Title: The Resolved Asteroid Program - Size, shape, and pole of (52) Europa Authors: W. J. Merline, J. D. Drummond, B. Carry, A. Conrad, P. M. Tamblyn, C. Dumas, M. Kaasalainen, A. Erikson, S. Mottola, J. Durech, G. Rousseau, R. Behrend, G. B. Casalnuovo, B. Chinaglia, J. C. Christou, C. R. Chapman, C. Neyman
With the adaptive optics (AO) system on the 10 m Keck-II telescope, we acquired a high quality set of 84 images at 14 epochs of asteroid (52) Europa on 2005 January 20. The epochs covered its rotation period and, by following its changing shape and orientation on the plane of sky, we obtained its triaxial ellipsoid dimensions and spin pole location. An independent determination from images at three epochs obtained in 2007 is in good agreement with these results. By combining these two data sets, along with a single epoch data set obtained in 2003, we have derived a global fit for (52) Europa of diameters (379x330x249) ± (16x8x10) km, yielding a volume-equivalent spherical-diameter of 315 ±7 km, and a rotational pole within 7 deg of [RA; Dec] = [257,+12] in an Equatorial J2000 reference frame (ECJ2000: 255,+35). Using the average of all mass determinations available for Europa, we derive a density of 1.5 ±0.4, typical of C-type asteroids. Comparing our images with the shape model of Michalowski et al. (A&A 416, 2004), derived from optical lightcurves, illustrates excellent agreement, although several edge features visible in the images are not rendered by the model. We therefore derived a complete 3-D description of Europa's shape using the KOALA algorithm by combining our imaging epochs with 4 stellar occultations and 49 lightcurves. We use this 3-D shape model to assess these departures from ellipsoidal shape. Flat facets (possible giant craters) appear to be less distinct on (52) Europa than on other C-types that have been imaged in detail. We show that fewer giant craters, or smaller craters, is consistent with its expected impact history. Overall, asteroid (52) Europa is still well modelled as a smooth triaxial ellipsoid with dimensions constrained by observations obtained over several apparitions.
On the evening of July 3 at 11:05:30 p.m. EDT -- at a distance of 280 millon miles into space that poses no threat to Earth -- 52 Europa will pass in front of star TYC 0292-00339-1 in the constellation Virgo. The asteroid will eclipse the star's light for 17.9 seconds in a process known as occultation. Here on Earth, astronomers can measure the exact length of time the star's light is blocked and use those calculations to help verify the size of 52 Europa. They'll also have alive Web chat to discuss how to measure the asteroid 52 Europa on the evening of July 3, 2011, from 9:30 p.m. to midnight EDT. Dr. Bill Cooke and his team from NASA's Meteor Environment Office at the Marshall Space Flight Center will be watching the sky on the evening of July 3, 2011. Join them from 9:30 p.m. to midnight EDT for a live Web chat to ask your questions and observe the occultation via a live Ustream feed. Amateur astronomers who are observing the event can also report their observations via the associated Twitter feed. Read more
Asteroid (52) Europa is at Opposition at 17:25 GMT, 27th March, 2011.
Magnitude=10.5 Distance to Sun=2.975 AU Distance to Earth=1.986 AU
52 Europa is one of the larger asteroids in the asteroid belt, having a diameter of 300 km. It was discovered on February 4, 1858, by Hermann Goldschmidt from his balcony in Paris. Read more