result is later verified by other observers, the implication is amazing: there’s about a thousand times less lithium-6 in the SMC than the Big Bang models predict. The Howk group has more telescope time scheduled this fall to find out.
How much is the “right” amount of lithium in the Universe? Do we really see too much, or too little? The answers may be coming soon.
In Quest of the Cosmic Origins of Silver
New work suggests that silver and gold find their origins in different stellar explosions.
(At the end of their lives, stars with ten times the mass of our sun explode as so-called supernovae. In the process, elements like silver are either hurled out into the universe or produced in the first place. The illustration is an artist’s impression of the first moments of such an explosion before the star is completely torn apart. Credit: European Southern Observatory/ESO)
“In the quest for the cosmic origins of heavy elements, Heidelberg scientist Dr. Camilla Hansen has established that silver can only have materialized during the explosion of clearly defined types of star. These are different from the kind of stars producing gold when they explode. The evidence for this comes from the measurement of various high-mass stars with the help of which the stepwise evolution of the components of all matter can be reconstructed. The findings from the investigations conducted by Dr. Hansen of Heidelberg University’s Centre for Astronomy (ZAH) in conjunction with other scientists in Germany and fellow astronomers in Japan and Sweden have been published in the journal Astronomy & Astrophysics.”
When I was in grade school, I remember watching some terrible educational films from the 70’s about where certain materials come from. One was about boron, for example, which I took in that case to be synonymous with “boring”. Another was about silver, which included cheesy shots of silver smelting and objects made out of silver with the narrator intoning “Sssssillveerrrr” in a literally hypnotic way. But the films never answered my question: where did these elements originate? The best answer was “deep within the Earth”, but in my mind that only satisfied the question “Where do we look for these elements?”
We have known for some time that certain elements — mostly those heavier than iron — originate in the catastrophic explosions of massive stars near the ends of their lives in something called the “r-process”. This means that light elements are rapidly (“r”) built into heavy elements by capturing the flood of neutrons created when a massive star’s iron core collapses under its own weight. The idea contrasts the “s-process” (“slow”) in which the elements capture one random neutron at a time and take millions of years to transmute into something heavier. In the r-process, this process takes mere seconds. But something is odd about the elements in the lighter range just beyond iron, and what we know about the r-process doesn’t fully explain how they’re made.
Now, C. Hansen and coworkers have illuminated the darkness shadowing metals like… (wait for it)… “ssssillveerrrr”. They have shown that a secondary r-process must exist to explain silver and it’s light metallic brethren, and which version of the r-process happens in the death of a star depends on the details of star doing the dying. The process for making silver needs a lower flux of neutrons, among other conditions, than the process for making, say, gold. The broad conclusion is that light metals are forming in one part of the explosion fireball, and heavy elements in another. “This is the first incontrovertible evidence for a special fusion process taking place during the explosion of a star,” says Dr. Hansen. “Up to now this had been mere speculation.” -JCB
Layers At The Base Of Mount Sharp
A chapter of the layered geological history of Mars is laid bare in this postcard from NASA’s Curiosity rover.
(Credit: NASA/JPL-Caltech/MSSS)
“The image shows the base of Mount Sharp, the rover’s eventual science destination. This image is a portion of a larger image taken by Curiosity’s 100-millimeter Mast Camera on Aug. 23, 2012. Scientists enhanced the color in one version to show the Martian scene under the lighting conditions we have on Earth, which helps in analyzing the terrain.”
This remarkable image is the first to be returned from the Mars Science Laboratory’s Curiosity rover telephoto camera. It shows an oblique view of the lower reaches of Mount Sharp (aka Aeolis Mons), the 5.5 km (18,000 ft) high peak in the center of Gale Crater, Curiosity’s landing site. It is thought that Mt. Sharp formed billions of years ago as the erosional remnant of the sediments — likely deposited in a lake of liquid water — that filled Gale nearly to its rim. Later, after the water receded, wind erosion probably sculpted the mountain out of the sediment. Evidence for layered deposits can be seen in the foothills of Mt. Sharp in the image above; these layers contain the post-impact history of the crater and are a prime target for Curiosity’s science instruments.
