Tag Archives: comets

How Far We Have Come(t)

It wasn’t that long ago, especially by cometary standards, that humans viewed the unpredictable and spectacular arrival of a comet, its tail spread across the sky unlike any star or planet, as an obviously unnatural event. How could an object flying so dramatically and briefly through the heavens be anything other than a message from a divine force? Even a few hundred years ago…

Today a human-engineered spacecraft descended out of the starry blackness and touched one.

We have known for quite some time that our ancestors widely maligned these icy rocks, often thinking them messengers of death and destruction.  Yes, a comet is, at some level, not much more than an icy rock. Yet, heated by the sun, it can create one of our sky’s most bewitching spectacles. Actually two, because not only can a comet itself be a fabulous sight, the dust it leaves behind can give us meteor showers for many years afterward.

But it doesn’t stop there.  For comets, believed to be frozen relics of the ancient past, born in the early days of the Sun and its planets, may have in fact been messengers not of death but of life.   When they pummeled our poor planet in its early years, far more often than they do today, their blows may have delivered the water for the Earth’s oceans and the chemical building blocks for its biology.   They may also hold secrets to understanding the Earth’s history, and perhaps insights into the more general questions of what happens when stars and their planets form.  Indeed, as scientific exploration of these objects moves forward, they may teach us the answers to questions that we have not yet even thought to ask.

Will the Philae lander maintain its perch or lose its grip? Will it function as long as hoped? No matter what, today’s landing was as momentous as the first spacecraft touchdowns on the Moon, Venus, Mars, Titan (Saturn’s largest moon), and a small asteroid — and also, the first descent of a spacecraft into Jupiter’s atmosphere. Congratulations to those who worked so hard and so long to get this far! Now let’s all hope that they, and their spacecraft, can hang on a little longer.

Comet ISON Befuddles the Experts

Take a ball of loosely aggregated rock and ice, the nucleus of a comet, fresh from the distant reaches of the solar system.  Throw it past the sun, really fast, but so close that the sun takes up a large fraction of the sky.  What’s going to happen?  The answer: nobody knows for sure.  Yesterday we actually got to see this experiment carried out by nature.  And what happened?  After all the photographs and other data, nobody knows for sure.  Comet ISON dimmed sharply and virtually disappeared, then, in part, reappeared [see the SOHO satellite’s latest photo below, showing a medium-bright comet-like smudge receding from the sun, which is blacked out to protect the camera.]  What is its future, and how bright will it be in the sky when it starts to be potentially visible at dawn in a day or two?  Nobody knows for sure.

[Note Added — Now we know: the comet did not survive, and the bright spot that appeared shortly after closest approach to the sun appears to have been all debris, without a cometary “core”, or nucleus, to produce the additional dust and gas to maintain the comet’s appearance.  Farewell, ISON!  Click here to see the video of the comet’s pass by the sun, its brief flare after passage, and the ensuing fade-out.]

I could not possibly express this better than was done last night in a terrific post by Karl Battams, who has been blogging for NASA’s Comet ISON Observing Campaign. He playfully calls ISON “Schroedinger’s Comet”, in honor of Schroedinger’s Cat, referring to a famous and conceptually puzzling thought-experiment of Erwin Schroedinger, in which a cat is (in a sense) put in a quantum state in which it is neither/both alive nor/and dead. Linking the comet and the cat is a matter of poetic metaphor, not scientific analogy, but the metaphor is a pretty one.

Battams’ post beautifully captures the slightly giddy mindset of a scientist in the midst of intellectual chaos, one whose ideas, expectations and understanding are currently strewn about the solar system. He brings to you the experience of being flooded with data and being humbled by it… a moment simultaneously exciting and frustrating, when scientists know they’re about to learn something important, but right now they haven’t the faintest idea what going on.

Icy Comet ISON’s Trial By Fire

Comet ISON, a pristine chunk of rock and ice from the extreme edges of the solar system, is making its first visit to the vicinity of the Earth and the Sun. And what a trip!

Today, in a few hours, at 1:45 in the afternoon on the U.S. east coast, the comet will pass exceptionally close to the Sun — much, much closer to the Sun than the Earth or even the planet Mercury. At its closest, the distance from the comet to the Sun’s center will be only 2.5 times larger than the distance from the surface of the Sun to its center.  To say it another way, the radius of the Sun is about 700,000 kilometers (430,000 miles) and the comet’s closest approach will be 1,200,000 kilometers (730,000 miles) above the Sun’s surface, or 1,900,000 kilometers (1,160,000 miles) from its center.

This will be a very fiery place for an icy object to find itself!! A comet may or may not survive such a close approach; its central core (or “nucleus”, an agglomeration of rock and ice, about the size of a big mountain on Earth) may fragment if the heat radiating from the sun sufficiently vaporizes and weakens the core. If it does survive, and perhaps even if it fragments, we may begin to see it in the sky in a couple of days, just before sunrise. And if we’re very lucky, it will be spectacular.  [Note Added (updated): It appears we are unlucky this time.  Indications are now strong that Comet ISON’s nucleus (mostly) did not survive its close approach to the sun, and began falling apart just before or shortly after this post went on-line.  You can see evidence of this in a video from SOHO’s close-up camera. Whether the remnants of its dust tail might be visible for a few days isn’t clear to me (or probably to anyone) yet.  We can now see that some fragment of the nucleus appears to remain, but the comet is a shadow of its former self.  We’ll know soon how visible it will be.  [Unfortunately it appears that was visible was all dust, and the comet is just debris now; it will not be visible at all.]]

Over the first few days of December, the comet will dim, but it will also move away from the sun and from the brightest light of dawn, and so it will also become easier to see. Try to look for it in the coming week!   My current amateur’s guess (to be updated when I know) is that its remnant dust trail will spread out and dim very rapidly; you should not wait too long if you want to try to see it.

For the moment, you can’t see the comet by eye; it is way too close to the incredibly bright light of the sun. The only way to observe the comet right now is via satellites. The close approach is best watched through the camera of SOHO (the Solar and Heliospheric Observatory satellite). There’s a recent movie here from SOHO that shows the comet has brightened very rapidly in the last 24 hours. [The sun lies at the center of the image, drawn as a white circle, and is shaded from SOHO’s camera by a shield that forms a larger black dot in the center of the image.] The bright star Arcturus sits at the lower left of the image, and the comet is [was, this morning,] much brighter than that! Its maximum brightness may eventually approach that of the brighter planets, Jupiter and even perhaps Venus. Click here for the latest SOHO image, and here for the latest closeup image (which as of writing doesn’t show the comet yet.)  A recent image is below.


Comet C/2012 S1 ISON from the NASA SOHO spacecraft on November 28th as it approached the sun.
[Image credit: NRL/NASA]