August 6 – Ain’t It Cool News!

Today’s factismal: For the first time ever, a human spacecraft is orbiting a comet.

If you plan to study the planets, you’ll need to learn a little geology, a little physics, a little chemistry, a little biology – and a lot of patience. You’ll need the first four because planets are complex places where everything interacts with everything else. And you’ll need the patience because it takes a lot of time to get the data you need to study a planet; heck, it can take a lot of time just to get to the planet you want to study! A typical planetology mission can take up to fifteen years to be approved, another ten years to build the probe, and yet another decade or so in space before it gets to where it needs to be just so you can start getting that data.

What they thought Rosetta's comet would look like (boy were they ever wrong!) (Image courtesy ESA)

What they thought Rosetta’s comet would look like (boy were they ever wrong!)
(Image courtesy ESA)

One of the best examples of the stick-to-it-iveness needed in planetology is the Rosetta mission which has just made history by becoming the first man-made object to go into orbit around a comet. This mission started in 1986 when Halley’s comet dropped by Earth for a visit. NASA, the ESA, and several other space agencies sent probes by the comet and learned quite a bit about how the Solar System formed. But they also learned that a probe really needed to spend more time near the comet if the scientists wanted to learn how comets work. And so the mission to a comet was born as a joint ESA/NASA project. But six years later NASA pulled out of the project due to cost constraints, leaving the ESA to carry on alone. That forced them to abandon the idea of a sample return mission (something that NASA would later do with the Stardust mission) and instead focus on in situ characterization of the comet’s material (something that NASA would do {with mixed success} with the Deep Impact mission).

The Rosetta probe (Image courtesy ESA)

The Rosetta probe
(Image courtesy ESA)

The Philae lander (Image courtesy ESA)

The Philae lander
(Image courtesy ESA)

 

 

 

 

 

 

 

 

 

While the bad news was that the ESA mission, dubbed Rosetta (after the stone), wouldn’t be able to return to Earth, the good news was that it would be able to stay at the comet; it could and did become the first human-made object to orbit a comet. And that’s where Rosetta is now. After the probe was built in 1999 and launched in 2004, it cruised around the Solar System for ten years making four orbits around the Sun and passing by Earth three times. Each time the probe passed by Earth, it stole a little of our orbital velocity in what is known as a “gravity assist“; this allowed the probe to get up to the same speed as the comet so that it could go into orbit when the two finally met.

What the comet looked like when Rosetta started its mission (Image courtesy ESA)

What the comet looked like when Rosetta started its mission
(Image courtesy ESA)

So now that we’ve got a probe in orbit around a comet, what’s next? Well, the first thing that we have to do is map out the comet’s surface. This is important for two reasons. First, it will help us decide where to park the lander Philae (after a temple where a Rosetta stone-like obelisk was found); it is that lander which will do most of the detailed chemical and geological composition work. And second, it will help us create a stable(ish) orbit around the comet. You see, one of the big surprises from this comet is that it appears to be two comets that collided early on and have been slowly evaporating ever since. (Think of it as two scoops of ice cream stuck together in God’s own freezer.) Because the comet isn’t a simple sphere, the orbit can’t be simple either.

What the comet looked like as Rosetta got closer (Image courtesy ESA)

What the comet looked like as Rosetta got closer
(Image courtesy ESA)

Once we’ve got Rosetta in a stable orbit around the comet and Philae safely on the comet, then the real work begins. We’ll study the composition of the surface using the lander’s instruments which include a high resolution camera, a spectrometer, and radar (for a view of the inside). And we’ll study the formation and composition of the gas and dust expelled by the comet as it comes further into the Solar System using Rosetta’s instruments which include a thermal camera, a high resolution camera, a spectrometer, a companion radar to Philae’s, and what amounts to an “owie counter” that will measure the number and size of the grains of dust that hit the orbiter. Over the next few years we’ll see a flood of new and amazing data from the probes, so stay tuned!

What the comet looks like now! (Image courtesy ESA)

What the comet looks like now!
(Image courtesy ESA)

Of course, if you are the sort who’d like to do some science right now, then why not head over to the SOHO Comet Identification page? They need the help of clever people like you to identify new comets as they pass close to the Sun:
http://sungrazer.nrl.navy.mil/

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