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Dr. rer. nat. Dörte Mehlert

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MIT - "Global Seed Fund" Promotes DSI Junior Scientists

Karsten Schindler and scientists at MIT jointly explore the edge of our solar system

February 11, 2019; Dörte Mehlert (mehlert@dsi.uni-stuttgart.de)

The "Global Seed Fund" of the Massachusetts Institute of Technology (MIT) funds ambitious young researchers at the University of Stuttgart to kick-start their research projects. In addition, it aims at strengthening the research partnership between MIT and University of Stuttgart. Karsten Schindler of the German SOFIA Institute (DSI) successfully proposed his project "A peek into the outer solar system through stellar occultations" in the last call for proposals, which has been awarded $24,200.

Surveying bodies at the edge of our solar system
Karsten Schindler collaborates with Amanda Bosh and her colleagues at MIT to measure stellar occultations. During such an event, a body in our solar system crosses the line of sight between an observer on Earth and a distant star, thus covering its light for a limited time – analog to a solar eclipse. Using a fast camera and an accurate clock, it is possible to estimate the size and shape of an object from the duration of the occultation. Moreover, based on the shape of the obtained light curve, astronomers are able to detect an atmosphere or a ring system. The vast majority of minor bodies in our solar system has such a large distance to Earth that even the most powerful telescopes cannot obtain a spatially resolved image. Thus, stellar occultations are practically the only way to obtain a direct size measurement of a distant body.

Insights on size, surface conditions, and shape
The scientists are particularly interested in trans-Neptunian objects, which are bodies in the outer solar system that orbit the Sun beyond the outermost planet Neptune. The most prominent member of this population is Pluto. Since the 1990s, a large number of such objects has been discovered in the outer solar system, eventually causing Pluto to lose its status as the ninth planet. Very little is known about the physical properties of these objects. Only during the last decade, some insights on the nature of these bodies were gained especially through observations of stellar occultations, revealing a surprising diversity in terms of size, reflectivity, surface properties, and shape.

In theory, the procedure is quite simple: Once the orbit of a body has been determined, it is possible to predict when and at which location on Earth an occultation of a star can be observed. In practice, this is much easier said than done. Only very recently, the position of stars has been determined very accurately thanks to the European space observatory Gaia. To exactly determine the orbital elements of the target body, its position must be measured again and again over time, ideally spanning a large fraction of its orbit. However, this is often difficult to realize for objects beyond Neptune that have orbital periods of several hundreds of years. Thus, the position measurements of an object must be very accurate, to be able to extrapolate its apparent path through the sky with sufficient precision that predictions of occultations can be made with high accuracy.

SOFIA enables outstanding observations of stellar occultations
The airborne Stratospheric Observatory for Infrared Astronomy (SOFIA), whose German contribution has its home at University of Stuttgart’s Institute of Space Systems, provides a unique platform to observe such events. SOFIA is able to fly at the right time to the right place, which enables observations of stellar occultations in remote, inaccessible regions, independently of weather conditions. Over the past years, several SOFIA missions have been successfully carried out under leadership of MIT researchers to observe occultations by Pluto, by Neptune’s moon Triton, and by Saturn’s moon Titan. “The Seed Fund project aims at predicting stellar occultations of other interesting targets even further away from Earth with such high accuracy, that we can precisely position SOFIA to observe them” explains Karsten Schindler. Recent advances in mapping the sky with unprecedented accuracy (the Gaia DR2 star catalog that was released in April 2018) must come into play, requiring the development of new tools that allow reaping the full benefits provided by this new data.

Joint observing program between MIT and University of Stuttgart
„We plan to actively involve students from Stuttgart in this research, and to enable them short research stays at MIT that especially act as a catalyst for master theses”, says Schindler. Visits by students and researchers from MIT shall foster the collaboration in data analysis, interpretation and publication of previously successful observations, and further strengthen and expand the jointly coordinated observing program on SOFIA. Additionally, students of both institutions shall support observations of stellar occultations at professional, ground-based telescopes in the US and in Europe, providing them with unique insights into the scientific landscape in astronomy early in their careers. And if a shadow of an occultation happens to cross California, the Astronomical Telescope of the University of Stuttgart (ATUS) is standing by ready to observe and to deliver valuable data as already demonstrated during previous events.

The Global Seed Fund program is administered by MIT’s International Science and Technology Initiative (MISTI).


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SOFIA, the "Stratospheric Observatory for Infrared Astronomy" is a joint project of the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; German Aerospace Center, grant: 50OK0901, 50OK1301 and 50OK1701) and the National Aeronautics and Space Administration (NASA). It is funded on behalf of DLR by the Federal Ministry for Economic Affairs and Energy based on legislation by the German Parliament, the State of Baden-Württemberg and the University of Stuttgart. Scientific operation for Germany is coordinated by the German SOFIA-Institute (DSI) of the University of Stuttgart, in the USA by the Universities Space Research Association (USRA).