Asteroid 2013 MZ5 as seen by the University of Hawaii's PanSTARR-1 telescope. Credit: PS-1/UH
That pale white dot up there? No. 10,000 in a list of near-Earth objects. This rock, 2013 MZ5, was discovered June 18. It is 1,000 feet (300 meters) across and will not come anywhere near to threatening Earth, NASA assures us.
But what else is out there? The agency still hasn’t found every asteroid or comet that could come by Earth. To be sure, however, it’s really trying. But is there more NASA and other agencies can do to search? Tell us in the comments.
A bit of history: the first of these objects was discovered in 1898, but in recent decades we’ve been more systematic about finding them. This means we’ve been picking up the pace on discoveries.
Congress asked NASA in 2005 to find and catalog 90 per cent of NEOs that are larger than 500 feet (140 meters) in size, about enough to level a city. The agency says it has also found most of the very largest NEOs, those that are at least six-tenths of a mile (1 kilometer) across (and none so far discovered are a threat.)
The two main smoke trails left by the Russian meteorite as it passed over the city of Chelyabinsk. Credit: AP Photo/Chelyabinsk.ru
Still, NASA says once it achieves its latest goal (which it is supposed to be by 2020), “the risk of an unwarned future Earth impact will be reduced to a level of only one per cent when compared to pre-survey risk levels. This reduces the risk to human populations, because once an NEO threat is known well in advance, the object could be deflected with current space technologies.”
The major surveys for NEOs in the United States are the University of Arizona’s Catalina Sky Survey, the University of Hawaii’s Pan-STARRS survey and the Lincoln Near-Earth Asteroid Research (LINEAR) survey between the Massachusetts Institute of Technology, the Air Force and NASA. Worldwide, the current discovery rate is 1,000 per year.
EDIT: And NASA also recently issued an Asteroid Grand Challenge to private industry to seek solutions to find these space rocks. Check out more information here.
What more can be done to find and track threatening space rocks? Let us know below.
ISON as seen by Hubble earlier this spring. (Credit: NASA/ESA/Z. Levay/STScl).
Comets are the big “question marks” of observational astronomy. Some, such as Comet Hyakutake and the Great Daylight Comet of 1910 present themselves seemingly without warning and put on memorable displays. Others, such as the infamous Comet Kohoutek or Comet Elenin, fizzle and fail to perform up to expectations after a much anticipated round of media hype.
And then there’s the case of Comet C/2012 S1 ISON. Discovered on September 21st, 2012 by Artyom Novichonok and Vitali Nevski while conducting the International Scientific Optical Network (ISON) survey, Comet ISON has captivated public interest. The media loves a good comet, or at least the promise of one.
But will Comet ISON perform up to expectations? Recently, veteran comet hunter and observer John Bortle weighed in on a Sky & Telescope post and an email interview with Universe Today on what we might expect to see this fall.
Dozens of comets are discovered every year. Most amount to nothing – a handful, like this year’s comet 2011 L4 PanSTARRS or 2012 F6 Lemmon, may become interesting binocular objects.
Part of what alerted astronomers that Comet ISON may become something special was its extreme discovery distance of 6.7 astronomical units (A.U.s) meaning it should be an intrinsically bright object, coupled with its close approach of 0.012 A.U.s (1.1 million kilometres, accounting for the solar radius) from the surface of the Sun at perihelion.
Universe Today recently caught up with Mr. Bortle, who had the following to say above tentative prospects for Comet ISON in late 2013:
“Comets coming into the near-solar neighborhood from the Oort Cloud for the very first time tend to behave rather differently from most of their other icy brethren. They often will show considerable early activity while still far from the Sun, giving a false sense of their significance. Only when they have ventured to within about 1.5-2.0 astronomical units of the Sun do they begin to reveal their true intrinsic nature in the way of brightness and development. When discovered far from the Sun, this situation has misled astronomers time and again into announcing that a grandiose display is in the offing, only to have the comet ultimately turn out to be a general disappointment. There have been exception to this, but they are rare indeed.”
Comet ISON bears similar characteristics to many of the great sungrazing comets of the past. In the last few months, word has made rounds that Comet ISON may be underperforming, stagnating around magnitude +16 (10,000 times fainter than naked eye visibility) as it crosses the expanse of the asteroid belt between Jupiter and Mars.
