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Worried About Comet Elenin? FAQs from Ian Musgrave

Orbit of Comet C/2010 X1 Elenin (red) visualised with Celestia, showing Elenin at closest approach to Earth. Image courtesy of Ian Musgrave

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.

Is Elenin a Moon of a Brown Dwarf Star? No.

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.

Other Good Links:

Leonid Elenin calculates what would happen to planets if a Brown Dwarf was in the inner solar system.

The Sceptics on Elenin.

Astronotes, 10 facts you need to know about Elenin.

Astronomy Beat on Elenin (PDF)

See this original post by Ian Musgrave on Astroblog


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Anonymous July 29, 2011, 8:00 AM

    Nice and neat :)
    Thanks for this post. But I have a question regarding Elenins size. So far, and I’ve been following the topic since Elenin was discovered, there is no information that holds the ground about the size of the comet. Only estimation, which is not good enough, at least for me.

    If anybody has information about the size, please let me know.

    Regarding cometrs tail I quote Wiki about the Great Comet from 1861 you are refering to.
    Quote: “The comet of 1861 interacted with the Earth in an almost unprecedented way. For two days, when the comet was at its closest (0.1326 AU), the Earth was actually within the comet’s tail, and streams of cometary material converging towards the distant nucleus could be seen. By day also the comet’s gas and dust even obscured the Sun.” Link: http://en.wikipedia.org/wiki/C/1861_J1


    • Anonymous July 29, 2011, 11:23 AM

      “By day also the comet’s gas and dust even obscured the Sun. ”

      Petar, notice that no references for this statement are given in Wikipedia (and in this case should be challenged). I’d be interested if a statement to this effect appeared in the popular press (likely) or a scientific journal.

      • Anonymous July 29, 2011, 4:46 PM

        Jon, point noted. There is no valid reference in that article.

        But that was exactly my point too. Let me explain.
        I understand this is a place we talk science. I have deep respect for todays science. We are greatly what we are today thanks to the science.
        What I’m pointing out here is that in nowadays scientific circles you can’t get scientific answer. In this case, they are stating that the size is 3km (or whatever). But in the reality, they don’t have a clue. They might know some stuff for certain, but the size is merely an estimate. Later would be scientific statement. Not doing so produces false conspiracy theories and undermines scientific credibility.
        And I’m hoping too nothing will harm us.


    • WaxyMary July 29, 2011, 3:13 PM


      This is a comet we are discussing after all, and like all such is going to change, decrease in mass on a daily basis, speed along its path to met the sun and then continue along the path to join the void, only to return since this comet is a long period comet.

      The size of what part of the comet. The length of which tail, the average diameter of the nucleus, the average diameter of the coma, the length and cubic of the debris swarm following. These are all figures which vary from day to day. Any figures you get will be superseded in spans of time we measure with charts on a wall.

      If what you wish to know is only estimation then ask yourself, is the estimation accurate enough, for you the answer is no, for others that set of figures and the limits of error are more than enough.

      What purpose do you have for the ‘exact’ size… why isn’t the average size of nucleus over time vs distance traveled enough for some reason. The remainder of figures for the terms such as I indicate above are ephemeral -they change rapidly. Some debris will not survive the passage round the sun, most of the gases in the coma will add to the thin gas of our system, these are just some of the reasons I ask the question.


      • Anonymous July 29, 2011, 4:49 PM

        of course, we all know it is not all about the size. I was making a point about one part of the article. See my reply to Jon if interested.

        • WaxyMary July 29, 2011, 5:59 PM


          Let us say, for the sake of argument, the ion or debris tail of that comet did appear to engulf the position the Earth was describing at that time in its travel about our Sun.

          1. If the tail is much as we commonly entertain from our current knowledge then the Earth’s sky was capturing some of the ionized gases from the outgassing of the comet. There is a lot of thickness to our atmospheric shell(s). Our magnetic field will also be impacted –to no great extent though.

          2. If the two tails happen to be aligned with the position of Earth there will be stony debris as well as the ionized gases. This would not be uncommon at all, each year the Earth passes through the paths described by prior comets’ tails. These events give rise to the meteor showers. In that event we would be within the passing tail and not just passing through the path the tail passed, if that makes any sense to you.

          3. The currents of space within our system are filled with remnants, debris from the passage of prior comets, asteroids and what not. The spalling of these tiny fragments is not the same as the calving of very large comets into additional large chunks.

          Unless these items are large enough to be seen in the EM spectrum we monitor and great enough in mass and/or EM field strength to effect our planet, and additionally pose a very close passage, there is never any need to pay much attention to them by the general public. We all like a great show in the skies, of course, and if this comet was to display such then we would all be looking up. The simple facts do not support that view though and those pseudo-facts being drummed in the scary night are so untrue as to make anyone who has a lick of common sense shudder at the onslaught of trivial questions, answers to which could be easily discovered by consulting any standard encyclopedic reference book or system. This comet, for example, will not come any nearer to our Earth than the distance of about 1/2 the distance from Earth to the Sun in length and will not track our plane of orbit.

          Additionally I wish to state very plainly that your several postings do indicate your thoughts. These thoughts about needing to know the exact size are very telling so please do not pretend you are just asking, or just talking about the ‘one thing’ in some article (which you posted as some type of evidence to support your fears).


  • Anonymous July 31, 2011, 6:59 PM

    I want to know if this asteroid 2005 YU 55 is a threat as it shows in this Graph to come very close to Earth passing by in November ? see the Graph jere in this Link that Shows asteroids and comets Elenin , Levy and 2005 YU 55 , here are 2 links that show the Graph ; http://www.ufo-blogger.com/2011/04/nasa-elenin-2011-comet-planetary.html , and , http://neo.jpl.nasa.gov/news/news171.html

    They say it misses but BUT what promoted this Letter that came out Last October from the Whitehouse Science CZAR John Holdren with Warnings as to preparing agencies of potential events ?? Source: http://www.whitehouse.gov/sites/default/files/microsites/ostp/ostp-letter-neos-house.pdf

    In breaking down this letter, it’s important to address several questions that have since more recent information come to light.

    After the letter above clearly shows how important it is to monitor such incoming objects due to their propensity to “change” orbit?

    Why was it that NASA turned off the granddaddy of all NEO (Near Earth Objects) telescopes & SETI ATA this year.

    Flashback Quote:

    The WISE spacecraft will remain in hibernation without ground contacts awaiting possible future use.
    Feb. 17, 2011Space.com http://www.space.com/10895-nasa-wise-space-telescope-mission-ends.html

    The SETI ATA has been in hibernation – a safe mode of sorts, where “the equipment is unavailable for normal observations since April 15, 2011. Universetoday.com http://www.universetoday.com/85121/budget-woes-put-setis-allen-telescope-array-into-hibernation/