67P/Churyumov-Gerasimenko's double lobed shape

By far the most interesting and defining quality of comet 67P, when the Rosetta Probe visited it earlier this year, was its double-lobed shape. While not being completely new, this was the first example of such a process happening with a comet.

Contact binaries are assumed to have been two asteroids (or comets) that joined together through a collision slow enough that they wouldn't fly past each other, or destroy each other. A defining quality for these is the notable double-lobe nature of them when a telescope points itself at them. Naturally, based on the images, that's what I would have thought if I didn't know better. However I have a couple of reasons to believe otherwise.

First, long exposure images of the comet have found that both lobes of the comet are erupting. And, based on a JPL small-body database search, asteroids outnumber comets just a bit over 200:1. The chances of two comets merging together is less than 0.1%. To further this, every picture taken shows most of the outgassing coming from the center of the comet, along with the shape of the comet indicating that the area was dug away rather than gravitationally connected- a contact binary owuld have a distinct divider between each asteroid, with gravitational attraction flattening only the closest parts to one another, giving it more of a bowling pin look than an apple-core look.

Second, the density of the comet is 0.4 g/cm³, which is typical of a comet, but based on such a size and a density, a contact binary alone would not be sufficient to mold the two lobes of the comet together to such a high degree. Plus, you would expect the density to be higher had two asteroids collided with each other, pushing each other together and giving a density of at least a few more decimals than the found density.

Lastly, notice that, contrary to the rest of the comet, the 'bridge' is relatively smooth, without any craters. This shows that the surface is young in comparison, and that any craters that form are quickly wiped away as the dust that they are imprinted upon flies off the comet.

Based on the given evidence, I can conclude that 67P is a single comet, but through an unknown force, the center of it is being melted away quicker than the rest of the comet, and that we are perhaps observing live exactly how comets fragment. It may be quite a while before this one fragments, but I think the mechanism behind this quicker core sublimation would be a good target for more in-depth study, and that it will help us better understand exactly how comets work.

Updates

again, sorry for the delay. I know the blog hasn't been very active, but I've never seen a blog that updates much more than once a week. Anyways, here's what happened since my last post.

I've finished my list of comets by type on wikipedia - https://en.wikipedia.org/wiki/List_of_comets_by_type

I also started another project to find transneptunian objects from SDSS data - so far I've found images of 10, two of which I found from before they were discovered, 2004 XR190 and 2011 GM27.

I recently found what should be precovery observations of the asteroid 2014 UM33, however it only has an observation arc of 2 days, and is currently magnitude ~20. If there's anyone who can observe it in the next few days, for me to get an observation from 2009-01-17, that would be quite helpful. The asteroid probably needs a 2-meter telescope or larger, or at least a telescope that can see to mag=20.

more updates in the next few months!

Have we already made first contact?

It's something science fiction readers and writers love to talk about all the time. Making first contact with another civilization would of course revolutionize everything about the way we live. Of course the typical science fiction book will lead you to believe that first contact is in the form of direct contact with alien races, as in meeting them in person, but it's much more likely that our first form of contact will be through signals sent to one another, and chances are that's going to take a long time, which brings me to the topic this post is on.

While we've only sent out signals to distant worlds for the last decade or two. Just traveling at the speed of light, not taking into account the decrease in signal strength over distance, we've only reached a few hundred stars, most of which are red or brown dwarfs. However, we've unintentionally been sending out signals for much longer, going back into the early 20th century, however most early signals were only intended for short-distance communication and likely wouldn't get beyond the orbit of the Moon, much less interstellar space. However more intense radio signals have been used over time, to a point where our planet is essentially a beacon of radio waves in space. Of course any civilization within 50 light years, with sufficient signal sensitivity, would have already noticed us and possibly recognized us as a civilization. But how long would it be before we made contact?

Well assume we send out a signal in 2000 AD, and it reaches an alien civilization 50 light years away. By the time it reaches them, it's 2050. It would be 2100 before we receive any signal whatsoever from them, and much longer for them to reach us. Even if they traveled at 1/10th at the speed of light, or ~1,086 miles per second it would take them 500 years. In other words, if a civilization recognized we exist recently, we won't know for quite some time, and if decide not to send any signals before arriving, it could take until at least 2500 AD before we know.

