The following interview was conducted with Dr. Eleanor Helin of JPL (NASA's Jet Propulsion Lab in Pasadena) on March 26, 1998. Her research position is to find and track any asteroid that might some day pass close to the earth. She is Principal Investigator for a program at JPL called NEAT (Near Earth Asteroid Tracking).
Recently an astronomer in Massachusetts thought that he had found a large asteroid (called 1997 XF11) that might come very close to earth and possibly hit the earth in the year 2028. This asteroid is about 1 mile (1.6 kilometers) wide. Dr. Helin had taken telescope images of this asteroid in 1990 during her photographic asteroid program. From these observations it was possible to confirm that this asteroid would not hit the earth. It would in fact come no closer to the earth than 570,000 miles (950,000 kilometers) at its closest approach to earth in year 2028. If you are interested in hearing more about this asteroid you might want to look at the March 23, 1998 TIME magazine or SCIENCE NEWS, March 21, 1998. Additional articles on this topic can be found in recent copies of NEWSWEEK, U.S. NEWS & WORLD REPORT, NATURE, and the NEW YORK TIMES. Since the announcement about the possible collision of asteroid 1997 XF11 with the earth, Dr. Helin has been very busy talking to dozens of magazine, newspaper, and television newspeople throughout the world as well as continuing her research at JPL. We are grateful that Dr. Helin would take the time from her busy schedule to talk with us and answer the questions from our students. Her interview follows.
Question from Kristina Chin: How did you start out to be an astronomer?
Answer from Dr. Helin: My first general science course was in 7th grade. Fortunately we now start teaching science in Kindergarten or even earlier. Most discoveries in science reveal many more interesting mysteries and questions to be answered someday. We continue to find new classes of bodies in the universe. It makes the study of science more interesting and rewarding all the time.
My formal education was in geology, and so I first studied minerals, rocks, and landforms on Earth. When I first started at Cal Tech I was the custodian for the meteorite collection. Meteorites are actually fragments of asteroids that were large enough to survive the plunge through our atmosphere and land on earth. I studied the composition, chemistry, and formation of these meteorites.
Question from Kristina Chin: Why did you set your target on asteroids as a career?
Answer from Dr. Helin: About 30 years ago I was also interested in minerals, rocks and landforms of the moon and how the surface of the moon became pocked with craters. NASA was planning their landing on the moon at that time and needed to know more about how and where to land on the surface of the moon. In the 1960's Dr. Bruce Murray and I started the first lunar laboratory in the country at Cal Tech. There was still some debate at that time whether the craters on the moon were caused by volcanoes or other bodies (comets or asteroids) colliding with the moon. The large craters on the moon called "mares" or seas are now thought to have resulted from large asteroids hitting the moon and melting all the older smaller rock craters in that location and causing large, smooth flat areas on the moon. We know now that our earth would have had many asteroid craters just like the moon, except that Earth's atmosphere burns up most asteroids before they hit and the weather and water on Earth erode most of the evidence of earlier asteroid collisions.
| For 25 years up until 1995 observations were made from the 18 inch (0.46 meter) and 48 inch (1.2 meter) wide-field photographic Schmidt telescopes at Palomar Observatory in California. This photographic method required significant manual interaction by a team of 4 people. |
Question from Ping: How do you study asteroids?: Where they are going? How big they are? What equipment do you use to study them?.
Answer from Dr. Helin: The telescope observations are made when there is no moonlight, so that the light from the moon doesn't hide the relatively dimmer light from the asteroids. For 25 years up until 1995 we made our observations from the 18 inch (0.46 meter) and the 48-inch (1.2 meter), wide-field, photographic, Schmidt telescopes at Palomar Observatory in California. This photographic method required significant manual interaction by a team of 4 people. One person did the telescope observations, another developed the film, a third person scanned and inspected the films with a special stereomicroscope, and a fourth person recorded the data and interacted with observers in other places. This team was responsible for two-thirds of the near-Earth asteroids that were found in the last 20 years before electronic search systems using CCD cameras directly linked to computers became available in 1995. The older method at Palomar Observatory discovered a total of 95 near-Earth asteroids, 17 comets, and many other independent discoveries. One of these independent discoveries that I made was the direct evidence that a comet becomes an asteroid after its supply of ice and volatiles evaporates. This evidence came from photographs of the same object taken 30 years apart. The earlier photographs clearly showed a comet and tail. Thirty years later the tail was gone and it had become an asteroid. I later named this asteroid 107P/Wilson-Harrington.
