Vesta seen from the Earth-orbit based Hubble Space Telescope in 2007 (left) and up close with the Dawn spacecraft in 2011. Hubble Credit: NASA, ESA, and L. McFadden (University of Maryland). Dawn Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Photo Combination: Elizabeth Howell
The Hubble Space Telescope is one of the best observatories humanity has. It’s been operating for nearly 25 years in space, is still highly productive, and is a key element to mission planning for NASA as it sends spacecraft out into the Solar System. When the agency was getting ready to send Dawn to Vesta, for example, it took pictures to help with calibration.
Then Dawn got up close to the dwarf planet in 2011 and found a few surprises — liquid water that possibly flowed temporarily on the surface, for example. And as the spacecraft draws near to Ceres for a close encounter next year, it also will be looking for water — in the form of its atmosphere.
That’s following on from research out of the Herschel Space Telescope published earlier this year, showing that Ceres has a thin water vapor atmosphere surrounding the dwarf planet. It could be producing water similarly to how a comet does, through sublimation, but investigators won’t know much until they get close-up.
“Ceres has some sort of mechanism that’s putting out water vapor and causing a thin, temporary atmosphere,” said Keri Bean, a mission operations engineer at the Jet Propulsion Laboratory who works on Dawn, in a Google+ Hangout yesterday (Dec. 11). “I think that we’re going to try to look into this, and we don’t know what else Ceres will have in store for us.”
Ceres as seen from the Earth-based Hubble Space Telescope in 2004 (left) and with the Dawn spacecraft in 2014 as it approached the dwarf planet. Hubble Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), L. McFadden (University of Maryland, College Park), and M. Mutchler and Z. Levay (STScI). Dawn Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Photo Combination: Elizabeth Howell
Dawn is now so close to Ceres that its pictures will soon exceed the best ones Hubble had to offer. The image above (at right) is modest compared to the space telescope, but in a planned photo session Jan. 26 Dawn will have slightly better pictures than Hubble. By Feb. 4 they will be twice as good in quality and then seven times as good Feb. 20.
The spacecraft’s images not only have science purposes, as they let investigators study the surface, but also serve as optical navigation aids. Ceres is a tiny body and hard to navigate to from far away, so as it gets closer these pictures are crucial for Dawn to figure out where to go next.
Dawn will get its close-up of Ceres in the spring when it arrives at the dwarf planet. To get the latest on the mission, check out the entire Google+ Hangout from yesterday.
Opportunity's robotic arm is cast in shadow as the Mars rover explores the rim of Endeavour Crater on Sol 3,854 (Nov. 26, 2014). Credit: NASA/JPL-Caltech
NASA’s aging Mars rover is still struggling with Flash memory after several months of controllers trying to work around frequent resets and amnesia events, according to a recent update.
The Opportunity rover is coming up on its 11th anniversary of landing on Mars, and is busy exploring the rim of Endeavour crater, en route to a region that could have clay minerals (showing evidence of water). But the rover has been dogged by frequent memory problems that forced a reformat in September, with only partial success.
While the updates have said the rover is still performing science, NASA says in a Dec. 4 to Dec. 9 update of the mission that the Flash memory was reformatted once again, and that controllers don’t plan to use any of it for the time being. Flash is useful because it retains data even when the rover is turned off. NASA is instead storing “data products” in RAM format.
“Longer term, the project is developing a strategy to mask off the troubled sector of Flash and resume using the remainder of the Flash file system,” NASA stated.
The Orion crew module was recovered Dec. 5, 2014 after splashdown in the Pacific Ocean about 600 miles off the coast of San Diego, California. Credit: U.S. Navy
After a brilliant first test flight, and historic Pacific Ocean splashdown and recovery on Dec. 5, 2014, NASA’s Orion spacecraft was brought onshore inside the USS Anchorage to the US Naval Base San Diego and has now been offloaded for the cross country trek back her home base in Florida.
Orion was off-loaded from the well deck of the USS Anchorage Monday night after the amphibious ship docked in San Diego.
NASA officials pronounced the two orbit, 4.5 hour flight maiden test flight of Orion on the Exploration Flight Test-1 (EFT-1) mission to be a complete success.
