Meteors Archives

December 11, 2014December 23, 2015 by David Dickinson

The Curious History of the Geminid Meteors

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 14^th, 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 26^th, 1803,… right on their doorstep. The universe, it seemed, was thumbing its nose at scientific enlightenment.

A fine Geminid — A fine 2004 Geminid as imaged by Frankie Lucena.

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 19^th century soon became identifying new meteor showers. Streams evolve over time as they interact with planets (mostly Jupiter), and the 19^th 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.

A possible early 2014 Geminid and the near Full Moon as seen by NASA’s All Sky Fireball Network.

The source of the Geminids, however, was to remain a mystery right up until the late 20^th 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.

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 14^th.

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 10^th, 2007, which boosted displays in the years after. And just three years from now, the asteroid will pass even closer on December 10^th, 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.

December 9, 2014December 23, 2015 by Bob King

Don’t Miss the Geminids this Weekend, Best Meteor Shower of the Year

Time lapse-photo showing geminids over Pendleton, OR. Credit: Thomas W. Earle

Wouldn’t it be nice if a meteor shower peaked on a weekend instead of 3 a.m. Monday morning? Maybe even showed good activity in the evening hours, so we could get our fill and still get to bed at a decent hour. Wait a minute – this year’s Geminids will do exactly that!

*Before moonrise this Saturday night December 13th, the Geminids should put on a sweet display. The radiant of the shower lies near the bright pair of stars, Castor and Pollux. Source: Stellarium*

What’s more, since the return of this rich and reliable annual meteor shower occurs around 6 a.m. (CST) on Sunday December 14th, both Saturday and Sunday nights will be equally good for meteor watching. After the Perseids took a battering from the Moon last August, the Geminids will provide the best meteor display of 2014. They do anyway! The shower’s been strengthening in recent years and now surpasses every major shower of the year.

The official literature touts a rate of 120 meteors per hour visible from a dark sky site, but I’ve found 60-80 per hour a more realistic expectation. Either way, what’s to complain?

The third quarter Moon rises around midnight Saturday and 1 a.m. on Monday morning. Normally, moonlight would be cause for concern, but unlike many meteor showers the Geminids put on a decent show before midnight. The radiant, the location in the sky from which the meteors will appear to stream, will be well up in the east by 9:30 p.m. local time. That’s a good 2-3 hours of meteor awesomeness before moonrise.

The author tries his best to enjoys this year's moon-drenched Perseids from the "astro recliner". Credit: Bob King — The author takes in this year’s moon-drenched Perseids in comfort.

Shower watching is a total blast because it’s so simple. Your only task is to dress warmly and get comfortable in a reclining chair aware from the unholy glare of unshielded lighting. The rest is looking up. Geminid meteors will flash anywhere in the sky, so picking a direction to watch the shower isn’t critical. I usually face east or southeast for the bonus view of Orion lumbering up from the horizon.

Bring your camera, too. I use a moderately wide angle lens (24-35mm) at f/2.8 (widest setting), set my ISO to 800 or 1600 and make 30-second exposures. The more photos you take, the better chance of capturing a meteor. You can also automate the process by hooking up a relatively inexpensive intervalometer to your camera and have it take the pictures for you.

As you ease back and let the night pass, you’ll see other meteors unrelated to the shower, too. Called sporadics, they trickle in at the rate of 2-5 an hour. You can always tell a Geminid from an interloper because its path traces back to the radiant. Sporadics drop down from any direction.

A Geminid fireball brighter than Venus streaks across the sky above New Mexico on Dec. 14, 2011. It was captured by an all-sky camera. Before disintegrating in the atmosphere the meteoroid was about 1/2 inch across. Credit: Marshall Space Flight Center, Meteoroid Environments Office, Bill Cooke — Captured by an all-sky camera, a Geminid fireball brighter than Venus streaks across the sky above New Mexico on Dec. 14, 2011. Before disintegrating in the atmosphere the meteoroid was about 1/2 inch across. Credit: Marshall Space Flight Center, Meteoroid Environments Office, Bill Cooke

Geminid meteors immolate in Earth’s atmosphere at a moderate speed compared to some showers – 22 miles per second (35 km/sec) – and often flare brightly. Green, red, blue, white and yellow colors have been recorded, making the shower one of the more colorful. Most interesting, the meteoroid stream appears to be sorted according to size with faint, telescopic meteors maxing out a day before the naked eye peak. Larger particles continue to produce unusually bright meteors up to a few days after maximum.

Most meteor showers are the offspring of comets. Dust liberated from vaporizing ice gets pushed back by the pressure of sunlight to form a tail and fans out over the comet’s orbital path. When Earth’s orbit intersects a ribbon of this debris, sand and gravel-sized bits of rock crash into our atmosphere at high speed and burn up in multiple flashes of meteoric light.

Phaethon sprouts a tail when close to the Sun seen in this image taken by NASA's STEREO Sun-observing spacecraft in 2012. Credit: Credit: Jewitt, Li, Agarwal /NASA/STEREO — Phaethon sprouts a tail (points southeast or to lower left) when close to the Sun in this image taken by NASA’s STEREO Sun-observing spacecraft in 2012. Credit: Credit: Jewitt, Li, Agarwal /NASA/STEREO

But the Geminids are a peculiar lot. Every year in mid-December, Earth crosses not a comet’s path but that of 3200 Phaethon (FAY-eh-thon), a 3.2 mile diameter (5.1 km) asteroid. Phaethon’s elongated orbit brings it scorchingly close (13 million miles) to the Sun every 1.4 years. Normally a quiet, well-behaved asteroid, Phaethon brightened by a factor of two and was caught spewing jets of dust when nearest the Sun in 2009, 2010 and 2012. Apparently the intense heat solar heating either fractured the surface or heated rocks to the point of desiccation, creating enough dust to form temporary tails like a comet.

While it looks like an asteroid most of the time, Phaethon may really be a comet that’s still occasionally active. Periodic eruptions provide the fuel for the annual December show.

Most of us will head out Saturday or Sunday night and take in the shower for pure enjoyment, but if you’d like to share your observations and contribute a bit of knowledge to our understanding of the Geminids, consider reporting your meteor sightings to the International Meteor Organization. Here’s the link to get started.

And this just in … Italian astronomer Gianluca Masi will webcast the shower starting at 8 p.m. CST December 13th (2 a.m. UT Dec. 14) on his Virtual Telescope Project site.

December 3, 2014December 23, 2015 by Matt Williams

Meteorite May Contain Proof of Life on Mars, Researchers Say

The idea that Mars could have supported life at one time is the subject of ongoing debate. Image credit: NASA

Mars is currently home to a small army robotic rovers, satellites and orbiters, all of which are busy at work trying to unravel the deeper mysteries of Earth’s neighbor. These include whether or not the planet ever had liquid water on its surface, what the atmosphere once looked like, and – most importantly of all – if it ever supported life.

And while much has been learned about Martian water and its atmosphere, the all-important question of life remains unanswered. Until such time as organic molecules – considered to be the holy grail for missions like Curiosity – are found, scientists must look elsewhere to find evidence of Martian life.

According to a recent paper submitted by an international team of scientists, that evidence may have arrived on Earth three and a half years ago aboard a meteorite that fell in the Moroccan desert. Believed to have broken away from Mars 700,000 years ago, so-called Tissint meteorite has internal features that researchers say appear to be organic materials.

The paper appeared in the scientific journal Meteoritics and Planetary Sciences. In it, the research team – which includes scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) – indicate organic carbon is located inside fissures in the rock. All indications are the meteorite is Martian in origin.

“So far, there is no other theory that we find more compelling,” says Philippe Gillet, director of EPFL’s Earth and Planetary Sciences Laboratory. He and his colleagues from China, Japan and Germany performed a detailed analysis of organic carbon traces from a Martian meteorite, and have concluded that they have a very probable biological origin.

Artist's conception of an fragment as it blasts off from Mars. Boulder-sized planetary fragments could be a mechanism that carried life between Mars and Earth, UA planetary scientist Jay Melosh says. (Credit: The Planetary Society) — *Artist’s conception of an fragment as it blasts off from Mars as a result of a meteor impact. Credit: The Planetary Society*

The scientists argue that carbon could have been deposited into the fissures of the rock when it was still on Mars by the infiltration of fluid that was rich in organic matter.

If this sounds familiar, you may recall a previous Martian meteorite named ALH84001, found in the Allen Hills region in Antarctica. In 1996 NASA researchers announced they had found evidence within ALH84001 that strongly suggested primitive life may have existed on Mars more than 3.6 billion years ago. While subsequent studies of the now famous Allen Hills Meteorite shot down theories that the Mars rock held fossilized alien life, both sides continue to debate the issue.

This new research on the Tissint meteorite will likely be reviewed and rebutted, as well.

The researchers say the meteorite was likely ejected from Mars after an asteroid crashed on its surface, and fell to Earth on July 18, 2011, and fell in Morocco in view of several eyewitnesses.

Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Several research teams have already shown that this component is organic in nature, but they are still debating where the carbon came from.

Chemical, microscopic and isotope analysis of the carbon material led the researchers to several possible explanations of its origin. They established characteristics that unequivocally excluded a terrestrial origin, and showed that the carbon content were deposited in the Tissint’s fissures before it left Mars.

This research challenges research proposed in 2012 that asserted that the carbon traces originated through the high-temperature crystallization of magma. According to the new study, a more likely explanation is that liquids containing organic compounds of biological origin infiltrated Tissint’s “mother” rock at low temperatures, near the Martian surface.

A piece of the Tissint meteorite that came to Earth via Mars. Credit: EPFL/Alain Herzog — *A piece of the Tissint meteorite that landed on Earth on July 18th, 2011. Credit: EPFL/Alain Herzog*

These conclusions are supported by several intrinsic properties of the meteorite’s carbon, e.g. its ratio of carbon-13 to carbon-12. This was found to be significantly lower than the ratio of carbon-13 in the CO2 of Mars’s atmosphere, previously measured by the Phoenix and Curiosity rovers.

Moreover, the difference between these ratios corresponds perfectly with what is observed on Earth between a piece of coal – which is biological in origin – and the carbon in the atmosphere.

The researchers note that this organic matter could also have been brought to Mars when very primitive meteorites – carbonated chondrites – fell on it. However, they consider this scenario unlikely because such meteorites contain very low concentrations of organic matter.

“Insisting on certainty is unwise, particularly on such a sensitive topic,” warns Gillet. “I’m completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars – at least in the past.”

Be sure to check out these videos from EPFL News, which include an interview with Philippe Gillet, EPFL and co-author of the study:

And this video explaining the history of the Tissint meteor:

Further Reading: EPFL

November 18, 2014December 23, 2015 by Vanessa Janek

The Origins of Life Could Indeed Be “Interstellar”

This image shows a star-forming region in interstellar space. A new study used AI and radiotelescope data to find 140,000 regions in the Milky Way that will eventually form stars like this region. Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

Some of science’s most pressing questions involve the origins of life on Earth. How did the first lifeforms emerge from the seemingly hostile conditions that plagued our planet for much of its history? What enabled the leap from simple, unicellular organisms to more complex organisms consisting of many cells working together to metabolize, respire, and reproduce? In such an unfamiliar environment, how does one even separate “life” from non-life in the first place?

Now, scientists at the University of Hawaii at Manoa believe that they may have an answer to at least one of those questions. According to the team, a vital cellular building block called glycerol may have first originated via chemical reactions deep in interstellar space.

Glycerol is an organic molecule that is present in the cell membranes of all living things. In animal cells this membrane takes the form of a phospholipid bilayer, a dual-layer membrane that sandwiches water-repelling fatty acids between outer and inner sheets of water-soluble molecules. This type of membrane allows the cell’s inner aqueous environment to remain separate and protected from its external, similarly watery world. Glycerol is a vital component of each phospholipid because it forms the backbone between the molecule’s two characteristic parts: a polar, water-soluble head, and a non-polar, fatty tail.

