Monthly Archives: June 2011

astronomy news, cassini, comet

Back from a Week Away

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Exploring an Ice World

An unprocessed image of the moon Helene, orbiting Saturn. Taken by the Cassini spacecraft, June 18, 2011. Courtesy NASA/Cassini Solstice Mission.

I took a week off from writing (everybody  needs a short vacation, right?) and am now back in front of the screen, going through the latest astro-news.

What caught my eye first thing today was the ongoing Cassini Solstice mission. It’s the little spacecraft that just keeps going and going. While her older sisters Voyager and Pioneer are out exploring the outer limits of our solar system, and her little sister New Horizons is headed to Pluto, Cassini keeps sending back images and data about the Saturnian system. The latest views are of a little moon called Helene.

It’s an icy world, which is why I tuned into the story.  Today, June 20, we woke up to snow (which has since turned to rain).  Seems rather incongruous the day before summer solstice (for the northern hemisphere). But, the snow outside reminded me of the snow “out there” – orbiting Saturn like a lopsided iceberg.

It doesn’t take a very close inspection of the image to see the mottled, serrated-looking surface of this little world and to figure out that it looks just plain cold. As to be expected, since temperatures of ice worlds are far, far colder than the conditions we experience here on Earth. Helene is really an irregularly shaped chunk of ice that orbits Saturn in the same orbital path as another moon, Dione. It appears to have been beat up by collisions with other debris in Saturn’s orbit.

Spotting Another Ice Chunk in Space

Animation showing the comet moving against the background of stars. Images taken at the Pan-STARRS 1 Telescope on the night of June 5-6, 2011. Hawaii time is 10 hours earlier than Universal Time (UT). Credit: Henry Hsieh, PS1SC

The distant solar system contains many icy bodies, including these chunky worlds orbiting the gas and ice giant planets. But, there are icy chunks out there that aren’t gravitationally bound to any planets — and astronomers using the Pan-STARRS telescope on Haleakala in Hawai’i spotted one of them just outside the orbit of Jupiter. It’s a comet, called C/2001 L4 (PANSTARRS).  A preliminary orbit computed by the Minor Planet Center in Cambridge, Mass., shows that the comet will come within about 30 million miles (50 million km) of the sun in early 2013, about the same distance as Mercury. The comet will pose no danger to Earth.

The good news about this find is that as it gets closer to the Sun, astronomers have excellent chances to study this comet and figure out just how bright it will appear to be in our skies. If conditions are right, once the comet gets close enough to Earth (say, within the orbit of Mars), it should start to sprout a plasma tail. That’s the tail of ionized gases that streams out from a comet when it gets close enough to the Sun for solar radiation to heat up the gases (and cause them to glow).

It’s tough to know right now just what the composition of the comet is — certainly it’s made of ice. But, how much dust is embedded in that ice?  What kind of ice is it?  Astronomers should be able to tell as they study the comet’s tail with spectrographs (instruments that break up the light from an object into its component wavelengths — and each gas gives off a specific “fingerprint” in the spectrum).

Astronomers think that this comet could be on its first trip around the Sun.  It mostly like comes from the Oort Cloud, that collection of icy objects left over from the formation of the Sun and planets, some 4.5 billion years ago. This cloud lies at the very fringes of the solar system and is a treasure trove of objects that can tell us what conditions were like ‘way back when.

Keep an eye out for this comet in a couple of years. It probably won’t be easy to spot, but if you do see it, you’ll be seeing an object that harks back to a time when our Sun was still forming and the planets were still a work in progress.

asteroid, astronomy news, Dawn, NASA, planetary science

Dawn at the Asteroid: The Approach

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Vesta Comes into View

A still from a short movie taken as the spacecraft Dawn gets closer to asteroid Vesta. Courtesy NASA/JPL_Caltech/UCLA/MPS/DLR/IDA

Well, this may not look like much, but it’s a big deal in the asteroid-study game. It’s an image of asteroid Vesta, taken with the Dawn spacecraft. If you visit the the mission’s web pages at NASA, you can watch a multi-still “movie” made from frames taken by the spacecraft’s framing cameras on June 1.  The video presents 20 frames, looped five times, that span a 30-minute period. During that time, Vesta rotates about 30 degrees. The images included here are used by navigators to fine-tune Dawn’s trajectory during its approach to Vesta, with arrival expected on July 16, 2011.

Why a mission to Vesta?   It is the only large asteroid with a basaltic surface that formed due to volcanic processes early in the solar system’s history. Asteroids, like comets, are treasure troves of information about what was going 0n in the infant solar system — some 4.5 billion years ago. Here’s how that works. During the earliest history of our solar system, the elements, minerals, and chemical compounds in the solar nebula were distributed throughout the nebula, with their exact locations varying due with their distance from the Sun (and its heat). As distance from the Sun increases, the temperature drops. The young Sun, hot and active, drove away or consumed gases and icy bodies, leaving behind rocky materials to form the inner (so-called “terrestrial” bodies) close by. The icy worlds and gas giants formed farther away.

So, the division of the solar system into terrestrial and gas/ice giant worlds is a large-scale division.  Our planets have changed over time, particularly the Earth, with its atmospheric change, its geological change, and the evolution of life (which has affected conditions on the planet as well). To learn more about the “pure” or what planetary scientists call, the “pristine” materials that made up the big parts of the solar system, we need to look at the smaller-scale objects: asteroids and comets. Studying asteroids (and comets) and studying their compositions are a way of peering into the distant past and learning what it was like, sort of like looking at your baby pictures and seeing what you were then and comparing it to what you are now.

You probably didn’t know this, but Vesta is considered a protoplanet because it is a large body that almost formed into a planet.  It is 330 miles (530 kilometers) across, and is the second most massive object in the Asteroid Belt — that region of space between Mars and Jupiter that is populated with asteroids.  In a few days, we’ll have even better images of this distant “almost-a-planet” world, so keep your eyes peeled for more news.

Speaking of news, this week’s Carnival of Space is up, posted over at John Williams’s Starry Critters web site. Check it out for some unique looks at places and spaces throughout the cosmos.