Monthly Archives: February 2011

comet, comet dust, stardust

Stardust Gets in Our Eyes

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Close Approach to Comet Tempel 1 in 3… 2…. 1….

Back when I was in graduate school, I studied comets for a living. The hunka hunka sublimating solar system ice I spent the most time on was Comet Halley.  My advisor, Jack Brandt, was part of the the Large-Scale Phenomenon Network of the International Halley Watch, and so my job was to go through all the images we had of Halley and select the best ones to do science with.

And do science we did! We tracked changes in the comet’s tail as it rounded the Sun during its orbit, and then afterwards came to some solid conclusions about how the plasma tail (the one made of ionized (charged) gas molecules) was affected by the action of the solar wind. It turns out that the plasma tail of a comet can magnetically disconnect — that is, break off — when it passes into a region of the solar wind that has a different electrical polarity than the one it formed in. If you know where the comet is in the solar wind, and you know the rotation rate of the streams in the solar wind, you can calculate about when the plasma tail will disconnect at different points in its orbit. And, if you take a series of images of the comet, you can capture that break-off and track the old tail as it floats away. Very cool stuff.  As an added bonus, you learn something about the solar wind, which is ever more important in these days when we have so many technologies that can be knocked out by a big solar outburst.

I didn’t know a lot about comets when I started on the project, but by the end, I could look at an image of Comet Halley and tell you when it was taken and if the plasma tail had disconnected. It was up to my colleague Yu Yi (who was working on his Ph.D thesis using Comet Halley data) to tell us what the conditions in the solar wind WERE for various times in the orbit.

We didn’t pay as much attention to the dust tails of our comets, nor to the coma clouds that formed around the nucleus, since they don’t respond the same way to the solar wind. Not that we ignored them, but they weren’t our primary focus. But they have their own tale to tell, and there’s an upcoming mission to explore another comet’s nucleus and coma. It’s called Stardust and it already has some solid, successful observations.

The first image of comet Tempel 1 taken by NASA's Stardust spacecraft is a composite made from observations on Jan. 18 and 19, 2011. The panel on the right highlights the location of comet Tempel 1 in the frame. On Valentine's Day (Feb. 14 in U.S. time zones), Stardust will fly within about 200 kilometers (124 miles) of the comet's nucleus. Image credit: NASA/JPL-Caltech

I was thinking about the good ol’ comet study days when I was reading about the upcoming close approach of Comet Tempel 1 by the Stardust spacecraft. That little visit will take place on Valentine’s Day, Feburary 14, 2011.  Unlike our team, which focused on those glowing blue plasma tails, the Stardust team will be focused on images of the comet’s nucleus, and measure the size, composition, and flux (flow) of dust that makes up the coma — the cloudy “crown” that surrounds the icy nucleus of the comet.

The nuclear centers of most (if not all) comets contain materials that date back to the formation of the solar system some 4.6 billion years ago. So, studying the gases that flow from a comet (which come from the cometary ices as they sublimate (dissolve away) as well as the dust that is embedded in those ices and which streams away from the comet, will tell scientists more about the frozen materials that existed in the nebula that formed the Sun and planets.  Chemically, they should be able to tell something about the conditions the comet has experienced (that is, how much those ices have been heated, what proportions of different ices there are in the comet, which could be a clue as to where they formed in the original solar nebula), as well.

In addition to the ices, comets have dust — and those dust grains also harken back to the early days of the solar system. They existed in the solar nebula, but their origins far predate the solar nebula — as grains of interstellar dust whose origins stem from elements ejected as older stars died and spread THEIR substance to the interstellar medium.

So, the Stardust folks aren’t just looking at a comet. They’re looking at a cosmic history ark — one that encapsulates our own solar system history, and maybe some clues to older, long-gone stars.  The scientists will be ecstatic as close approach day gives them that long-awaited closeup of the comet. I, for one, think it’s great that we’re lifting the veil on these orbiting ice chunks.  There’s so much they can tell us about our solar system’s early history.  And, for people who have never seen a comet up-close and personal, it will be a great exploration. Check it out and stay tuned!

astronomy, solar physics, solar studies, STEREO, stereo spacecraft, sun, sunspots

The Sun in Stereo

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Two Perspectives

The is the Sun from my place on February 6, 2011.

