Thursday, 18 September 2014

Dawn over dwarf planet

Dawn is a space probe that was launched in 2007 and has already visited protoplanet Vesta, the second-largest body in the asteroid belt. Now it is heading for Ceres - a dwarf planet that constitutes one third of the asteroid belt mass. Believe it or not, but since its discovery in 1801 we couldn’t get a better look at this body than this photo by Hubble Space Telescope you see on the left.

Initially regarded as planet, then demoted to asteroid, Ceres was reclassified as a dwarf planet along with Pluto and few other large (but not large enough) bodies in the solar system. Now, for the first time in history, we will see it in glorious detail.

Christopher T. Russell is Dawn’s Principal Investigator, meaning when NASA has a complaint or praise for the mission, he’s the man they call. Before leading Dawn mission he led an experiment that mapped Earth’s magnetosphere with Polar satellite. He is also the head of the Space Physics Center at UCLA, he has an asteroid named after him,

...and he was kind enough to find time to answer my questions about Dawn Mission.

How will meeting with Ceres be different from rendezvous with Vesta?

From technical standpoint, the mission will not differ that much. The spacecraft trajectory, the instruments and the measurement philosophy will be very similar. When we arrive at Ceres, we will enter a “high altitude survey orbit” and map the entire surface at low resolution and obtain gravity and navigation data necessary for further stages of the mission. We acquire the full coverage of the surface using the visible light and infrared mapping spectrometer to analyse the mineral composition of Ceres’ surface. Then we go closer but but still maintain relatively high altitudes (“high altitude mapping orbit”) and from that vantage point we map the surface in more detail and take data for stereo/altimetric purposes. Finally we enter a “low altitude mapping orbit” to take high resolution gravity data and obtain gamma ray and neutron data on elemental composition.

But while the approach is the same, we expect Ceres to be totally different than Vesta. It has no family member asteroids and it has no meteorites to study, so we know next to nothing.

[Side comment: Let me jump in for a second here. Asteroid family is a group of asteroids that have similar orbital parameters and share origin, meaning they may be parts of a larger body shattered in a collision. Some of them may fall on Earth and give us a chance to learn about the whole family. For example HED meteorites enabled us to learn about Vesta before Dawn reached it.]

Did any unexpected data about Vesta or Ceres emerge after Dawn was launched? We found new moons around Pluto while New Horizons was on its way, anything similar in regards of Vesta and Ceres?

We know of no moons at either Vesta or Ceres. We were learning from meteorites about Vesta all the time before we arrived, but the new knowledge was evolutionary and not revolutionary. Now at Ceres, Hershel [Space Observatory] has made some observations of water in Ceres atmosphere. Still we already had strong indications from earlier observations and from Ceres density that it was a wet body.

Once the primary objectives are met, what's in store for Dawn?

Dawn is expected to stay in orbit around Ceres.

Thank you for your time.

Dawn is now less than 0.03 astronomical units from Ceres. You can track its position on this website. Dawn is expected to reach Ceres in March/April 2015.

Handful of useful links:

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