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------------ 2757 - - COMETS - visiting us and visiting them?
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- The Moon has little atmosphere so erosion on the surface is minimal and the evidence is still there. In contrast, Earth has much greater gravity and can hold on to the light gases that make up our atmosphere. It is the rain and wind in the atmosphere plus volcanism that has removed most of the evidence of this pummeling we took.
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- Finally, a billion years later Earth hits back. On July 4th, 2005, while we were watching fireworks at home NASA was watching its own fireworks in deep space. The NASA mission, “Deep Impact“, shot an 800 pound copper ball into the “Comet Tempel 1” and watched the fireworks that resulted from the impact.
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- The goal of the mission was to learn what comets were made of. If we knew the material in comets and we know the make up of Earth, we could learn how much of the Earth was created by incoming comets and how much was already here, or created by other means.
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- The Big Bang only created hydrogen and helium (and a few other light elements). It was the exploding stars in supernovae that created all the other higher level, heavier elements in the periodic table.
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- 118 elements have been identified on Earth. When the 800 pound probe smashes into the comet the compression pressure will cause an explosion on the surface. The elements that are vaporized by the impact will release radiation that we can measure on instruments that are on the satellite that delivered the probe to Tempel 1.
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- Just hitting the comet was a major feat. It was like shooting a bullet, that fired another bullet, that hit a third bullet traveling at 23,000 miles per hour. Nice shot!
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- The radiation released by the impact was analyzed by instruments called spectrometers. A flash of visible light was part of this radiation that was released. We saw the flash. Our eyes are a type of spectrometer. The rods and cones in our retinas detect red, green and blue colors in visible electromagnetic radiation, light.
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- The cones detect only the three colors. The wavelength of these frequencies are what the retina cones are sensitive to. These wavelengths are about the size of bacteria.
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- The spectrometers that scientists use see all the colors. There are millions of different colors in visible light. The spectrometers see them all. They also see the invisible radiation that has shorter wavelengths than visible light. They can detect ultraviolet, x-rays, and gamma rays which have wavelengths the size of molecules. They can see longer wavelengths. Infrared, microwaves - wavelengths size of baseballs, radio wavelengths - wavelengths the size of people, radio towers, and the tallest buildings.
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- The entire spectrum of electromagnetic radiation is being studied. Each element and molecule has different configurations of electrons in the shells around their nucleus. As these atom configurations are broken apart each emits a specific radiation.
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- As the atoms recombine they absorb these same frequencies of radiation. It is this emission and absorption the scientists study with the spectrometers. The emissions show up as brighter lines and the absorptions show up as darker lines in the spectrographs.
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- Each element and molecule has its own unique signature that can be identified with the trained eye of scientists. Scientists are still studying the data retrieved from Deep Impact, but, what have we learned so far?
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- The first thing we learned was that comets are extremely porous. The comet is mostly empty like a dirty snowdrift. There is no bulk of solid ice. The ice is all in the form of tiny grains. This material is unbelievably fragile. It is loose powder-like particles held together by weak gravity. The particles are laced with carbon which some experts believe may well have been what kick-started life on Earth billions of years ago.
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------------------------ Comets contain a substantial amount of organic material
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------------------------ Water vapor
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------------------------ Carbon dioxide, vapor from “dry ice”
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------------------------ Clays
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------------------------- Iron compounds
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------------------------ Carbonates, like found in seashells
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------------------------ Crystallized silicates, like olivine found on beaches and in the gemstone peridot
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------------------------ Polycyclic aromatic hydrocarbons
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------------------------ Carbon compounds, like found in car exhauset and burnt toast
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------------------------ Spinel, the reddish-brown gem
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- Scientists can see the porous composition of comets is very complex. They contain many of the higher level elements that we find on Earth. The contain even organic material that we find in life on Earth.
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- The largest asteroid so far discovered is Ceres. It is 580 miles in diameter, the size of the state of Texas. Recent studies of this asteroid indicate that it is rich in water ice. In fact, it has more fresh water ice than the fresh water on Earth.
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- Earth has 1,400,000,000 kilometers^3 of water, 41,000,000 of which is fresh water. Ceres has 200,000,000 kilometers^3, five times as much as Earth. Possibly all the water on Earth came from incoming comets and asteroids.
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- Comets and asteroids are basically the same thing, debris orbiting the Sun, zipping around the Solar System like us. Except, comets are softer and tend to have been formed farther out from the Sun. Asteroids are harder rocks and tend to have formed closer into the Sun. Both have pummeled Mother Earth for billions of years.
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- You could say comets and asteroids are what Earth came from. You might even say that is where you came from, or, at least, the material you are made of. It is the conscious mind inside that material that I am still not sure about.