Bortle, however, cautioned against writing off ISON just yet in a recent message board post. “With this comet’s exceedingly small perihelion distance, the ultimate situation is less clear.” He also continues to note that the prospects for ISON are “really difficult to predict at the moment,” but estimates that Comet ISON “will not actually attain naked eye brightness until just a week or two before perihelion passage.”
Regarding naked eye visibility of Comet ISON, Mr. Bortle also told Universe Today:
“In all probability this will not occur until around early to mid-November. It will not become any sort of impressive sight before disappearing into the morning twilight only a couple of weeks thereafter.”
And that’s the big question that may make the difference between a fine binocular comet and the touted “Comet of the Century…” Will this comet survive its perihelion passage on November 28th?
Concerning the comet’s perihelion passage, Mr. Bortle told Universe Today:
“This is currently a matter of some concern to me. Basing my answer on ISON’s apparent brightness when it was last seen before disappearing into the evening twilight recently suggests that it might be close in intrinsic brightness to the survival/non-survival level for such an extremely close encounter with the Sun. We will know much better once we can view ISON again in September.”
Comet Ikeya-Seki was another sungrazing comet that went on to become a splendid naked eye comet in 1965. The late 1880’s hosted a slew of memorable comets, including two long-tailed sungrazers, one each in 1880 and 1887.
In more recent times, Comet C/2011 W3 Lovejoy survived its December 16th, 2011 perihelion passage 140,000 kilometres from the surface of the Sun to become the surprise hit for southern hemisphere observers.
“IF” comet ISON breaks a negative magnitude, it’ll join the ranks on the top brightest comets since 1935. If it tops -10th magnitude, it’ll best Comet Ikeya-Seki at its maximum in 1965. The magic “brighter than a Full Moon” threshold sits right about at magnitude -12.5, but Bortle cautions that this peak brightness will only persist during the hours surrounding perihelion, when the comet will be very close to the Sun and difficult to see.
Mr. Bortle also voiced a concern to Universe Today that “the initial announcements by professional astronomers concerning ISON’s potential future brightness (“Brighter than the Full Moon”, etc.) were wildly excessive, as was the idea that the comet would be obvious to the general public in the daytime sky as it rounded the Sun in late November. This claim was totally unjustified from the word go.” Mr Bortle also warns that this may be “headed us down the exact same road as the Kohoutek fisaco of 1973/74.”
We’re currently losing Comet ISON behind the Sun as it crosses through the constellation Gemini, not return to morning skies until late August. The comet will cross the orbit of Mars in early October and should also cross the +10th magnitude threshold and become visible in binoculars and small telescopes around this date.
The track of Comet ISON through the constellations Gemini, Cancer and Leo prior to perihelion. (Credit: NASA/GSFC/Axel Mellinger).
From October on in, things should get really interesting. Mr. Bortle predicts that the comet will “develop more slowly in the autumn sky than initially thought,” and won’t become a naked eye object until around November 10th or so. What this sort of lag might do to the internet pundits and prognosticators might be equally interesting to watch.
ISON will also track near some interesting morning objects as seen from Earth, including Mars (October 18th), Spica (November 18th), and Mercury & Saturn low in the dawn on November 26th. It will also have another famous comet nearby on November 25th (photo op!) short period Comet 2P Encke.
If Comet ISON survives perihelion, the true show could begin in early December. Comet ISON will re-emerge in the dawn skies, passing a pairing of Mercury and the very old crescent Moon on December 1st. Comet tails are even less predictable than comet magnitudes, but if Comet ISON is to unfurl a long photogenic tail, the weeks leading up to Christmas may be when it does it.
The projected view of Comet ISON from 30 degrees north latitude 30 minutes prior to local sunrise on December 1st. The orbital path of the comet and the ecliptic are also depicted. (Created by the author in Starry Night).
Mr. Bortle predicts a 10 to 15 degree long tail for a post-perihelion ISON as it passes through the constellation Ophiuchus into morning skies. It may become a “headless wonder” similar to the fan-shaped display put on by Comet 2011 L4 PanSTARRS earlier this spring. We’ve even seen models projecting a great fan-shaped dust tail seeming to “loop” around the Sun as seen from our Earthly vantage point!
