Tag: comet

Rosetta's cometary goal now in sight

By Phil Plait | June 9, 2011 11:03 am

Rosetta is an amazing probe launched by the European Space Agency. In 2014 it will go into orbit around the comet 67P/Churyumov-Gerasimenko, and actually deploy a lander to sample the surface!

That rendezvous is still years away, but the target is now in sight: Rosetta has returned its first image of the comet.

Oh, very cool! The top image is the wide angle shot, showing a densely-populated star field toward the center of our galaxy; from Rosetta that’s the direction to the comet. The second image zooms in a bit, and you can see some distant stars and nebulosity. The bottom one has been processed to remove the stars, and the nucleus of Churyumov-Gerasimenko stands out.

Note that this image was taken when Rosetta was still 163 million kilometers (100 million miles) from the comet — that’s more than the distance from the Earth to the Sun! That’s why it took a total of 13 hours of exposure time to see the comet in these images; it’s still extremely faint from that great distance.

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CATEGORIZED UNDER: Astronomy, Cool stuff, Space

Stardust snaps close-ups of a second-hand comet!

By Phil Plait | February 15, 2011 2:33 pm

A philosopher once asked, "Are we human because we gaze at the stars, or do we gaze at them because we are human?" Pointless, really… "Do the stars gaze back?" Now that’s a question.
-Narrator, "Stardust"

Late last night, the NASA mission Stardust flew within 178 km (110 miles) of the nucleus of the comet Tempel 1, seeing it up close for the first time since July 2005! Here’s one of the better images from closest approach:

[Click to embiggen.]

Wow! The whole flyby sequence has been posted on NASA’s Stardust site (and Emily Lakdawalla at The Planetary Society blog has created a nifty animation of it too).

Ian O’Neill, from Discovery News, posted a nice animation of it as well on YouTube:

To give you an idea of what you’re seeing here, the comet is roughly 7.6 x 4.9 kilometers (4.7 x 3.0 miles) in size.

So, why did NASA fly Stardust past this comet? Ah, set the way-back machine for 5.5 years ago…
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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

The Top 14 Astronomy Pictures of 2010

By Phil Plait | December 14, 2010 7:01 am

Use the thumbnails and arrows to browse the images, and click on the images themselves to go through to blog posts with more details and descriptions.


A comet creates its own snowstorm!

By Phil Plait | November 18, 2010 1:00 pm

NASA has just released new results and images from the EPOXI spacecraft’s visit to the comet Hartley 2 from November 4… and like the previous ones, these are absolutely stunning jaw-droppers. What scientists have found is that the comet’s solid nucleus is sitting in the middle of a veritable snowstorm!


Wow! Most of those dots are not stars: they are actual snowballs, frozen matter that has been ejected by the comet itself! They range in size from a few centimeters to a few dozen across, so they really are about the size of snowballs you’d use in a snowball fight… or to make a snowman. But I wouldn’t recommend it: a lot of that material is not frozen water, it’s actually frozen carbon dioxide, or dry ice.

epoxi_hartley2_snowflakesAs I wrote a few days ago, the comet nucleus — the solid part of the comet at its heart — is only a couple of kilometers across, and composed of rock, water ice, and dry ice. As the nucleus gets close to the Sun, the dry ice turns directly into a gas and spews out of vents in the surface. These plumes of material shoot out, enveloping the nucleus to become the fuzzy head of the comet, and stream away to form the tail.

But we’ve never been close enough and had good enough images to see just what these plumes look like in detail… until now. It’s not just gas, but actual chunks of ice flying out from the nucleus! The comet, for all intents and purposes, is having its own cosmic snowball fight. As you can see in the cleaned picture on the right (click to ensublimate) the comet is sitting in a cloud of thousands, millions of these snowflakes.

How awesome is this?

In fact, so much material is blowing out from the comet that the nucleus is able to cast a shadow in space:


Oh my. How lovely.

But there’s far more than just gorgeous pictures. Read More

MORE ABOUT: comet, EPOXI, Hartley 2

Ancient ice, wet and dry, from deep inside a comet

By Phil Plait | November 15, 2010 7:00 am

The comet Hartley 2 has come and gone, and the NASA mission EPOXI is also moving on after an exceedingly close flyby of the comet’s solid nucleus. The pictures we got were fantastic and beautiful… but their real power comes from coupling them with spectra.


In the picture above — an enhanced version of one of the images taken during the space probe’s flyby — you can see fan-like emission coming from the comet’s nucleus. These are jets; sprays of material coming out of the nucleus. Comets are made of rock and ice, and when the comet nears the Sun, the heat can turn that ice directly from a solid to a gas. This gas then shoots out from pockets on the nucleus, creating these jets. The EPOXI team (including my old boss, Don Lindler!) made a fantastic animation from a series of observations showing these jets in action.

But what are these ices made of? Lots of things we normally think of as liquids or gas (water, ammonia, carbon dioxide, and so on) exist in comets. In many comets, we see lots of water, and in fact the Swedish satellite Odin detected about 200 kg/sec (440 pounds per sec) of water coming off Hartley 2! So is water powering these jets?

hartley2_irplotWe can find out… using spectra. By breaking up the light from an object into its component colors, we can learn all manners of things including what it’s made of. EPOXI did just that with the jets streaming from Hartley 2, and while it did find water, amazingly, it found a lot more carbon dioxide!
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Amazing close-ups of comet Hartley 2!

