The mysterious case of asteroid Oljato’s magnetic disturbance
Press Release Ref. PN: EPSC12/05
Back in the 1980s, the arrival of asteroid 2201 Oljato inside the orbit of Venus heralded a flurry of magnetic activity. Now, results from ESA’s Venus Express spacecraft suggest that Oljato has lost its magnetic mojo. Dr Christopher Russell will present an explanation for Oljato’s strange behaviour at the European Planetary Science Congress in Madrid on Tuesday 25th September.
Oljato orbits the Sun once every 3.2 years. During its lifetime, NASA’s Pioneer Venus Orbiter observed three passages of Oljato between Venus and the Sun. Each time, there was a marked increase in the region of unusual magnetic peaks known as Interplanetary Field Enhancements (IFEs), both ahead and behind the asteroid.
Russell said, “This is not typical asteroidal behaviour! These magnetic increases are rare, occurring in Venus orbit about 10 times per year. Pioneer observed that when Oljato was just in front or just behind Venus, the rate of IFEs approximately trebled. And yet, in more recent observations with Venus Express, the occurrence of IFEs is now lower than the average we find outside this region.”
Russell and his team believe that the answer to this discrepancy lies with collisions between Oljato and debris in its orbit. When objects collide in interplanetary space, they become electrically charged and dust particles are accelerated by the solar wind.
Russell explained, “At one point in time Oljato shed boulders – mostly a few tens of metres in diameter – into its orbit and they formed a debris trail in front and behind Oljato. These impactors then hit other targets as they passed between Venus and the Sun. The large amount of fine dust released by these collisions was picked up by the solar wind, producing the IFEs observed by Pioneer, and was accelerated out of the solar system.”
The reduced rate of IFEs observed during the Venus Express epoch suggests that the collisions with Oljato’s co-orbiting material have reduced the general debris in the region as well as the co-orbiting material shed by Oljato.
“The IFEs observed by Pioneer suggest that more than 3 tonnes of dust was being lost from the region each day. Effects associated with solar heating and gravitational perturbations have gradually nudged larger chunks of debris away from Oljato’s orbit. From once being unusually crowded, the region has become unusually clear and free of IFEs,” said Russell.
Hubble Space Telescope observation of an asteroid trailing debris following a suspected collision. Credit: NASA, ESA, and D. Jewitt (UCLA)
Dr Christopher Russell
Los Angeles, USA
From 24-28 September Dr Russell can be contacted through the EPSC 2012 Press Office
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PIONEER VENUS ORBITER
Pioneer Venus consisted of two spacecraft to study Venus: the Orbiter and the Multiprobe. The Orbiter was launched on the 20 May 1978 from the Kennedy Space Center aboard an Atlas-Centaur rocket. It went into orbit around Venus on 4 December 1978. Its primary objective was to investigate the solar wind in the Venusian environment, map Venus’ surface through a radar imaging system, and study the characteristics of the upper atmosphere and ionosphere. Although originally intended to operate in orbit for one Venusian year, most of the Orbiter instruments, including the gamma ray burst detector, were still operating when the spacecraft entered the atmosphere on 8 October 1992. For more details, see: http://www.nasa.gov/mission_pages/pioneer-venus/index.html
The European Space Agency’s Venus Express spacecraft is optimised for studying the atmosphere of Venus, from the surface right up to the ionosphere. It has been successfully operating in orbit around Venus since April 2006. For more details, see: http://www.esa.int/esaMI/Venus_Express/SEMEE3808BE_0.html
EUROPEAN PLANETARY SCIENCE CONGRESS 2012 The European Planetary Science Congress (EPSC) is the major European meeting on planetary science and attracts scientists from Europe and around the World. The 2012 programme includes more than 50 sessions and workshops. The EPSC has a distinctively interactive style, with a mix of talks, workshops and posters, intended to provide a stimulating environment for discussion.
This year’s meeting is taking place at the IFEMA-Feria de Madrid, Spain, from Sunday 23 September to Friday 28 September 2012. EPSC 2012 is organised by Europlanet, a Research Infrastructure funded under the European Commission’s Framework 7 Programme, in association with the European Geosciences Union, with the support of the Centro de Astrobiología of Spain’s Instituto Nacional de Técnica Aeroespacial (CAB-INTA).
Details of the Congress and a full schedule of EPSC 2012 scientific sessions and events can be found at the official website: http://www.epsc2012.eu/
EUROPLANET The Europlanet Research Infrastructure is a major (€6 million) programme co-funded by the European Union under the Seventh Framework Programme of the European Commission.
The Europlanet Research Infrastructure brings together the European planetary science community through a range of Networking Activities, aimed at fostering a culture of cooperation in the field of planetary sciences, Transnational Access Activities, providing European researchers with access to a range of laboratory and field site facilities tailored to the needs of planetary research, as well as on-line access to the available planetary science data, information and software tools, through the Integrated and Distributed Information Service. These programmes are underpinned by Joint Research Activities, which are developing and improving the facilities, models, software tools and services offered by Europlanet RI.
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