For those of us who had the opportunity to chase Comet Garradd this weekend, half the joy was catching it crossing the “Coathanger” cluster! In this great shot by Mike Romine, the comet appears along the curve of the upside down 2 of the asterism. Mike took this shot without a telescope, using a Canon EOS 50D, 135mm lens, F/5.6, ISO 1600, 90 seconds, mounted on a Celestron SCT on a CG5-GT mount at 12:45 AM. Nice catch!
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Comet Garradd passing by M71. Credit: Brian McGaffney
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We asked for ’em and you sent ’em in. Here are your photos of Comet Garradd, the best-looking comet in the sky right now, as it is brightening and moving faster as it gets closer to us and the Sun. This comet will reach perihelion on December 23, 2011. We start with Brian McGaffney who captured this photo of the Comet C/2009 P1 Garradd when it crossed star cluster M71. The image was taken from the Nutwood Observatory in Bancroft, Ontario on August 26th, 2011 at 11PM. Brian took the photo using an Apoggee U16M and a 14 inch astrograph and an ME mount.
But wait — there’s more!
Garradd and M71. Credit: Rich Richins. Click image to see larger version on Richard's website, Enchanted Skies.
Richard Richins sends us this image from his location in Las Cruces, New Mexico. Check out his website, Enchanted Skies.
Comet Garradd passing by the open cluster M71 on August 27, 2011. Credit: Efrain Morales Rivera. Click to view on Flickr
This image was taken on August 27, 2011 in Victoria, Aguadilla, Puerto Rico by Efrain Morales Rivera from the Jaicoa Observatory. “Comet Garradd’s tail is brushing along the core of cluster M71,” Effrain noted, adding the equipment he used was LX200ACF 12 inch. OTA, F6.3, CGE mount, ST2000xm Ccd, AO8, CFW9, Astronomik LRGB filterset.
Comet 2009 P1 Garradd+M71 Mercer. Credit: Leonard Ellul Mercer.
Leonard Ellul Mercer sent in this nice view from Malta in the Mediterranean Sea.
A set of 78 - 30 second exposures of Comet Garradd taken on August 4, 2011 by Suraky on Flickr.
Suraky on Flickr from British Columbia, Canada shares his first astrophotos shot from his new and improved darker backyard. This is a set of 78 – 30 second exposures taken between 1:16am and 2:40am GMT-7 on August 4, showing the motion of the comet across the sky during that time. Comet is magnitude 8.7, and 1.5AU from Earth. Two satellite traces also shown. Suraky used DeepSky Stacker, set to Maximum, “so it’s very noisy but it shows more of the comet tail.” There is also an inverted view available on Flickr. Equipment: Newtonian 190mm F5.3. LXD75 Mount. Canon T1i DSLR, ISO800
A collection of images of Comet Garradd from August 20, 2011 by Flickr user 37 Hz.
Flickr user 37Hz put together this collection of images from Saturday, August 20, 2011, taken from “Light polluted Zeist,” the Netherlands. 37Hz said, “Wouldn’t have found this comet without the “precise GOTO” function of my NexStar and the exact coordinates of the comet according to Carinasoft Voyager software.” Equipment: Celestron NexStar 5SE. Meade DSI II pro ccd camera, with about 10 seconds for each frame.
Comet Garradd on August 19, 2011 by jamieball833
jamieball833 submitted this image to Universe Today’s Flickr Group, saying “Now that the comet is at a distance of 1.394 AU from Earth and at magnitude 8.3 it is starting to get a little brighter!
Info:44 x 45 seconds, iso 1600 f/6.25
Right Ascension : 20h 25.8m
Declination : +17′ 34′
Comet Garradd C/2009 P1 passing M71 Cluster. Credit John Chumack.
Want to get your astrophoto featured on Universe Today? Join our Flickr group, post in our Forum or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
For the observing weekend warriors, the last few days have been a very exciting time. Not only have we been treated to a supernova event in Messier 101, but we’ve had the opportunity to watch Comet C/2009 P1 Garradd silently slip by Messier 71! Wish you were there? Step inside and you can be…
A few days ago we brought you a “live” broadcast of the comet thanks to Bareket Observatory. Thousands of UT readers had the opportunity to view and enjoy for a full six hours and – thankfully – the weather cooperated. Want to see the results? You can check out the comet video here.
On Friday, August 27th, comet Garradd had another “picturesque” moment… It swept by an often over-looked Messier object – M71.
But it didn’t pass by John Chumack!
At a distance of 1.402 AU from Earth and 2.193 AU from the Sun, Comet Garradd continues to brighten and will reach perihelion on December 23, 2011. That’s quite a difference from M71’s 13,000 light year distance! Right now the two are almost of identical magnitude, and while the comet has moved on, you can still find M71 in the constellation of Sagitta at Right Ascension: 19 : 53.8 (h:m) – Declination: +18 : 47 (deg:m).
And this isn’t the first time a comet has crossed paths with this star cluster. As a matter of fact, it was in looking for a comet that this bundle of stars was discovered by Pierre Mechain and dutifully and correctly logged by Charles Messier on October 4, 1780. Said Messier, “Nebula discovered by M. Mechain on June 28, 1780, between the stars Gamma and Delta Sagittae. On October 4 following, M. Messier looked for it: its light is very faint and it contains no star; the least light makes it disappear. It is situated about 4 degrees below [south of] that which M. Messier discovered in Vulpecula. See No. 27. He reported it on the Chart of the Comet of 1779.”
Imagine how impressed Mechain and Messier would be if they could see what John did 222 years later! He used a QHY8 CCD Camera and compressed the two and half hour video into the segment you see above. It was done at his Yellow Springs, Ohio observatory and shot through his 16″ homemade telescope.
Now that’s cookin’!
Many thanks to John Chumack of Galactic Images for sharing this incredible video with us!
C/2010 X1 Elenin, on Aug 29, 2011. Credit: Michael Mattiazzo. Used by permission
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Astronomers monitoring Comet Elenin have noticed the comet has decreased in brightness the past week, and the coma is now elongating and diffusing. Some astronomers predict the comet will disintegrate and not survive perihelion, its closest approach to the Sun.
On August 19, a massive solar flare and coronal mass ejection hit the comet, which may have been the beginning of the end for the much ballyhooed lump of ice and dirt.
Comet Elenin as seenby the STEREO HI1-B on Aug. 6, 2011, from about 7 million kilometers from the spacecraft. Credit: NASA/STEREO
“We’ve been following it in the STEREO spacecraft images and a number of amateurs have been following it in their telescopes,” said Australian amateur astronomer Ian Musgrave, author of the Astroblog website. “Shortly after the coronal mass ejection the comet flared up and you could see some beautiful details in the tail, with the tail was twisting about in the solar wind. But shortly after that Earth- bound amateurs reported a huge decrease in the intensity of the comet. We think it may presage a falling apart of the comet.”
“It really has been a beautiful little comet and it deserves a better fate than to be overhyped by doom-sayers,” said Musgrave.
Elenin is a long period comet originating from the outer edges of our solar system, and Musgrave noted that comets coming from the Oort cloud which are making their first pass through the solar system tend to be under-performers in terms of brightness. “They don’t brighten as quickly as comets that come around more than once,” he said, “and in looking at the relationship between the brightness and the distance from the Sun, we find empirically that comets that brighten on roughly the same speed as Elenin tend to be likely to fall apart at perihelion.”
However, Musgrave added, each comet is unique. “Some comets will survive and some won’t. The fact that this comet decreased in brightness after the CME, possibly indicates that the comet will not survive. Another possibility is that merely the CME wiped away the coma — the bright cloud of particles around the comet — and the volatiles of the comet might take awhile to come back and recreate the coma, if it does survive.”
Elenin’s mass is smaller than average and its trajectory will take it no closer than 34 million km (21 million miles) of Earth as it circles the Sun. It will make its closest approach to Earth on October 16th, but be closest to the Sun on Sept. 10.
Animation of 5 images taken Aug 19,22,23,27,29 displaying the nucleus of Comet Elenin in the process of disintegrating. Credit: Michael Mattiazzo. Used by permission
Another Australian amateur Michael Mattiazzo has been taking images of the comet (see his website, Southern Comets) and he has noticed that the nucleus appears to be elongating. When that occurs, usually the comet disintegrates or splits apart. Above is an animation Mattiazzo created from images he took of Comet Elenin on August 19, 22, 23, 27 & 29.
