September 27, 2007 – those were the days: The space probe Dawn starts full tank towards the asteroid belt, roughly in the middle of the solar system. Her journey took Dawn to Vesta, the second largest asteroid out there, between the planets of Mars and Jupiter. Then it went on to the dwarf planet Ceres. Over the past three and a half years, Dawn has been orbiting this largest chunk of the asteroid belt, in different orbits, sometimes closer, farther away. She has proven among other salt and ice deposits. Geologists still can not rule out that there are still liquid waters in deeper layers today.
"Our plan for Dawn has always been to transfer the probe to a cemetery sorbite on which it will orbit Ceres for a long time, so we are sure it will not come into contact with any liquid water."
Keri Bean is an engineer for the Dawn mission at the Jet Propulsion Laboratory (JPL) in Pasadena, California. International planets protection guidelines dictate that space probes that are not completely free of germs should not land or strike on celestial bodies on which it could give life. Dawn was not sterile enough from the start, and she did not expect to fall on Ceres at the end of her mission, for example.
Requirements for life available
"We do not want to get Dawn too close to Ceres, the dwarf planet probably has water, organic matter, and through the sun a constant supply of energy, three essential conditions that could lead to the creation of life, this untouched world must not contaminate a spacecraft from Earth that is itself contaminated with terrestrial organisms. "
In order for the probe to reach its cemetery orbit, the engineers had switched on and off the probe's ion drive several times during the summer. So she reached the end of June their final orbit to Ceres. At its lowest point, it comes close to the dwarf planet up to 35 kilometers, at its farthest it is up to 40,000 kilometers from him.
The probe is exactly where NASA would have wanted it, says Marc Rayman, Dawn's mission director, also at the JPL. After the electric engines had been shut down, since June Dawn had only left the hydrazine with him to stabilize the situation.
"When the supply of hydrazine is exhausted, the probe is no longer able to maintain its orientation in the room, so it can no longer align its solar sails with the sun, which means that sunlight will no longer be converted to electricity As their antennas continue to Earth longer, their cameras and sensors continue to align with Ceres. "
Radio silence since Wednesday
When exactly the hydrazine supply would be used up, was difficult to calculate. After all, no one on the ground could even look up how much fuel is left. Since August, NASA had counted daily on the death of their probe. But she kept sending data to Earth all through September, and throughout October – almost the whole of October, until Wednesday. There was suddenly no radio – just like on Thursday. None of the antennas on NASA's global deep space network yet received data from Dawn – not in California, not in Australia, not in Spain. Dawn does not answer. The hydrazine is consumed; Aligning the radio antennas to earth no longer possible. So this mission is now history, according to Marc Rayman. And on her cemetery orbit the probe was in good hands:
"This orbit will be stable for a very long time, we were aiming for 50 years, but we have simulated that Dawn Ceres will continue to orbit for 10,000 years."
With a crash of Dawn and thus a contamination of the dwarf planet by terrestrial bacteria must therefore not be expected for the time being. There are already plans for a follow-up mission, which should then even sell a lander on the dwarf planet.