A Comet Kerfuffle

On September 24th a very faint comet was discovered in the constellation of Cancer at a distance from Earth of about one billion kilometers.  Now named C/2012 S1, or colloquially “Comet ISON” it has picked up quite a bit of press in the past weeks.  Looking at the orbit of this comet it certainly looks like it has the potential to be “spectacular” as seen from Earth.  It will pass close (within 1.2 million kilometers) to the Sun in late November 2013, and then pass by the Earth at about 40% of the Earth-Sun distance (~ 65 million kilometers).  The comet already seems to be active, that is showing some fuzziness as a result of gas and dust being liberated from its surface, even though it is still out beyond the orbit of Jupiter.  These two things have a whole lot of folks talking about this being a great comet, one that will put on a heck of a visible show in the night sky.  The idea being that this comet will produce a tremendous cloud and tail of gas and dust as it passes by the Sun, and will shine brightly in the night sky.  Some have even proclaimed that Comet ISON could put on a show similar to that of the Great Comet of 1680. Or, you know, it could be a total dud, viewable by almost none <cough Kohoutek cough>

The Great Comet of 1680 by Lieve Verschuier

Now, how can people on one had be comparing this comet to very visible, spectacular looking comets like the Great Comet of 1680, or even Comet Hale-Bopp, yet at almost the same time caution that we may end up seeing nothing?  It all has to do with how a comet behaves, and how unpredictable that behavior actually is.

What we see of the comet in the sky is not the object itself: The actual comet is a small, dark, potato-shaped object made up of rocks, carbon, and ices.  In 1950 Fred Whipple described comets as “Dirty Snowballs,” and that’s how we still see them, although recent observations, and fly-bys of several comets have me leaning toward calling them“Icy-Dirtballs” to better describe them.  As these objects (the comet nucleus) nears the sun, many of the ices near the surface will vaporize, producing a “coma” or cloud of gas and dust around the comet.  This is what we see when we look at the head of a comet.  This gas and dust interacts with the solar wind and gravity and eventually produces tails for the comet, completing our mental image of what a comet is.

That said, the exact processes and amounts of gas and dust to be liberated are unknown quantities on a comet-by-comet basis.  How much ice is left near the surface from previous passages through the solar system?  How deep can the Sun actually warm the comet?  Will the comet crack, or break apart under the gravitational and thermal stresses as it passes by the Sun?  Will a large amount of dust be liberated with the vaporizing gasses?  All of these questions play a vital role in determining how a comet will look in the sky.  A very gassy, dusty comet that dredges up material from deep within could put on quite a show.  At the same time, one that only vaporizes a thin surface layer of ice could certainly be a “dud” for the eyes (although it could still have quite a bit of scientific value!).

So what will happen in late November 2013 when Comet C/2012 S1 comes by?  No one has any clue, but we may get lucky and have a really nice comet hanging in the sky at the end of that year.  Or not.

Yes Virginia, you can see the flags on the Moon!

One of the all-time questions that people ask about any big telescope is “can you see the flags on the Moon?”  The answer for all ground based, and Earth orbiting (e.g the. Hubble Space Telescope) is no for a variety of reasons: too small at that distance, on too bright of a surface, etc.  In fact the Hubble website has this question (with answer)  in their FAQ!  With the fantastic images from the Lunar Reconnaissance Orbiter Camera (LROC) in Lunar orbit however, we can indeed see many of the objects left behind by the Apollo astronauts.  The landers, footpaths, rovers, and science experiments are all visible in amazing detail.  For example, below is a recent LROC image of the Apollo 11 landing site at the Sea of Tranquility.

LROC image credit NASA / GSFC / ASU 

But what about the flags?  Now in many of the images there seems to be something around where the flags were planted, but it’s really tough to tell anything about them from a single image.  Even with shadows, it is hard to make out if the shadow is from the flag, or from the flagpole!  Quite a number of people, myself included, have postulated that the flags on the Moon have deteriorated away during the 4+ decades that these flags have been there.  Harsh UV, charged particle, and micrometeorite bombardment – all things that our atmosphere and magnetic field protect us from – might have easily destroyed a standard nylon flag, which indeed was all that the Apollo flags were.

That said, you can indeed make out the “flag” site of most of the Apollo landings in the LROC images, and something is there!  But are they the flags, or just the poles with a pile of nylon dust?  A recent round of LROC observations has answered that question:  Despite my pessimism on their survivability, the flags are still there.  Having now observed the landing sites at many angles, the LROC team has been able to look at the shadows cast by the flags, and those shadows not only match those expected by a flag+pole, but change orientation with the sun from image to image!  Below is a recent image of the Apollo 17 site, along with a blow-up of the portion with the descent stage and flag – that shadow is certainly more than just the pole!