You can see a wide-field view of the comet by astrophotographer Rob Kaufmanns, comparing the view from August 19, 23 and 26 at this link.
A similar process took place just a few weeks ago with another comet, 213P Van Ness.
Do comets break apart often?
“You don’t see it it that often, but it happens surprisingly more than people think,” Musgrave said. “Van Ness just happened, but ever couple of years there is a comet that visibly breaks up into fragments, maybe about 6 comets in the last 10 years — excluding the Kreutz-sun-grazer family of comets which split and vaporize on a regular basis.”
A closeup photo of the breakup of Comet S4 LINEAR taken on August 6, 2000 by the European Very Large Telescope (VLT) in Chile. Credit: ESO
Unfortunately, the likely demise of Comet Elenin hasn’t put a lid on the doomsdayers who have predicted earthquakes or three days of darkness or a collision with Earth.
“The doomsdayers are just saying that more bad things will happen!” laughed Musgrave. “But you have to remember that when a comet breaks up, the fragments stay in the same orbit. If it evaporates, you’ll have a mass of rubble and gas on the same orbit. People don’t seem to get that space is big, really big, and when a comet breaks up it follows Newtons Laws and the fragments will slowly draw apart, but over the timescale that we see them, the difference will be so miniscule.”
Example Of LIVE Image From Bareket Observatory - Viewer Located Inside This Article
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Are you ready for some excitement? How would you like to watch a LIVE broadcast of Comet C2009 P1 Garradd right here on Universe Today?! Thanks to our good friends at Bareket Observatory and clear skies in Israel, we can do just that! Step inside to our virtual observatory…
Before you get upset and think there’s something wrong, there are a few things you must remember about watching a live telescope broadcast. If there are clouds – you will see no image. If the camera isn’t turned on and broadcasting – you will only see the blue “frame” below where the image is meant to be. Because the data load is so huge from the incoming images, it limits itself to refreshing about every 30 to 60 seconds. This means the image will appear static, then reset itself. If you watch for a period of perhaps 10 minutes or so, you will notice appreciable movement against the background stars. The tracking is set on the nucleus of the comet, so the comet won’t appear to move – the background stars will each time it refreshes. There can also be unforeseen glitches, (such as viewer overload) so please be patient! Last… There will be no image until the broadcast time. You don’t have to click anywhere else – when the broadcast is happening it will be right here where you see the frame below.
The live broadcast of Comet Garradd will take place on Monday, August 22 – 2100-0300 local Israel time (UTC+3). To give you some help figuring times, here’s a very brief listing that’s in absolutely no particular order:
Shanghai – Tue 2:00 AM – Tue 8:00 AM
Sydney – Tue 4:00 AM – Tue 10:00 AM
Zurich – Mon 8:00 PM – Tue 2:00 AM
Moscow – Mon 10:00 PM – Tue 4:00 AM
Rome – Mon 8:00 PM – Tue 2:00 AM
London – Mon 7:00 PM – Tue 1:00 AM
New York – Mon 2:00 PM – Mon 8:00 PM
Mexico City – Mon 1:00 PM – Mon 7:00 PM
Vancouver – Mon 11:00 AM – Mon 5:00 PM
Honolulu – Mon 8:00 AM – Mon 2:00 PM
New Delhi – Mon 11:30 PM – Tue 5:30 AM
Johannesburg – Mon 8:00 PM – Tue 2:00 AM
Tokyo – Tue 3:00 AM – Tue 9:00 AM
Denver – Mon 12:00 Noon – Mon 6:00 PM
San Francisco – Mon 11:00 AM – Mon 5:00 PM
San Juan – Mon 2:00 PM – Mon 8:00 PM
Anchorage – Mon 10:00 AM – Mon 4:00 PM
That having been said, the frame right below these words will be your virtual eyepiece!
Feel free to “take” any images you want and stitch together a video – or post ’em to your favorites sites. If you enjoyed the broadcast, won’t you take a few minutes and thank the hardworking, generous crew at Bareket Observatory? I am very sure they would appreciate it!
