Dawn’s going down. The spacecraft, which has been orbiting Ceres since March 2015, will maneuver to its final and lowest orbit ever to take incredibly detailed photos and compositional measurements of the dwarf planet. As you read this, NASA engineers are firing Dawn’s ion engine to lower the probe into a snug loop less than 30 miles (50 km) above Ceres’ surface. That’s 10 times closer than we’ve ever put an eye on the inner solar system’s only dwarf planet and on par with NASA’s Lunar Reconnaissance Orbiter, which can photograph objects the size of a kitchen table from 22 miles (35 km) up, the lowest point in its orbit.
Dawn will collect gamma ray, neutron and infrared spectra, which will help scientists gain a more complete understanding of the minerals that compose Ceres’ crust. Astronomers use a spectrograph to spread the light reflecting from the dwarf planet into a sort of “bar code rainbow.” Elements in the minerals absorb light in narrow slices of that rainbow which show up as dark lines (missing light) along its length. Particulars arrangements of those lines betray the presence of particular minerals.
Dawn’s operations team has worked for months to plot the new course for this second extended mission, mapping out more than 45,000 routes before coming up with one that will allow for the best science observations. The mission has been underway for more than 10 years. Launched in 2007, the probe visited Vesta from July 2011 to September 2012, departed and then entered Ceres’ orbit in March 2015. Vesta and Ceres are the two largest bodies in the main asteroid belt located between Mars and Jupiter.
“The team is eagerly awaiting the detailed composition and high-resolution imaging from the new, up-close examination,” said Dawn’s Principal Investigator Carol Raymond of NASA’s Jet Propulsion Laboratory. “These new high-resolution data allow us to test theories formulated from the previous data sets and discover new features of this fascinating dwarf planet.”
Ceres and Pluto along with Haumea, Makemake and Eris, which orbit the sun beyond Pluto, are the five currently known dwarf planets. The last three orbit between 6.5 and 10 billion miles away or about twice to three times the distance to Pluto. The time it takes them to go around the sun ranges from 283 years for Haumea to 561 for Eris. The farther you are from the sun, the slower you go!