Then its also possible we've already found alien signals long ago. On August 15, 1977, Jerry Ehman, working for SETI using the Big Ear radio telescope, detected a radio signal coming from the constellation Sagittarius. The location is fairly uncertain, and is limited to between two narrow bands in the area, neither of which contains any remarkable stars. Chances are that whatever the signal came from is very distant, leaving one to wonder how strong the signal sender would have to be. According to one source, it would have to be approximately 2,200,000 watts of power. For comparison the strongest signal transmitter on Earth is only 2,500 watts, roughly 1/1000th of the required amount. Whether or not it came from an intelligent civilization is likely something we won't know for quite a long time.

An attempted explanation of Dark Matter and Dark Energy

My blog is listed as a Planetary Science blog, and that's what all the topics have been about so far. However the thing is that planetary science is an awfully small topic when considering all of astronomy, so with this post I widen the topic of this blog to all of astronomy, from planetary science to orbital mechanics to astrophysics. As a result, for this post I will be attempting to explain what dark matter and dark energy are. They're often explained and implied to be much more mysterious than they are, and my explanation will attempt to simplify what exactly they are and their effect on the universe.

Dark Matter was first hypothesized in the early-to-mid 1900s to explain the missing mass needed for galaxies to hold together at the speed they travel, as their visible mass alone could not account for that. Dark matter is essentially what the name suggests- just matter that does not in any way interact with light or directly with matter. Imagine it as a pane of glass; light travels through it, does not interact with it, and is not stopped by it. However while we can see the refraction caused by light's slight change in direction while traveling through glass, light simply does not interact with dark matter. However it interacts with gravity, which slightly bends light, letting us use gravitational lensing to view its effect on the universe. Imagining space like Einstein's famous flat, stretchable sheet analogy, photons traveling across the sheet would be bent in very slight, nearly unnoticeable ways that can be measured to see how much gravity is in a certain area. Scientists compare the lensing effect and the amount that the visible mass of an object could account for, and the difference is the amount of dark matter in the area.

Like normal matter, Dark Matter was created in the Big Bang ~13.8 billion years ago, and today it still makes up the majority of matter in the universe, but when it was first created it made up over 60% of all matter. Eventually, the clumps of Dark Matter formed in the Big Bang began to form into clusters and filaments, and formed the structures that galaxies and galaxy clusters now occupy, akin to plaster pouring into a mold.

But where did all of that dark matter go? In the 1990s, studies of the universe's speed of expansion showed that the universe is accelerating faster and faster, and at a loss to explain it any other way, physicists hypothesized that space itself has an energy in it that has a sort of negative gravitational effect, causing the universe to get larger, making more space to further enlarge the universe in a gigantic feedback loop.

Unlike the names suggest, dark matter and dark energy aren't actually at all related to one another except the fact that they don't interact with light. However the effects of them are very much at odds with one another, with dark matter pulling the universe in on itself, and dark energy pulling the universe outwards in a cosmic tug-of-war,a game that dark matter is destined to lose.

Expect long breaks, and no this blog is not dead.

I've had this blog for 6 months now, and it is certainly not at the height of its activity. I've taken several breaks, some much longer than others, but I will make no promise not to have these. I've been doing a lot of work recently and there's no indication of any of that changing, so expect several days to a month between new posts. However, on the bright side, previously I had been discussing topics, nearly copied word-for-word from Wikipedia. In future posts, I'll be trying to upload more 'original' content, and I plan to give this blog more activity in the coming weeks and months, starting with a special post next tuesday.

I need you! (click to help!)

Hello again. Previously, I've just been posting planetaryscience-related articles, but now I need you to help me with something!

For a while, I've noticed that there's no central, easily-navigable database on comets for people to browse, and if there is one, it's not seen very often. So, I've decided to start working on a 'list of comets by type' on Wikipedia. I've made good progress, getting up to C/1913 R1 as of now, but the progress is continuing slowly, and I'll need your help to help me compile the list!

Here's how you can help:


First, no Wikipedia account is required, but one would be required to receive recognition for it. Minimal HTML experience is required, along with being able to follow basic rules and guidelines:

First of all, I'm getting my work from the JPL Small-Body Database Browser, searching for comets using the search term "C/19*" to search for every non-periodic comet found in 1900. But how do you work?