Comet C2009 P1 Garradd and Perseids imaged by students at Bareket Observatory.
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What are you waiting for? If it’s an engraved invitation, then consider this your pass to get out and start looking for Comet C/2009 P1 Garradd! It’s well within reach of average binoculars and it’s even in a position that’s easy for the average observer! Step on out here into the backyard and I’ll show you…
At close to magnitude 8, Comet C/2009 P1 Garradd is currently grazing its way along the eastern line of the Summer Triangle. Even if you live in a moderately light polluted area, you should be able to make out the three bright stars, Deneb to the north, Vega to the west and Altair to the south. Just aim your binoculars roughly halfway between Altair and Deneb and begin scanning on binocular field at a time for a faint, fuzzy poofball that signifies the comet’s presence. What you will see in binoculars will appear to be like a “fuzzy star” – while a telescope will reveal the beginnings of a tail.
Comet Elenin -- the little fuzzy blob in the middle of the image -- as it appeared on May 22, 2011. Credit: Peter Lake
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Lord knows, we’ve tried. We’ve featured a couple of articles about Comet Elenin to try and answer questions and allay any fears about this comet; how it will just pass by Earth — harmlessly at 35 million km (22 million miles) at its closest approach — and an FAQ showing how much of the “information” being dished out by breathless scaremongers of how the comet will hit Earth, or cause Earthquakes and floods, or block out the Sun, and the dangers are being covered up by the government is just plain rubbish. But the questions and panic keep coming to our inboxes and in the comments sections of our articles. Scientists at NASA have been bombarded with questions as well, so they have now put together a list of the most asked questions they’ve received, with various scientists answering the questions. Bottom line: Comet Elenin poses no threat to Earth.
Before the questions, just a little info about Comet Elenin, also known by its astronomical name C/2010 X1. The comet was first detected on Dec. 10, 2010 by Leonid Elenin, an observer in Lyubertsy, Russia, who made the discovery “remotely” using an observatory in New Mexico. At that time, Elenin was about 401 million miles (647 million kilometers) from Earth. Since its discovery, Comet Elenin has – as all comets do – closed the distance to Earth’s vicinity as it makes its way closer to perihelion, its closest point to the Sun.
Compiled below are the some of the most-asked questions, with answers from Don Yeomans of NASA’s Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and David Morrison of the NASA Astrobiology Institute at the NASA Ames Research Center in Moffett Field, Calif.
When will Comet Elenin come closest to the Earth and appear the brightest?
Comet Elenin should be at its brightest shortly before the time of its closest approach to Earth on Oct. 16, 2011. At its closest point, it will be 22 million miles (35 million kilometers) from us.
Will Comet Elenin come close to the Earth or between the Earth and the moon?
Comet Elenin will not come closer to Earth than 22 million miles (35 million kilometers). That’s more than 90 times the distance to the moon.
Trajectory of comet Elenin. Image credit: NASA/JPL-Caltech
Can this comet influence us from where it is, or where it will be in the future? Can this celestial object cause shifting of the tides or even tectonic plates here on Earth?
There have been incorrect speculations on the Internet that alignments of comet Elenin with other celestial bodies could cause consequences for Earth and external forces could cause comet Elenin to come closer. “Any approximate alignments of comet Elenin with other celestial bodies are meaningless, and the comet will not encounter any dark bodies that could perturb its orbit, nor will it influence us in any way here on Earth,” said Don Yeomans, a scientist at NASA JPL.
“Comet Elenin will not only be far away, it is also on the small side for comets,” said Yeomans. “And comets are not the most densely-packed objects out there. They usually have the density of something akin to loosely packed icy dirt.
“So you’ve got a modest-sized icy dirtball that is getting no closer than 35 million kilometers [about 22 million miles),” said Yeomans. “It will have an immeasurably miniscule influence on our planet. By comparison, my subcompact automobile exerts a greater influence on the ocean’s tides than comet Elenin ever will.”
I’ve heard about three days of darkness because of Comet Elenin. Will Elenin block out the sun for three days?
“As seen from the Earth, comet Elenin will not cross the sun’s face,” says Yeomans.