What can Curiosity expect to learn about Gale? The sediments read like a history book, with a (mostly) orderly progression of events in the evolution of the mountain as it built up and was carved out to its current appearance. We should be able to work out the wet and dry periods of its past, which indicate something about the changing global climate history of Mars itself. Did Martian bodies of water behave like lakes and oceans on Earth? What forces resulted in the landscape we now see in Curiosity’s panoramas? Are there chemical signatures of past life in the rock layers of Mt. Sharp? These are prime questions to be addressed in Curiosity’s years-long mission, and the image above is a tantalizing preview of what’s yet to come. -JCB
Robots To Go Spelunking In Martian Caves?
Robots that rappel, hop or lower themselves by tether into Martian skylights could reshape the hunt for life beyond Earth.
(A skylight opens into an underground cavern on the slopes of Mars’ Pavonis Mons volcano, as observed by NASA’s Mars Reconnaissance Orbiter. Credit: NASA/JPL-Caltech/Univ. of Ariz.)
“Scientists are beginning to sketch out plans for NASA’s new Mars rover Curiosity to climb Mount Sharp, but future robots may have a more direct way to access the planet’s history books. Recent discoveries of ‘skylights’ (pictured here) and lava tubes on the surface of Mars, as well as the moon, are sparking the development of robotic probes that can descend into caves and explore tunnels.”
“Curiosity’s landing site inside an ancient impact basin was selected because of the three-mile high mound of layered rock, known as Mount Sharp, rising from the crater’s floor… An even richer treasure trove may be hidden underground, where potential habitats would be more shielded from the radiation that constantly blasts the planet’s surface.”
There’s every reason to think caves exist on Mars, and the “skylight” phenomenon seen from orbit provides ample evidence. What are they? That we see them mostly on the slopes of Mars’ giant shield volcanoes likely tells us that they’re probably like “skylights” seen on the slopes of terrestrial volcanoes. Here’s a photo of one at Kilauea in Hawai’i, with some humans for scale:
(Credit: Martin Ruzek; USGS Hawaiian Volcano Observatory)
Skylights are windows into lava tubes, structures in which molten rock flows in defined channels below ground. Occasionally the thin, rocky “ceiling” above the tube collapses, allowing a view of the inside. If we could somehow carefully lower a probe through a skylight into a lava tube on Mars, we could potentially follow its course for miles, and get an up-close look at past volcanic processes on Mars.
But what about more familiar caves? Think of the grand underground chambers and delicate formations of cave systems like Carlsbad, Mammoth, or Wind. What do all these caves have in common? Water. And lots of it. That’s something Mars doesn’t currently have much of, at least not in a liquid state. But there’s ample evidence that Mars once had lots of water. On Earth, caves take millions of years to form; there may have been sufficient time early in Mars’ history to make them, before it lost its water to space or climate change locked it away as ice in its interior. If they exist, these caves would be harder to find, because their natural entrances may well not be visible to orbiting spacecraft.
Why should we look for water-formed Martian caverns? They may preserve evidence of past life. If connected to geothermal hot springs, underground caves may have provided both shelter from harsh ultraviolet light exposure as well as a liquid environment after outside water froze. Even if life were once relatively abundant in Mars’ ancient oceans, it may well have gone extinct as those oceans disappeared, and caves offer a safe harbor where it could “hide out” for some unknown length of time — at least until the caves dried up. So while no Mars missions have found indisputable proof of current (or past) life on Mars at the surface, we may one day find it in the deep, dark recesses of a Martian cave. -JCB
Big Bang Was Actually a Phase Change, New Theory Says
A new theory envisions the Big Bang as the moment the familiar dimensions of our Universe “crystallized”, much as ice crystallizes suddenly as the temperature of water drops below freezing.
(The Big Bang may have been the moment that a water-like universe froze to form the ice-like universe we see today, a new theory holds. Credit: Image via Shutterstock)
“How did the universe begin? The Big Bang is traditionally envisioned as the moment when an infinitely dense bundle of energy suddenly burst outward, expanding in three spatial directions and gradually cooling down as it did so. In [a] new study, lead author James Quach and colleagues at the University of Melbourne in Australia say the hypothesis can be tested by looking for defects that would have formed in the structure of space-time when the universe crystallized. ”
”’Think of the early universe as being like a liquid,’ Quach said in a statement. ‘Then as the universe cools, it ‘crystallises’ into the three spatial and one time dimension that we see today. Theorized this way, as the universe cools, we would expect that cracks should form, similar to the way cracks are formed when water freezes into ice.’ If they exist, these cracks should be detectable, the researchers said, because light and other particles would bend or reflect off of them as they trek across the cosmos.”