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- The Deep Impact probe was launched January 12, 2005. The impact occurred July 4, 2005. So the trajectory was only 6 months. The project started in 1999 so it took 5 years of preparation before launch, < $300 million.
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- The comet, “Temple 1“, is 1.5 AU from the Sun. The Earth is 1 AU, 1 astronomical unit, away from the Sun. So, the comet is 50% farther out. It’s mass is 800 pounds. It is 4.7 by 3 miles shaped like a baked potato. It rotates every 42 hours and is traveling 20,000 miles per hour. It takes 5.5 years to orbit the Sun. In comparison, comet Halley is 9 by 4 miles in size and orbits in 76 years.
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- The Deep Impact mission objective was to smash the probe into the comet to learn what it was made of. The telescopes and instruments on the mother ship would measure the results of the impact.
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- The Comet was very porous, about the consistency of fresh fallen snow ( a density of 0.6 grams/cubic centimeter). But, comets are anything but white. Temple 1 only reflects 4% of the sunlight that strikes it. 96% of the sunlight is absorbed. Even charcoal has a 10% reflection. Earth reflects 37%. So, the comet is very black, mostly due to powdered carbon.
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- The dust cloud that arose from the impact was extremely fine dust, about the size of bacteria. When the probe hit is ejected 22,000 tons of this fine dust going 10 to 50 meters into the surface.
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- By studying the spectrograph of the impact scientists could identify the elements that evaporated. Comets have a very complex chemistry: Formaldehyde (2H2O), Methane (CH4), Ethylene (C2H4), Ammonia (NH3), Acetonitrile (CH3CN), water (H2O).
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- These compounds get broken down and later ionized by the solar ultraviolet radiation as the comet approaches the Sun. The broken down compounds are water (H2O), carbon (C2,C3),carbon dioxide (dry ice, CO2), Hydrogen (H).
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- The Earth was born too close to the Sun to have had much water in the beginning. Comets were born far out in the solar system where it was much colder and water ice, carbon dioxide ice could from into giant snow balls.
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- There were natural craters on the surface of the comet as well as the unnatural crater that the probe made. Scientists studied both these craters which were very similar. They duplicated the crater shapes by firing projectiles into porous materials in the lab. They were able to recreate the crater on a small scale almost exactly using the right porous material, density, temperature, angle of impact, etc.
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- The comet was amazingly warm for being 50% farther out from the Sun than Earth. It was 26 to 134 Fahrenheit, depending on the angle of the Sun. It is so black and absorptive that its surface remains relatively warm.
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- There were over 250 astronomers at 130 locations around the world observing the Deep Impact with telescopes. They were capturing light curves that could be analyzed over the entire electromagnetic spectrum. These data are all being compared an analyzed to see what more we can learn about the comets composition.
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- Many people around the world were interested in this event. The Deep Impact web site took over 1 billion hits in July more than Hubble or any other astronomical event to date. People are interested in this type of science.
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- The most amazing part to me is that the composition of comets were likely what delivered water and amino acids, RNA and DNA, that were the molecules for life on Earth.
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- The comets pummeled Earth 4,400,000,000 years ago, life started 3,800,000,000 years ago. There is so much more yet to be discovered. Comets are being credited with starting life and taking it away. The collisions built the planets and the collisions destroyed them.
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- Life somehow arose out of the ashes and here we are today.
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----------------------------- Reviews available about other comets;
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- #1797 - Visiting the Rosetta Comet. It does contain water but different isotope than Earth’s. It did contain 16 different organic compounds.
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- #1707 - December, 2014. A dirty snowball 4.6 billion years old. Calculates the density of several moons and planets.
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- #1696 - How much ice landed on the surface of Earth over 400,000,000 years ago. The water on Earth’s oceans totals 1.33 billion kilometers ^3.
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- #1692 - Rosetta Mission lands on the Comet. How mass is calculated to be 2.8 billion tons.
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- #1688 - November 12, 2014 Rosetta lands on a comet.
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- #1623 - Math calculations for the water loss as the comet loops around the Sun, 76,646,000 tons.
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- #1612 - How many comets have made close flybys to Earth? 60 comets were discovered in 2012. Seven came within 31,000,000 miles of impact. 60 new comets were discovered in 2012. 7 were close encounters.
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- #1600 - Comet ISON November 2013. Nothing in the Universe disappears, it just changes forms.
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- #1338 - Did comets bring water to Earth?
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- #1292 - Calculus used to measure the mass of the comet.
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- # There is more ….
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- June 7, 2020 549 577 2757
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--------------------- Sunday, June 7, 2020 -------------------------
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