But even if it could cross the sun, which it can’t, astrobiologist David Morrison notes that comet Elenin is about 2-3 miles (3-5 kilometers) wide, while the sun is roughly 865,000 miles (1,392,082 kilometers) across. How could such a small object block the sun, which is such a large object?
Let’s think about an eclipse of the sun, which happens when the moon appears between the Earth and the sun. The moon is about 2,500 miles (4,000 kilometers) in diameter, and has the same apparent size as the sun when it is about 250,000 miles (400,000 kilometers) away — roughly 100 times its own diameter. For a comet with a diameter of about 2-3 miles (3-5 kilometers) to cover the sun it would have to be within 250 miles (400 kilometers), roughly the orbital altitude of the International Space Station. However, as stated above, this comet will come no closer to Earth than 22 million miles.
I’ve heard there is a “brown dwarf” theory about Comet Elenin. Would its mass be enough to pull Comet Honda’s trajectory a significant amount? Could this be used to determine the mass of Elenin?
Morrison says that there is no ‘brown dwarf theory’ of this comet. “A comet is nothing like a brown dwarf. You are correct that the way astronomers measure the mass of one object is by its gravitational effect on another, but comets are far too small to have a measureable influence on anything.”
If we had a black or brown dwarf in our outer solar system, I guess no one could see it, right?
“No, that’s not correct,” says Morrison. “If we had a brown dwarf star in the outer solar system, we could see it, detect its infrared energy and measure its perturbing effect on other objects. There is no brown dwarf in the solar system, otherwise we would have detected it. And there is no such thing as a black dwarf.”
Will Comet Elenin be visible to the naked eye when it’s closer to us? I missed Hale-Bopp’s passing, so I want to know if we’ll actually be able to see something in the sky when Elenin passes.
We don’t know yet if Comet Elenin will be visible to the naked eye. Morrison says, “At the rate it is going, seeing the comet at its best in early October will require binoculars and a very dark sky. Unfortunately, Elenin is no substitute for seeing comet Hale-Bopp, which was the brightest comet of the past several decades.”
“This comet may not put on a great show. Just as certainly, it will not cause any disruptions here on Earth. But, there is a cause to marvel,” said Yeomans. “This intrepid little traveler will offer astronomers a chance to study a relatively young comet that came here from well beyond our solar system’s planetary region. After a short while, it will be headed back out again, and we will not see or hear from Elenin for thousands of years. That’s pretty cool.”
This comet has been called ‘wimpy’ by NASA scientists. Why?
“We’re talking about how a comet looks as it safely flies past us,” said Yeomans of NASA’s Near-Earth Object Program Office. “Some cometary visitors arriving from beyond the planetary region – like Hale-Bopp in 1997 — have really lit up the night sky where you can see them easily with the naked eye as they safely transit the inner-solar system. But Elenin is trending toward the other end of the spectrum. You’ll probably need a good pair of binoculars, clear skies and a dark, secluded location to see it even on its brightest night.”
Why aren’t you talking more about Comet Elenin? If these things are small and nothing to worry about, why has there been no public info on Comet Elenin?
Comet Elenin hasn’t received much press precisely because it is small and faint. Several new comets are discovered each year, and you don’t normally hear about them either. The truth is that Elenin has received much more attention than it deserves due to a variety of Internet postings that are untrue. The information NASA has on Elenin is readily available on the Internet. (See http://www.jpl.nasa.gov/news/news.cfm?release=2011-135) If this comet were any danger to anyone, you would certainly know about it. For more information, visit NASA’s AsteroidWatch site at http://www.jpl.nasa.gov/asteroidwatch/.
I’ve heard NASA has observed Elenin many times more than other comets. Is this true, and is NASA playing this comet down?
NASA regularly detects, tracks and characterizes asteroids and comets passing relatively close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called “Spaceguard,” discovers these objects, characterizes a subset of them and predicts their paths to determine if any could be potentially hazardous to our planet. For more information, visit the NASA-JPL Near Earth objects site at http://neo.jpl.nasa.gov/ .
However, neither NASA nor JPL is in the business of actively observing Elenin or any other comet. Most of the posted observations are made by amateur astronomers around the world. Since Elenin has had so much publicity, it naturally has attracted more observers.
