Journey to the Dawn of the Solar System

This week should see the launch of NASA’s mission to very the dawn of our solar system. It’s name? Appropriately enough, Dawn. The goals of the Dawn mission are to understand what it was like at the beginning of the solar system, and to understand how the solar system formed. The mission will do this by making an up-close study of “protoplanets.” According to the current theory of planetary formation, protoplanets are the early stage in the development of planets, condensing out of gas clouds surrounding a young star.

The Dawn mission will carefully examine two of the largest protoplanets that remain. They are Ceres, which has recently been classified as a dwarf planet, and the asteroid Vesta. Both of these bodies orbit the sun with many other smaller bodies in the large area between Mars and Jupiter that is called the asteroid belt. These protoplanets, or baby planets, were interrupted in their process of becoming something larger, by the formation of Jupiter, with its tremendous gravity. Ceres, Vesta, and the rest of the bodies in the asteroid belt have followed different evolutionary paths because of the many different processes that operated during the first few million years of the solar system.

The biggest question that the Dawn mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The instrumentation to be flown is complete, flight- proven and similar to that used for Mercury, Mars, the Moon, Eros and comets. The science team consists of leading experts in the investigation of the rocky and icy planets using proven measurement and analysis techniques.

Dawn has the potential for making many discoveries that could change the way scientists think. For example, Ceres may have active hydrological (water-based) processes leading to seasonal polar caps of water frost, altering our understanding of the interior of these bodies. Vesta may have rocks more strongly magnetized than on Mars, altering our ideas of how and when dynamos arise with important lessons for Mars, Earth and Mercury. Ceres may have a thin, permanent atmosphere distinguishing it from the other minor planets. These are just examples, but even more unexpected discoveries may be made along the journey.

The Dawn mission has three principal scientific drivers. First, to capture the earliest moments in the origin of the solar system, enabling us to understand the conditions under which these bodies formed. Second, to determine the nature of the building blocks from which the terrestrial planets formed and thereby improve our understanding of this formation. Finally, to contrast the formation and evolution of two small bodies that followed very different evolutionary paths, so that we can understand what controls that evolution.

And continuing the theme of “threes,” the Dawn mission accomplishes three goals for NASA. First, the gathered data will provide some context for interpreting the growing observations of extra solar-planetary systems. Second, the mission will provide information on the role of size and water in planetary evolution and form a bridge between the exploration of the rocky inner solar system and the icy outer solar system. Finally, the mission completes the first order exploration of the inner solar system, addressing NASA's goal of understanding the origin and evolution of the solar system and complements NASA’s ongoing investigations of Mercury, Earth and Mars.

Background on Ceres and Vesta

Ceres is the largest asteroid (designated 1 Ceres), the first to be discovered and was recently designated as a dwarf planet. Ceres is named after the Roman goddess of agriculture. It was discovered by Giuseppe Piazzi of the Palermo Observatory on Jan. 1, 1801. Additional observations by Piazzi were cut short due to illness. Carl Friedrich Gauss, at the age of 24, was able to solve a system of 17 linear equations to determine Ceres' orbit and to allow it to be rediscovered, a remarkable feat for this time. As a result within one year of its initial discovery, both Heinrich Olbers and Franz von Zach were able to relocate Ceres. It revolves around the Sun in 4.6 terrestrial years and has a diameter estimated at about 960 km (600 miles).

Vesta, the brightest asteroid (designated 4 Vesta), is named for the ancient Roman goddess of the hearth and is the only asteroid ever visible with the naked eye. Found on March 29, 1807, by Heinrich Olbers, it was the fourth minor planet to be discovered. It is the second most massive and the third largest asteroid. It revolves around the Sun in 3.6 terrestrial years and has an average diameter of about 520 km (320 miles). Its surface composition is basaltic.

Dawn Mission Timeline

At of this writing, the launch is scheduled for Wednesday, September 26, 2007, with a launch window of 7:25 a.m. - 7:54 a.m. EDT. The eight-year Dawn mission timeline is as follows:

September 2007, Launch – Dawn will launch from … and goes into a solar orbit, moving out to the orbit of the planet Mars.

March 2009, Mars gravity assist – Dawn will make a close approach to Mars and steal a bit of inertia from the planet, making the spacecraft go fast enough to move farther out, toward the main asteroid belt.

September 2011, Arrival at Vesta – Dawn will go into orbit around Vesta and will study the body for approximately seven months.

April 2012, Depart Vesta – Dawn will gradually spiral away from Vesta and begin to journey farther out toward Ceres.

February 2015, Arrival at Ceres – Dawn will go into orbit around Ceres and will study the body for approximately five months.

July 2015, End of primary mission – The end of the study of Ceres will mark the completion of the Dawn primary mission. Depending on the health of the spacecraft, the mission might be extended, with possibly other targets to study, but there are no details available at this time.

Please check out the Dawn Mission’s most excellent and informative website:
http://dawn.jpl.nasa.gov/