Tag Archives: Cosmos

Ripples in Planetary Rings Are Traces of Decades-Old Cometary Collisions

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Information gleaned form Cassini, Galileo and New Horizons missions seems to indicate that ripples seen in the rings of Saturn and Jupiter were caused by comets. Shoemaker-Levy 9 (famous for a multiplicity of impacts on Jupiter in 1994) left one set of ripples. Saturn’s cometary clues date to a cloud of icy debris passing through the inner rings in 1983.

“What’s cool is we’re finding evidence that a planet’s rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago,” said Matthew Hedman, a Cassini imaging team associate, lead author of one of the papers, and a research associate at Cornell University, Ithaca, N.Y. “The solar system is a much more dynamic place than we gave it credit for.”

Well, I suspect that was already suspected … how likely is it that the rings around these large planets were formed billions or even millions of years ago and have remained untouched? Clearly, they must reform and even re-accrete material over time as varoius snowballs and rocks mess them up now and then.

But, knowing the details is interesting and important, and it is rather impressive that we can see decades old evidence. This may mean that multiple ancient (but how ancient we do not know) events can be reconstructed by studying the rings:

“We now know that collisions into the rings are very common – a few times per decade for Jupiter and a few times per century for Saturn,” Showalter said. “Now scientists know that the rings record these impacts like grooves in a vinyl record, and we can play back their history later.”

The ripples also give scientists clues to the size of the clouds of cometary debris that hit the rings. In each of these cases, the nuclei of the comets – before they likely broke apart – were a few kilometers wide.

“Finding these fingerprints still in the rings is amazing and helps us better understand impact processes in our solar system,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Cassini’s long sojourn around Saturn has helped us tease out subtle clues that tell us about the history of our origins.”

Read the whole press release, find out about the published papers, and see the pretty pictures here.

Death by Black Hole: And Other Cosmic Quandaries

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Yes, yes, I know … Death by Black Hole: And Other Cosmic Quandaries by Neil deGrasse Tyson did not just come out, and it is not part of any current news story, so I’m not supposed to mention it in a blog post, because blog posts are only about things that happened during the last forty-five minutes or so. But what did happen in the last few minutes is that I finished reading it, and I’m recommending it to you.

It is said that Neil deGrasse Tyson is a modern day Carl Sagan … an astronomer who is superb at communicating science to the masses. That is sort of true but not exactly. Sagan and Tyson actually practice in different subfields of astronomy (rather pedantic of me to point out) and Tyson’s style is different. Aside from being a bit edgier, I find Tyson to be more like Asimov in his discussion of stuff about the universe. I’m reminded, when reading Death by Black Hole, of the Intelligent Man’s Guide to the Universe. Which, I admit, I read when it came out, so it has been a few years…

Death by Black Hole is a fairly comprehensive review of the main issues in modern astrophysics. In particular, Tyson focuses on how we know things, and how the how part sometimes interferes with, or at least makes more difficult, the dissemination of that knowledge. He points out, for instance, that to explain the details of one of the most interesting fairly recent finds in astro-science … the nature and composition of interstellar gas clouds … one needs to explain spectroscopy. Explaining spectroscopy, or any other fairly technical methodology, is often a deal-killer when it comes to getting people excited about something. I had this problem the other night when I had to explain to a bunch of people how optically stimulated luminescence worked in order to say something interesting about the recent pre-Clovis archaeological find in Texas. Fortunately, I was able to relate the esoteric dating technique to baseball and glow-in-the-dark plastic Virgin Marys, so it wasn’t as bad as it could have been.

Death (the book) is a collection of previously written essays edited slightly to account for natural redundancies and cross references.

The best part about the book is simply Neil deGrasse Tyson’s approach to explaining things that can be hard to explain. He also interjects the extra enthusiasm one gets when an author is speaking about pet peeves, about things like how the sun is depicted in art and how certain science is depicted in certain movies. The book is NOT about death by black holes. That is only one of the many topics covered. There are, it turns out, a whole bunch of other ways to die. He covers all the important ones.

If you haven’t read it, then read it. The Kindle edition is less than 9 bucks.