All interesting conjecture to watch unfold as Comet ISON approaches perihelion this November. Hopefully, the hysteria that follows great cometary apparitions won’t reach a fevered pitch, though we’ve already had to put some early conspiracies to bed surrounding comet ISON.
Will ISON be the “Comet of the Century?” Watch this space… we’ll have more on the play-by-play action as it approaches!
-Read John Bortle’s predictions for Comet ISON in his recent Sky & Telescope post.
Images of Comet ISON obtained using the Gemini Multi-Object Spectrograph at Gemini North on February 4, March 4, April 3, and May 4, 2013 (left to right, respectively; Comet ISON at center in all images). Color composite produced by Travis Rector, University of Alaska Anchorage. Credit: Gemini Observatory/AURA
As Comet C/2012 S1 (ISON) heads closer to Earth, we’re getting a better view of what has been billed by some as the “Comet of the Century.” Astronomers say these new photos from the Gemini North telescope on Mauna Kea, Hawai‘i provide hints of how well this comet might survive one of the closest comet encounters with the Sun ever recorded, on November 28, 2013.
With astronomy enthusiasts hopeful and optimistic about having a spectacular comet visible in our skies, it’s anyone’s guess if the comet will actually survive its extremely close pass of the Sun to become early morning eye-candy in early December 2013.
The time-sequence images, spanning early February through May 2013, show that the comet is quite active, despite how distant it is from the Sun.
When Gemini obtained these images, the comet ranged between roughly 455-360 million miles (730-580 million kilometers; or 4.9-3.9 astronomical units) from the Sun, or just inside the orbital distance of Jupiter. Each image in the series, taken with the Gemini Multi-Object Spectrograph at the Gemini North telescope on Mauna Kea, Hawai‘i, shows the comet in the far red part of the optical spectrum, which emphasizes the comet’s dusty material already escaping from the nucleus. The final image in the sequence, obtained in early May, consists of three images, including data from other parts of the optical spectrum, to produce a color composite image.
Gemini astronomers say the images show the comet sporting a well-defined parabolic hood in the sunward direction that tapers into a short and stubby tail pointing away from the Sun. These features form when dust and gas escape from the comet’s icy nucleus and surround that main body to form a relatively extensive atmosphere called a coma. Solar wind and radiation pressure push the coma’s material away from the Sun to form the comet’s tail, which we see here at a slight angle (thus its stubby appearance).
“Early analysis of our models shows that ISON’s brightness through April can be reproduced by outgassing from either carbon monoxide or carbon dioxide,” said Karen Meech, at the University of Hawaii’s Institute for Astronomy (IfA) in Honolulu. “The current decrease may be because this comet is coming close to the Sun for the first time, and a “volatile frosting” of ice may be coming off revealing a less active layer beneath. It is just now getting close enough to the Sun where water will erupt from the nucleus revealing ISON’s inner secret.”
Comet ISON will come within 800,000 miles (1.3 million km) of the Sun’s surface on November 28. Shortly before that critical passage, the comet may appear bright enough for expert observers using proper care to see it close to the Sun in daylight.
“Comets may not be completely uniform in their makeup and there may be outbursts of activity as fresh material is uncovered,” added IfA astronomer Jacqueline Keane. “Our team, as well as astronomers from around the world, will be anxiously observing the development of this comet into next year, especially if it gets torn asunder, and reveals its icy interior during its exceptionally close passage to the Sun in late November.”
NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.
NASA’s Swift satellite and the Hubble Space Telescope (HST) have also imaged Comet ISON recently in this region of space. Swift’s ultraviolet observations determined that the comet’s main body was spewing some 850 tons of dust per second at the beginning of the year, leading astronomers to estimate the comet’s nucleus diameter is some 3-4 miles (5-6 kilometers). HST scientists concurred with that size estimate, adding that the comet’s coma measures about 3100 miles (5000 km) across.
The comet gets brighter as the outgassing increases and pushes more dust from the surface of the comet. Scientists are using the comet’s brightness, along with information about the size of the nucleus and measurements of the production of gas and dust, to understand the composition of the ices that control the activity. Most comets brighten significantly and develop a noticeable tail at about the distance of the asteroid belt (about 3 times the Earth-Sun distance –– between the orbits of Mars and Jupiter) because this is when the warming rays of the Sun can convert the water ice inside the comet into a gas. This comet was bright and active outside the orbit of Jupiter — when it was twice as far from the Sun. This meant that some gas other than water was controlling the activity.