Well, Here is my main workplace, full of unfinished projects that I should really get around to. Just go start editing the table there, and I'll give some guidelines if you still need help there. Thanks for the help!

I'll be posting about the final 'rings' post on the weekend, so stay tuned!

not so large now. The rings of Uranus

Continuing from my previous post of the rings of Saturn, we'll keep going out to the last 2 planets with rings: Uranus and Neptune.

First of all, I apologize for the delayed post; I came back late yesterday and didn't have much time, and spent the rest of the day messing around with imgur and writing this: Enjoy!

Uranus's rings, unlike the inner gas giants, are very thin and dim. The ε ring, the brightest of the rings, is only a fraction of Saturns' rings brightness. Despite these obvious differences, we'll list the rings as regular from closest to Uranus to furthest.

The ζ & 1986U2R rings
The rings begin pretty much as soon as Uranus ends. The ζcc ring, the closest of the rings, is one of a couple of extensions of the ζ (Zeta) ring orbiting, in full, between 26,840 and 41,350 kilometers from the center of Uranus (~1,300-15,800 km from the surface.) Aside from being the closest, however, it isn't exactly the brightest. The ring is around 100 times fainter than the brightest ring in the system usually, but is very bright if looked at the right way (no, not like those 3D paintings). Since nearby 1986U2R's discovery in 1986, though, the ring has moved in slightly. These rings are fairly dynamic, unlike Saturn's, changing over the course of mere months or years.

An image of the 1986U2R ring showing its irregular ring arcs and ever-
changing shape. Credit: NASA

The numbered (4, 5, and 6) rings
Slightly further out from the ζ ring, we find a system of bright, narrow rings elevated slightly from Uranus's equatorial plane. These rings were designated the 6, 5, and 4 rings radiating out from the surface for lack of an appropriate Greek symbol. These rings, unlike the ζ ring, don't have much dust in them.

The α & β rings
These rings are the first of the Greek-lettered rings, but unfortunately not the last. These rings are the 2nd and 3rd brightest after the ε ring, but for some reason don't have any dust in them. They are each about half the mass of the brighter ε ring.

More Greek alphabetics: the η ring, ηc ring, and γ ring
The next few rings on our journey are all narrow and a bit dim, but that doesn't make them any less fun. The η ring is pretty dense, but the ηc ring is more broad and dim. The γ ring is much more eccentric than the other rings, and slightly wider than the η ring.

Done yet? the δc and δ rings, and why not add in the λ and ε, too?
These rings, comprising the outer parts of Uranus's thin section of the ring system, also mark the beginning of the moons. Circling just inside the λ ring is Cordelia, only about 40 km across. Despite its small size, it's still large enough to pack a bit of a punch on the ring, acting as its inner Shepard moon. Furthest out and brightest is the ε ring, also one of the largest in the system. The outer Shepard moon for this ring is Ophelia, larger than Cordelia by only 3 kilometers.

The ν ring
Not last, or least, comes the ν ring. This ring, much dimmer than the other rings, is one of two outer very dusty rings. The ring, discovered in 2003-5, is clearly bordered by the moons Portia and Rosalind (inside and outside respectively.) The ring is much larger and broader than all of the other rings closer to Uranus than it, and doesn't appear to be changing much.

Last, and least, the μ ring
The furthest of Uranus's rings, the μ ring, orbits the planet at more than twice the distance of the ε ring, and also has a few guides of its own: Puck, the largest of the inner moons, orbits on the inner part of the ring, and slightly smaller Mab orbits the ring near the center, where it's brightest. This ring, in unlike the red ν ring, is blue in color, probably made of water ice from minor collisions and/or geysers on Mab, and then slowly traveling inwards until it is picked up by Puck's gravity.


Well, that's it. Hope you enjoyed!

P.S. I made a diagram of the rings:

A diagram of Uranus's rings. Credit: Me

 Enlarged (inner halo rings):

The inner rings of Uranus Credit: Me

 Enlarged (thin, central rings):

The bright, central rings of Uranus. Credit: Me

 Enlarged (v ring and surrounding moons):

Uranus's v ring and the numerous moons around it. Credit: Me

Enlarged (μ ring):

The μ ring in all its boring glory. Credit: Me