18th Jul. 2011 :: Dawn Enters Vesta Orbit
NASA's Dawn spacecraft edged into orbit around Vesta on 16th July. Dawn will spend a year mapping one of the solar system's largest unexplored worlds.
Vesta is in the main asteroid belt between Mars and Jupiter, it has an average diameter of 530 kilometres, and it is estimated to contain 9% of the mass of the entire asteroid belt. It is however smaller than the dwarf planet Ceres which has a diameter of about 950km, and contains 32% of the mass of the asteroid belt.
Dawn is the first craft to orbit an object in the main asteroid belt so it is certainly a very important first for NASA. The main mission will begin in August with mapping and imagery collections before moving closer to Vesta (120 miles at it's closest approach) for more detailed observations and measurements.
Vesta as seen by Dawn in July 2011 :: NASA Image
By comparison Vesta as seen by Hubble in 2007 :: NASA/ Hubble Image
It is believed that Vesta was one of the earliest bodies to form in the early solar system and therefore expected to hold in it's make-up a record of that early history. Vesta may well be very similar to (or may even been one of) the planetary building blocks which collided and joined to create the Earth and the other rocky solar system planets, making it a highly valuable scientific target.
It's scientific payload includes a camera for scientific imaging of the two targets Ceres and Vesta. A Visible & Infrared Spectrometer (VIR) which accomplishes the mission's scientific and measurement objectives of producing spectral images. A Gamma Ray and Neutron Spectrometer (GRaND) which measures elemental abundances on the surface of Vesta and Ceres. And in addition a gravity science package that allows accurate measurements of the spacecraft's orbit from which scientists can determine the gravity fields of Vesta and Ceres.
Once Dawn's mission at Vesta is complete in July 2012, the crafts ion engines will ignite to propel the spacecraft toward its second destination. After another two-and-half years journeying through the solar system, Dawn will enter orbit around the dwarf planet Ceres in February 2015. The visit to Ceres will make the spacecraft the first to ever orbit two objects in the solar system.
Vesta's size and bright surface make it the brightest asteroid, and it is occasionally visible to the naked eye from dark skies. In May and June 2007, Vesta reached a peak magnitude of +5.4. At that time, opposition and perihelion were only a few weeks apart it was visible in the constellations Ophiuchus and Scorpius.
Vesta will next come to opposition on August 5th 2011, in the constellation of Capricornus at about magnitude 5.6.
Should be interesting to see if anyone can locate and image it.