Okay, everybody and his or her cat is jumping on this story about the Sun today — and for several good reasons:  1)  it’s great science about our nearest star and 2) it’s freaking cold out throughout much of the U.S. (and probably the rest of the Northern Hemisphere, and some of us will take any Sun we can get.

We get irrationally attached to that bright thing in the sky during the cold winter months — it’s our lifeline, the source of our warmth, and the hottest thing in the solar system. Small wonder we look for it after a few days of snow and when it shows up, some of us go outside and marvel at it (and the snowplows, who come, tank-like, to liberate us) after the storms.

But, there’s another perspective we can take on the Sun — and that’s our study of it as a star.  Sure, we all know it’s a giant sphere of superheated gases, plasmas if you will. And that heat is what powers the solar system, warms our planet, and bathes us in light.

That scientific perspective is what fuels today’s release of the STEREO mission’s first (darned-near-180-degree) view of the Sun. It shows us our nearest star in virtual stereo quality, as seen by two spacecraft that are studying it from opposite sites of Earth’s  orbit.

Latest image of the far side of the Sun based on high resolution STEREO data, taken on February 2, 2011 at 23:56 UT when there was still a small gap between the STEREO Ahead and Behind data. This gap will start to close on February 6, 2011, when the spacecraft achieve 180 degree separation, and will completely close over the next several days. Credit: NASA (Click to luxuriate.)

In the next few days, the STEREO spacecraft will be at a true 180 degrees apart (the images shown here were taken when the spacecraft were 179.7 degrees apart, and closing in on their final positions fast).

The image we see here is how STEREO sees the far side of the Sun. The first thing you notice is that line of black — that’s a data gap that will be closed when the two spacecraft are in their final positions. The true beauty of STEREO’s work is that it will allow scientists to study the Sun in true 3D.  It’s a big step forward for solar physics because 3D shows us that the Sun truly is a sphere of hot plasma, and that plasma gets woven and threaded through some incredibly intricate and ever-changing magnetic fields.

The action of those magnetic fields powers the incredible activity we see on the “surface” of the Sun and in it s superheated atmosphere. STEREO’s images and data are finally giving solar physicists the ability to fly around the Sun and study it year-round.

The STEREO spacecraft configuration. Courtesy NASA.

This is because the two spacecraft are at two separate points along Earth’s orbit and they virtually DO fly around the Sun over the course of a year, giving us a long-term view of our star and its activity.

Using STEREO, it is now possible to follow the evolution of an active sunspot or flare region on the opposite side of the Sun from Earth, all by using the twin spacecrafts’ abilities to see the Sun in both hemispheres. Scientists will be able to track that active region before it rotates around to face us — giving us plenty of time to take action if the activity is going to mess with our satellites, the ISS,  and power grids and telecommunications systems.

In fact, the National Oceanic and Atmospheric Administration’s Space Environment Laboratory is using data from the STEREO spacecraft to make ever-more-accurate models of outbursts from the Sun called “coronal mass ejections”. These explosions belch out huge masses of charged particles out from the Sun. They create what’s known as “space weather” — changes in the geomagnetic environment in near-Earth space. When those clouds of charged particles hit our planet’s magnetic field, the result can be as benign as a gorgeous display of northern or southern lights, or as disastrous as a power grid failure or fried satellite electronics. So, STEREO will be a huge help in predicting solar storms and helping us avoid the worst consequences of them.

Check out the STEREO web page for more images and cool videos.  And, keep following this story — there’s a LOT more we’re going to learn about the Sun from the STEREO perspective!

Finally, here’s a big shout-out to my old friend and grad school office “roomie”, Dr. Lika Guhathakurta. She’s the STEREO program scientist at NASA and I imagine she’s just thrilled with the data she and her team are seeing.  Hey Lika!  This one’s for you!