Since 1995 hundreds of observations are made each night of the observation cycle from a 3 foot (1-meter) diameter Air Force telescope located at an elevation of 10,500 ft. at the summit of Haleakala, an extinct volcano on the island of Maui. In one night four to five gigabytes (4,500,000,000 bytes) of data are collected and transmitted to a computer at JPL in Pasadena. The computer automatically calculates the orbit of asteroids for up to perhaps the next 1000 years. Another computer in Maui controls the telescope to look at the optimum locations in the sky for maximum coverage and data collection.
Other groups also observe the composition of asteroids by using telescopes with spectrometers with color filters and other instruments. The chemistry or composition of the asteroids is determined by looking at the light reflected from asteroids.
The U.S. has already launched a mission called NEAR (Near Earth Asteroid Rendezvous) which will begin orbiting around a large asteroid called Eros in early 1999. In 2002 the Japanese plan to launch a mission to another near-Earth asteroid called Nereus that was discovered by me in 1982. That mission will take several years and deploy and return a micro-rover to the surface of the asteroid. This will return to Earth with an actual sample of material from Nereus.
Question from Kristina Chin: When you see an asteroid closer to earth than others, what do you do?
Answer from Dr. Helin: We see this frequently. We continue tracking it. We need to observe it several times over a period of time to predict its trajectory. We need to predict more accurately where it will be going and if it will ever actually pass the earth's orbit at a time when it will also be close to the earth. We also ask other observers throughout the world to help us observe it. We also ask people with telescopes with spectrometers attached to them to observe the light that is reflected by or emitted from these objects to try to predict their composition (what the asteroid is made of) just in case we have to try to defend the earth from a collision. The article in Time (March 23, 1998) referred to using missiles with nuclear weapons to break up a large asteroid headed toward the earth or push it into another trajectory that would miss the earth. Such options are probably being given serious consideration by the Department of Defense and would seem to be appropriate alternatives to accepting a direct hit from a large asteroid or comet. If there was very little time we would rather use nuclear weapons than accept the loss of life from the asteroid colliding with the Earth.
| This is a picture of the asteroid, Gaspra, taken by the Galileo spacecraft. Gaspra is approximately 11.5 miles (19 kilometers) wide at its widest point |
Question from Kristina Chin: Are you concerned if an asteroid is close to earth?
Answer from Dr. Helin: Up until now we think we have found only about 5 to 10% of the near earth asteroid population. We don't know where more than 90% of the near earth asteroids are located. Most observations of near-Earth asteroids are limited to two locations in the world right now. One observation site is an Air Force telescope in Maui that feeds data to us at JPL. The other observation site is near the Univ. of Arizona in Tucson. Those two sites between them can only observe about 10% of sky, so about 90% of the sky and asteroids are not now being observed. We are now discussing how to increase the observations with other telescopes with CCD camera and computer systems developed at JPL so that about 90% of the sky and asteroids and other objects near the earth can be observed. Hopefully the Air Force and JPL will collaborate to identify more near-Earth asteroids which could possibly threaten the Earth.
Question from Ben and Ben: How many asteroids have hit the earth? How big were they?
Answer from Dr. Helin: Countless asteroids of all sizes have hit the surface of earth over time. On a typical day the earth receives perhaps tens of thousands of tons of asteroid or meteoric dust and debris entering our atmosphere measuring up to at least one or two meters in width before it enters our atmosphere. Sometimes one of these objects is large enough to survive the plunge through Earth's atmosphere. Last Sunday just after dark in west Texas there was a "witnessed fall" of a meteorite burning up and fragmenting. They followed the meteorite's path to a location where they were able to find a piece of fresh meteorite from this event. You may have seen a picture of this in the news. Certainly, it has been very rare that meteorites ever injured anyone. However, we now know that an asteroid that was approximately 6 miles (10 kilometers) in diameter hit the Yucatan peninsula about 65 million years ago. This area of the earth just happened to be rich is sulfur. We have found evidence that the extreme heat of this asteroid collision vaporized huge quantities of poisonous sulfur compounds that poisoned much of Earth's atmosphere. A large sulfur cloud was formed around the world that disrupted the sunlight that normally strikes the Earth's surface thereby cooling down the Earth. This is thought to have directly or indirectly killed all the dinosaurs and many other life forms on the land by poisoning the air, cooling down the Earth, and disrupting the food chain.
