NASA's Dawn spacecraft on Saturday successfully entered the orbit around the asteroid known as Vesta.
Dawn sent a message to NASA confirming that it entered Vesta's orbit, but it will take a bit longer to determine its exact arrival time. The time of capture depends on Vesta's mass and gravity, which scientists have only been able to estimate thus far.
The larger the asteroid, the stronger its gravitational pull. If Vesta is larger than anticipated, it likely pulled Dawn into its orbit earlier than expected. If it's smaller, it probably took longer. With Dawn now in orbit, NASA scientists can take more accurate measurements of Vesta's gravity and determine a more precise timeline. Last week, NASA estimated that Dawn would enter Vesta's orbit around 1am Eastern time Saturday.
"Today, we celebrate an incredible exploration milestone as a spacecraft enters orbit around an object in the main asteroid belt for the first time," NASA Administrator Charles Bolden said in a statement. "Dawn's study of the asteroid Vesta marks a major scientific accomplishment and also points the way to the future destinations where people will travel in the coming years. President Obama has directed NASA to send astronauts to an asteroid by 2025, and Dawn is gathering crucial data that will inform that mission."
Dawn will study Vesta for one year, gathering observations that NASA said will help scientists understand the earliest chapter of our solar system's history. Dawn will then depart for its second destination, the dwarf planet Ceres, in July 2012.
This milestone has been several years in the making; Dawn departed Earth in 2007 and when it completes its journey, it will become the first spacecraft to orbit two solar system destinations beyond Earth, NASA said.
Dawn has been snapping photos during its approach, the most recent of which was taken about 26,000 miles from Vesta. Images taken by Dawn are twice as sharp as those captured by NASA's Hubble Space Telescope, but surface details about the asteroid are still unknown, something this mission will help clear up. The first "close" shots of Vesta will be captured about 1,700 miles away from the asteroid before moving about 420 miles above it, and then, 120 miles.