Many scientists believe that cell membranes such as these were a necessary prerequisite to the evolution of multicellular life on Earth; however, their complex structure requires a very specific environment – namely, one low in calcium and magnesium salts with a fairly neutral pH and stable temperature. These carefully balanced conditions would have been hard to come by on the prehistoric Earth.

Icy bodies born in interstellar space offer an alternative scenario. Scientists have already discovered organic molecules such as amino acids and lipid precursors in the Murchison meteorite that landed in Australia in 1969. Although the idea remains controversial, it is possible that glycerol could have been brought to Earth in a similar manner.

The Murchison Meteorite. Image credit: James St. John — The Murchison Meteorite.
Image credit: James St. John

Meteors typically form from tiny crumbs of material in cold molecular clouds, regions of gaseous hydrogen and interstellar dust that serve as the birthplace of stars and planetary systems. As they move through the cloud, these grains accumulate layers of frozen water, methanol, carbon dioxide, and carbon monoxide. Over time, high-energy ultraviolet radiation and cosmic rays bombard the icy fragments and cause chemical reactions that enrich their frozen cores with organic compounds. Later, as stars form and ambient material falls into orbit around them, the ices and the organic molecules they contain are incorporated into larger rocky bodies such as meteors. The meteors can then crash into planets like ours, potentially seeding them with building blocks of life.

In order to test whether or not glycerol could be created by the high-energy radiation that typically bombards interstellar ice grains, the team at the University of Hawaii designed their own meteorites: small bits of icy methanol cooled to 5 degrees Kelvin. After blasting their model ices with energetic electrons meant to mimic the effects of cosmic rays, the scientists found that some molecules of methanol within the ices did, in fact, transform into glycerol.

While this experiment appears to be a success, scientists realize that their laboratory models do not exactly replicate conditions in interstellar space. For instance, methanol traditionally makes up only about 30% of the ice in space rocks. Future work will investigate the effects of high-energy radiation on model ices made primarily of water. High-energy electrons fired in a lab are also not a perfect substitute for true cosmic rays and do not represent effects on ice that may result from ultraviolet radiation in interstellar space.

More research is necessary before scientists can draw any global conclusions; however, this study and its predecessors do provide compelling evidence that life as we know it truly could have come from above.

November 17, 2014December 23, 2015 by Tim Reyes

We are not Alone: Government Sensors Shed New Light on Asteroid Hazards

This diagram maps data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors (bolides). The location of impacts from objects ranging from 1 meter (3 feet) to nearly 20 meters (60 feet) in size such as Chelyabinsk asteroid are shown globally. (Credit: Planetary Science, NASA)

How hazardous are the thousands and millions of asteroids that surround the third rock from the Sun – Earth? Since an asteroid impact represents a real risk to life and property, this is a question that has been begging for answers for decades. But now, scientists at NASA’s Jet Propulsion Laboratory have received data from a variety of US Department of Defense assets and plotted a startling set of data spanning 20 years.

This latest compilation of data underscores how frequent some of these larger fireballs are, with the largest being the Chelyabinsk event on February 15, 2013 which injured thousands in Russia. The new data will improve our understanding of the frequency and presence of small and large asteroids that are hazards to populated areas anywhere on Earth.

On Feb. 28, 2009, Peter Jenniskens (SETI/NASA), finds his first 2008TC3 meteorite after an 18-mile long journey. "It was an incredible feeling," Jenniskens said. The African Nubian Desert meteorite of Oct 7, 2008 was the first asteroid whose impact with Earth was predicted while still in space approaching Earth. 2008TC3 and Chelyabinsk are part of the released data set. (Credit: NASA/SETI/P.Jenniskens) — On Feb. 28, 2009, Peter Jenniskens (SETI/NASA), finds his first 2008TC3 meteorite after an 18-mile long journey. “It was an incredible feeling,” Jenniskens said. The meteorite which impacted in the Nubian Desert of Africa on Oct 7, 2008 was the first asteroid whose impact with Earth was predicted while still in space approaching Earth. Meteorite 2008TC3 and Chelyabinsk’s are part of the released data set. (Credit: NASA/SETI/P.Jenniskens)

The data from “government sensors” – meaning “early warning” satellites to monitor missile launches (from potential enemies) as well as infrasound ground monitors – shows the distribution of bolide (fireball) events. The data first shows how uniformly distributed the events are around the world. This data is now released to the public and researchers for more detailed analysis.

The newest data released by the US government shows both how frequent bolides are and also how effectively the Earth’s atmosphere protects the surface. A subset of this data had been analyzed and reported by Dr. Peter Brown from the University of Western Ontario, Canada and his team in 2013 but included only 58 events. This new data set holds 556 events.

The newly released data also shows how the Earth’s atmosphere is a superior barrier that prevents small asteroids’ penetration and impact onto the Earth’s surface. Even the 20 meter (65 ft) Chelyabinsk asteroid exploded mid-air, dissipating the power of a nuclear blast 29.7 km (18.4 miles, 97,400 feet) above the surface. Otherwise, this asteroid could have obliterated much of a modern city; Chelyabinsk was also saved due to sheer luck – the asteroid entered at a shallow angle leading to its demise; more steeply, and it would have exploded much closer to the surface. While many do explode in the upper atmosphere, a broad strewn field of small fragments often occurs. In historical times, towns and villages have reported being pelted by such sprays of stones from the sky.

NASA and JPL emphasized that investment in early detection of asteroids has increased 10 fold in the last 5 years. Researchers such as Dr. Jenniskens at the SETI Institute has developed a network of all-sky cameras that have determined the orbits of over 175,000 meteors that burned up in the atmosphere. And the B612 Foundation has been the strongest advocate of discovering of all hazardous asteroids. B612, led by former astronauts Ed Lu and Rusty Schweikert has designed a space telescope called Sentinel which would find hazardous asteroids and help safeguard Earth for centuries into the future.

