This Wednesday, a European landing craft called "Philae" will attempt humanity's first landing on a fast-moving comet (a complex chunk of ice approaching from the depths of space.)
After a 10-year, 4-billion mile journey to Comet Churyumov-Gerasimenko (C-G for short), the Rosetta spacecraft (which is now orbiting the comet) will drop a probe about the size of a kitchen range from a height of 13 miles. Taking some 7 hours to slowly land on its icy target, Philae will be moving at only 2 miles per hour at the end. Still, the gravity of the two-mile wide comet is so low, it could bounce off and move away or simply fall over and roll. To prevent this, the designers have equipped Philae with harpoons to grab the comet and with legs that have rotating screws in them to hold on to the ice for dear life.
Our robot representatives have only landed on six worlds so far: the Moon, Mars, Venus, Saturn's moon Titan, and two asteroids. None of those landings were quite as difficult and strange as this one. It takes radio signals from Rosetta about half an hour to get back to Earth even at the speed of light. Thus the European Space Agency controllers can't help Philae if it gets into trouble. Its own computer software will have to make the decisions that will lead to its survival or loss.
For a complete picture of Comet C-G, see my August 6 post. The photo accompanying today's post is a fantasy montage, showing the Philae lander safely on the comet's icy, boulder-strewn surface. The full comet has a weird L-shaped structure, as if two oval comets had somehow stuck together at a weird angle. Because its shape is so complex, its gravity is not simple either, making landing even more challenging. But if Philae lands, its 10 instruments will give us our first-ever up-close look at one of the chunks of ancient ice that are building blocks left over from the early days of our solar system.
Keep your fingers and toes crossed that the landing succeeds. For a basic animation of what the spacecraft will do and what instruments it carries, please see: http://www.youtube.com/watch?v=szKZ77MbF9Q
A fuller documentary about the Rosetta mission, see: http://www.youtube.com/watch?v=cArihDTnOZg
Today the Rosetta spacecraft closed in on Comet 67P (the P stands for periodic comet, meaning it comes around again and again every six and a half years. ) It's also known as Comet Churyumov–Gerasimenko (C-G). Look at the amazing image our cameras sent back, taken from a distance of only 177 miles.
The comet and the spacecraft are currently still about half way between the orbit of Jupiter and the orbit of Mars. In this exciting rendezvous, Rosetta will match course with the icy comet and then stay with it as it gets closer and closer to the Sun and its ice begins to "sublimate" (turn from ice directly to a vapor in the vacuum of space.)
We hope to stay with the comet for a year, as it goes inward and then swings back outward again, watching the Sun's light and heat playing with the comet all the while. In November, part of Rosetta will actually land on the icy surface of Comet 67P.
But for now, just enjoy the weird and wonderful image. The comet's shape is definitely not symmetrical. Is it two ice pieces that stuck together in an ancient collision? Have past encounters with the Sun's heat resulted in this odd shape?
The comet is 2.5 miles wide, and you can see details as small as 17 feet (5.3 meters) across on our picture. Can you see the individual "boulders" or "ice rocks" sitting on the comet's surface?
If you'll pardon the expression, what a cool picture!
By the way, click on the photo to see it bigger and with more detail.
On Wednesday, August 6, the European spacecraft Rosetta is going to have a close encounter of the best kind with a comet (a chunk of cosmic ice mixed with dirt.) It's called Comet 67P (the P stands for periodic comet, meaning it comes around again and again every six and a half years.) Its more informal name is Comet Churyumov–Gerasimenko, after the two astronomers who discovered it on a 1969 photograph.
In mid-July when our photo was taken, the spacecraft was still more than 7000 miles from the comet, but it was already becoming clearer in the camera. And, as you can see, 67P/C-G is weird looking. Instrument project manager project manager Carsten Güttler said,“The images faintly remind me of a rubber ducky with a body and a head."
What could cause the icy body of this comet, which is roughly two and a half miles across, to look like this. One possibility is that it is really two comets stuck together, something we have seen in other comets (such as 8P and 103P). Or maybe it was one comet that broke apart into pieces when it got too close to the gravity pull of a big planet like Jupiter, and this odd fragment is all that's left.
Another possibility is that early in its life the comet got hit by other chunks of cosmic ice or rock, carving out big pieces of it and leaving great rounded valleys behind.
We should learn more when we get closer to this ancient icy visitor, and especially when part of Rosetta attempts a landing. Stay tuned.
In the meantime, here is a great animation of the images from this past week, showing the comet spinning in the majestic darkness of
space: http://sci.esa.int/rosetta/54356-rotating-view-of-comet-67pc-g-on-14-july-2014/
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