Meech said that Comet ISON “…could still become spectacularly bright as it gets very close to the Sun” but also added caution. “I’d be remiss, if I didn’t add that it’s still too early to predict what’s going to happen with ISON since comets are notoriously unpredictable,” she said.
Comet C/2011 L4 PANSTARRS on May 21, 2013, when its anti-tail had grown to more than 12 full moons in length. The original main tail of the comet - to the right of the head - has faded and shortened. Credit: Damian Peach
While comets can’t tell lies, they do sometimes grow long noses. As the weeks click by and our perspective on Comet L4 PANSTARRS changes, its original plume-like dust tail has shrunk and faded while a second tail just won’t stop growing.
Comet PANSTARRS’ orbital plane slices (marked by gray lines) slices right through the plane of the planets. Earth crosses that orbital plane on May 27. As we look up into space at the comet (blue arrow), all the dust it shed along its path – including a fine sheet of particles – stacks up to create a narrow, streak-like tail pointing toward the sun. The shorter, active dust tail sticks up and away (top). Credit: NASA with my own additions
I’m talking about the anti-tail, so called because it points toward the sun instead of away. Like the normal dust tail, an anti-tail is formed from fresh dust blown back from the comet’s head by the pressure of sunlight. As the comet continues along its orbital path, last week’s dust lingers behind, forming a “trail of breadcrumbs” in its wake. Right now those breadcrumbs look like a light saber straight out of Star Wars. Time exposure photographs show a striking sunward-pointing appendage more than 6 degrees (12 full moons) long. I’ve been keeping an eye on Comet PANSTARRS here at home and can report that the anti-tail is plainly visible with a telescope under dark skies. Watching it grow from a short nub to the most dominant feature of this remarkable object has been the highlight of many a clear night.
Our current “edge on” view of Comet PANSTARRS is similar to looking down on it from high above the Earth’s north pole, where the dust stacks up to create a bright, streak-like tail. Credit: NASA/JPL/my own additions
Nothing stands still in our solar system. Earth’s moving, the comet’s moving. Later this week on May 26-27, Earth will pass directly through the comet’s orbital plane, which slices through the plane of the planets at a very steep angle. As the Earth approaches this intersection, we look up (from the northern hemisphere) and stare squarely into the long trail of dusty debris deposited by PANSTARRS during its recent swing around the sun in March. It gets better.
If we step back in time to May 9, we see that the anti-tail was neither as long nor as pronounced because the Earth was further from the comet’s orbital plane. Because we were more broadside to the comet then, the dust sheet is much more obvious. It extends millions of miles into space but is only 5,000-10,000 miles thick. Credit: Michael Jaeger
Sunlight pushes the smaller particles into a vast, thin sheet or fan extending millions of miles into space well beyond the path traveled by the comet’s nucleus. Since we now see PANSTARRS almost “edge-on”, all that dust overlaps from our perspective to form a thick, bright line sticking out of the comet’s head. It’s as if we’re seeing the ghost of PANSTARRS from the recent past still lingering in space. If we could somehow see the whole works broadside, the comet would appear fainter, spread out and much more diffuse.
Simulated views of dust shed by PANSTARRS’ in its orbit around the sun. Dust piles up in the edge-on view to create a skinny, saber-like tail vs. a faint, broad tail (right). Illustration: Bob King
The Milky Waystands out as a band of light distinct from the thin scree of stars for the very same reason; our gaze cuts edge-on through our galaxy’s flattened disk where stars are most concentrated. Like comet dust, they pile atop one other to create a distinct ribbon of fuzzy light slicing across the night sky.
Going back even further to April 10, the anti-tail (short stub to left of bright head) was just getting started. It’s completely dwarfed by the comet’s main dust tail and fan of tinier dust particles. Compare this photo to the current view. Click to enlarge. Credit: Michael Jaeger
In the next few days the tail could grow considerably longer and intensify in brightness as we move closer to the comet’s orbital plane. Unfortunately the moon will be at or near full at the same time, making it tougher to fully appreciate this amazing apparition at least with binoculars and telescopes. Cameras will have better luck. Will that stop you from looking? I hope not. Either way, you can use this map to help you find Comet PANSTARRS and check it out yourself.