LROC image credit NASA / GSFC / ASU

The LROC team has also made an animation out of the still images of the Apollo 12 site, you can watch the shadows move around during a “lunar day” reconstructed from the LROC observations:

Ok, to be fair, the flags might not be intact.  While we can now see that they are still standing, the 40+ years they’ve spent on the Moon may have “bleached” out their colors, but it’s still pretty flipping cool that 5 out of 6 Apollo Flags have been found.  Buzz Aldrin mentioned that he thought he saw the flag get knocked over as he and Neil Armstrong took off from the Moon, and what do you know, he was right.  The only Apollo flag not identified in the LROC images is Apollo 11’s.

Short Break!

Lots of stuff going on - I've got blog snippets about images of Earth from other Worlds, cool results from LRO about the Apollo flags still standing on the moon, and of course MSL Curiosity landing on Mars, including the NASAsocial (tweetup) at the NASA Langly Research Center prior to the entry, descent, and landing portion of the MSL mission.  It is also almost time for courses to begin and I'm putting the wraps on my Fall Solar System course, so that's been where most of my writing time has gone.  I'll have some official babbling on stuff again real soon.

Home library organization

Well, the moving truck finally brought our stuff to us in Virginia, and that meant it was time to organize and shelve all of our books.  How to do it?  By subject?  By author?  By color?  By sum of all ISBN digits? By how loud the book is when dropped from 4.5 feet?  Well being the giant academic nerd that I am, I suggested “why not just use the Library of Congress?”  We did.

Now really, even though my family has a lot of books, we don’t have nearly enough to call what we have “a library,” and so the Libraray of Congress system isn’t exactly a perfect fit, but it made the decision for us, and it was both a little fun, and turned up a couple of surprises along the way.  Here are a couple that stood out while we were sorting and shelving:

Anthony Bourdain, the opinionated trash-talking chef and travel guide of No Reservations (among other shows) has written a number of books about his career and experiences as a chef and world traveler.  Where does the LoC put his books? Why TX – Home Economics of course!

The Physics of Christmas by Roger Highfield gets put into GT - Manners and Customs, as the subject has been determined to be 1. Christmas and then 2. Science.  Also in the G section (subsection GF - Human ecology. Anthropogeography) are the The Worst Case Scenario Survival Handbook line of books.  Except, oddly enough, The Worst Case Scenario Survival Handbook: Work  Which ends up in PN - Literature (General).

Historical creative non-fiction also end up in weird places.  The creative non-fiction The Perfect Storm by Sebastian Junger gets sorted into QC – Physics, and Seabiscuit: An American Legend by Laura Hillenbrand goes into SF - Animal husbandry, Animal science.

Now I’m not a librarian, nor do I have any training in library science.  I’m not knocking the classification system here at all – in fact I may have even been poorly informed by the various search engines I used to look up the LoC classifications for my books that didn’t have them printed on the copyright page.  I’m just an astronomer with a couple bookcases of books who is rather amused by where this classification scheme puts some of them.  With that disclaimed I’ll sign off with one last placement oddity: The Pursuit of Happyness by Chris Gardner (now a movie starring Will Smith) gets filled under HG – Finance.

And then there were five…

134340 Pluto has a new moon, bringing the distant dwarf planet’s collection of satellites to 5.  No official name for the little guy yet, but this 10 to 25 km piece of (more than likely) ice takes about 20 days to orbit Pluto at a distance of about 42,000 km, placing it between Charon (the largest and innermost know moon) and Nix.  With the New Horizons probe on the way to Pluto, the little world’s family of moons continues to grow.

Pluto’s system of five moons.  Pluto and Charon are added into this composite image from a different source – the light from them needs to be blocked in order to make out the much fainter satellites.

Pluto’s first satellite, Charon was discovered by James Christy in 1978.  He noticed a “bump” in the images of Pluto that changed position (and even disappeared) from image to image.  Since then studies of Charon has allowed for much better mass measurements of Pluto, as well as revealing information about the moon itself.  Charon is, in relation to its parent, the largest object we consider a “moon.”   Charon’s diameter is about half that of Pluto, with 12% the dwarf planet’s mass.  Compare that to the Earth-Moon system: our Moon is about a quarter the diameter of the Earth in size with only 1.2% of the mass of the Earth, and our Moon is abnormally large compared to most planetary satellites (e.g. Saturn’s largest moon Titan is about than .02% the mass of Saturn!).  Charon is so massive compared to Pluto that it causes Pluto to actually orbit a point ouside of itself in space.  Really Pluto-Charon could be considered a double dwarf planet (or a binary Kuiper Belt Object) as they both orbit around a point partway between each other.

Now you see me now you don’t: The “bump” that would become known as Charon is visible to the upper right of Pluto in the first image, but not in the second.