Speed is everything. While Chelyabinsk had just 1/10th the mass of Nimitz-class super carrier, it traveled 1000 times faster. Its kinetic energy on account of its speed was 20 to 30 times that released by the nuclear weapons used to end the war against Japan – about 320 to 480 kilotons of TNT. Briefly, asteroids are considered to be any space rock larger than 1 meter and those smaller are called meteoroids.

Two earlier surveys can be compared to this new data. One by Eugene Shoemaker in the 1960s and another by Dr. Brown. The initial work by Shoemaker using lunar crater counts and the more recent work of Dr. Brown’s group, utilizing sensors of the Department of Defense, determined estimates of the frequency of asteroid impacts (bolide) rates versus the size of the small bodies. Those two surveys differ by a factor of ten, that is, where Shoemaker’s shows frequencies on the order of 10s or 100s years, Brown’s is on the order of 100s and 1000s of years. The most recent data, which has adjusted Brown’s earlier work is now raising the frequency of hazardous events to that of the work of Shoemaker.

The work of Dr. Brown and co-investigators led to the following graph showing the frequency of collisions with the Earth of asteroids of various sizes. This plot from a Letter to Nature by P. Brown et al. used 58 bolides from data accumulated from 1994 to 2014 from government sensors. Brown and others will improve their analysis with this more detailed dataset. The plot shows that a Chelyabinsk type event can be expected approximately every 30 years though the uncertainty is high. The new data may reduce this uncertainty. Tungunska events which could destroy a metropolitan area the size of Washington DC occur less frequently – about once a century.

The estimated cumulative flux of impactors at the Earth. The bolide impactor flux at Earth (Bolide flux 1994-2013 - black circles) based on ~20 years of global observations from US Government sensors and infrasound airwave data. Global coverage averages 80% among a total of 58 observed bolides with E > 1 kt and includes the Chelyabinsk Chelyabinsk bolide (far right black circle). This coverage correction is approximate and the bolide flux curve is likely a lower limit. The full caption is at bottom. (Credit: P. Brown, Letter to Nature, 2013, Figure 3) — The estimated cumulative flux of impactors at the Earth. The bolide impactor flux at Earth (Bolide flux 1994-2013 – black circles) based on ~20 years of global observations from US Government sensors and infrasound airwave data. Global coverage averages 80% among a total of 58 observed bolides with E > 1 kt and includes the Chelyabinsk Chelyabinsk bolide (far right black circle). This coverage correction is approximate and the bolide flux curve is likely a lower limit. The full caption is at bottom. (Credit: P. Brown, Letter to Nature, 2013, Figure 3)

Asteroids come in all sizes. Smaller asteroids are much more common, larger ones less so. A common distribution seen in nature is represented by a bell curve or “normal” distribution. Fortunately the bigger asteroids number in the hundreds while the small “city busters” count in the 100s of thousands, if not millions. And fortunately, the Earth is small in proportion to the volume of space even just the space occupied by our Solar System. Additionally, 69% of the Earth’s surface is covered by Oceans. Humans huddle on only about 10% of the surface area of the Earth. This reduces the chances of any asteroid impact effecting a populated area by a factor of ten.

Altogether the risk from asteroids is very real as the Chelyabinsk event underscored. Since the time of Tugunska impact in Siberia in 1908, the human population has quadrupled. The number of cities of over 1 million has increased from 12 to 400. Realizing how many and how frequent these asteroid impacts occur plus the growth of the human population in the last one hundred years raises the urgency for a near-Earth asteroid discovery telescope such as B612’s Sentinel which could find all hazardous objects in less than 10 years whereas ground-based observations will take 100 years or more.

Reference:
New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population

Full Caption of the included plot from LETTERS TO NATURE, The Chelyabinsk airburst : Implications for the Impact Hazard, P.G. Brown, et al.

The estimated cumulative flux of impactors at the Earth. The bolide impactor flux at Earth (Bolide flux 1994-2013 – black circles) based on ~20 years of global observations from US Government sensors and infrasound airwave data. Global coverage averages 80% among a total of 58 observed bolides with E > 1 kt and includes the Chelyabinsk Chelyabinsk bolide (far right black circle). This coverage correction is approximate and the bolide flux curve is likely a lower limit. The brown-coloured line represents an earlier powerlaw fit from a smaller dataset for bolides between 1 – 8 m in diameter15. Error bars represent counting statistics only. For comparison, we plot de-biased estimates of the near-Earth asteroid impact frequency based on all asteroid survey telescopic search data through mid- 2012 (green squares)8 and other earlier independently analysed telescopic datasets including NEAT discoveries (pink squares) and finally from the Spacewatch (blue squares) survey, where diameters are determined assuming an albedo of 0.1. Energy for telescopic data is computed assuming a mean bulk density of 3000 kgm-3 and average impact velocity of 20.3 kms-1. The intrinsic impact frequency for these telescopic data was found using an average probability of impact for NEAs as 2×10-9 per year for the entire population. Lunar crater counts converted to equivalent impactor flux and assuming a geometric albedo of 0.25 (grey solid line) are shown for comparison9, though we note that contamination by secondary craters and modern estimates of the NEA population which suggest lower albedos will tend to shift this curve to the right and down. Finally, we show estimated influx from global airwave measurements conducted from 1960-1974 which detected larger (5-20m) bolide impactors (upward red triangles) using an improved method for energy estimation compared to earlier interpretations of these same data.

November 7, 2014December 23, 2015 by Bob King

Mind-blowing Meteor Shower on Mars During Comet Flyby, Say NASA Scientists

We can only imagine what the meteor storm from Comet Siding Spring must have looked like standing on the surface of Mars on October 19, 2014. NASA scientists announced today that the planet experienced an exceptional shower during the comet's flyby, saturating the sky. Source: Stellarium

“Thousands of meteors per hour would have been visible — truly astounding to the human eye.” That’s Nick Schneider’s description of what you and I would have seen standing on Mars during Comet Siding Spring’s close flyby last month. “It would have been really mind-blowing,” he added. Schneider is instrument lead for MAVEN’s Imaging Ultraviolet Spectrograph (IUVS).