I was looking at the orbital diagram of Comet Elenin on the JPL website, and I was wondering why the orbit shows some angles when zooming? If you pick any other comet, you can see that there are no angles or bends.
Many people are trying to plot the orbit of the comet with the routine on the JPL website, without realizing that this is just a simple visualization tool. While the tool has been recently improved to show smoother trajectories near the sun, it is not a scientific program to generate an accurate orbit. Yeomans explains that the orbit plotter on the Near-Earth Object website is not meant to accurately depict the true motion of objects over long time intervals, nor is it accurate during close planetary encounters. For more accurate long-term plotting, Yeomans suggests using the JPL Horizons system instead: http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=C/2010%20X1 .
Comet Garradd on Aug. 1. 2011 as seen from Australia. Credit: Peter Lake.
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If you haven’t already, it’s time to start looking for Comet Garradd! This comet, with the nomenclature C/2009 P1, is now coming into small telescope/binocular view so here’s your chance to see the brightest comet in the current night sky. You can find it in the late evening sky in the constellation Pegasus. Viewing it now, Garradd is just coming out the “fuzzball” stage, and its tail is just coming into view. Some say it’s much better looking than that other comet, Elenin, that has been needlessly grabbing some headlines. Comet Garradd was discovered two years ago by Gordon Garradd from the Siding Spring Observatory in Australia, and is currently visible through a small telescope at about magnitude nine.
Throughout the next couple of months, Comet Garradd will get higher and brighter and cut through the Summer Triangle north of Altair. By September, it will drop lower in the west but remain visible in the evening sky until year’s end for observers at mid-northern latitudes. Comet Garradd will peak in brightness late next February at around 6th magnitude, so it could be visible with the naked eye if you have really dark skies. Closest approach to Earth happens next March 5, when Garradd will be 117.7 million miles away. At that time, the comet will be seen flying though the Little Dipper.
Other comets are also currently falling towards the Sun and brightening as they get closer include C/2010 X1 (Elenin), expected to peak near magnitude six in early September, 45P/Honda-Mrkos-Pajdusakova expected to peak brighten past magnitude eight in mid-August, and C/2011 L4 (PANSTARRS) which may become visible to the unaided eye during the early months of 2013.
Barringer Crater, also known as Meteor Crater, in Arizona. This crater was formed around 50,000 years ago by the impact of a nickel-iron meteorite. Near the top of the image, the visitors center, complete with tour buses on the parking lot, provides a sense of scale. Credit: National Map Seamless Viewer/US Geological Service
Is the Earth more likely or less likely to be hit by an asteroid or comet now as compared to, say, 20 million years ago? Several studies have claimed to have found periodic variations, with the probability of giant impacts increasing and decreasing in a regular pattern. Now a new analysis by Coryn Bailer-Jones from the Max Planck Institute for Astronomy (MPIA), published in the Monthly Notes of the Royal Astronomical Society, shows those simple periodic patterns to be statistical artifacts. His results indicate either that the Earth is as likely to suffer a major impact now as it was in the past, or that there has been a slight increase impact rate events over the past 250 million years.
The results also lay to rest the idea of the existence of an as-yet undetected companion star to the Sun, dubbed “Nemesis.”
Giant impacts by comets or asteroids have been linked to several mass extinction events on Earth, most famously to the demise of the dinosaurs 65 million years ago. Nearly 200 identifiable craters on the Earth’s surface, some of them hundreds of kilometers in diameter, bear witness to these catastrophic collisions.
Understanding the way impact rates might have varied over time is not just an academic question. It is an important ingredient when scientists estimate the risk Earth currently faces from catastrophic cosmic impacts.
Since the mid-1980s, a number of authors have claimed to have identified periodic variations in the impact rate. Using crater data, notably the age estimates for the different craters, they derive a regular pattern where, every so-and-so-many million years (values vary between 13 and 50 million years), an era with fewer impacts is followed by an era with increased impact activity, and so on.