The Big Bang model of the origin of the Universe is now, decades after its original formulation, widely accepted within astronomy as the explanation which best fits our observations. The important feature of the model that distinguishes it from others is a distinct event occurring in time — the “Big Bang” — that holds the Universe is not infinitely old. But this leaves scientists in a conundrum: having predicted the existence of a “time zero”, whatever happened before this becomes essentially impossible to test with experiments. We have a good “what happened” description but are left without a “how”, and with great philosophical implications, without a “why”.
The “new” theory, which has its origins in the past decade, explains the Big Bang as something we see everywhere in nature: matter changing from one state, or phase, to another. The analogy used in this story is the phase change that occurs when liquid water becomes water ice at 0℃ (at least at our familiar, atmospheric pressure). The random, unordered positions of water molecules in a liquid becomes the orderly arrangement of molecules with constant spacing and angles between them that results in water ice. A byproduct of this effect is that the molecules have to move further apart from each other such that they take up more space — causing ice to float.
Instead of freezing water molecules, the Big-Bang-as-phase-change idea suggests that the invisible (to us) units of spacetime were once all randomly mixed up, like molecules in a liquid. Going from point A to point B in this arrangement wouldn’t be like it is in our Universe, where points A and B are related through simple rules of geometry, so space and time wouldn’t mean the same things they do to us. Then something happened; the “temperature” of the proto-Universe dropped below a critical threshold, and the invisible units of spacetime suddenly assumed the relative positions we now see everywhere. Suddenly the Universe had a geometry, and that’s probably when the physical laws and constants as we know them assumed their “final” nature.
How could we test this idea? Crystallization is often imperfect; witness, for examples, the bubbles and fractures in ice cubes than render them less than crystal clear. Such defects might exist in the “lattice” of spacetime, and we could detect them as light propagated through these regions. The effect would be very subtle, however, and seeing it may involve technology we do not yet possess. For now, this construct makes a seemingly impossible problem easier to wrap the mind around — and may lead us toward solutions. -JCB
A Trip To The Deep Future
Where will you be in 10100 years?
(A computer simulation of the cosmic web of dark matter and ordinary matter. Image credit: NASA, ESA, and E. Hallman, University of Colorado)
“Yes, I know, we’ll all be long gone by then. But if you could somehow stick around around to experience the universe ten thousand trillion trillion trillion trillion trillion trillion trillion trillion years from now, what would it be like?”
“Given sufficient time, even the protons and neutrons that make up the stuff of universe will fall to pieces. How long will it take? That is still a mystery, though a combination of experiment and theory suggests that it will happen some time between 1033 and 1045 years after the Big Bang… Given enough time—as long at 10100 years—even the biggest black holes will evaporate away.”
“Will the lonely monotony of the dark era ever end? Maybe. The same energy that has been driving the accelerating expansion of the universe could suddenly change character, a phenomenon theorists call vacuum energy decay. It happened once before—when the era of inflation ground to a halt soon after the Big Bang—and theorists believe that it should happen again.”
It’s something all of us in astronomy have considered at some point: what happens in the very distant future? Does the Universe go on forever? Does it change substantially? Does it interact with other “universes” in some higher-dimension space in which we all exist? The tools of astronomers efficiently let us look back in time; because the speed of light is not infinitely fast, looking out in distance means looking back at an earlier period of time in the history of the Universe. But those tools offer us little in the way of looking forward.
We have a way of making educated guesses about what will happen in the future. The predictive nature of science means that we can take what we have learned about the physical laws that govern the behavior of the Universe and “run the clock forward”; the equations usually don’t much care about whether time is specified in the past or in the future. But it turns out nature isn’t a very deterministic place. At the microscopic level, quantum physics dissolves the natural world into a place only of probabilities. At the other end of the scale, in the macroscopic Universe, chaos and thermodynamics yield a “law-of-averages” approach to predicting the behavior of systems. We also don’t (yet) know just how constant the physical constants are, something that can have an enormous amplifying effect on the time evolution of the Universe. There are many unknowns, but we have many ways to approach knowing them. -JCB
Milky Way's Black Hole Once Active
Evidence continues to mount that our galaxy’s supermassive black hole was not always the quiet neighbor it is now.