He and a group of scientists who work as lead investigators for instruments on the MAVEN and Mars Reconnaissance Orbiter (MRO) spacecraft shared the latest results from the comet flyby during a media teleconference earlier today. There were many surprises. Would we expect anything less from a comet?

Here’s a summary of the results:

A very dusty ice ball – The comet’s dust tail and the amount of dust in its coma were much larger than expected, prompting Jim Green, director of NASA’s Planetary Science Division in Washington, to remark: “It makes me very happy we hid them (the spacecraft) on the backside of Mars. That really saved them.” Siding Spring dumped several tons of fine dust into the Martian atmosphere prompting a spectacular meteor shower and possibly causing a yellow, twilight afterglow above the Curiosity landing site from vaporizing sodium atoms contained in the minerals. That, and dust in the mid-levels of the atmosphere at the time contributed to the rover’s difficulty in getting good photos of the comet itself. Scientists are still examining the images.

MAVEN's Ultraviolet Imaging Spectrograph (IUVS) uses limb scans to map the chemical makeup and vertical structure across Mars' upper atmosphere. It detected strong enhancements of magnesium and iron from ablating incandescing dust from Comet Siding Spring. Credit: NASA — MAVEN’s Ultraviolet Imaging Spectrograph (IUVS) uses limb scans to map the chemical makeup and vertical structure across Mars’ upper atmosphere. It detected strong enhancements of magnesium and iron from ablating incandescing dust from Comet Siding Spring. Credit: NASA

I'm not big into graphs either, but check out the heavy metal drama in this. On the left is the "before" scan from MAVEN's IUVS instrument; on the right, during the comet's close approach. The spike in magnesium from vaporizing comet dust is impressive. Ionized magnesium is the strongest spike with neutral and ionized iron on the left in smaller amounts. Both elements are common in meteorites as well as on Earth. Credit: NASA — I’m not big into graphs either, but check out the heavy metal drama going on here. On the left is the “before” scan from MAVEN’s IUVS instrument; on the right, during the comet’s close approach. The spike in magnesium from vaporizing comet dust is impressive. Ionized magnesium is the strongest spike with neutral and ionized iron on the left in smaller amounts. Both elements are common in meteorites as well as on Earth. Credit: NASA

Profiles showing spikes in the amounts of eight different metals detected in Mars' atmosphere during the flyby by MAVEN's Neutral Gas and Ion Mass Spectrometer (NGIMS). The emissions faded with a short time. Credit: NASA — Profiles showing spikes in the amounts of eight different metals over time detected in Mars’ atmosphere by MAVEN’s Neutral Gas and Ion Mass Spectrometer (NGIMS). The emissions faded within a short time, but chemicals from the comet will continue to interact with the Martian atmosphere over time. Credit: NASA

Chemistry of Mars’ atmosphere changed – Dust vaporized in the intense meteor shower produced a striking increase in the amount of magnesium, iron and others metals in Mars’ upper atmosphere. “We were pressed back in our chairs,” said Mike Schneider. The bombardment created a temporary new layer of comet-tainted air and may have acted as condensation nuclei for the formation of high-altitude clouds. MAVEN’s Neutral Gas and Ion Mass Spectrometer (NGIMS) recorded huge spikes in the levels of eight different metals during the comet’s passage and then trailed off a day or so later. “They came to MAVEN as a free sample from no less than an Oort Cloud comet,” said Mehdi Benna, instrument scientist for MAVEN’s Neutral Gas and Ion Mass Spectrometer.

The MARSIS instrument on the Mars Express is a ground penetrating radar sounder used to look for subsurface water and ice. It can also make soundings of the ionosphere. It was used to see the new ionospheric layer formed by vaporizing comet dust on October 19th. Credit: ESA

The Mars Express radar probed the ionosphere (upper atmosphere) at three different times. At top, before the comet arrived; middle, 7 hours later after the comet's closest approach and bottom, hours later after the comet had departed. The middle graph shows a strong signal (blue horizontal bar) from the creation of newly-ionized layer of the planet's lower atmosphere from hot, fast-moving comet dust. Credit: ESA — The Mars Express radar probed the ionosphere (upper atmosphere) at three different times. At top, before the comet arrived; middle, 7 hours later after the comet’s closest approach and bottom, hours later after the comet had departed. The middle graph shows a strong signal (blue horizontal bar) from the creation of a newly-ionized layer of the planet’s lower atmosphere from hot, fast-moving comet dust. Credit: ESA

Flaming comet dust creates new ionospheric layer – Comet dust slamming into the atmosphere at 125,000 mph (56 km/sec) knocked electrons loose from atoms in the thin Martian air 50-60 miles (80-100 km) high, ionizing them and creating a very dense ionization layer in the planet’s lower ionosphere seven hours after the comet’s closest approach. Normally, Mars ionosphere is only seen on the dayside of the planet, but even when the MARSIS instrument on Mars Express beamed radio waves through the atmosphere on the nightside of the planet, it picked up a very strong signal.

54 red-filtered images of the comet's nucleus-coma taken by the MRO's HiRISE camera show changes in the flow of material leaving the comet. Credit: NASA — 54 red-filtered, false-color images of the comet’s nucleus-coma taken by the MRO’s HiRISE camera show changes in the flow of material leaving the comet. Based on the photos, the comet’s nucleus spins once every 8 hours. Credit: NASA

The five closest photos made with the HiRISE camera show the combined light of the nucleus and coma. Scale is 140-meter per pixel at top and 177-meters at bottom. Scientists will further process these images to separate the nucleus from the coma. Credit: NASA

Nucleus spins once during your work day – Comet Siding Spring’s icy core spins once every 8 hours and its irregular shape causes strong variations in the comet’s brightness. The comet’s size appears less certain – at least for the moment – with estimates anywhere between a few hundred meters to 2 km (1.2 miles). More analysis on images taken by MRO’s HiRISE camera should narrow that number soon.

CRISM photo and spectrum of Comet Siding Spring. The spectrum is "flat", indicating we're seeing sunlight reflected off comet dust. The intriguing color variations in the image tell of dust particles of varying size leaving the nucleus. Credit: NASA — CRISM photo and spectrum of Comet Siding Spring. The spectrum is “flat”, indicating we’re seeing ordinary sunlight reflecting off comet dust. The intriguing color variations in the image tell us the comet’s spewing dust particles of many sizes. Credit: NASA

Dust motes of many sizes – Color variations across Siding Spring’s coma seen by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) indicate it’s releasing dust particles of different sizes – big and little.

The scientists involved in the encounter couldn’t be happier with how the instruments functioned and the amount of hard data returned. Said Jim Green: “We are so lucky to observe this once-in-a-lifetime event.” How true when you consider that it takes about 8 million years for a comet from the Oort Cloud, that vast reservoir of frozen comets extending nearly a light year from the Sun, to get here in the first place. Nick Schneider put it another way:

“Not only is this a free sample of the Oort Cloud in Mars’ atmosphere, but it gives us a chance to learn more about Mars itself.”

If you’d like to listen in to the hour-long teleconference at any time, it’ll be up for the next week or so HERE.

November 6, 2014December 30, 2015 by Nancy Atkinson

Persistent Train: Exploding Meteor Captured in New Timelapse

The Milky Way likes to amaze us, and this great video shot by Wes Eisenhauer outside of Custer, South Dakota, shows an amazing exploding meteor and what is known as a persistent train from the fireball. The “remains” of the fireball persisted for several minutes (just a few seconds in the timelapse) and upper atmosphere wind shear twisted and swirled the expanding debris.

This was shot on October 16th, 2014, before the official start of the Orionid meteor shower, so this was perhaps a random larger meteor streaking through the sky.

Continue reading “Persistent Train: Exploding Meteor Captured in New Timelapse”

October 22, 2014December 23, 2015 by Bob King

Beastly Sunspot Amazes, Heightens Eclipse Excitement

Ron Cottrell captured the sunspot in all its swirly magnetic goodness in hydrogen-alpha light on October 19. To appreciate its size, he included the Earth (lower left) for reference. Credit: Ron Cottrell

That’s one big, black blemish on the Sun today! Rarely have we been witness to such an enormous sunspot. Lifting the #14 welder’s glass to my eyes this morning I about jumped back and bumped into the garage.

Properly shielded, it was very easy to see with the naked eye. Unlike some other naked eye sunspots, this one showed structure. The eastern end was darker, the western half grayer and more extended.

Watch the giant spot rotate into view and grow right before your eyes in this 72-hour time-lapse video taken by SOHO’s HMI imager Oct. 18-20, 2014

Through a small telescope, the mix of dark umbras scattered amid weirdly sculpted penumbral “islands” was incredible to see. Photographs like the one above are wonderful documents, but witnessing this beautiful complex magnetic mess with your own eyes is another experience altogether. Region 2192 continues to grow and size and complexity and is now the largest sunspot group of solar cycle 24 which began in 2009 – more than five years ago!

Active region 2192 is now the largest sunspot group to appear in over five years. Credit: Alex Young — Active region 2192 is now the largest sunspot group to appear in over five years. Compare to Jupiter and the Earth. Credit: SDO/HMI/Alex Young

Every sunspot marks a region on the Sun’s shiny outer skin called the photosphere where magnetic energy is concentrated. Strong magnetic fields within a sunspot group quell the turbulent churning of the photosphere, chilling the region by several thousand degrees. Sunspots appear dark against the Sun’s blazing disk because they’re cooler. Cooler meaning 8,000 F instead of 11,000 F, so yes, they’re still VERY hot.

Watch as Region 2192 crackles with energy and flares as seen in far ultraviolet light with NASA’s Solar Dynamics Observatory.

Energy stored in sunspots’ twisted magnetic fields can suddenly be released in violent, explosions called solar flares. Billions of tons of solar plasma – the sizzling mix of protons and electrons that composes the Sun – are heated to millions of degrees during the explosion and rapidly accelerated into space. Radiation from radio waves to X-rays and gamma rays fans out at the speed of light. Fortunately for us, our atmosphere and planetary magnetic field protect us from most of what flares can fling our way.

NASA's Solar Dynamics Observatory took this photo of the sun and Jupiter-sized sunspot 2192 this morning Oct. 22 at 8:45 a.m. CDT. The view in a small telescope equipped with a safe solar filter is even better! Credit: NASA — NASA’s Solar Dynamics Observatory took this photo of the Sun and Jupiter-sized sunspot region 2192 this morning Oct. 22 at 8:45 a.m. CDT. The view in a small telescope equipped with a safe solar filter is even better! Credit: NASA

But as the Sun rotates this monster into our line of sight, possibilities for Earth-directed flares and coronal mass ejections increase as do geomagnetic storms, the bringer of auroras. Already in the past 48 hours, the spot has dished out seven M-class flares and a powerful X-1 flare even before it has fully come into view. There’s more to come – Region 2192 harbors an unstable beta-gamma-delta magnetic field ripe for additional flaring including more of the X-class variety.

The sun on October 21 showing smaller sunspot regions along with our featured group. Credit: Sarah and Simon Fisher — The Sun on October 21 showing smaller sunspot regions along with our featured group. Credit: Sarah and Simon Fisher

There’s no doubt now that this behemoth will stick around to add a whole new dimension to tomorrow’s partial solar eclipse. I can’t wait to see the Moon’s black curve approach and at least partially occult the group from view. If you’re interested in getting some one-of-a-kind pictures of the scene, please see our own Dave Dickinson’s excellent guide on photographing the partial eclipse.