One proposed mechanism for these variations is the periodic motion of our Solar System relative to the main plane of the Milky Way Galaxy. This could lead to differences in the way that the minute gravitational influence of nearby stars tugs on the objects in the Oort cloud, a giant repository of comets that forms a shell around the outer Solar System, nearly a light-year away from the Sun, leading to episodes in which more comets than usual leave the Oort cloud to make their way into the inner Solar System – and, potentially, towards a collision with the Earth. A more spectacular proposal posits the existence of an as-yet undetected companion star to the Sun, dubbed “Nemesis”. Its highly elongated orbit, the reasoning goes, would periodically bring Nemesis closer to the Oort cloud, again triggering an increase in the number of comets setting course for Earth.
For MPIA’s Coryn-Bailer-Jones, these results are evidence not of undiscovered cosmic phenomena, but of subtle pitfalls of traditional (“frequentist”) statistical reasoning. Bailer-Jones: “There is a tendency for people to find patterns in nature that do not exist. Unfortunately, in certain situations traditional statistics plays to that particular weakness.”
That is why, for his analysis, Bailer-Jones chose an alternative way of evaluating probabilities (“Bayesian statistics”), which avoids many of the pitfalls that hamper the traditional analysis of impact crater data. He found that simple periodic variations can be confidently ruled out. Instead, there is a general trend: From about 250 million years ago to the present, the impact rate, as judged by the number of craters of different ages, increases steadily.
There are two possible explanations for this trend. Smaller craters erode more easily, and older craters have had more time to erode away. The trend could simply reflect the fact that larger, younger craters are easier for us to find than smaller, older ones. “If we look only at craters larger than 35 km and younger than 400 million years, which are less affected by erosion and infilling, we find no such trend,” Bailer-Jones explains.
On the other hand, at least part of the increasing impact rate could be real. In fact, there are analyses of impact craters on the Moon, where there are no natural geological processes leading to infilling and erosion of craters, that point towards just such a trend.
Whatever the reason for the trend, simple periodic variations such as those caused by Nemesis are laid to rest by Bailer-Jones’ results. “From the crater record there is no evidence for Nemesis. What remains is the intriguing question of whether or not impacts have become ever more frequent over the past 250 million years,” he concludes.
Orbit of Comet C/2010 X1 Elenin (red) visualised with Celestia, showing Elenin at closest approach to Earth. Image courtesy of Ian Musgrave
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Astronomer and blogger Ian Musgrave from South Australia has been active in debunking the misinformation and nonsense that is being disseminated about Comet Elenin. He has written several wonderful posts featuring the actual realities of this long-period lump of dirty ice that has, for some reason, attracted the attention of doomsdayers, 2012ers, and end-of-the-world scaremongers. Earlier this week, Ian’s Elenin posts on his Astroblog were taken down by the web host, as someone filed a claim for alleged violation of the Digital Millennium Copyright Act (DMCA). “Given that there is no copyrighted material on these pages, with either material generated entirely by me or links to and citation of publicly available material, I believe this was just a frivolous attack on people countering Elenin nonsense” Ian said. Astroblog was not the only site that was targeted, and thankfully, Ian’s web host agreed that the claim was without merit, and the posts are back online. In the interim, however, Universe Today offered to publish Ian’s excellent “Comet Elenin, a FAQ for the Worried” post, and even though the original is now available again, Ian and I decided to still post this on UT so that more people with questions about Comet Elenin would have the chance to have their worries allayed. Have your questions answered below.
Will Comet Elenin Hit Earth?: No, its closest approach is 0.23 AU on Oct 16, 2011, where 1 AU is the distance from the Earth to the Sun. To put this in perspective, this is only a little closer than the closest approach of Venus to Earth, and roughly 100 times the distance from the Earth to the Moon. This distance is from the latest MPEC ephemeris which is based on over 100 observations from multiple observatories that have been continuously tracking the comet, so it won’t change appreciably.
Surely if Elenin Was Going to Hit the Earth NASA/the Government Would Hush it Up? Which government? The Australian Government, the UK Government? The Italian Government? The South African Government? Amateur astronomers world wide are following this comet and continually talking to each other. The have the programs to work out where the comet is going. If the comet was coming anywhere near us, the amateur community would be first to know, and there is no keeping them quite. Consider how wide spread the information is about Apophis, which is a real, if extremely marginal, hazard.