Charon and Pluto are also tidally locked to one another, Pluto’s rotation, the rotation of Charon and the the orbit of Charon all take the same amount of time, roughly 6 days, 9 hours.  This situation results Pluto and Charon always “facing” each other.  Charon will always be in the same place in the sky for an observer on Pluto (and the other way around too!).


The rest of Pluto’s family of satellites are more recent discoveries.  The dwarf planet had been under detailed study to prepare for the New Horizon’s mission, which was launched in 2006, and is scheduled to fly-by Pluto and its moons in 2015.   By blocking the light from the bright sources of Pluto and Charon, the region near Pluto may be searched for additional, small and faint bodies.  In 2005 a team conduced a search for companions of Pluto using the Hubble Space Telescope and discovered two new satellites of Pluto, later officially designated Nix and Hydra.  In 2011 a 4th moon of Pluto was discovered, “P4”  Which brings us up to today, with the recent announcement that a 5th moon of Pluto, “P5” had been identified through HST images.  All four of these newer moons are pretty small, with the largest one, Hydra, between 60 to 170 km across, while the smallest moon,  the newly discovered “P5,” being only 10-25 km in diameter.  Quite a bit of the uncertainty in size comes from not knowing how reflective these moons are.  If they have very dark surfaces, they will be larger than if they had very reflective surfaces since these size estimates are based on how bright the sunlight is that has reflected off of their surface and been collected by our telescopes.


Of interest is the relationship that the orbits of Pluto’s moons have with each other.  They are all very close to mean motion resonances with the Pluto-Charon system.  From closest P5, Nix, P4, and Hydra are almost in a 1:3:4:5:6 resonance with the Pluto-Charon.  That means that every 6th time Charon orbits Pluto, P5 will have completed 5 orbits, Nix will complete 4, P4 will have completed 3 and Hydra will have finished one orbit of Pluto.  Details are being studied right now, but it seems as though none of them are in a “perfect” resonance – but the orbital dynamics of the Pluto system are getting very interesting indeed.


In fact a colleague of mine, Dr. Alex Parker at the Harvard–Smithsonian Center for Astrophysics, has made a wonderful demonstration of how close to resonance these moons are.  By translating their orbital frequency into sound, and boosting it by 29 octaves (to be in the auditory range) Dr. Parker has turned the Plutonian orbits into “music”.  One can visit his SoundCloud page: http://soundcloud.com/alexhp-1/plutos-five-moons and hear the slight difference between a perfect resonance, and what we have measured the Plutonian system to be in.  Seriously, check it out – it is super cool.

Off the air for a week or so.

A Sky Full of Rocks will resume its normally sporadic schedule later this month.  I’m moving across the country and will be at the whim of when the cable folks show up to the new place.  That said, cool stuff is happening, from the CERN / Higgs Boson stuff on the 4th of July, to the MSL Curiosity Rover’s landing on Mars on August 6th, and bunch of things between then too.

Flag Day - The Updating!

Turns out I’ve already got an update to my Flag Day! post from a little bit ago.  I had speculated that like Pathfinder, the flag decals on the Mars Exploration Rovers, Spirit and Opportunity, were under the camera-mast, and thus not imaged by the rovers.  Boy was I wrong!

Here’s the flag on the instrument deployment device (IDD), the rover’s “arm” on Opportunity.  All that dust on the instrument is left over from using its rock abrasion tool (sort of a grinder/drill) on the exposed rocks during Opportunity’s 31^st Martial day.

I also missed an obvious “2-fer” on Spirit!  Beyond the decal on the IDD, Spirit also carried with it a memorial to the crew of the Space Shuttle Columbia, STS-107. 

The above memorial plaque carries the US flag, along with the names of the Astronauts who were lost on the Columbia.  If you look closely you can see an additional Israeli flag next to the name of Ilan Ramon, Israel’s first astronaut.

As a bonus here’s a shot of the first “nationally branded” object deployed to the surface of the Moon

These two steel spheres (diameters 7.5 and 12 cm respectively) were carried to the Moon by the Soviet Union’s Luna-2 spacecraft.  Each of these spheres was filled with a an explosive designed to fragment them like a very large grenade, showering the Lunar surface with the little pentagonal pennants that the spheres were crafted out of.  It is really unlikely that any of these little medals survived.  On September 13, 1959 Luna-2 didn’t land gently on the Moon, but rather plowed into it at over 3 km/s.  The energy generated by the impact of a 400kg spacecraft at the speed would generate enough heat to vaporize steel.  One of the ideas behind the explosives inside the spheres was to try and remove some of the impact velocity, and thus allow at least some of them to survive.  It’s possible but, in my opinion, unlikely that they made it through the impact intact.

The first Soviet Moon probe, Luna-1, also carried a similar sphere, but missed the moon (Luna-1 passed within 6,000 km of the Moon on January 4, 1959), and is now in a 450 day orbit about the Sun.