Map showing Comet C/2011 L4 PANSTARRS’ location tonight through June 21. Positions are marked off every three nights with stars are shown to about 8th magnitude. Credit: created with Chris Marriott’s SkyMap software
When you do spot the anti-tail, don’t be fooled. It may appear to be pointing at the sun, but it’s only dust spread along a path once tread.
A magnificent view of the very thin anti tail of Comet PANSTARRS, as seen on May 22, 2013 from near Payson, Arizona. Credit and copyright: Chris Schur.A negative image showing Comet PANSTARRS and its very thin anti tail, as seen on May 22, 2013 from near Payson, Arizona. Credit and copyright: Chris Schur.
Image from May 5, 2013 of a the inner region of Comet ISON using the 2-meter Liverpool telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.
In April, when the Hubble Space Telescope looked out towards Jupiter’s orbit and observed what has been billed as the “Comet of the Century” – Comet C/2012 S1 ISON – the space telescope photographed a unique feature in the comet’s coma. Now, a team of ground-based astronomers have performed follow-up observations, imaging Comet ISON as it heads towards the Sun and was just outside the orbit of Mars. They, too, have seen something in the coma and suspect it’s a similar feature to what Hubble imaged. The object is thought to be a jet blasting dust particles off the sunward-facing side of the comet’s nucleus.
These very useful follow-up observations are providing more insight on this highly anticipated comet, as well as helping to predict what might happen when it makes its closest approach to the Sun in November 2013.
“The hype surrounding this comet has been extreme” said Nick Howes from the Remanzacco Observatory, “with some wildly optimistic estimates for magnitude. We’re hoping this measured scientific approach will yield results just as exciting to the science community, even if the comet doesn’t end up meeting everyone’s expectations visually, for whatever reason.”
NASA’s Hubble Space Telescope provides a close-up look of Comet ISON (C/2012 S1), as photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the sun. Credit:NASA, ESA, J.-Y. Li (Planetary Science Institute), and the Hubble Comet ISON Imaging Science Team.
Some have predicted ISON may briefly become brighter than the full Moon. But right now the comet is far below naked-eye visibility, and larger telescopes are needed to makes observations.
Howes and Ernesto Guido from the Remanzacco Observatory in Italy used a suite of Hubble-sized ground-based telescopes in Australia, Hawaii and the Canary Islands to make their observations. They are collaborating with with Nalin Samarasinha, a Senior Scientist at the Planetary Science Institute (PSI) in an attempt to get high spatial resolution data on Comet ISON.
Howes and Guido have been imaging Comet C/2012 S1 ISON since the day it was discovered and actually played a small role in its discovery. They work on a variety of programs with professional and amateur astronomers around the world, but for this comet, their focus is on the so-called Afrho, a measure of a comet’s dust production. (Learn more about Arfho here.)
Samarasinha, a specialist in comets at the Planetary Science Institute, has been looking at the detailed structure of the near-nucleus coma of comet C/2012 S1 ISON using data, which the Remanzacco team is delivering in to the PSI.
Recently, Samarasinha had looked at image comparisons for the Remanzacco team’s dataset from May 2, 5, and 7 taken with the F10 2-meter Liverpool telescope on La Palma, using an extremely sensitive camera, perfectly suited for detailed comet work.
Image from May 2, 2013 of a the inner region of Comet ISON, using the 2 meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.
The images shown here are 28×28 pixel crops of the inner region of the comet.
“This comparison shows that the sunward feature Nick’s team suspected from images taken on 02/05/2013 is originating slightly north of west and then the position angle of the feature (measured from north through east) increases as one moves away from the optocenter,” said Nalin.
Nalin’s interpretation is that the curvature of this feature (which the team suspected was not caused by image enhancing initially, but can now categorically state is real) is not due to any rotational effects but is due to radiation pressure pushing dust grains towards the tail. Ultimately, this feature merges in with the tail. Image from May 7, 2013 of a the inner region of Comet ISON, as seen with the 2-meter Liverpool Telescope at La Palma. Credit: Nick Howes and Ernesto Guido, Remanzacco Observatory; Nalin Samarasinha, Planetary Science Institute.
The team says these observations are in close agreement with features detected by the Hubble Space Telescope in April this year. As the comet comes closer to the Earth the spatial resolution will improve, and the team should get more detailed views on the coma structure.
