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Our dwarf planet neighbour sent a meteorite message before disappearing
This week–
From a lost dwarf to Antarctica DAVID SHIGA, HOUSTON
THE origin of two unusual meteorites has been puzzling researchers ever since they were found in Antarctica in 2006. Now they think they have found the culprit – a dwarf planet in our solar system that has apparently fled the scene. The chemical composition of the rocky fragments – named GRA 06128 and GRA 06129 after the Graves Nunataks area they struck – differs from that of the majority of meteorites, ruling out a shattered asteroid as their source. Nor do they appear to be shards of
14 | NewScientist | 22 March 2008
the moon, Mars, Venus, Mercury, or any other known planet. The clue that has solved the problem comes from their high concentrations of a mineral called feldspar, which makes up 75 to 90 per cent of their volume. Feldspar is a relatively lightweight material that crystallises from magma. On large bodies with a gravitational pull, lightweight feldspar floats to the surface, forming a concentrated layer. Small asteroids with weak gravity do not sort minerals into layers, so the meteorites must have come from something much bigger, the researchers concluded. Measurements of the feldspar
by Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, indicate that this body was probably smaller than the moon, with a diameter of 3500 kilometres, but larger than Vesta, the thirdlargest asteroid in our solar system at 578 kilometres across. So it seems the fragments came from a dwarf planet in our solar system that no longer exists. “We have here a sample of a strange, new world, a sample we’ve never seen before,” says Treiman, who presented the findings at the Lunar and Planetary Science Conference in Houston last week. What happened to this body? Radioactive dating shows the fragments formed about 4.5 billion
“The clue to the source of the fragments comes from their high concentrations of feldspar: 75 to 90 per cent of their volume”
years ago, when Earth and the other planets were coalescing and many dwarf planet-sized objects were flying around the solar system. Some of these would have been flung into interstellar space, while others would have merged to create planets. However, there may still be fragments floating around today that could be spotted by looking for a signature spectrum of the sunlight they reflect, says Treiman. Three other groups who studied the fragments also presented their work at the conference. All agree that the body the fragments originated from was big enough to separate into mineral layers. One other group, led by Tomoko Arai of the National Institute of Polar Research in Tokyo, Japan, says that features such as the abundance of sodium in the fragments hint that the body may have contained a lot of water. G
www.newscientist.com
From a lost dwarf to Antarctica DAVID SHIGA, HOUSTON
THE origin of two unusual meteorites has been puzzling researchers ever since they were found in Antarctica in 2006. Now they think they have found the culprit – a dwarf planet in our solar system that has apparently fled the scene. The chemical composition of the rocky fragments – named GRA 06128 and GRA 06129 after the Graves Nunataks area they struck – differs from that of the majority of meteorites, ruling out a shattered asteroid as their source. Nor do they appear to be shards of
14 | NewScientist | 22 March 2008
the moon, Mars, Venus, Mercury, or any other known planet. The clue that has solved the problem comes from their high concentrations of a mineral called feldspar, which makes up 75 to 90 per cent of their volume. Feldspar is a relatively lightweight material that crystallises from magma. On large bodies with a gravitational pull, lightweight feldspar floats to the surface, forming a concentrated layer. Small asteroids with weak gravity do not sort minerals into layers, so the meteorites must have come from something much bigger, the researchers concluded. Measurements of the feldspar
by Allan Treiman of the Lunar and Planetary Institute in Houston, Texas, indicate that this body was probably smaller than the moon, with a diameter of 3500 kilometres, but larger than Vesta, the thirdlargest asteroid in our solar system at 578 kilometres across. So it seems the fragments came from a dwarf planet in our solar system that no longer exists. “We have here a sample of a strange, new world, a sample we’ve never seen before,” says Treiman, who presented the findings at the Lunar and Planetary Science Conference in Houston last week. What happened to this body? Radioactive dating shows the fragments formed about 4.5 billion
“The clue to the source of the fragments comes from their high concentrations of feldspar: 75 to 90 per cent of their volume”
years ago, when Earth and the other planets were coalescing and many dwarf planet-sized objects were flying around the solar system. Some of these would have been flung into interstellar space, while others would have merged to create planets. However, there may still be fragments floating around today that could be spotted by looking for a signature spectrum of the sunlight they reflect, says Treiman. Three other groups who studied the fragments also presented their work at the conference. All agree that the body the fragments originated from was big enough to separate into mineral layers. One other group, led by Tomoko Arai of the National Institute of Polar Research in Tokyo, Japan, says that features such as the abundance of sodium in the fragments hint that the body may have contained a lot of water. G
www.newscientist.com