A sliver of a Moon rises in morning twilight today October 22 just a day away from its appointment with the Sun. Credit: Bob King

While we’re on the Moon, early morning risers had the pleasure of its company just one day before New Moon and solar eclipse. I was out watching the Orionid meteor shower. While not rich like the Perseids or Geminids I managed to catch a few including a few lucky shots with the camera.

An Orionid meteor slashes across the top of the frame directly above the constellation Orion early this morning October 22, 2014. Details: 24mm lens, f/2.8, 30-seconds at ISO 1600. Credit: Bob King

The shower has peaked but will still be active the remainder of the week if you’re inclined to take a look. And I can’t resist. How about one last sweet close-up photo of sunspot group 2192? I have a feeling you won’t mind.

Monster Sunspot AR12192 taken by Karzaman Ahmad on October 21, 2014 from Langkawi Nagtional Observatory, Malaysia credit: Karzaman Ahmad and shared at spaceweather.com — Monster Sunspot AR12192 taken by Karzaman Ahmad on October 21, 2014, from Langkawi Nagtional Observatory, Malaysia. Credit: Karzaman Ahmad and shared at spaceweather.com. Click the image to see additional animations and photos on Alex Young’s site

October 13, 2014December 23, 2015 by David Dickinson

Get Ready for the Fireballs of October

A recent fireball captured over the UK on October

On October 31^st 2005, trick-or-treaters across the central U.S. eastern seaboard were treated to a brilliant fireball, a celestial spectacle that frequently graces October skies.

Mid- to late October is fireball season, a time when several key meteor showers experience a broad peak. We’re already seeing an uptick in fireball activity as monitored by numerous all-sky cameras this month, including NASA’s system positioned across the United States. Three lesser known but fascinating showers are the chief culprits.

A Bay area fireball captured in 2012. Credit: NASA/Robert P. Moreno Jr.

The main meteor shower on tap for the month of October is the Orionids. This shower radiates from the Club of the constellation Orion, and is the product of that most famous comet of them all, 1P Halley. Halley’s Comet is actually the source of two annual meteor showers, the October Orionids and the May Eta Aquarids. We’re seeing the inward stream of Halley debris in October, and Orionid velocities average a swift 66 kilometres a second. The radiant rides highest for northern hemisphere observers at 4 AM local, and 2014 sees an estimated zenithal hourly rate (ZHR) of 20 predicted to arrive on the mornings of October 21^st through the 22^nd. The Orionids experience a broad peak spanning October 21^st through November 7^th, and 2014 sees the peak arrive just two days prior to the Moon reaching New phase. The Orionids have exhibited an uptick in activity as high as 50-75 per hour from 2005-2007, and it’s been suggested that a 12 year peak cycle may govern the Orionids, as the path of meteoroid debris stream is modified by the gravitational influence of the giant planet Jupiter.

Two other nearby radiants in the sky also produce an exceptionally large number of fireballs in late October: the Southern Taurids and Northern Taurids. These are complex streams laid down by the periodic comet 2P Encke, which possesses the shortest orbital period of any comet known at 3.3 years. Though the ZHR for both is only slightly above the background sporadic rate for northern hemisphere Fall at about five per hour, the Taurids also produce a high ratio of fireballs. The southern Taurids peak in early October and are already active, and the Northern Taurids peak in late October through early November, earning them the nickname the “Fireballs of Halloween”. Unlike many meteor showers, the Northern Taurids are approaching the Earth from behind in our orbit and have a slow relative atmospheric entry velocity of 28 kilometres per second. This makes for long, stately meteor trains often visible in the evening hours before local midnight.

The Taurids also seem to exhibit a seven year periodicity that begs for further study. 2008 was a fine year for Taurid fireballs… could 2015 be next?

Of course, the exact definition of a “fireball” meteor varies by source, though we prefer the definition of a fireball as a meteor brighter than magnitude -3. A fireball reaching -14 (a Full Moon equals magnitude -13, about 2.5 times fainter) is often termed a bolide.

Halley's orbit — Comet 1P/Halley’s orbital path through the inner solar system. (Credit: NASA/JPL).

Observing meteor showers such as the Orionids is as simple as sitting back and patiently watching the skies. Our own personal rule while starting a meteor vigil is to scan the skies for 10 minutes; one or more meteor sightings is a good sign to keep on watching, while no meteors means it’s time to pack it in and instead maybe write about astronomy. Dark, moonless skies are key, and you can report how many meteors you see to the International Meteor Organization. Be sure to keep a pair of binoculars handy to examine any lingering smoke trails post-fireball passage.

Of course, seeing a Taurid fireball is largely a matter of luck and looking at the right place in the sky at the right time. All-sky cameras work great in this regard, and many amateurs now use tripod mounted DLSRs set to take wide-field exposures of the sky automatically throughout the night. Just watch out for dew! Nearly every meteor we’ve caught on camera turned up only in post review, a testament to how much of the sky a lone pair of eyes still misses.

Spot a fireball? The American Meteor Society maintains a great online database of recent sightings and reports. Keep in mind, lots of “meteor-wrongs” inevitably crop up on Facebook and Twitter during any event, posted by folks eager for likes and retweets. Faves of such spoofers are: the Peekskill meteor train, the reentry of Hyabusa, Mir, and scenes (!) from the movie Armageddon. We’ve seen ‘em all passed off as legit, though you’re more than welcome to try and be original… a majority of initial meteor images almost always come from dash cams (remember Chelyabinsk?) and security cameras.

Finally, in addition to fireballs, there’s another astronomical tie-in for Halloween, as it’s one of four cross-quarter tie-in days approximately mid-way between a solstice and an equinox. The other three are: Lammas Day (August 1st), Groundhog’s Day (February 2nd) and May Day (May 1^st). We just think that it’s great — if a bit paradoxical — to see modern day suburbanites dress up as ghouls and goblins as they reenact archaic rites and holidays…

Don’t forget to keep an eye out for the fireballs of October this Halloween!