Estimates suggest that the nucleus of ISON is no larger than 4-6 km (3-4 miles) across while the comet’s dusty coma, or head of the comet is approximately 5,000 km (3,100 miles) across, or 1.2 times the width of Australia. A dust tail extends more than 92,000 km (57,000 miles).
Ongoing observations seem to reveal this comet is ‘shedding’ quite a bit of mass, leaving astronomers to wonder if it will have enough body left to survive its perhihelion, the closest approach to the Sun on November 28, 2013.
Excitingly, Comet ISON observations are in the works for when the comet dashes past Mars, and the Curiosity rover is on tap to try imaging it from Mars’ surface with its high resolution Mastcam 100 camera, as well as on-orbit observations with the Mars Reconnaissance Orbiter (MRO).
As the comet performs a hairpin turn around the Sun in November, its ices will vaporize in the intense solar heat. Assuming it defies death by evaporation, some predict it could become as bright as the full Moon. If so, that would occur for a brief time around at perihelion when the comet would only be visible in the daytime sky very close to the Sun. When safely viewed, ISON might look like a brilliant, fuzzy star in a blue sky.
As C/2012 S1 ISON is now heading in to the evening twilight glare, Howes and Guido will turn from large aperture instrumentation on this comet for a while, and work on observations with a wider field CCD, more sensitive in the R’ band, and also imaging with the Polarimeter instrument which will allow them to create detailed maps of the inner coma region.
Howes said that these ongoing collaborations with scientists with the amateur community are delivering valuable scientific data on a hugely interesting object.
Comet PANSTARRS as seen in the early morning Arizona skies on May 17, 2013. Credit and copyright: Chris Schur.
The comet show is still not over! Early on May 16, 2013, astrophotographer Chris Schur from central Arizona was able to see two comets at once, Comet PANSTARRS AND Comet Lemmon. “We set up on our 14 foot tall balcony observing pad and was able to get the very low Comet Lemmon as it rose in the eastern sky,” Chris told Universe Today via email. “While PANSTARRS was up high by 2:30am, we had to wait until 3:30 before we could try Lemmon.”
While neither comet was visible to the naked eye, Chris reported that both were seen quite clearly in the 11×80 binoculars. “It was fun to go back and forth rapidly between the two objects to compare,” he said. “While PANSTARRS is now a very low surface brightness wedge shaped object, Lemmon was just a huge ball of light, about two magnitudes brighter.”
Comet Lemmon as seen over central Arizona on May 16, 2013. Credit and copyright: Chris Schur.
If you look carefully you can see the comets are stationary, and the stars are slightly trailed from the motion against the starry background.
“One point Id like to make is that PANSTARRS is currently exhibiting one of the most spectacular anti tails I have ever seen,” Chris said. “I have imaged hundreds of comets but never one with such a long sunward spike. This comet is VERY special.”
When viewed edge on from Earth, the anti tail appears as a spike projecting from the comet’s coma towards the Sun It is geometrically opposite to the other tails: the ion tail and the dust tail.
Thanks to Chris for sharing his great images of these comets!
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A relatively new cluster of impact craters on Mars as seen by the HiRISE camera on the Mars Reconnaissance Orbiter. Credit: NASA/JPL-Caltech/MSSS/Univ. of Arizona
One of the benefits of having a spacecraft in orbit around another planet for several years is the ability to make long-term observations and interpretations. The Mars Reconnaissance Orbiter has been orbiting Mars for over seven years now, and by studying before-and-after images from the High Resolution Imaging Science Experiment (HiRISE) camera, scientists have been able to estimate that the Red Planet gets womped by more than 200 small asteroids or bits of comets per year, forming craters at least 3.9 meters (12.8 feet) across.
“It’s exciting to find these new craters right after they form,” said Ingrid Daubar of the University of Arizona, Tucson, lead author of the paper published online this month by the journal Icarus. “It reminds you Mars is an active planet, and we can study processes that are happening today.”
New impact site on Mars formed between November 2005 and October 2010. Credit: NASA/JPL-Caltech/MSSS/Univ. of Arizona
Over the last decade, researchers have identified 248 new impact sites on parts of the Martian surface in the past decade from spacecraft images, determining when the craters appeared. The 200-per-year planetwide estimate is a calculation based on the number found in a systematic survey of a portion of the planet.