Will it Cause Earthquakes, Abnormally High Tides or Other Disasters: No, Elenin is a mere 3-5 kilometres across and has less than a billionth of the tidal force of the Moon at closest approach (as well as a negligible magnetic field). If the Moon can’t cause the poles to tip, cause massive tidal floods or earthquakes, Comet 2010 X1 Elenin won’t. We’ve been closer to other comets before with no ill effect.
But What About Mensur Omerbashich’s Paper that Says Elenin is Causing Earthquakes? It shows nothing of the sort, earthquakes are no more common during comet alignments than at any other time.
But it’s bigger than Jupiter! No, that’s the coma , the thin haze of gas and dust that surrounds the comet nucleus. The nucleus of C/2010 X1 Elenin is roughly 3-4 Km in diameter and Elenin has a coma around 50,000 km wide at the time of writing (which is a third of the diameter of Jupiter). The average density of the coma is about the same as the density of the atmosphere on the Moon. A coma is a feature of all comets that approach the Sun closely, for example comet 81P Wild (nucleus 4 Km diameter) had a coma of 50,000 Km and 103P Hartley had a coma of 150,000 Km. The Great Comet of 1811 had a nucleus of around 30km in diameter and had a coma nearly as big as the Sun. Comet Halley is 6×15 km and had a coma 100,000 km wide when it last approached Earth. We survived them all (and 103P Hartley came nearly twice as close as Elenin will), and we will survive Elenin without incident.
But I Can See a Picture of it in WikiSky, it’s HUGE! That is the carbon star CW Leonis.
But Brown Dwarf Stars are so Cold, you Can’t See Them. No, coldest detected so far is ~370K (about the temperature of a hot cup of tea), the the warmest are around 2200 K, and most range between 500-1000 K. They may not produce much visible light, but they reflect light. Jupiter has a composition similar to those of Brown Dwarf stars. Jupiter’s cloud tops are a chilly 128 K and it reflects light just fine. Any Brown Dwarf in the inner solar system would be painfully obvious.
Will Going Through the Comets Tail Affect Us? No, should the rather small tail of Elenin actually pass over us, it’s doing a pretty good imitation of a vacuum (about 100 atoms per cm3). We have been through bigger and denser comet tails before with no effect whatsoever (especially the Great Comet of 1861).
Why isn’t Comet Elenin in the News? For the same reason that the other 16 comets discovered in 2010 didn’t get in the news, or the 5 comets discovered in 2011. They are all dim. The News is only interested in comets that are spectacular, readily visible to the unaided eye or are being visited by spacecraft. Comet 2009 P1 will be as bright, if not brighter than C/2010 X1 Elenin, but that’s not in the news either. Amateur and professional astronomers are watching comet Elenin and others avidly, but the news channels don’t care about our obsessions with faint fuzzies.
Why Can’t I Find Information of Elenin at the NASA Website? Because NASA is not the arbiter of all things astronomical. You won’t find information on C/2009 P1, C/2011 C1 or any of the faint comets discovered during 2010 and 2011. NASA does have information of comets that its spacecraft have visited, or are interesting in some other way, but it’s not an exhaustive comet site like Cometography or Aerith.
(editor’s note, NASA and JPL’s Near Earth Object Office did publish an article about Comet Elenin in May, 2011, which can be found at this link, confirming it will safely fly past Earth.)
I Saw Comet Elenin Near the Sun in August 2010/Now: In August 2010 only really powerful telescopes could see Elenin. You saw Venus. If you are seeing something bright near the Sun in the morning sky now, it’s Venus.
How Can I Tell What IS in the Sky and Avoid The Venus Confusion? For freeware standalone programs there is Cartes du Ciel and Stellarium (my favourite). For Web based solutions Skyview Cafe, Sky-Map and GoogleEarth (KMZ file here) all work.
Where Can I Find Orbital Elements for Celestia or Stellarium?Here.
Where Can I Find Images of Elenin? Here, and here and a nice image of C/2010 X1 near to NGC 3376 is here.
I have Photographed/ Seen a Photograph of a Double Sun, is this Elenin? It’s lens flare.
