reply to post by mcx1942
Thanks for posting. (S and F.)
I am becoming very interested in this sort of stuff.
What are S-, C-, and D-type asteroids?
Asteroid Explorer “Hayabusa2” is a successor of “Hayabusa” (MUSES-C), which revealed several new technologies and returned to Earth in June 2010. While establishing a new navigation method using ion engines, Hayabusa brought back samples from the asteroid “Itokawa” to help elucidate the origin of the solar system. Hayabusa2 will target a C-type asteroid “1999 JU3” to study the origin and evolution of the solar system as well as materials for life by leveraging the experience acquired from the Hayabusa mission. To learn more about the origin and evolution of the solar system, it is important to investigate typical types of asteroids, namely S-, C-, and D-type asteroids.
Hayabusa2 will utilize new technology while further confirming the deep space round-trip exploration technology by inheriting and improving the already verified knowhow established by Hayabusa to construct the basis for future deep-space exploration.
1 C: they are carbonaceous---made of silicate materials with a lot of carbon compounds so they appear very dark. They reflect only 3 to 4% of the sunlight hitting them. You can tell what they are made of by analyzing the spectra of sunlight reflecting off of them. This reflectance spectra shows that they are primitive, unchanged since they first solidified about 4.6 billion years ago. A sizable fraction of the asteroids are of this type. The asteroid called Mathilde, explored by the NEAR spacecraft is an example of this type
2 S: they are made of silicate materials without the dark carbon compounds so they appear brighter than the C types. They reflect about 15 to 20% of the sunlight hitting them. Most of them appear to be primitive and they make up a smaller fraction of the asteroids than the C types. Gaspra and Ida, explored by the Galileo spacecraft on its way to Jupiter, and Eros, orbited by the NEAR spacecraft for a year, are examples of this type
3 M: they are made of metals like iron and nickel. These rare type of asteroids are brighter than the S and C types. We think they are the remains of the cores of differentiated objects. Large objects were hot enough in the early solar system so that they were liquid. This allowed the dense materials like iron and nickel to sink to the center while the lighter material like ordinary silicate rock floated up to the top. Smaller objects cooled off quicker than larger objects, so they underwent less differentiation. In the early solar system, collisions were much more common and some of the differentiated large asteroids collided with one another, breaking them apart and exposing their metallic cores.Full Article/Source
Gerald's report on Apophis: After 3.8 years of observations, we project that Apophis will pass by (and miss) the Earth by about 23,600 miles on April 13 (yeah—Friday the 13th) 2029 (in case you want to plan a party). Then, Apophis will revisit the Earth's vicinity on April 13th (not a Friday) 2036.
And here's the meat of the deal with Apophis: if its trajectory on the 2029 flyby is anywhere near what is predicted, then there is no chance at all that it will hit us in 2036. There is only a small chance that within the range of uncertainty the 2029 passage will aim Apophis for a 2036 impact with Earth–but the probability of that are calculated at less than 0.002%. That's roughly the same probability as drawing a straight flush right off the top of the deck (to you non-poker-players, the odds of that are about 72,000 to 1).source