The orbiters took pictures of the fresh craters at sites where before-and-after images by other cameras helped figure out when the impacts occurred. This combination provided a new way to make direct measurements of the impact rate on Mars. This will lead to better age estimates of recent features on Mars.
Daubar and co-authors calculated a rate for how frequently new craters at least 3.9 meters in diameter are excavated. The rate is equivalent to an average of one each year on each area of the Martian surface roughly the size of the U.S. state of Texas. Earlier estimates pegged the cratering rate at three to 10 times more craters per year. They were based on studies of craters on the moon and the ages of lunar rocks collected during NASA’s Apollo missions in the late 1960s and early 1970s.
“Mars now has the best-known current rate of cratering in the solar system,” said HiRISE Principal Investigator Alfred McEwen of the University of Arizona, a co-author on the paper.
Examples of craters listed in the paper ‘The Current Martian Cratering Rate.’ Credit: NASA/JPL/Univ. of Arizona.
These asteroids, or comet fragments, typically are no more than 3 to 6 feet (1 to 2 meters) in diameter. Space rocks too small to reach the ground on Earth cause craters on Mars because the Red Planet has a much thinner atmosphere.
For comparison, the meteor over Chelyabinsk, Russia, in February was about 10 times bigger than the objects that dug the fresh Martian craters.
HiRISE targeted places where dark spots had appeared during the time between images taken by the spacecraft’s Context Camera (CTX) or cameras on other orbiters. The new estimate of cratering rate is based on a portion of the 248 new craters detected. It comes from a systematic check of a dusty fraction of the planet with CTX since late 2006. The impacts disturb the dust, creating noticeable blast zones. In this part of the research, 44 fresh impact sites were identified.
Estimates of the rate at which new craters appear serve as scientists’ best yardstick for estimating the ages of exposed landscape surfaces on Mars and other worlds.
One of many fresh impact craters spotted by the UA-led HiRISE camera, orbiting the Red Planet on board NASA’s Mars Reconnaissance Orbiter since 2006. (Photo: NASA/JPL-Caltech/MSSS/UA).
A few of the many trees felled by the 1908 Tunguska explosion, photographed in 1929 (Wikipedia Commons)
Last week, Russian researcher Andrei Zlobin announced that stony fragments collected from a riverbed in 1988 are “probably Tunguska meteorites,” and are likely the remains of whatever cosmic object — thought to be either a comet or an asteroid — entered Earth’s atmosphere over the boggy region of Siberia on June 30, 1908, detonating with an estimated force of 5 megatons and leveling over 800 square miles of forest.
So far, definitive pieces of the original object have yet to be found despite numerous expeditions to the remote impact site. In a paper submitted on April 29, Zlobin cites the melted appearance of several stones found at the bottom of the Khushmo River as a good argument to “confirm the discovery” of Tunguska meteorite fragments.
According to Natalya Artemyeva of the Russian Academy of Sciences’ Geosphere Dynamics Institute, however, Zlobin’s claim is “ridiculous.”
In an article published May 4 on RIA Novosti, Artemyeva stated “There are many meteorites on Earth. For 100 plus years since the fall of the Tunguska space body, the weight of meteoric dust and small meteorites that have fallen out in that region has exceeded the mass of Tunguska.”
Stones found by Andrei Zlobin in the Khushmo River (A. Zlobin)
An estimated 100 tons of space debris enters Earth’s atmosphere on a daily basis.
Although Zlobin admits in his submitted paper that “strict confirmation of discovered melted stones as Tunguska meteorites is possible only after attentive chemical analysis of substance,” it seems that he is making rather bold claims based on appearance alone — especially considering the enigmatic and iconic nature of this particular impact event.
“It’s ridiculous,” Artemyeva said. “You can’t say by the appearance of a stone that it’s a meteorite. I don’t think there is ground for scientific discussion here.”
And, according to Artemyeva, even if the stones are found to be actual meteorites, connecting them to the 1908 event will still be a challenge.
Zlobin’s samples, which were in storage until 2008, are still awaiting full chemical analysis.
Read more on RIA Novosti here and on the MIT Technology Review here.
View of Comet ISON on May 2, 2013. Credit: Ernesto Guido & Nick Howes, Remanzacco Observatory.
