Geminid meteor shower: why spectacular light show puzzles scientists

By Pete Spotts, Staff writer / December 13, 2011

Gemenid meteor shower watchers can’t figure out where all the material in the event comes from. Asteroid 3200 Phaethon, the apparent source of the Gemenid meteor shower, doesn’t seem to shed enough rock and dust to account for the shower’s intensity.

The Gemenid meteor shower lights up the sky over the Mexican volcano Popocatepetl. Daniel Aguilar/REUTERS/File

The Geminid meteor shower peaks tonight. Don’t miss it!
Geminid meteor shower gets rave reviews as best of 2010
By now you’ve probably heard that tonight’s the night for what is arguably one of the most spectacular meteor showers of the year, the Geminids.

The shower earns its name from its apparent point of origin, or radiant, in the constellation Gemini.

But where many meteor showers represent Earth’s encounter with dust from a comet, the Geminids appear to have an odd duck of a source: an asteroid that some now call a rock comet.

And it’s not clear from recent observations whether the object, known as 3200 Phaethon, is kicking off enough material to account for the intensity of the meteor shower Earth encounters.

A team of astronomers identified the debris gap in a paper published in the Astronomical Journal in November 2010. And researchers are still puzzling over it.

Although the first recorded observations of the Geminids don’t appear until the early 1860s, modeling studies of the debris’ orbit suggests that the stream is anywhere from 200 to 6,000 years old.

3200 Phaethon was discovered by NASA’s Infrared Astronomical Satellite in 1983. Once scientists determined its orbit, the orbit closely matched with the orbit of the debris stream.

One of the asteroid’s key features is its proximity to the sun at closest approach. It comes nearer the sun than any known asteroid, well inside the orbit of Mercury. This allows surface temperatures to reach 1,400 degrees Fahrenheit.

In their 2010 paper, David Jewitt and Jing Li at the University of California at Los Angeles looked at images from one of a pair of NASA sun-watching satellites taken of 3200 Phaethon during its close approach to the sun. Its brightness increased suddenly, indicating that it was shedding material, just as a comet might.

Given the asteroid’s rocky makeup, the team posited that the object’s relatively quick swing into and out of this hot zone leads to rock fracturing when heated. Comets, on the other hand, shed material when the ices they contain heat and shift directly from solid to gas. In the process, a comet also ejects dust and rock bound up with the ices.

To account for the intensity of the Geminid stream, the duo calculated, the 30-mile-wide 3200 Phaethon would have to repeat the shedding process 10 times per orbit, something no one has observed.

Dr. Jewitt allows in an e-mail exchange that their mass estimate could be off, and that additional outbursts during each orbit could emerge with more-systematic observations.

But for now, the grit gap remains.

So, bundle up, grab a chaise lounge, a Thermos of hot chocolate, and head out to see the show overnight tonight or even Wednesday night. The peak actually is expected to occur at about 2 p.m. Eastern Standard Time Wednesday.

But the shower, which typically produces more than 100 meteors an hour during its peak under dark skies, will be a bit less spectacular than it otherwise might be. Blame the bright, if waning, moon. Moonlight will wash out the dimmer meteor streaks.

Geminid meteor shower: why spectacular light show puzzles scientists –


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Asymmetrical Shape of Heliosphere Raises Questions

By Walter Cruttenden, July 7, 2008

Ever since the Voyager 2 data confirmed the nonsymmetrical shape of the solar system scientists have pondered its cause (i). In summary, the edge of the heliosphere (the place where the solar wind slows to sub sonic speeds) appears to be 1.2 billion kilometers shorter on the south side of the solar system (and in the general direction of the winter solstice, the direction of Voyager 2), than it is on the edge of the planetary plane (where Voyager 1 exited approximately a year earlier). This indicates the heliosphere is not a sphere at all but a bullet shape. More data is required to determine the exact shape in all directions.

The initial explanation was there must be some sort of gas cloud pressing against one side of our solar system. While this hypothesis is plausible there is another possibility that deserves consideration; stellar wind.

The sun’s solar winds are primarily driven by its magnetic field. When magnetic storms arise on the sun it produces coronal mass ejections (CME’s), which are like waves or ripples on the solar wind. The solar wind is constantly pushing on the daylight side of the earth’s magnetosphere squashing it in a pattern similar to the way the sun’s magnetic field seems to be squashed where Voyager 2 exited the solar system. Thus it is possible that the dented solar system might be due to the same type of cause; stellar winds from a not too distant star.

Some indication of this might reside in the data recently received by NASA’s sun-focused STEREO spacecraft. The twin STEREO spacecraft were launched in 2006 into earth’s orbit about the sun to obtain stereo pictures of the sun’s surface and to measure magnetic fields and ion fluxes associated with solar explosions. Between June and October 2007, the STEREO spacecraft detected atoms “originating from the same spot in the sky: the shock front and the heliosheath beyond, where the sun plunges through the interstellar medium”, and found “energetic neutral particles from beyond the heliosphere” that are moving toward the sun (ii). While this might be due to other causes such as “charge exchange between hot ions and neutral atoms” as hypothesized by scientists at UC Berkeley, it may also indicate the source of the asymmetrical solar system is due to the stellar wind from another star rather than an interstellar gas cloud. More data is needed and should be forthcoming with the pending launch of the Interstellar Boundary Explorer (IBEX), due to begin receiving data some time in the next year.

(i) Science Daily, Voyager 2 Proves Solar System is Squashed, December 13, 2007
(ii) E Science News, First Images of Solar System’s Invisible Frontier, July 2, 2008

Binary Research Institute.