Our Infrared and radar cameras on our satellites can now see below the silt and dust and erosion of the surface of the Earth that now hides visible evidence of the asteroid collisions that occurred many millions of years ago. Using this satellite data which sees below the surface of the Earth, we have found evidence in Africa of collisions of asteroids with the earth where the asteroids were as large as several hundred miles (400 kilometers) in width.
| Since 1995 hundreds of observations are made each night of the observation run from a 3 ft. (1-meter) diameter Air Force telescope located on the island of Maui. In one night four to five gigabytes (4,500,000,000 bytes) of data are collected and transmitted to a computer at JPL in Pasadena. The computer automatically calculates the orbits of asteroids for up to perhaps the next 1000 years. Another computer in Maui controls the telescope to look at the optimum locations in the sky for maximum coverage and data collection. |
Question from Kristina Chin: When do you think another asteroid will crash into the earth?
Answer from Dr. Helin: Our measurements and statistical calculations show that the earth is overdue (within our lifetime) for a significant impact from say an asteroid of about 150 feet (50 meters) in width. If the asteroid was only 150 feet (50 kilometers) in width when it hit the earth, it would destroy all life and property within miles of the impact. Even if it landed in the ocean it would cause an enormous tidal wave that would cause great damage to the coastlines. This is based partly upon the collision of a comet or an asteroid that was as large as 300 feet (100 kilometers) in diameter that burst close to the ground over Siberia in 1908.
Question from Joe: Why are there asteroids only between Mars and Jupiter?
Answer from Dr. Helin: They aren't just between Mars and Jupiter. The near-Earth asteroids come from a number of sources that we know about. We now think that perhaps 55% originate in the main belt between Mars and Jupiter and then become mavericks as a result of random collisions and gravitational forces that cause them to venture from the main asteroid belt. We think that perhaps 45% of the near-Earth asteroids that we now observe were once comets that still orbit about the sun. For example we were able to observe the Shoemaker-Levy comet crashing into Jupiter in 1996. We think that the ice and volatiles finally evaporate from these comets after they pass by the sun thousands of times. This leaves only the solid core of an object that is then identical with an asteroid. The population of near-Earth asteroids does not seem to be diminishing. It seems to be replenished by asteroids from the main belt and by dead comets.
| This is another picture taken by the Galileo spacecraft as it was passing by another asteroid, Ida. When the astronomers looked closely they realized that there was also a small moon orbiting around Ida. This moon has been named Dactyl. If you look closely you can see Dactyl about 1/2 inch from the right border of the picture. |
Question from the Carver team: What are the rewards of such a career? How should a young student prepare for a career such as yours?
Answer from Dr. Helin: Just pick anything that really interests you and realize that there is always more and more to be discovered by anyone who enjoys the process of discovery. This process includes your education, your observation, working with other scientists and observers and interested people, and teaching students who ask new and important questions. Don't hesitate to make contacts with the scientists doing research in a field that truly interests you. These scientists will probably surprise you with their appreciation for your interest. If you are in high school they might even offer to let you help them make their studies during your summer vacation. It's a wonderful adventure. My career seems like a convoluted journey but it mostly makes sense. Early in my career as a geologist I looked at large photographic plates of the moon made by the Mt. Wilson telescope to help determine where our astronauts would land. I studied very simple and subtle color differences on the surface of the moon that later became quite complex. Then I began to look at the history of craters on the moon and what caused them. At the time we only had located12 near-Earth asteroids (Earth "Crossers" as well as Earth "Approachers"). Now we have ldentified 460 near-Earth asteroids. If you are enthused and curious about something, it is very rewarding to study it. The hard work of studying it all the time and keeping up with the latest research is all worth the effort. You can have an exciting life if you pursue something that you are really curious about or think is important. Then you can put your heart and soul into it. You don't give up everything for science. You can also have a family and children and other interests.
If you have more interest in asteroids, you might want to check out the NEAT website at http://huey.jpl.nasa.gov/~spravdo/neat.html. You can link your ThinkQuest web site to ours if you wish. There will be an educational fair and also an open house at JPL in the near future which you might wish to attend. I also recommend a book called Asteroids, Invaders from Space, by Robert Kraske, Simon & Schuster, NY. Dr. Helin collaborated with Robert Kraske in the research for this book. Also the Challenger Center will be having a free electronic field trip (Embrace Space and Space Day 1998 celebration) for students in grades 5 thru 8 on May13, May 20, and May 21, 1998. For registration information on the electronic field trip visit www.challenger.org or call (703) 503-7492.
