In a paper to be published in the April 2007 issue of the journal Icarus, a team of University of California, Berkeley, and Paris Observatory astronomers depict the asteroid 90 Antiope as two slightly egg-shaped rubble piles locked in orbit, like two twirling dancers facing one another with linked arms.
This new view of Antiope is the culmination of research that started in 2003 and that eventually included data supplied by both professional and amateur astronomers from around the globe.
Before the year 2000, Antiope was just another main-belt asteroid, one of millions between the orbits of Mars and Jupiter. But that year, it was resolved into a doublet, thanks to sharper pictures obtained with adaptive optics (AO) on the largest ground-based telescope, the 10-meter Keck II telescope in Hawaii. Yet, even with AO, these two asteroids were too small for astronomers to discern their shape or to see more than two bright blobs revolving around their center of mass.
Two years ago, with improved images from the European Southern Observatory's 8-meter Very Large Telescope (VLT) in Chile and Keck II, University of California, Berkeley astronomer Franck Marchis and colleagues in France were able to determine the approximate orbit of the two asteroids, each of them about 86 kilometers in diameter and separated by about 171 kilometers.
But uncertainties remained, and in 2005 the team invited observers around the world to turn their telescopes on the asteroid pair during a time when they predicted a mutual eclipse or occultation would cause a drop in brightness. In an eclipse, one of the pair casts a shadow over the other; in an occultation, one passes in front of, and completely blocks light from, the other.
Sure enough, at the appointed time on May 31, 2005, one of the asteroids eclipsed the other, and team member Tadeusz Michalowski e-mailed Marchis and their colleagues from South Africa to confirm the eclipse. Michalowski, an astronomer at Adam Michiewicz University's Astronomical Observatory in Poznan, Poland, recorded the dip in Antiope's brightness from the South African Astronomical Observatory.
Over the next six months, at Marchis' invitation, amateurs and professionals from as far afield as Brazil, France, Réunion Island in the Indian Ocean and Grass Valley, Calif., observed repeated occultations, as well as shadows passing over one of the pair.
"This is the first publication I've had in a professional journal, and I'm really happy about it," said amateur astronomer Peter Dunckel, 75, a retired paper company executive who observes from the backyard of his vacation home in Grass Valley. "What is really a thrill is to have my little 7-inch telescope along with an 8-meter telescope on the same paper; it is unbelievable."
Dunckel observed the binary pair for 35 hours over a period of six weeks, recording Antiope's brightness every minute with a CCD camera attached to his Maksutov Newtonian reflector telescope.
"Amateurs can be used for professional studies, compensating for the small size of their telescopes by the large numbers of observations and the frequency of observations they can do," Marchis said. "You can time the orbits more precisely when a mutual event happens, which allows you to extract also the size, shape and surface detail of each component, and also what it's made of."
The asteroid pair is itself the remnant of an ancient asteroid, dubbed Themis, which astronomers estimate was destroyed around 2.5 million years ago, probably hit by another asteroid. The rubble spread out from the point of impact but continued to follow approximately the same orbit around the sun in the outer part of the main asteroid belt. Themis was a carbonaceous chondrite left over from the formation of the solar system 2.5 billion years ago.
Evidently, either another asteroid hit Antiope again to split it in two, or two of the Themis pieces remained bound to one another after the initial break up, possibly even remaining attached. However the doublet arose, computer simulations by another group suggest that the spinning, elongated rubble pile would have separated into two egg-shaped rubble piles, each the shape of a Roche ellipsoid, the theoretical shape predicted for a system if their composition was liquid or loosely aggregated, rather than solid, and if the components are deformed due to mutual gravitation.
The eclipse and occultation observations, combined with previous observations of Antiope during a grazing occultation, confirmed the ellipsoid shape of each component of the asteroid, Marchis said. Each component differs from a sphere by less than 7 percent, or 6 kilometers out of 86. They orbit around their center of mass every 16.5 days
"Due to mutual gravitation, both components took a shape very close to the pure hydrostatic shape, the Roche ellipsoid, as if the asteroid was a fluid," Marchis said. "This result indicates that the internal strength in the components must be low, so possibly a rubble pile structure."
They were able to calculate the density as 1.25 grams per cubic centimeter (water is one gram per cubic centimeter), which, if one assumes that the rock component is carbonaceous chondrite, means the asteroid pair is 30 percent empty space.
"Despite this intensive study, the origin of this unique doublet still remains a mystery," said team member Pascal Descamps, an astronomer at the Institut de Mécanique Céleste et de Calculs des Éphémérides (IMCCE) of the Observatoire de Paris. "The formation of such a large double system is an improbable event and represents a formidable challenge to theory. It is possible that a parent body was spun up so much that it broke apart, but this seems very hard to do for asteroids in the main belt, unlike, for example, near-Earth asteroids."
Marchis and his team are employing both amateur and professional astronomers to observe more of these mutual events between components of binary asteroid systems. These partnerships are a powerful way to get direct and accurate insights about these systems, he said.
As for Dunckel, who commutes from San Francisco to the Grass Valley vacation home he refers to as "Rattlesnake Creek Observatory," he says he's hooked on scientific amateur observing, "now that I've broken the dam, so to speak." He has upgraded to a 10-inch reflecting telescope and is excited about applying a new computer program that will allow him to create 3D models of asteroids from light curves he obtains in collaboration with others.
Robert Sanders | EurekAlert!
Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences