Spaceflight Insider

NASA gives Dawn mission second extension

Dawn at Ceres

CGI rendition of NASA’s Dawn spacecraft above the dwarf planet Ceres – as seen in images from the mission. NASA/JPL-Caltech

NASA’s Dawn spacecraft, which has been orbiting Ceres since March 2015, has just been given a second mission extension, which will be used to bring the probe into the closest orbit yet around the dwarf planet.

Mission scientists will study Ceres’ surface layer of ice as the dwarf planet approaches its April 2018 perihelion, the closest position to the Sun in its elliptical orbit.

In a challenging maneuver, mission engineers will spiral the probe to an elliptical orbit just 120 miles (200 kilometers) above the surface, a move they are still currently refining.

The closest Dawn has ever been to the dwarf planet’s surface so far is 240 miles (385 kilometers). Once the spacecraft reaches its new low altitude, its visible light cameras will photograph Ceres’ surface geology while its visible and infrared mapping spectrometer will measure the small world’s mineral composition.

In a major goal of the extended mission, Dawn’s gamma ray and neutron spectrometer, which measures the amount and energy level of gamma rays and neutrons, will focus on learning more about the depth of Ceres’ surface ice and the composition of its top surface layer. The extended mission is expected to run through most of 2018.

Observing Ceres as it heads toward perihelion will provide scientists with an opportunity to learn more about its thin, transient atmosphere, which was first detected by the European Space Agency’s (ESA) Herschel Space Observatory before Dawn arrived at Ceres. Significantly, Herschel on three of four occasions detected water in Ceres’ upper atmosphere, known as its exosphere.

As the dwarf planet heads toward the Sun, scientists expect some of its surface ice to sublimate into water vapor and possibly increase the size of its thin atmosphere.

This animation shows dwarf planet Ceres overlaid with the concentration of hydrogen determined from data acquired by the gamma ray and neutron detector (GRaND) instrument aboard NASA’s Dawn spacecraft. The hydrogen is in the upper yard (or meter) of regolith, the loose surface material on Ceres. Animation & Caption Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / PSI

Based on Dawn’s findings, researchers now think that Ceres’ atmosphere is an effect of solar activity rather than of the dwarf planet’s proximity to the Sun. They theorize that energetic particles emitted by the Sun during solar flares and coronal mass ejections hit the ice at or slightly beneath Ceres’ surface, transferring energy to water molecules and causing them to sublimate, creating a thin, temporary atmosphere.

While Dawn observes Ceres up close, scientists will conduct concurrent ground-based observations of the dwarf planet with the goal of combining the findings to obtain a better understanding of its atmospheric and surface dynamics.

The probe, which orbited protoplanet Vesta from 2011 through 2012 before heading for Ceres, will not land or crash onto the small world due to concerns about potentially contaminating it with microbes from Earth. Ceres is thought to have a subsurface ocean that could potentially host microbial life.

After completing its science operations, Dawn will remain in a stable orbit around Ceres even though it will eventually run out of hydrazine fuel and no longer be capable of communicating with Earth



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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