(NASA’s Fermi spacecraft has discovered a pair of enormous gamma-ray-emitting bubbles extending from the Milky Way’s center. Although not apparent in an all-sky gamma-ray map (upper panel), the dumbbell-shaped feature became evident after removing other sources (lower panel). Credit: NASA / DOE / Fermi LAT / D. Finkbeiner & others)
“There’s a dragon dozing in the Milky Way’s core. Hidden from sight by our galaxy’s dusty disk, a supermassive black hole sleeps fitfully. Sometimes a cloud of gas might whisk around its nostrils or a star fall on its head and make the dragon snort a bit of flame, then go back to sleep. But a few million years ago, something managed to rouse the beast so completely that it spewed plasma jets and a couple of big bubbles into space.”
“That’s the picture of our galaxy that’s been developing over the past eight years. Mounting evidence from microwave and gamma-ray observations suggests that the Milky Way’s central supermassive black hole threw a right fit a few million years ago, creating a haze that stretches several thousand light-years above and below the galaxy’s disk. It’s been unclear whether this haze is actually from a short-lived upsurge in the black hole’s activity, but a new study by Gregory Dobler (Kavli Institute for Theoretical Physics at the University of California, Santa Barbara) might help close the case.”
I’ve often wondered whether the supermassive black hole known to inhabit the center of the Milky Way was ever recently turned “on”, and we’re now much closer to answering that question affirmatively. How do we know? We see examples of currently-active galaxies elsewhere in the nearby universe that serve as models for what an active Milky Way would look like. Compare the image of the Milky Way at the top of this post with the two active galaxies below, Centaurus A (left) and M82 (right):
(Credit, left: NASA/CXC/CfA/R. Kraft et al./ESO/VLT/ISAAC/M. Rejkuba et al.; right: NASA, ESA and the Hubble Heritage Team STScI/AURA)
The “Fermi bubbles” in the WMAP images of the Milky Way are strikingly similar to the emission out of the plane of these two galaxies (the orange and blue in the Centaurus A image and the bright red in the M82 image). Further, the properties of the emission are similar in all the cases, being bright in both high-energy light (gamma rays) and low-energy light (radio waves). This appears to be the “smoking gun” evidence in support of the idea that our home galaxy was one a much more happening place than it is in our time. -JCB
Glenelg: The Curiosity Rover's Palindromic First Stop
“This image shows a closer view of the landing site of NASA’s Curiosity rover and a destination nearby known as Glenelg. Curiosity landed inside Gale Crater on Mars on Aug. 5 PDT (Aug. 6 EDT) at the blue dot. It is planning on driving to an area marked with a red dot that is nicknamed Glenelg. That area marks the intersection of three kinds of terrain. Starting clockwise from the top of this image, scientists are interested in this brighter terrain because it may represent a kind of bedrock suitable for eventual drilling by Curiosity. The next terrain shows the marks of many small craters and intrigues scientists because it might represent an older or harder surface. The third, which is the kind of terrain Curiosity landed in, is interesting because scientists can try to determine if the same kind of rock texture at Goulburn, an area where blasts from the descent stage rocket engines scoured away some of the surface, also occurs at Glenelg.”
“The science team thought the name Glenelg was appropriate because, if Curiosity traveled there, it would visit the area twice — both coming and going — and the word Glenelg is a palindrome. After Glenelg, the rover will aim to drive to the base of Mount Sharp.”
“These annotations have been made on top of an image acquired by the High Resolution Imaging Science Experiment on NASA’s Mars Reconnaissance Orbiter.”
Glenelg is just the first stop of what will likely be many on Curiosity’s itinerary. The view below shows how relatively close Glenelg is to the ultimate prize: the geologically-stratified foothills of Mount Sharp. -JCB
(Images credit: NASA/JPL-Caltech/Univ. of Arizona)
Astronomy news, recent research results, and pretty pictures from the media along with context, commentary, and explanations for folks who dig this sort of thing. Written by a quasi-professional astronomer affiliated with the University of Texas at Austin.