Vesta

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This is the picture of Vesta, which is an object in our solar system:

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That’s the picture that Wikipedia uses as of this writing, and it was taken by the Hubble. The key thing to note is that Vesta, which lies in the asteroid belt and has been thought of as a big asteroid, is very globular like a planet. This is unusual for an asteroid.

This is a picture of Vesta as conceptualized by NASA scientists. It is a model, not a photograph.

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Model of Vesta This image shows a model of the protoplanet Vesta, using scientists’ best guess to date of what the surface of the protoplanet might look like. It was created as part of an exercise for NASA’s Dawn mission involving mission planners at NASA’s Jet Propulsion Laboratory and science team members at the Planetary Science Institute in Tuscon, Ariz. Other resolutions, desktop images here. Click the image to embiggen.

The images incorporate the best data on dimples and bulges of the protoplanet Vesta from ground-based telescopes and NASA’s Hubble Space Telescope. The cratering and small-scale surface variations are computer-generated, based on the patterns seen on the Earth’s moon, an inner solar system object with a surface appearance that may be similar to Vesta.

Vesta makes up about 9% of the entire asteroid belt. In fact, if you take the largest handful of objects in the asteroid belt, Ceres (that’s the largest), Vesta, Pallas and 10 Hygiea, you’ve got half of the mass of the entire thing, according to the most current estimates. This sort of thing makes one wonder if some or all of these objects should be thought of as something other than asteroids. And this is a question that has been raised in relation to NASA’s Dawn project.

“I don’t think Vesta should be called an asteroid,” said Tom McCord, a Dawn co-investigator based at the Bear Fight Institute, Winthrop, Wash. “Not only is Vesta so much larger, but it’s an evolved object, unlike most things we call asteroids.”

The layered structure of Vesta (core, mantle and crust) is the key trait that makes Vesta more like planets such as Earth, Venus and Mars than the other asteroids, McCord said. Like the planets, Vesta had sufficient radioactive material inside when it coalesced, releasing heat that melted rock and enabled lighter layers to float to the outside. Scientists call this process differentiation.

McCord and colleagues were the first to discover that Vesta was likely differentiated when special detectors on their telescopes in 1972 picked up the signature of basalt. That meant that the body had to have melted at one time.

Special sensors. I gotta get one of those.

Anyway, this July, the Dawn Space Robot will approach Vesta and spend about a year in the vicinity. We’ll see how close that model is, and hopefully, Wikipedia can get a better portrait of the protoplanet/minorplanet/asteroid!

More details on the project are here.

Stardust Ends Its Mission

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This just in from NASA:

PASADENA, Calif. — NASA’s Stardust spacecraft sent its last transmission to Earth at 4:33 .m. PDT (7:33 p.m. EDT) Thursday, March 24, shortly after depleting fuel and ceasing operations. During a 12-year period, the venerable spacecraft collected and returned comet material to Earth and was reused after the end of its prime mission in 2006 to observe and study another comet during
February 2011.

Continue reading Stardust Ends Its Mission →

Weather Forecast for Titan: Methane Rain

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For the first time, rain has been observed falling at low altitude on this moon of Saturn.

Extensive rain from large cloud systems, spotted by Cassini’s cameras in late 2010, has apparently darkened the surface of the moon. The best explanation is these areas remained wet after methane rainstorms. The observations released today in the journal Science, combined with earlier results in Geophysical Research Letters last month, show the weather systems of Titan’s thick atmosphere and the changes wrought on its surface are affected by the changing seasons.

“It’s amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite,” said Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Md., and lead author of today’s publication. “These observations are helping us to understand how Titan works as a system, as well as similar processes on our own planet.”

Details and numerous pictures

How old is the earth, and how do we know?

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How old is the earth?


Short answer: 4,540,000,00/H30 Earth-years, plus or minus 1%.

