Rosetta’s wild 3-legged orbit around comet 67P/C-G
Now that the Rosetta spacecraft has arrived at the comet, it’s busy following a three-legged triangular orbit. At each apex of the triangle, the probe fires its thruster to turn to follow the next leg of the triangle. Each triangle not only brings Rosetta closer to 67P/Churyumov-Gerasimenko but also serves to measure the comet’s mass. Until we know the comet’s precise mass and center of gravity, the spacecraft can’t enter a direct orbit around it.
While that’s happening, Rosetta has been taking more detailed measurements of 67P’s temperature and found variations across the surface. The warmest spot recorded so far is -63° F (-53° C), very close to the lowest temperature (-60°F) ever recorded in my home state of Minnesota. Still, this is a relatively high temperature especially considering the comet’s great distance from the sun, suggesting that 67P/C-G’s surface is devoid of icy materials, because these compounds are not capable of removing heat.
MIRO or Microwave Instrument for Rosetta Orbiter has been measuring the amount of ice vaporizing off the comet’s nucleus. If you could somehow gather it up and convert it to liquid, 67P/C-G is releasing the equivalent of two glasses of water a second. Some or much of that water departs in geyser-like fashion as jets seen in the photo above.
Meanwhile, Rosetta is now close enough to its target to study the dust in the coma or comet atmosphere using COSIMA (Cosmic Secondary Mass Analyzer). This Sunday August 10, it will expose the first of 24 target-holders that will collect single dust particles. The instrument will analyze their composition and determine if the material is organic (carbon-containing) or inorganic.
Once collected, the dust will be bombarded with beams of indium ions, kicking ions out of the comet dust. Another instrument called a mass spectrometer will fingerprint and determine the amount of atoms and molecules that make up the dust by analyzing the escaping ions.
An ion, by the way, is an atom that has gained or lost an electron and no longer in its neutral state.
Landing sites are being studied for the November touchdown of the mini-probe Philae, and more detailed images are on their way. Exciting stuff!