The EFT-1 spacecraft was recovered at sea, brought to land, and off-loaded by a combined team from NASA, the U.S. Navy, and Orion prime contractor Lockheed Martin.
NASA’s Orion spacecraft is being offloaded from the well deck of the USS Anchorage at Naval Base San Diego in California and has been secured in its crew module recovery cradle to prepare for return to Kennedy Space Center in Florida. Credit: NASA/Amber Philman
Years of planning, rehearsals, and hard work on land, in the air, and at sea paid off handsomely for the Orion Recovery Team, led by the Ground Systems Development and Operations Program (GSDO) based at NASA’s Kennedy Space Center in Florida.
“The recovery of Orion was flawless,” said Jeremy Graeber, NASA recovery director. “We wanted to be patient, take our time. We didn’t rush.”
Navy teams in Zodiac boats had attached a collar and winch line to Orion at sea and then safely towed it into the flooded well deck of the USS Anchorage and positioned it over rubber “speed bumps.”
Next they secured Orion inside its recovery cradle and transported it back to US Naval Base San Diego where it was off-loaded from the USS Anchorage.
Orion has now been moved about a mile to the “Mole Pier” where Lockheed Martin has conducted the first test inspection of the crew module and collected test data.
The Orion crew module is being moved into a covered structure at the Mole Pier at Naval Base San Diego in California where it will be prepared for return to NASA’s Kennedy Space Center in Florida. Orion was secured on its crew module recovery cradle in the well deck of the USS Anchorage after it was recovered from the Pacific Ocean. Credit: NASA/Cory Huston
Next, it was placed into the crew module transportation fixture with a rigorous environmental control system and generator to ensure the crew module’s safety during transport.
Orion will be hauled on a flatbed truck across the US for a nearly two-week trip back to Kennedy where it will arrive just in time for the Christmas holidays.
Technicians at KSC will examine every nook and cranny of Orion, and will disassemble it for up close inspection and lessons learned.
NASA’s first Orion spacecraft blasts off at 7:05 a.m. atop United Launch Alliance Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida on Dec. 5, 2014. Launch pad remote camera view. Credit: Ken Kremer – kenkremer.com
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Illustration of a rocky planet being bombarded by comets. (Image credit: NASA/JPL-Caltech)
Where did all of our water come from? What might seem like a simple question has challenged and intrigued planetary scientists for decades. So results just released by Rosetta mission scientists have been much anticipated and the observations of the Rosetta spacecraft instruments are telling us to look elsewhere. The water of comet 67P/Churyumov-Gerasimenko does not resemble Earth’s water.
Because the Earth was extremely hot early in its formation, scientists believe that Earth’s original water should have boiled away like that from a boiling kettle. Prevailing theories have considered two sources for a later delivery of water to the surface of the Earth once conditions had cooled. One is comets and the other is asteroids. Surely some water arrived from both sources, but the question has been which one is the predominant source.
There are two areas of our Solar System in which comets formed about 4.6 billion years ago. One is the Oort cloud far beyond Pluto. Everything points to Comet 67P’s origins being the other birthplace of comets – the Kuiper Belt in the region of Neptune and Pluto. The Rosetta results are ruling out Kuiper Belt comets as a source of Earth’s water. Previous observations of Oort cloud comets, such as Hyakutake and Hale-Bopp, have shown that they also do not have Earth-like water. So planetary scientists must reconsider their models with weight being given to the other possible source – asteroids.
The question of the source of Earth’s water has been tackled by Earth-based instruments and several probes which rendezvous with comets. In 1986, the first flyby of a comet – Comet 1P/Halley, an Oort cloud comet – revealed that its water was not like the water on Earth. How the water from these comets –Halley’s and now 67P – differs from Earth’s is in the ratio of the two types of hydrogen atoms that make up the water molecule.
