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| Nasa's Dawn probe set for Ceres arrival | Nasa's Dawn probe set for Ceres arrival |
| (35 minutes later) | |
| The US space agency's Dawn probe is set to go into orbit around Ceres, the largest object in the Solar System between Mars and Jupiter. | |
| It has taken the satellite 7.5 years to reach its destination, and it will spend the next 14 months mapping the diminutive world. | It has taken the satellite 7.5 years to reach its destination, and it will spend the next 14 months mapping the diminutive world. |
| Ceres is the first of the dwarf planets to be visited by a spacecraft. | Ceres is the first of the dwarf planets to be visited by a spacecraft. |
| It is expected to retain information about the Solar System's beginnings, four and a half billion years ago. | It is expected to retain information about the Solar System's beginnings, four and a half billion years ago. |
| Dawn is travelling at a relatively slow pace with respect to its quarry and it should just be captured very gently by the gravity of Ceres. | Dawn is travelling at a relatively slow pace with respect to its quarry and it should just be captured very gently by the gravity of Ceres. |
| Unlike on some other space missions, there will be no need to fire a big engine to insert the satellite into orbit. | Unlike on some other space missions, there will be no need to fire a big engine to insert the satellite into orbit. |
| Engineers have timed the moment of capture to be about 12:20 GMT. | Engineers have timed the moment of capture to be about 12:20 GMT. |
| At closest approach, the separation between Dawn and Ceres will be roughly 40,000km. | At closest approach, the separation between Dawn and Ceres will be roughly 40,000km. |
| "That's about 10 times closer than the Moon is to the Earth," explained Robert Mase, the Dawn project manager at Nasa's Jet Propulsion Laboratory (JPL). | "That's about 10 times closer than the Moon is to the Earth," explained Robert Mase, the Dawn project manager at Nasa's Jet Propulsion Laboratory (JPL). |
| "Over the next month, we'll re-shape the orbit and get ready to begin the prime science phase." | "Over the next month, we'll re-shape the orbit and get ready to begin the prime science phase." |
| The intention is to progressively lower the orbit until the probe is just a few hundred km above the surface. | The intention is to progressively lower the orbit until the probe is just a few hundred km above the surface. |
| Similar narrative | Similar narrative |
| The satellite is turning up at Ceres having previously visited asteroid Vesta. | The satellite is turning up at Ceres having previously visited asteroid Vesta. |
| Both objects reside in the belt of rocky debris that circles the Sun beyond Mars. | Both objects reside in the belt of rocky debris that circles the Sun beyond Mars. |
| Of the two, Ceres is the bigger at 950km across; Vesta has a diameter of 525km. | Of the two, Ceres is the bigger at 950km across; Vesta has a diameter of 525km. |
| The pair should tell a similar story, says Dr Carol Raymond, the mission's deputy principal investigator at JPL. | The pair should tell a similar story, says Dr Carol Raymond, the mission's deputy principal investigator at JPL. |
| "Both Ceres and Vesta, we believe, are proto-planets. They were on their way to forming larger planetary embryos and they were the type of object that merged to form the terrestrial planets," she told the BBC's Inside Science programme. | "Both Ceres and Vesta, we believe, are proto-planets. They were on their way to forming larger planetary embryos and they were the type of object that merged to form the terrestrial planets," she told the BBC's Inside Science programme. |
| "But these two stopped before they reached that evolutionary stage, and so they are essentially these intact 'time capsules' from the very beginning of our Solar System; and that's really the motivation for why Dawn is going there to explore them in detail." | "But these two stopped before they reached that evolutionary stage, and so they are essentially these intact 'time capsules' from the very beginning of our Solar System; and that's really the motivation for why Dawn is going there to explore them in detail." |
| Dwarf status | Dwarf status |
| Researchers think Ceres' interior is dominated by a rocky core topped by ice that is then insulated by rocky lag deposits at the surface. | Researchers think Ceres' interior is dominated by a rocky core topped by ice that is then insulated by rocky lag deposits at the surface. |
| A big question the mission hopes to answer is whether there is a liquid ocean of water at depth. Some models suggest there could well be. | A big question the mission hopes to answer is whether there is a liquid ocean of water at depth. Some models suggest there could well be. |
| The evidence will probably be found in Ceres' craters which have a muted look to them. That is, the soft interior of Ceres has undoubtedly had the effect of relaxing the craters' original hard outline. | The evidence will probably be found in Ceres' craters which have a muted look to them. That is, the soft interior of Ceres has undoubtedly had the effect of relaxing the craters' original hard outline. |
| One big talking point has dominated the approach to the object: the origin and nature of two very bright spots seen inside a 92km-wide crater in the Northern Hemisphere. | One big talking point has dominated the approach to the object: the origin and nature of two very bright spots seen inside a 92km-wide crater in the Northern Hemisphere. |
| The speculation is that Ceres has been struck by something, exposing deeply buried ices. | The speculation is that Ceres has been struck by something, exposing deeply buried ices. |
| These will have vaporised on the airless world, perhaps leaving behind highly reflective salts. | These will have vaporised on the airless world, perhaps leaving behind highly reflective salts. |
| Ceres is classed as a dwarf planet in the nomenclature, and Dawn takes the honour of being the first spacecraft to visit such a body. | Ceres is classed as a dwarf planet in the nomenclature, and Dawn takes the honour of being the first spacecraft to visit such a body. |
| The second encounter will occur in a matter of months when Nasa's New Horizons probe makes a close flyby of Pluto. | The second encounter will occur in a matter of months when Nasa's New Horizons probe makes a close flyby of Pluto. |
| The far more distant Pluto was demoted from full planet to dwarf status at an international astronomy meeting in 2006. | The far more distant Pluto was demoted from full planet to dwarf status at an international astronomy meeting in 2006. |
| Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos | Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos |