- Asteroids have been in the news lately. Some are called comets. There is really little difference. Asteroids are rocks and Comets are loose rocks with water ice that makes for a great tail when they orbit near the Sun. Asteroids too may be loose rocks and not always solid rocks. This is important because loose rock asteroids would form planets more quickly. Knowing the density of asteroids would help us understand how our Solar System first formed.
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- Knowing how our Solar System formed would help us understand the more than 1,500 planets we have now discovered orbiting other suns. What are the differences between our solar system and their solar system? Our Solar System formed in 200,000,000 years 4.5 billion years ago, just a billion years after the Sun formed. If we can understand solar system formation we may be able to predict the chances of life evolving on other planets.
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- Density is mass / volume. The density of water is 1 gram / cubic centimeter. A density of 3 to 5 grams/ cm^3 would be a rocky asteroid. Density of 1 to 2 gm/cm^3 would be a rocky rubble, a comet, a dirty snowball.
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- There are 551,621 registered asteroids. Registered means their size has been estimated and their orbits have been calculated. However, we do not know the mass or the volume of most asteroids. Most asteroids lie between the orbits of Mars and Jupiter. Some “Trojan” asteroids are in the same orbit of Jupiter, either ahead or trailing. The belt of asteroids would have formed another planet except for the fact the that Jupiter’s gravity created tidal forces that kept pulling them apart.
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- The biggest asteroid in the belt is Ceres, 1,000 kilometers in diameter. Vesta is the second biggest. See Review # 1572 to learn about a spacecraft that visited Vesta in 2012. Now the same spacecraft , “ Dawn” has left Vesta and is on its way to Ceres.
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- There are millions of asteroids that have not been registered. Some are greater than 150 meters in diameter and are in Near Earth orbits. There are 6,000 of these Near Earth asteroids that are known. 15 of them have been visited by spacecraft. “Lutetia” had a recent visit. It is a dumbbell shaped asteroid that is 100 kilometers long. “ Mathilde is 53 kilometers and has a 30 kilometer crater.
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- See the pictures of these asteroids by google” “ Cosmic Diary Network” a blog by Franck Marchis.
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- We know the Sun formed with an accretion disk of dust and rocks and water and gas. And, gravity within the disk caused a chaos of collisions between all this material. As collisions grew bigger and gravity became stronger more collisions created big enough asteroids to be called planets. When asteroids get a certain size gravity pulls them into a perfect sphere and creates a core at the center. We believe this planet formation took only 200,000,000 years. Back to the density problem:
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- Most asteroids are not spherical because they are not massive enough. If their density is solid rock it is hard to calculate how solid rock collisions could have formed planets in 200,000,000 years. However, if asteroids are low density “ rubble piles” then collisions could collect into larger planet sized rocks more readily. That is where the four Terrestrial Planets came from, asteroid collisions.
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- In 1994 spacecraft visited asteroid “ Ida” and it was found to have a moon. To date 205 asteroids have been found to be binaries, or have moons. “87 Sylvia” has 2 moons. Its mass is 1.48*10^19 kilograms, its size is 192 km by 132 km by 116 km. It is 25 to 60 % porous and has a density of 1.2 gm/cm^3. This information could all be calculated because the asteroid had a moon. The orbit velocity and distance of orbit allowed calculations of mass. Dimensions gave us volume. The conclusion came from the density being not much more than pure water. This can not be a solid rock asteroid.
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- Adaptive optics are now being used on telescopes to see the moons orbiting asteroids. Many more density calculations will tell astronomers better how our Solar System formed. They can then compare this knowledge with what they learn about the exoplanets in other solar systems.
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- Nano-telescope satellites have been funded to do the job like Hubble but using much smaller ad cheaper telescopes just for studying asteroids. Light curves of these asteroids can be studied to determine orbits and their spectrum to determine mineral composition.
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- Protecting us from and Earth- asteroid collision is not the only motivation for studying asteroids. Having time to send a spacecraft to deflect its trajectory is certainly a worthy goal. But, learning how our Solar System formed and the potential for life on other planets is too. An announcement will be made shortly, stay tuned.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Saturday, March 23, 2013
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1580 - Asteroids the bricks that build Solar Systems. Knowing the density of asteroids would help us understand how our Solar System first formed.
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