Illustration of the Rosetta spacecraft showing the location of the ROSINA mass spectrometer instrument, DFMS. The difference between a Deuterium and Hydrogen atom is also illustrated. A water molecule with Deuterium is known as heavy water due to the additional mass of Dueterium vs. Hydrogen (i.e., an extra neutron). (Credit: ESA/Rosetta)
Measurements by spectrometers revealed how much Deuterium – a heavier form of the Hydrogen atom – existed in relation to the most common type of Hydrogen in these comets. This ratio, designated as D/H, is about 1 in 6000 in Earth’s ocean water. For the vast majority of comets, remote or in-situ measurements have found a ratio that is higher which does not support the assertion that comets delivered water to the early Earth surface, at least not much of it.
Most recently, Hershel space telescope observations of comet Hartley 2 (103P/Hartley) caused a stir in the debate of the source of Earth’s water. The spectral measurements of the comet’s light revealed a D/H ratio just like Earth’s water. But now the Hershel observation has become more of an exception because of Rosetta’s latest measurements.
A plot displaying the Deuterium/Hydrogen (D/H) ratio of Solar System objects. Asteroids have a D/H ratio that matches that of the Earth, while comets – except for two measured to date – have higher ratios. Objects are grouped by color: planets & moons (blue), chrondritic meteorites from the asteroid belt (grey), Oort cloud comets (purple), and Jupiter family comets (pink). Diamond markers = In Situ measurements; circles = remote astronomical measurements. (Credit: Altwegg, et al. 2014)
The new measurements of 67P were made by the ROSINA Double Focusing Mass Spectrometer (DFMS) on board Rosetta. Unlike remote observations using light which are less accurate, Rosetta was able to accurately measure the quantities of Deuterium and common Hydrogen surrounding the comet. Scientists could then simply determine a ratio. The results are reported in the paper “67P/Churyumov-Gerasimenko, a Jupiter Family Comet with a high D/H ratio” by K. Altwegg, et al., published in the 10 December 2014 issue of Science.
New Rosetta mission findings do not exclude comets as a source of water in and on the Earth’s crust but does indicate comets were a minor contribution. A four-image mosaic comprises images taken by Rosetta’s navigation camera on 7 December from a distance of 19.7 km from the centre of Comet 67P/Churyumov-Gerasimenko. (Credit: ESA/Rosetta/Navcam Imager)
The ROSINA instrument observations determined a ratio of 5.3 ± 0.7 × 10-4, which is approximately 3 times the ratio of D/H for Earth’s water. These results do not exclude comets as a source of terrestrial water but they do redirect scientists to consider asteroids as the predominant source. While asteroids have much lower water content compared with comets, asteroids, and their smaller versions, meteoroids, are more numerous than comets. Every meteor/falling star that we see burning up in our atmosphere delivers a myriad of compounds, including water, to Earth. Early on, the onslaught of meteoroids and asteroids impacting Earth was far greater. Consequently, the small quantities of water added delivered by each could add up to what now lies in the oceans, lakes, streams, and even our bodies.
A timelapse photo taken by Don Pettit on the International Space Station. Credit: Don Pettit/NASA
When you’re flying above Earth in a spaceship or space station, taking a clear picture below is more than a point-and-shoot job. As NASA astronaut Don Pettit explains in this video, you need to account for the motion of your little craft to get the best pictures below. And Pettit should know, being a photographer who captured many stunning timelapses in space.
“Apart from everything else an astronaut does on orbit, photography is actually part of our job,” Pettit said in the video. “We take pictures of Earth and the surroundings of Earth, the upper atmosphere. These pictures, in themselves, represent a scientific dataset, recorded now for over 14 years.”
The video is called “From Above” and is a production of SmugMug films, who also did an interview with Pettit. As it turns out, much of the photography taken in space is not of Earth — it’s engineering photography of window smudges or electrical connections to help diagnose problems happening in space.
“These things need to be documented so the images can be downlinked for engineers on the ground to assess what’s happening to the systems on space station,” Pettit said in the interview. “We get training specifically on doing these engineering images, which, for the most part, are not really interesting to the public.”
An artistic image of the explosion of a star leading to a gamma-ray burst. (Source: FUW/Tentaris/Maciej Fro?ow)
Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.
There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.
Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.
In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.
Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.
In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.
