CONVERSATION WITH …Dr. David Rabinowitz By Stacey Dresner Yale researcher helps to discover a new planet April 16, 2004 - Last November, Yale University researcher David L. Rabinowitz was part of a team of scientists who discovered a new "proto-planet" orbiting our solar system. Called a planetoid because of its size n it is one-quarter the size of Pluto n this new discovery was named first "2003 VB12" then "Sedna." A native of New Haven, Rabinowitz, 44, has been interested in space and the universe for some time. A graduate of Amity High School in Woodbridge, he graduated from Yale University in 1979 with a B.S. in physics. He got his Ph.D. in physics from the University of Chicago in 1983. His thesis was "Source Map for the Dust Jets in Halley's Comet." Since then he has worked tirelessly in the field of space research: searching for near-Earth asteroids with the Spacewatch Telescope at the University of Arizona, working as a research associate at the Department of Terrestrial Magnetism at Carnegie Institution of Washington working on theoretical studies of the origin of near-Earth asteroids, and as a research scientist at the Jet Propulsion Laboratory of California Institute of Technology searching for near-Earth asteroids, working on astronomical software and CCD camera instrumentation. Since 1999, he has been a research scientist in Yale's Physics Department working on instrument development and continuing his search for distant solar-system objects. He has been honored with NASA/JPL achievement awards and was the namesake for an asteroid named Rabinowitz. He recently spoke with the Ledger to explain how he and his team of scientists discovered the new planet Sedna. Q: Can you tell me how this new planet was discovered by you and your team? A: The planet was discovered as a part of a special search that we are making for distant objects in the solar system. We are using one of the largest electronic cameras ever built. It is called the QUEST camera, and was designed and built at Yale and also at Indiana University. It has over 160 million pixels and records images of the sky 40 times larger than the moon. I was a part of the team that built the camera. To search for distant planets, we are collaborating with astronomers at Caltech (Mike Brown) and Gemini Observatory (Chad Trujillo). Caltech owns the Samuel Oschin Telescope at Palomar Observatory which has one of the widest fields of view for any professional telescope. This telescope was used previously to map the whole sky photographically. We are now using it to search the sky electronically, with 100 times greater sensitivity. To find distant objects, we take images of the sky three times in one night, and use a computer to map the location of every star in each image. If the computer finds a star that moves by a small amount between exposures, we know that it must be a distant object in the solar system. We then make follow up observations with other telescopes to determine the orbit precisely and to characterize the physical properties of the object. I am also working with other collaborators to study the expansion history of the universe and to probe the conditions at the time of formation of the first galaxies. Our search for distant objects is just part of the full use we are making of the Palomar - QUEST camera. Q: Had Sedna ever been sighted before and how did you determine that it was a planet? A: I believe we are the first ones to recognize Sedna. In all previous observations of the sky, Sedna was overlooked. Tracking its orbit backwards in time, we were able to find it as a very faint spot in archived, digital images of the sky that had been used to look for nearby asteroids. But there its motion was not apparent. We were able to recognize its motion in our images only because we allowed a long enough time between exposures for significant motion, and because our camera was more sensitive. Q: Can you tell me the vital statistics of the new planet - size, its location in the universe, how far away from Earth it is? A: It's the most distant solar-system object we know of. It's 90 times farther from the Sun than we are. It's three times farther than Pluto. It's probably about 1/2 to 3/4 the size of Pluto. It has an extremely elongated orbit for a planet. At its farthest point, it is 1,000 times farther from the Sun than Earth is. If you draw a picture of the orbit scaled to cover a sheet of paper, the entire known solar system occupies a tiny ring in the center of the page. It is amazing how far away Sedna is. How it got there is currently a mystery. Q: What was it like for you to be a part of this great discovery? A: It has been exciting, gratifying, and enlightening. Exciting, because we have never seen an object in the solar system like this. Gratifying, because it was very hard work making the instrument, and it is great to see it actually working. Enlightening because people all over the world are also excited about the discovery. Rarely in my work as a scientist have I seen such an enthusiasm and interest from the public. Q: Why was this new planet named Sedna? A: Hopefully Sedna will become the permanent name. But that will not come until the observations of the orbit have been confirmed from several years of data. Until then, the object is listed as "2003 VB12." The reason we chose the name Sedna is because the astronomical community has agreed that all the objects in the outer solar system should be named after characters from creation myths (or underworld figures if their orbits are coupled like Pluto's to Neptune). We might have chosen Greek or Roman gods, but they have all been used. So we looked at Inuit mythology. The Inuits are naturally familiar with the cold appropriate for distant planets. Sedna's association with the icy seas and sea creatures is also appropriate for the outer solar system since Uranus and Neptune are also associated with the ocean. Q: What is this discovery so meaningful for us on Earth and for the universe? A: Sedna is telling us something about how the solar system formed. When we look at the most distant objects, we are looking at the oldest objects. These are the relic planetisimals, left over from the time when the planets first formed. We believe that these smaller bodies originally coalesced from a primordial disk of dust and ice, the same disk that formed the sun. Most of the original planetesimals joined in collisions to form the larger planets. Many were ejected from the solar system. But some have remained. Sedna is one of them. Sedna is special because it has been preserved in an orbit removed from the planetary regions of the solar system. It may be the best preserved relic ever observed. By studying its properties, we learn the properties of the first solar system objects - their composition, size, and number. Hopefully this will lead us to a better understanding of how the solar system formed. Q: Are there other planets out there waiting to be discovered? A: Since we believe that there were many other objects like Sedna when the solar system formed, there should be a lot more out there waiting to be found. We don't know if they will be as big as Sedna, or on similar orbits. We'll just have to keep looking and find out.