- 3602 - STARDUST - Catching a Comet’s Tail. “Stardust” was the first mission to explore a comet and return samples. It is the second mission to bring back samples from space. The first being Apollo that brought back rock samples from the Moon.
--------------------- 3602 - STARDUST - Catching a Comet’s Tail
- In February, 1999, a spacecraft named “Stardust” was launched to catch a comet named “Wild 2“, (pronounced Vilt Two).
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- In January, 1974, Comet Wild 2 almost collided with the planet Jupiter. Its orbit was deflected to bring it closer to the Sun, and closer to Earth. Wild 2 was 167,000,000 miles from Earth, in between the orbits of Mars and Jupiter.
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- In January 2, 2004, “Stardust” caught up with Wild 2 and flew through the tail coming within 150 miles of the comet nucleus. Stardust had a special shield made of five sheets of carbon filament and ceramic clothes spaced 2 inches apart to protect it form the dust particles.
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- Stardust was traveling 13,400 miles per hour. The dust grains were smaller in diameter than the human hair, but if a space walker were to encounter this dust storm he would be quickly reduced to particles of dust as well.
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- Stardust opened a special container to capture some of the dust particles as it passed through the coma, the cloud of dust and gas coming off the comet’s nucleus. It actually flew through the part of the coma ahead of the comet nucleus, not the tail.
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- The container contained a special “areogel” that is so lightweight it is barely visible and almost floats in air. It is a silicon gel, the lowest density solid material ever made, just the right stuff to collect the dust particles and bring them to a gentle stop inside the container.
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- The gel cracks like glass, but it is able to bring the dust particle, traveling 13,400 miles per hour to a stop in a few centimeters. The container collector looked like an ice cube tray with the aerogel in each rectangular box 3 centimeters thick. The front side of the collector was used to collect interstellar dust on the way to the comet. Then, when it reached the Comet’s coma, it turned the collector around and used the backside to collect the Comet’s tail dust.
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- The total journey for Stardust to reach the comet was 2,000,000,000 miles because in order to use a smaller rocket Stardust came back twice and on the third orbit was slingshot with Earth’s gravity to launch it again toward Wild 2.
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- The smaller rocket cost $40 million, a larger rocket for a direct shot would have cost $500 million. As the crow flies Wild 2 was only 167,000,000 miles away. The journey home will be a more direct route of 1,000,000,000 miles at an average speed of 48,000 miles per hour.
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- On January 15, 2006, the spacecraft Stardust arrived home and 4 hours out, a distance of about have way to the Moon, the collector’s capsule was jettisoned for reenter into the Earth’s atmosphere. The spacecraft then fired its rockets in order to fly past the Earth and back into space.
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- It was an accurate release of the capsule because the canister parachuted and landed right on target in the Utah desert, entering the atmosphere at 28,600 miles per hour. 28,600 mph was the fastest reentry ever experienced, but it successfully made a soft landing on to the desert sand.
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- Stardust was the first mission to explore a comet and return samples. It is the second mission to bring back samples from space. The first being Apollo that brought back rock samples from the Moon.
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- Comet Wild 2 formed 4,600,000,000 years ago at the time of our solar system’s formation. It was orbiting in the cold reaches of the Kuiper Belt of comets just outside the orbit of Pluto before it got too close to Jupiter and got yanked out of its orbit and into an inner solar orbit closer to Earth.
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- These comets in the Kuiper Belt are thought to be mostly ice and dust, and frozen carbon monoxide, carbon dioxide, and methane. Comets are the leftovers after the formation of the Solar System that did not make it into planets.
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- Comets have tails because their elliptical orbits bring them closer to the Sun. When this happens the gas and dust burns off the nucleus of the comet. This atmosphere formed around the nucleus is called the “coma”. The solar winds cause the tail to form in the direction away from the Sun.
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- Comet tails can get to be 1,000,000 miles in diameter and up to 100,000,000 miles long. Comets are seen only when they get close to the Sun and their coma forms. It is the coma and coma tail that is visible. The comet nucleus is too small to see.
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- A comet in an inner solar orbit will loose 0.1% of its mass each time it orbits the Sun. Therefore, most comets that we see will only survive about 1,000 years.
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- The oldest known comet is Halley’s comet that is thought to be 3,000 years old. Halley has a 76 year orbit. Wild 2 has a 6.5 year orbit. There are over 1 trillion comets in our Solar System mostly orbiting in the cold reaches of the Kuiper Belt.
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- There are trillions more comets outside our Solar System, beyond the reach of the Sun’s gravity. These comets form a spherical shell around our Solar System extending out 2 lightyears distance from the Sun.
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- Meteorites are different than comets. These bodies come form the Asteroid Belt that orbit’s the Sun in between the orbits of Mars and Jupiter. Asteroids are rocks. Solid material that can withstand the reentry burn through Earth’s atmosphere and land on its surface.
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- Comets are ice cold, puffy, powdery, ice and dirt balls loosely held together by their own gravity. Comet Wild 2 was 4.5 kilometers in diameter and had an internal temperature of 180 Kelvin (-136 Fahrenheit) and a surface temperature of 30 Kelvin (65 Fahrenheit, room temperature).
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- Four comets have been studied closely enough to determine their composition. “Halley” in 1986, “Deep Impact” on Temple 1 July 2005, “Wild 2” January 2006, and ?. Some 800 comets have been studied enough to determine their orbits.
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- The largest particle brought back by Wild 2 was 1 centimeter in diameter. Over 1,000 particles were collected many as small as 10 micrometers. Upon initial analysis of the particles astronomers are amazed to find minerals that can only be formed at very high temperatures. Certainly not at those temperatures that exist in the Kuiper Belt at the coldest reaches of our Solar System.
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- Among the minerals was Olivine. This is an iron, magnesium crystal that is found on the green Hawaiian beaches. Other minerals found include calcium, aluminum, titanium, iron sulfide, nickel sulfide, chromium, titanium nitride, silicon, vanadium. Some of these minerals require over 2,000 Kelvin temperatures in order to form. These minerals had to have formed close to the surface of our Sun, or some other star.
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- How did these minerals which are formed in the inner most part of the solar system get into comets in the far reaches of the Kuiper Belt at the edge of our Solar System?
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- Some 200 scientists from around the world are studying over 1,000 particles returned by Stardust. Even a grain 10 microns thick (10^-5 meters) can be sliced into 100 samples for scientists to study. They hope to be able to answer the question: How did those particles get there?
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- This material came from Dr. Donald Brownlee, April 3, 2006, University of Washington. who lectured at Sonoma State Library. Doug and I were there. His slide show had 3-D pictures showing the 4.5 kilometer comet surface with 14 meter resolution. Go to the JPL, Jet Propulsion Laboratory, website to see the pictures.
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June 14, 2022 STARDUST - Catching a Comet’s Tail 629 3602
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