Image of the Sunrise Solstice captured over Stonehenge. Image Credit: Max Alexander/STFC/SPL
For most of here on planet Earth, sunrise, sunset, and the cycle of day and night (aka. the diurnal cycle) are just simple facts of life. As a result of seasonal changes that happen with every passing year, the length of day and night can vary – and be either longer or shorter – by just a few hours. But in some regions of the world (i.e. the poles) the Sun does not set during certain times of the year. And there are also seasonal periods where a single night can last many days.
Naturally, this gives rise to certain questions. Namely, what causes the cycle of day and night, and why don’t all places on the planet experience the same patterns? As with many other seasonal experiences, the answer has to do with two facts: One, the Earth rotates on its axis as it orbits the Sun. And two, the fact that Earth’s axis is tilted.
Earth’s Rotation:
Earth’s rotation occurs from west to east, which is why the Sun always appears to be rising on the eastern horizon and setting on the western. If you could view the Earth from above, looking down at the northern polar region, the planet would appear to be rotating counter-clockwise. However, viewed from the southern polar region, it appears to be rotating clockwise.
Earth’s axial tilt and its relation to the rotation axis and plane of orbit as viewed from the Sun during the Northward equinox. Credit: NASA
The Earth rotates once in about 24 hours with respect to the Sun and once every 23 hours 56 minutes and 4 seconds with respect to the stars. What’s more, its central axis is aligned with two stars. The northern axis points outward to Polaris, hence why it is called “the North Star”, while its southern axis points to Sigma Octantis.
Axial Tilt:
As already noted, due to the Earth’s axial tilt (or obliquity), day and night are not evenly divided. If the Earth’s axis were perpendicular to its orbital plane around the Sun, all places on Earth would experience equal amounts of day and night (i.e. 12 hours of day and night, respectively) every day during the year and there would be no seasonal variability.
Instead, at any given time of the year, one hemisphere is pointed slightly more towards the Sun, leaving the other pointed away. During this time, one hemisphere will be experiencing warmer temperatures and longer days while the other will experience colder temperatures and longer nights.
Seasonal Changes:
Of course, since the Earth is rotating around the Sun and not just on its axis, this process is reversed during the course of a year. Every six months, the Earth undergoes a half orbit and changes positions to the other side of the Sun, allowing the other hemisphere to experience longer days and warmer temperatures.
Artist’s rendition of the Earth’s rotation and the precession of the Equinoxes. Credit: NASA
Consequently, in extreme places like the North and South pole, daylight or nighttime can last for days. Those times of the year when the northern and southern hemispheres experience their longest days and nights are called solstices, which occur twice a year for the northern and southern hemispheres.
The Summer Solstice takes place between June 20th and 22nd in the northern hemisphere and between December 20th and 23rd each year in the southern hemisphere. The Winter Solstice occurs at the same time but in reverse – between Dec. 20th and 23rd for the northern hemisphere and June 20th and 22nd for the southern hemisphere.
According to NOAA, around the Winter Solstice at the North Pole there will be no sunlight or even twilight beginning in early October, and the darkness lasts until the beginning of dawn in early March. Conversely, around the Summer Solstice, the North Pole stays in full sunlight all day long throughout the entire summer (unless there are clouds). After the Summer Solstice, the sun starts to sink towards the horizon.
Another common feature in the cycle of day and night is the visibility of the Moon, the stars, and other celestial bodies. Technically, we don’t always see the Moon at night. On certain days, when the Moon is well-positioned between the Earth and the Sun, it is visible during the daytime. However, the stars and other planets of our Solar System are only visible at night after the Sun has fully set.
“Night Sky”. On a clear night, the stars and the glowing band of the Milky Way Galaxy are generally visible. Credit: Sam Crimmin
The reason for this is because the light of these objects is too faint to be seen during daylight hours. The Sun, being the closest star to us and the most radiant object visible from Earth, naturally obscures them when it is overhead. However, with the Earth tilted away from the Sun, we are able to see the Moon radiating the Sun’s light more clearly, and the stars light is detectable.
On an especially clear night, and assuming light pollution is not a major factor, the glowing band of the Milky Way and other clouds of dust and gas may also be visible in the night sky. These objects are more distant than the stars in our vicinity of the Galaxy, and therefore have less luminosity and are more difficult to see.
Another interesting thing about the cycle of day and night is that it is getting slower with time. This is due to the tidal effects the Moon has on Earth’s rotation, which is making days longer (but only marginally). According to atomic clocks around the world, the modern day is about 1.7 milliseconds longer than it was a century ago – a change which may require the addition of more leap seconds in the future.
We have many interesting articles on Earth’s Rotation here at Universe Today. To learn more about solstices here in Universe Today, be sure to check out our articles on the Shortest Day of the Year and the Summer Solstice.
Apollo 17 commander Eugene Cernan with the lunar rover in December 1972, in the moon's Taurus-Littrow valley. Credit: NASA
For a brief period in the 1960s and 1970s, 12 people ventured all the way to the surface of the Moon. The accomplishment at the time was hailed as a political victory over the Soviet Union, but as decades have passed the landings have taken on more symbolic meaning with NASA — a time of optimism, of science and of the American spirit.
The last lunar landing was Apollo 17, which took place on Dec. 11, 1972. Commander Eugene Cernan and lunar module pilot Harrison Schmitt did three moonwalks in the Taurus-Littrow valley, scoping out the highlands to try to get a geologic sense of the area. Among their more memorable findings are orange soil. You can see some pictures from their sojourn below.
Apollo 17’s Saturn V rocket poised on the launch pad before its Dec. 7, 1972 takeoff. Credit:Apollo 17’s lunar rover, flag and part of the lunar module in this view taken out the module’s window. Credit: NASAApollo 17 commander Gene Cernan with a gravimeter experiment. The lunar rover is at right. Credit; NASAOrange soil (from volcanic glass beads) is clearly visible in this image from Apollo 17. Credit: NASAThe Apollo 17 command module America and its service module, as photographed by the returning lunar module Challenger. Credit: NASA
When you see the beautiful pictures from the Hubble Space Telescope, you’re looking at a lie. They’re specially colored images, done for science. But what does space really look like?
Do you love the beautiful pictures from the Hubble Space Telescope? Do you ever wonder what it would look like to fly through space and see places like the Orion Nebula up close? Just imagine hiding the Enterprise in the Mutara Nebula, and getting the jump on Khan? Have you ever wondered… what does this stuff actually look like? Looks like we’re back to wrecking sci-fi Christmas again, as I’ve got some bad news.
Nothing, nothing will ever look as cool as the pictures you see on your computer, or even have the same colors. If you were flying right through the Orion Nebula, it wouldn’t look anything like the pictures. In fact, it would kinda suck.
When looking out into the night sky with your own eyeballs, you don’t see any beautiful nebulousness. Just the stars and the faint glow of the Milky Way. You might be able to see a few fuzzy bits, hint of nebulae, galaxies and star clusters. We’re back to a familiar problem, which those of you who are considering Venus as a vacation spot know too well. We’re made out of meat, and in this case, it’s certainly not doing us any favors.
Imagine building a camera out of meat. Pop into a deli, grab a fistful of cold cuts, a pickled egg, and a light sensor, and make that into a camera. Well, that’s your eyes. With the modern advances in camera technologies, we’ve learned that apparently meat cameras are not great cameras.
The biggest advantage to the inorganic kind is that they can gather light for minutes and even hours, soaking up all the photons streaming from a distant object. They, do however, make terrible sandwiches. For example, the famous Hubble Deep Field photograph, which peered into a seemingly empty part of space, turned up thousands of galaxies. Hubble stared for more than 130 hours to create this image.
Our meat cameras refresh themselves every few seconds. Even in the darkest skies, with the most perfectly light-adjusted eyes, if you keep your eyes perfectly still and stare at a spot in space, you can’t gather more than 15-20 seconds of light with your eyes. So we’ll never see these objects because they’re so faint and deliver such a tiny amount of light for every second you stare at them.