Long answer: We don’t know exactly because direct dating of the earliest material on the surface of the Earth will only tell use a minimum age; Prior to that, the Earth’s surface was probably molten, and even after that, it may be that the earliest non-molten material has been recycled into the planet’s interior by tectonic processes. Also, the earth is a big round ball of stuff that condensed into this shape from part of a large disk-shaped blob of stuff known as the Solar Nebula. When exactly, given this, did the Earth become the Earth? Since the process took millions of years, we can’t pinpoint the age of the Earth more exactly than a certain range.

What are the oldest rocks?

The oldest rock formations on Earth are between about 3.8 and 3.9 billion years old., but there are older bits of more ancient rocks that were incorporated into these early rocks, and they date to something closer to 4.4 billion years old. These and other early materials are dated primarily using a variety of parent-daughter radiometric techniques, with the most effective for this time period being a lead-lead system.

Since rock from the time of the Earth’s formation isn’t available (because it didn’t really exist or was gobbled up in the fiery beginnings of the big round ball) the preferred method of dating the Earth is to calculate the age of meteorites. The earliest meteorites essentially date the condensation of materials in the solar system into the planets, and thus, the date of these meteorites indicates the date of the early Earth. (The Earth existed prior to this condensation in the form of whatever parts of the early solar nebula would eventually condense into this particular planet, of course.)

Meteorites from other planets?

Some meteorites are known to be fragments of Mars, so the oldest dates among these can also verify the date of accretion of material into planets in our solar system.

Rocks from the moon have not been remelted or otherwise messed up by tectonic processes and therefore would provide an excellent estimate of the age of the Earth as well. Also, since there is no real weathering of rocks on the moon, methods other than parent-daughter decay can be used, such as Fission Track dating (the older a rock, the more cosmic rays pass through it, blasting tiny little tracks in the otherwise homogeneous matrix).

Zeroing in on the age of the earth

There are hundreds of published dates of various older materials, but the following table gives a reasonable summary of some of the more important dates, culled from various sources (see list of references below):

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If we chart this on a graph, we see one date that is much earlier than all the other dates, and a few that are younger.

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The younger dates are simply of materials that we don’t think date the Earth’s formation, but that we know would post date it by not much. These dates verify the earlier cluster of dates that would correspond to the actual formation of the planet. The single earlier date is an obvious outlier.

Taking this series of dates, notice that the oldest (non-outlier) dates are about four and a half billion years old. As stated in the short answer.

Further information about the age of the Earth:

Dalrymple, G. Brent. 2001. The age of the Earth in the twentieth century: a problem (mostly) solved. Geological Society, London, Special Publications 2001, v. 190, p. 205-221. Click Here.

Dalrymple, G. Brent. 2006. How Old is the Earth: A Response to “Scientific” Creationism. The TalkOrigins Archive. Click Here.

Norman, M. D., Borg, L. E., Nyquist, L. E., and Bogard, D. D. (2003) Chronology, geochemistry, and petrology of a ferroan noritic anorthosite clast from Descartes breccia 67215: Clues to the age, origin, structure, and impact history of the lunar crust. Meteoritics and Planetary Science, vol 38, p. 645-661.

Stassen, Chris. 2005. The Age of the Earth. The TalkOrigins Archive. Click here.

Wikipedia, Teh. 2010. Age of the Earth. Click here.

NASA shoots comet, looks at hole it made

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On the left is the comet minding its own business. On the right is a blobish roundish area where NASA’s impactor probe hit the comet.
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I know, I know, it looks mainly like they just unfocused the image. It turns out that many of the images in the “after” sequence have a crappy focus, but there are enough of them here to prove that it really happened.
Continue reading NASA shoots comet, looks at hole it made →

Comet Hunting Space Robot Spots Quarry

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Stardust, the NASA probe, has downloaded a snapshot of Tempel 1, a comet that the comet seeking craft will sidle up to on February 14th. Here is the picture:

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On the night of encounter, the navigation camera will be used to acquire 72 high-resolution images of the comet’s surface features. Stardust-NExT mission scientists will use these images to see how surface features on comet Tempel 1 have changed over the past five-and-a-half years. (Tempel 1 had previously been visited and imaged in July of 2005 by NASA’s Deep Impact mission).

I don’t know why they call it night. Perhaps because NASA is playing up the whole romance theme. Anyway, details here.