By Phil Plait | November 4, 2010 9:37 am

Just an hour ago as I write this, the NASA spacecraft EPOXI passed just 700 km from the nucleus of comet Hartley 2! The flyby was successful, and it took incredible images of the comet’s solid heart:


Wow! These images are in order of approach (left to right, top to bottom), as EPOXI flew by. We knew from ground-based radar that the nucleus wasn’t round, but these pictures clearly show it to be shaped like a peanut. That’s not too surprising; this shape is common in asteroids and comet nuclei. But what detail! You can see the surface is irregular and contoured. There’s a groove of some sort on the left side, and what might be an impact crater or pit on the very left tip.

And those bright streamers of light? Those are jets of gas shooting away from the comet, formed when frozen material on the comet surface gets heated by the Sun, expands, and shoots away!

Amazing. And very lovely.

Here’s the fourth image a bit bigger:
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MORE ABOUT: comet, EPOXI, Hartley 2

Three views to a comet

By Phil Plait | October 8, 2010 7:00 am

103P/Hartley 2 is the somewhat prosaic name for a pretty nice comet in our skies right now. It’s still a little bit too faint to see without aid of binoculars or a telescope, but it’s getting brighter: on October 20th it’ll pass by the Earth at a distance of a mere 18 million km (11 million miles)!

Astronomers all over the planet are jumping at a chance to see a comet up close… and the views they’re getting are really, really cool. Behold!


That’s Hartley 2 as seen by WISE, an orbiting NASA mission designed to survey the sky in the infrared, so it’s very sensitive to objects that astronomers consider warm — that is, a few degrees above absolute zero! It’s seen comets before, since they fit the warm-to-astronomers-but-freezing-to-anyone-else category.

Mind you, the actual solid part of the comet is only a few kilometers across, far smaller than a single pixel in this picture. But it’s loaded with frozen ices which turn into gas as the comet nears the Sun, enshrouding the nucleus with fuzz, and streaming behind it as that long, long tail. In this picture, the tail is nearly 2 million kilometers in extent — well over a million miles!

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CATEGORIZED UNDER: Astronomy, Pretty pictures

Actually, if you're a comet, it *is* easy being green

By Phil Plait | June 9, 2010 10:00 am

Yesterday, I wrote about the comet 2009 R1 McNaught which is currently in the extreme northern sky in the early morning. By coincidence, just hours after posting it, I got an email from the amateur astronomer Anthony Ayiomamitis (the same guy who took the very cool picture of the ISS and Jupiter in the daytime), who sent me this picture of the comet he took in Greece at just around the same time that post went live:


Wow, very pretty! The solid part of the comet, called the nucleus, is far smaller than a single pixel in this image, since the comet was more than 175 million km (110 million miles) away when he took this shot. The nucleus of even a huge comet is only a few dozen km across, so at that great distance is just a tiny dot. Anthony has details on his observations on his McNaught page.

The comet looks huge — and the fuzzy part can be bigger than planets! — because what you’re seeing is gas expanding away from the nucleus. Far from the Sun that gas is frozen, and the comet is solid. But heat it up, and that ice turns into a gas, creating the comet’s coma (Latin for hair). In that gas methane, water, ammonia, and lots of other things, many of which are pretty nasty.

But why is it green?

Ah, that’s a good question (I’m glad I asked it!) and takes just a little bit of background.

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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Possible naked eye comet on the rise

By Phil Plait | June 8, 2010 2:15 pm

If you’re an early riser in the mid-northern latitudes of our planet (and statistically speaking, the odds are good for the latter part), then there’s a comet you might want to check out.

Comet McNaught (C/2009 R1) is currently moving rapidly across the northern sky, and it’s just on the edge of being bright enough to see with your unaided eye. Over the next few days it may even get bright enough to see easily in dark skies.


This picture, taken by Ernesto Guido and Giovanni Sostero, shows the comet and its long tail. It’s a multiple exposure centered on the comet, which is why you see several star images for each star. You won’t get a view this nice (probably) with binoculars, but you should be able to spot the tail.

The CometChasing website provides a helpful map of the comet’s location over the next few days. On June 21 it’s pretty close to the bright star Capella (one of the brightest in the sky) but it’s not known how bright the comet will be by then. Also, McNaught reaches perihelion (closest point in its orbit to the Sun) on July 2/3, so it’ll be tough to see in a few weeks (though probably brighter; as they gets closer to the Sun most comets get much brighter, but their proximity to the Sun makes them very difficult to spot). With comets it’s always good to get them while the getting’s good. Go look now!

You can find more info on the Cometography site, a spectacular picture on APOD, and an interesting animated GIF showing the motion of the comet, too.

As a bonus for early risers, Jupiter and Uranus will have a series of close approaches to each other in the sky, so you can check that out as well.

CATEGORIZED UNDER: Astronomy, Cool stuff

Jupiter gives us a taste of Armageddon

By Phil Plait | June 3, 2010 11:05 am

Last year, in July, something smacked Jupiter. Hard.

It was discovered when an amateur astronomer found a black spot marring Jupiter’s cloud tops. Followup observations saw the spot glowing in the infrared, meaning it was hot, and therefore was not just a storm (which are common). For real and for sure, something impacted Jupiter and exploded – and I mean exploded, releasing the equivalent of hundreds of thousands of nuclear weapons.

But what was it?


A new paper just published indicates that it was an asteroid that hit Jupiter. However, since it wasn’t seen beforehand, how do we know?
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