Humans have been studying the cosmos for generations .. from Earth till the advent of satellites and from satellite platforms later. Even there were times when a deployed probe landed on heavenly bodies or even man set his foot on moon a few times.
But the year 2014 gave a few never before opportunities of Comet studies in space watch from near. For example the comet Siding Spring happened to be near Mars when two new probes ( launched in the end of 2013 ) reached in the vicinity of Mars in addition to those which are already revolving around it. They provided ample observations to study its nature and composition from a distance of a few thousand kilometers for the first time in human history. But we are one of the most lucky lot in the history of mankind to witness an oncoming event in comet study .
Already the European Space agency's probe Rosetta has come within a few kms of Comet 67P/Churyumov–Gerasimenko ( we will refer to it as Comet 67P/C-G henceforth in this blog ) and sent a few stunning images.
On left: Image taken on 18 October from a distance of about 8 kilometers from the surface. Are covered is about 1.4 kilometers wide. It contains a wide variety of remarkable landforms, circular pits and scallop-shaped scarps, that result from weird comet surface modification processes.
( Image: ESA / Rosetta / NavCam / Damia Bouic )
Rosetta is currently less than 10 km from comet travelling along with it at a breathtaking speed of 60 000 km/h, Later in mid Nov 2014 it will send a lander - yes you read it correctly, a LANDER - Philae on the comet surface which will soft-land on it and grout/anchor itself there by drilling 3 screws in the surface where its 3 legs will rest. Unlike the Moon lander which moved around the moon's surface and studied various landscapes and rocks, the Philae will carry out exploration about the comet composition apart from obtaining images from the actual surface of comet from this ' base station ' using 10 instruments which it carries with it.
|Philae island in Nile River|
Philae by the way, obtains its name from the island in the river Nile where an obelisk - made out of Rosetta stone - was found that had names of Cleopatra and Ptolemy engraved on it which helped in understanding the Egyptian civilization. ESA hopes that the spacecraft will similarly unravel the secrets of galactic origin. )
Want to win a prize? Create a suitable name for the location where Philae will land. Last date for entry 3rd Nov 2014 : https://in.news.yahoo.com/esa-rosetta-mission-partners-invite-names-landing-061416327.html
Philae though is NOT the first man-made object to touch the comet. In July 2005, Deep Impact, a NASA probe intentionally crash-landed with a high speed on comet Tempel 1 burying itself in its nucleus and sent images of the surrounding shaft walls that it created.
The story of Rosetta spacecraft by itself is quite interesting. Launched on 2 March 2004 aboard an Ariane 5G+ from Kourou. After four gravity assists - one by Mars and three by Earth - it reached its destination viz. Comet 67P/C-G.
Figure shows what is meant by the term gravity assist by plotting the 1st Earth assist used to change the direction of Rosetta on 4th March 2005. ( Event B in the overall life-cycle explained later )
Green line in left figure is the path that Rosetta traveled. Hourly positions of it are marked by dots and the big Red dot represents Earth. Earth's gravity 'pulls' the craft increasing its speed ( see right side figure ) from 30kms/sec to over 38 kms /sec but a retro rocket fired just in time brings down the speed to 34 kms/sec. Effectively the spacecraft gains speed from 30kms/sec to 34 kms/sec. Due to this increase in speed the spacecraft orbit around Sun changed to a new orbit which actually is a Trans Martian orbit.
We quickly travel with the spacecraft:
One orbit around Earth A to B for a year. The 1st Earth assist explained above transferred it towards Mars and with Mars assist (C) it deviated back to Earth but with a higher speed. 2nd Earth assist (D) sent the spacecraft to a still higher orbit beyond Mars with a 2 year orbital period. So it returned to Earth ( Nov'07 to Nov'09 ) and a third Earth assist ( F ) sent it to its final orbit ( about just less than 6 years ) during which it encountered the 67P/C-G comet.
Figure below shows the paths of various bodies ( SUN, Earth, Mars, 67P/C-G and Rosetta ) about solar system for over a decade. Notice that after meeting the Comet in August ’14 the Rosetta follows it continuously and is expected to follow upto Dec ‘ 15 ( i.e. near ‘16 in top left corner ) covering the crucial phase (bright green line ) near comet’s perihelion in August 2015, at 186 million kilometres.
In between Rosetta has made observations of a couple of Asteroids viz. 2867 Steins (in 2008) and 21 Lutetia (in 2010). In June 2011 it went into hibernation till January 2014.
Today ( Oct 29, 2014) it is 495 million kms from Earth but along the curved path that it has traveled over years it has covered 6527 million kms. Even as I write this I got the news that a very crucial maneuver has been carried out by pushing the spacecraft away from its 10 kms orbit. After it travels in this orbit for 3 days another correction will bring the orbit to 30 kms from comet in preparation for releasing Philae from a distance of 22.5 kms on 12th Nov to land on the planet the last correction will be carried out 2 hours prior to release of Philae.
Again the complex path that the craft will take can be seen in this video:
Once Philae anchors itself to the comet head, it will communicate to Earth through the mother aircraft Rosetta which will be hovering nearby.
It is expected that the system will continue to send data to Earth till end 2015.