Dawn Begins Approach To Dwarf Planet Ceres

Dawn approaches the dwarf planet Ceres as seen in this artist illustration. The spacecraft will arrive at the asteroid on March 6. Credit: NASA/JPL-Caltech

NASA’s Dawn spacecraft officially began its approach to the dwarf planet Ceres this week. Ceres was the first asteroid discovered and at 590 miles (950 km) across, the largest of the Main Belt asteroids that cycle between the orbits of Mars and Jupiter. No probe’s ever visited Ceres, and our best photos taken by the Hubble Space Telescope show only a mottled, blurry disk.

Dawn is currently 400,000 miles (640,000 km) from Ceres, approaching it at around 450 miles per hour (725 km/hr). It’s the only spacecraft ever to orbit two solar system targets. You probably recall its first mission (2011-2012) to the asteroid Vesta, also in the Main Belt. There we learned that Vesta mimicks a planet in miniature, having “differentiated” through radioactive heating into core, mantle and crust.

Millions of miles and more than a year separated that success from its next eagerly awaited target now just 9 weeks away.

Dual targets of Dawn – the impact-gouged asteroid Vesta (left) and still-mysterious Ceres. Credit: NASA/JPL-Caltech

“Ceres is almost a complete mystery to us,” said Christopher Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles. “Ceres, unlike Vesta, has no meteorites linked to it to help reveal its secrets. All we can predict with confidence is that we will be surprised.”

Yes, meteorites. We have tons of samples of Vesta in pieces fallen to Earth as eucrite, Howardite and diogenite meteorites, a subset of a larger clan of meteorites called achondrites. Achondrites (Ay-KON-drites) are rocks that have been melted and processed on asteroids and resemble volcanic rocks on Earth.

The two planetary bodies are thought to have gone down different evolutionary roads. Ceres likely formed later than Vesta and possesses a cooler interior. The fact that Vesta appears to have very little water tells us it formed earlier, when radioactive material was more abundant. Heat from radioactivity would have cooked out the water. Ceres, in contrast, has a thick ice mantle and may even have an ocean beneath its icy crust.

Great explainer on Dawn’s ion propulsion engine

NASA employed ion propulsion to travel the many millions of miles of the dual mission cheaply and efficiently. Instead of conventional rocket fuel, an electric charge is applied to atoms of xenon, a gas used in photographic flashes (strobes). Next, an electrically-charged plate at the back of the engine accelerates the electrified atoms out of the thruster. As they leave, they push back against the engine, nudging the spacecraft forward.

Ion engines thrust with a light touch that begins slowly but adds up soon enough in the frictionless environment of space. Check the video for more details.

Later next month, we’ll start to receive better images of Ceres than Hubble’s been able to provide. We’ll update the mission’s progress at that time.

12 Responses

  1. concernedperson

    Are we going to have no gravity for 5 min on Jan 4th at 9:47am??? People are saying it will cause alot of problems. Are we to worry??? Has this ever happened before?

    1. astrobob

      Hi Concerned,
      Not to worry. This won’t and can’t happen. Just one of those crazy made-up things going around the Internet.

    1. astrobob

      100% genuine fakeness. Trust me on this. Completely made up. Won’t happen. No matter how many sites repeat that it’s going to happen, it’s impossible. Planetary alignments cannot make you float off the ground. You can’t even feel one happening. The person quoted, Patrick Moore, died two years ago. Also, Pluto is nowhere near Jupiter in the sky.

        1. astrobob

          Critical thinking should be the number one skill a high school grad leaves with nowadays. There’s just so much trash to sort through online and we need better mental filters.

          1. caralex

            Very true. Critical thinking is badly neglected. Ignorance, and being proud of being ignorant, are, sadly, too much in favour.

  2. Ben

    Gee, I heard it WAS going to happen but your date is all wrong.
    It WILL happen on Feb 30, 2015 at 12:34 AM by Feb 31st at the latest. πŸ˜‰ This will also cause Facebook. twitter and smart phones to not work then too. πŸ˜‰

  3. Luke

    Yesterday January 7 around 9:30 at night AZ time we saw this bright green light in the sky for couple seconds. What was it? Never seen anything like that!

    1. astrobob

      Hi Luke,
      No, that wouldn’t have been the comet. It sounds like you saw a fireball – a bright meteor.

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