But sure, what if you got close? What if I stuck my meat camera on a tripod right outside one of these gaseous structures. Here’s the crazy part. Nebulae never get any brighter even as you get closer. In optics, there’s a rule called “the conservation of surface brightness”. As you get closer to a nebula, it also gets bigger in the sky. The increased brightness is spread out over a larger area, and the average brightness remains exactly the same. You could be right beside the Orion Nebula, and it wouldn’t look any brighter or majestic than we see it from here on Earth. In other words… it would still suck.
But what about the colors? Here’s where astronomers are lying to you in a grand conspiracy of Roswellian proportions. So, watch out for those black helicopters, it’s time for another meeting of the Guide To Space Tinfoil Hat Society.
Charged Coupled Devices (CCD) for Ultra-Violet and Visible Detection. Credit: NASA
Astronomers generally use black-and-white CCD cameras to make their observations. Then they’ll put filters in front of their cameras to only let through very specific wavelengths of light. Those filters can match the specific colors that make up the visible spectrum: red, blue and green. But usually they’re using filters that reveal scientific information. For example, astronomers want to detect the presence of hydrogen, oxygen and sulfur in a nebula. They’ll use one filter that reveals each one of the elements. And then in a program like Photoshop, they’ll assign red to hydrogen, blue to oxygen and green to sulfur. The resulting image can look beautiful, but the colors have nothing to do with reality. That’s right, your inspirational desktop of the week is a lie.
True color images typically have no value for astronomers, but occasionally they’ll throw us a bone. They’ll produce an image using red, blue, and green filters which roughly match the capabilities of the human eye. And NASA’s Curiosity rover has a pair of color cameras, which allow it to capture images of the surface of Mars that match what you might see if you were standing on the surface of the planet… Because that robot gets us, I mean, he really gets us.
I’m sorry to be the bearer of bad news. You’ll never be able to see a nebula more beautifully with your own eyes than you do right now. But good news! Those pictures are amazingly beautiful and you don’t have to wait to see them up close!
You tell us. Even though we’ve revealed this terrible secret, what would you still want to see up close?
UPDATE: Tune in this Sunday as the good folks over at the Virtual Telescope Project feature a live webcast covering the Geminid meteor shower this Sunday on December 14th at 2:00 UT.
This weekend presents a good reason to brave the cold, as the Geminid meteor shower peaks on the morning of Sunday, December 14th. The Geminids are dependable, with a broad peak spanning several days, and would be as well known as their summer cousins the Perseids, were it not for the fact that they transpire in the dead of northern hemisphere winter.
But do not despair. While some meteor showers are so ephemeral as to be considered all but mythical in the minds of most meteor shower observers, the Geminids always deliver. We most recently caught a memorable display of the Geminids in 2012 from a dark sky locale in western North Carolina. Several meteors per minute pierced the Appalachian night, offering up one of the most memorable displays by this or any meteor shower in recent years.
The Geminids are worth courting frostbite for, that’s for sure. But there’s a curious history behind this shower and our understanding of meteor showers in general, one that demonstrates the refusal of some bodies in our solar system to “act right” and fit into neat scientific paradigms.
A composite of the 2013 Geminids. Credit: the UK Meteor Observation Network
It wasn’t all that long ago that meteor showers — let alone meteorites — were not considered to be astronomical in origin at all. Indeed, the term meteor and meteorology have the same Greek root meaning “of the sky,” suggesting ideas of an atmospheric origin. Lightning, hail, meteors, you can kind of see how they got there.
In fact, you could actually face ridicule for suggesting that meteors had an extraterrestrial source back in the day. President Thomas Jefferson was said to have done just that concerning an opinion espoused by Benjamin Silliman of a December 14th, 1807, meteorite fall in Connecticut, leading to the apocryphal and politically-tinged response attributed to the president that, “I would more easily believe that two Yankee professors would lie, than that stones would fall from heaven.”
Indeed, no sooner than The French Academy of Sciences considered the matter settled earlier in the same decade, then a famous meteorite fall occurred in Normandy on April 26th, 1803,… right on their doorstep. The universe, it seemed, was thumbing its nose at scientific enlightenment.
