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.
Moon and Jupiter close midnight to dawn September 8
See the Moon pass very close to Jupiter tonight.
“he darkness after midnight and before daybreak belongs to the waning gibbous moon and the planet Jupiter tonight. These two beautiful worlds – Jupiter and our companion moon – will appear in the east after midnight on Friday night. They’ll steadily climb upward until dawn breaks Saturday morning. Jupiter outshines all the true stars in the sky, and is only exceeded in brilliance by the planet Venus, which you’ll also find before dawn tomorrow – closer to the horizon than Jupiter and the moon.”
“The moon will be very close to its last quarter phase tomorrow morning as seen in the U.S. This month’s last quarter moon falls at 8:15 a.m. CDT (13:15 UTC) on Saturday, September 8.”
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
Turning Blue: Friday’s Full Moon a ‘Blue Moon’
For the first time since March 2010, we’ll gaze upon a blue moon this Friday.
(A “blue” moon. Credit: Getty Images)
“This Friday, Aug. 31, might not be all that much fun for you, especially if you’re someone who vows to only do obligatory tasks once in a blue moon. Then again, if you’re a believer that good luck comes your way only once in a blue moon, Friday might be just the day you’ve been waiting for. After Friday, you’ll have to wait another 36 months — until July 2015 — for the next one. So, it’s time to loosen up Friday and do all those things you say you do ‘once in a blue moon.’”
“Once in a blue moon” is a colloquialism that has come to mean some kind of event that only happens incredibly rarely. Real ‘blue moons’ aren’t that rare at all, despite the association our culture has made with them. The period of the Moon’s orbit around the Earth is about 29.5 days, which (importantly) is very nearly the length of the months in the Gregorian calendar we use. However, the month isn’t defined to be 29.5 days in length, for a variety of reasons. Some months are longer, and one is always shorter. That means every now and then — quite by accident — the Moon and our calendar sync up in a weird and coincidental way.
A “blue moon” is defined as two full moons occurring in the same calendar month, or alternately, the third full moon in a season with four full moons. Because the period of the Moon’s orbit doesn’t exactly match either the length of our months, and the Earth’s year isn’t an integer number of lunar orbital periods, the date that a given phase of the Moon occurs wanders through the calendar. Quite by accident, the lunar cycle and our calendar line up in a way that appears to produce an “extra” full moon (or any other given lunar phase) in some defined period of time. Every two to three years, that “extra” full moon appears, leading to the colloquial expression. The important thing to keep in mind is that the Moon doesn’t actually appear bluish in color during one of these events.
The exact origin of the term is unclear, historically, but there have been instances in history when various atmospheric effects on Earth have caused the Moon (or even the Sun!) to appear blue in color. These instances are coincident with situations where a great number of very small particles were injected into the atmosphere; notable examples are after volcanic eruptions such as Krakatoa in 1883, and a series of large wildfires in Alberta, Canada in September 1950. When particles of anything — drops of water, bits of pulverized volcanic rock, or ash from wildfires — are comparable in size to the wavelengths of light passing through them, they preferentially scatter those wavelengths. Particles of about 1 micron in size are highly efficient at scattering long wavelengths of visible light, while transmitting longer and shorter wavelengths. Under exceptionally rare circumstances, the right-sized particles are aloft long enough to “deredden” moonlight and render it truly “blue”. -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
See The Moon And Two Planets Tonight (August 22)
“The moon has been awesome these past few nights in the western twilight sky! It’s been moving past the very noticeable triangle there, consisting of two planets – Mars and Saturn – and the star Spica in the constellation Virgo. But of course the moon never stops moving. As darkness falls this evening in North America, the rather wide waxing crescent moon appears to the south of the constellation Libra, and to the east of the planets Saturn and Mars. In the Eastern Hemisphere – Europe, Africa, Asia, Australia and New Zealand – tonight’s moon will be closer to Mars and Saturn than it is in the Western Hemisphere.”
Look to the southwest tonight at dusk and find the Moon, then use the chart above to lead you on to Saturn and Mars. And when you find Mars, think about the fact that right now, there’s a rover from Earth there with a laser beam strong enough to vaporize solid rock… -JCB
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.
