Dawn mission to Ceres extended by NASA
Extended mission will study dynamics of transient atmosphere as Ceres approaches perihelion.

By Laurel Kornfeld | 5 hours ago

NASA has approved a second extension of the Dawn mission to Ceres, which will involve the spacecraft spiraling closer to the dwarf planet in a new elliptical orbit.

In orbit around the dwarf planet since March 2015, Dawn will now come slightly closer than 120 miles (200 km) of its surface. From that position, its cameras will take visible light images of surface geology while its visible and infrared mapping spectrometer will measure Ceres' mineralogical composition.

Maneuvering the spacecraft to this close position is challenging, and mission engineers are currently studying the best ways to accomplish it. Plans for this next phase and its data collection are still being refined.

One particular goal of the extended mission will be to better understand the composition and thickness of Ceres' outer layer of ice, which will be done by studying it with the spacecraft's gamma ray and neutron spectrometer. This instrument measures the number and energy levels of gamma rays and neutrons.

With enough hydrazine fuel to operate through most of 2018, Dawn will be orbiting Ceres as it reaches perihelion, the closest point to the Sun in its orbit, this coming April.

As the dwarf planet comes nearer to the Sun, it may warm up enough for surface ice to sublimate into water vapor, thickening its thin atmosphere.

Discovered by the European Space Agency's (ESA) Herschel Space Observatory before Dawn arrived at Ceres, that atmosphere is transient and believed to be caused by high levels of solar activity rather than by proximity to the Sun.

Subsequent analysis of Dawn's findings along with those of Herschel indicate interaction between energetic particles emitted by the Sun and Ceres' surface ice produces its atmospheric water vapor.

Scientists plan to conduct ground-based observations coinciding with Dawn's studies with the goal of better understanding this phenomenon.

Because Ceres may have a subsurface ocean that could harbor microbial life, NASA will not land or crash Dawn onto its surface when the mission ends, as this could inadvertently contaminate the small planet with microbes from Earth.

Instead, the spacecraft will be left in orbit around Ceres after completing the science for its extended mission, where it will stay even after it runs out of fuel and becomes incapable of further communications with Earth.

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