Update: Here’s a brand new image of Comet C/2012 S1 ISON, as seen on May 2, 2013 by Ernesto Guido and Nick Howes of the Remanzacco Observatory (their image from May 1, which we featured earlier, is below.) For this latest image, they used the 2-meter Ritchey-Chretien Liverpool Telescope. Via Facebook, Howes said they have been able to identify almost the same tail structure which was seen in the Hubble Space Telescope images of this comet from April 10.
From the May 1 observations, their initial approximation of the tail length is around 28 arcseconds, which Howes told Universe Today is bigger than some recent reports from smaller scopes.
Below is their image from May 1, using the 2 meter La Palma Telescope:
View of Comet ISON on May 1, 2013. Credit: Ernesto Guido & Nick Howes, Remanzacco Observatory.
As of May 2, Comet ISON was approximately 3.885 AU from the Sun, which is about 581 million kilometers (361 million miles) distant from the Sun. ISON will makes its close approach to the Sun when it passes within 1.2 million km (730,000 miles) of the Sun on November 28, 2013.
Here’s a video from NASA about this comet’s path through the Solar System:
Image of potential meteorite fragments from the Tunguska event, from a paper by Andrei E. Zlobin, 'Discovery of probably Tunguska meteorites
at the bottom of Khushmo river's shoal.'
The 1908 explosion over the Tunguska region in Siberia has always been an enigma. While the leading theories of what caused the mid-air explosion are that an asteroid or comet shattered in an airburst event, no reliable trace of such a body has ever been found. But a newly published paper reveals three different potential meteorite fragments found in the sandbars in a body of water in the area, the Khushmo River. While the fragments have all the earmarks of being meteorites from the event – which could potentially solve the 100-year old mystery — the only oddity is that the researcher actually found the fragments 25 years ago, and only recently has published his findings.
Like the recent Chelyabinsk airburst event, the Tunguska event likely also produced a shower of fragments from the exploding parent body, scientists have thought. But no convincing evidence has ever been found from the June 30, 1908 explosion that occurred over the Tunguska region. The explosion flattened trees in a 2,000 square kilometer area. Luckily, that region was largely uninhabited, but reportedly one person was killed and there were very few people that reported the explosion. Forensic-like research has determined the blast was 1,000 times more powerful than a nuclear bomb explosion, and it registered 5 on the Richter scale.
Previous expeditions to the region turned up empty as far as finding meteorites; however one expedition in 1939 by Russian mineralogist Leonid Kulik found a sample of melted glassy rock containing bubbles, which was considered evidence of an impact event. But the sample was somehow lost and has never undergone modern analysis.
The expedition in 1998 by Andrei Zlobin from the Russian Academy of Sciences was initially unsuccessful in finding meteorites or evidence of impacts. He made several drill holes in the peat bogs in the area and while he found evidence of the explosion, he didn’t find any meteorites. He then decided to look in the nearby river shoal.
Zlobin gathered about 100 samples of rocks that had features of potential meteorites, but further examination produced just three rocks with tell-tale features like melting and regmalypts – the , thumblike impressions found on the surface of meteorites which are caused by ablation as the hot rock falls through the atmosphere at high speed.
Zlobin writes that “After the expedition the author focused his efforts on experimental investigation of thermal processes and mathematical modeling of the Tunguska impact [Zlobin, 2007],” and he used tree ring evidence to estimate the temperatures from the event, and concluded that rocks already on the ground would not have been changed or melted from the blast, and therefore any rocks having evidence of melting should be from the impactor itself.
Zlobin says he has not yet carried out a detailed chemical analysis of the rocks, which would reveal their chemical and isotopic composition. But he does say the stony fragments do not rule out a comet since the nucleus could easily contain rock fragments. However, he has calculated the density of the impactor must have been about 0.6 grams per cubic centimeter, which is about the same as nucleus of Halley’s comet. Zlobin says that initially, the evidence seems “excellent confirmation of cometary origin of the Tunguska impact.”
While there is nothing definitive yet from Zlobin’s new paper – and there is the question of why he waited so long to conduct his study – his work provides hope for a better explanation of the Tunguska event as opposed to some rather off-the-wall ideas that have been proposed, such as a Tesla death-ray or an explosion of methane gas from the bogs.
The Technology Review blog writes that “clearly there is more work to be done here, particularly the chemical analysis perhaps with international cooperation and corroboration.”