October 10, 2014December 23, 2015 by Bob King

How to See Comet Siding Spring as it Encounters Mars

Comet C/2013 A1 Siding Spring passes just north of the sparking Butterfly Cluster on October 9. Credit: Rolando Ligustri

With excitement building as Comet Siding Spring rapidly approaches the Red Planet, we’ll soon have the opportunity to spot it through our own telescopes. Dark skies return this week with the moon now past full and rising later each night. Until recently, the comet could only be seen by skywatchers living in southern latitudes. Now it’s popped high enough above the southern horizon to see from mid-northern latitudes, albeit low in the sky. Observers with 8-inch (20 cm) or larger telescopes can follow the comet as it travels from Scorpius north to Ophiuchus and its encounter with Mars on October 19.

adsfdf — JPL Horizons light curve for Comet C/2013 A1 Siding Spring shows it brightening as it approaches Earth and then fading after late September. For our purposes we’re interested in the purple squares which are visual magnitude estimates of the whole comet submitted to the Comet Observation Database. Recently, the comet has faded faster than predictions. Click for more details. Credit: CIOC

Until late September, the comet had been brightening as forecast based on the simple principle that the closer an object is to Earth the brighter it appears in the sky. Siding Spring came just shy of 1 A.U. of Earth in early September and has since been slip-sliding away. All through the first weeks of September it glowed at magnitude +9-10 and could be spotted in small telescopes trekking across the south polar constellations. Now on the cusp of its big moment with Mars, Siding Spring has been fading faster than expected.

It could be running low on exposed ice or concluding a long, slow outburst. Maybe it’s as simple as our changing perspective on the comet’s tail – we see it from the side now instead of looking down the tail where reflective dust piles up along our line of sight. No one knows exactly why, but given that comets are famous for their unpredictability due to their fragile nature and the varying rates at which they sputter away ice and dust, we shouldn’t be too surprised.

The paths of Mars and Comet Siding Spring are clearly on a (near) collision course! Watch over the coming nights as they draw ever closer. Source: Chris Marriott's SkyMap — The paths of Mars and Comet Siding Spring are clearly on a (near) collision course! Watch over the coming nights as they draw ever closer. This map shows the sky facing southwest at nightfall from Kansas City, Missouri. From the central U.S. the comet will be about 13-15º high but only ~5-8º altitude in the northern border states. Source: Chris Marriott’s SkyMap

So what does that mean for observers? The most recent observations put the comet at about magnitude +11 with a loosely condensed coma and diameter of about one arc minute or a little larger than Jupiter appears in a telescope. It’s a small, relatively faint object now but should be visible in 8-inch and larger telescopes from a dark sky assuming it doesn’t “drop off the deep end” and fade even faster. With Mars nearby, finding the general location of Siding Spring is easy. The maps will help you pinpoint it.

Daily positions of Comet Siding Spring October 10-20 from the central U.S. at nightfall. Stars shown to magnitude +11.5. Closest approach to Mars is October 19. Brighter stars like 3 Sagittarii, 44 and 51 Ophiuchi and Theta Ophiuchi are labeled. Source: Chris Marriott's SkyMap — Daily positions of Comet Siding Spring October 10-20 from the central U.S. at nightfall. Stars shown to magnitude +11.5. Closest approach to Mars is October 19. The brighter stars 3 Sagittarii, 44 and 51 Ophiuchi and Theta Ophiuchi are labeled. Click for large version to print and use at the telescope. Source: Chris Marriott’s SkyMap

The good news is that the comet is heading straight north and getting higher in the sky every night. The bad news is that it’s also dropping westward each evening mostly negating its northerly altitude gains. Those in the southern U.S. will have the best viewing window with Siding Spring 20º high at nightfall (14º in the central states and 6º in the north). To ensure success, find a spot with a wide open view as far down to the southwestern horizon as possible. You’ll make best use of your time and see the comet highest if you set up during evening twilight and begin searching as soon as the sky is dark. Given that Mars is 1st magnitude and the comet has faded more than expected, it may be difficult to see against the planet’s glare on the 19th. Not that I want to dissuade you from trying, but the nights leading up to and after the encounter will prove better for comet spotting.

Need to get in closer yet? This map shows Mars and Comet Siding Spring on five nights closer to its flyby with stars to magnitude +12. Time and location are the same as the map above. Click for larger version. Source: Chris Marriott's SkyMap — Need to get in closer? This more detailed map shows Mars and Comet Siding Spring nightly October 15-20 with stars to magnitude +12. Time and location are the same as the map above. Click for larger version. Source: Chris Marriott’s SkyMap

The fluffball passed the glittery Butterfly Cluster (M6) in Scorpius on October 9 displaying an attractive curved tail pointing southeast. Tim Reyes of Universe Today calculated the current tail length at ~621,000 miles (1 million km) with a coma ~19,900 miles across (32,000 km). Closest approach occurs around 1:28 p.m. Central Daylight Time (18:28 UT) October 19 when the comet will miss Mars by only 88,000 miles (141,600 km). Dust particles leaving the coma will rip by the planet at ~125,000 mph (56 km/sec). Will they pass close enough to set the Martian sky a-sparkle with meteors?

Not only will the Mars orbiters gather information about the comet and its dust before, during and after the encounter, a fleet of additional telescopes will be making the most of the rare opportunity. Credit: NASA — Not only will the Mars orbiters gather information about the comet and its dust before, during and after the encounter, a fleet of additional telescopes will make the most of the rare opportunity. Credit: NASA

According to a recent NASA press release, the period of greatest risk to orbiting spacecraft will start about 90 minutes after the closest approach of the comet’s nucleus and will last about 20 minutes, when Mars will come closest to the center of the widening trail of dust flying from the comet’s nucleus. Since the comet will barely graze the planet, dust impacts on orbiting spacecraft may or may not happen.

Back on Earth we can watch the daredevil pass by telescope or catch it live on the Web here:

* SLOOH: broadcast begins Sunday Oct. 19 at 9:51 a.m. CDT (14:51 UT)

* Gianluca Masi’s Virtual Telescope: streaming begins Sunday, Oct. 19 at 11:45 a.m. CDT (16:45 UT)