Things really heated up with the spectacular display known as the Leonid meteor storm in 1833. On that November morning, stars seemed to fall like snowflakes from the sky. You can imagine the sight, as the Earth plowed headlong into the meteor stream. The visual effect of such a storm looks like the starship Enterprise plunging ahead at warp speed with stars streaming by, as if imploring humanity to get hip to the fact that meteor showers and their radiants are indeed a reality.
Still, a key problem persisted that gave ammunition to the naysayers: no new “space rocks” were found littering the ground at sunrise after a meteor shower. We now know that this is because meteor showers hail from wispy cometary debris left along intersections of the Earth’s orbit. Meteorite Man Geoff Notkin once mentioned to us that no meteorite fall has ever been linked to a meteor shower, though he does get lots of calls around Geminid season.
The name of the game in the 19th century soon became identifying new meteor showers. Streams evolve over time as they interact with planets (mostly Jupiter), and the 19th century played host to some epic meteor storms such as the Andromedids that have since been reduced to a trickle.
The Geminids are, however, the black sheep of the periodic meteor shower family. The shower was first noticed by US and UK observers in 1862, and by the 1870s astronomers realized that a new minor shower with a Zenithal Hourly Rate (ZHR) hovering around 15 was occurring near the middle of December from the constellation Gemini.
The source of the Geminids, however, was to remain a mystery right up until the late 20th century.
In the late 1940s, astronomer Fred Whipple completed the Harvard Meteor Project, which utilized a photographic survey that piqued the interest of astronomers worldwide: debris in the Geminid stream appeared to have an orbital period of just 1.65 years, coupled with a high orbital inclination. Modeling suggested that the parent body was most likely a short period comet, and that the stream had undergone repeated perturbations courtesy of Earth and Jupiter.
In 1983, the culprit was found, only to result in a deeper mystery. The Infrared Astronomical Satellite (IRAS) discovered an asteroid fitting the bill crossing the constellation Draco. Backup observations from the Palomar observatory the next evening cinched the discovery, and today, we recognize the source of the Geminids as not a comet — as is the case with every other major meteor shower — but asteroid 3200 Phaethon, a 5 kilometre diameter rock in a 524 day orbit.
Asteroid 3200 Phaethon (arrowed) imaged by Marco Langbroek from the Winer Observatory in Sonita, Arizona. Credit: Wikimedia Commons.
So why doesn’t this asteroid behave like one? Is 3200 Phaethon a rogue comet that has long since settled down for the quiet space rock life? Obviously, 3200 Phaethon has lots of material shedding off from its surface, as evidenced by the higher than normal ratio of fireballs seen during the Geminid meteors. 3200 Phaethon also passes 0.14 AUs from the Sun — 47% closer than Mercury — and has the closest perihelion of any known asteroid to the Sun, which bakes the asteroid periodically with every close pass.
One thing is for certain: activity linked to the Geminid meteor stream is increasing. The Geminids actually surpassed the Perseids in terms of dependability and output since the 1960s, and have produced an annual peak ZHR of well over 100 in recent years. In 2014, expect a ZHR approaching 130 per hour as seen from a good dark sky site just after midnight local on the morning of December 14th as the radiant rides high in the sky. Remember, this shower has a broad peak, and it’s worth starting your vigil on Saturday or even Friday morning. The Geminid radiant also has a steep enough declination that local activity can start before midnight… also exceptional among meteor showers. This year, the 52% illuminated Moon rises around midnight local on the morning of December 14th.
The Geminid radiant looking to the northeast at 11PM local. Note the radiant of the December 22nd Ursids is also nearby. Credit: Stellarium.
And there’s another reason to keep an eye on the 2014 Geminids. 3200 Phaethon passed 0.12 AU (18 million kilometers) from Earth on December 10th, 2007, which boosted displays in the years after. And just three years from now, the asteroid will pass even closer on December 10th, 2017, at just 0.07 AUs (10.3 million kilometers) from Earth…
Are we due for some enhanced activity from the Geminids in the coming years?
All good reasons to bundle up and watch for the “Tears of the Twins” this coming weekend, and wonder at the bizzaro nature of the shower’s progenitor.
