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Nemesis: Does the Sun Have a 'Companion'?
By Robert Roy Britt
Senior Science Writer
posted: 07:00 am ET
03 April 2001
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The galactic plane, Planet X and black holes
Other ideas have been put forth to explain the alleged periodicity in mass extinctions.
The most widely accepted is the suggestion that the solar system, as it revolves around the center of the Milky Way, bobs up and down through the plane of the galaxy. This plane is full of gas and dust that never became stars, which collectively has a certain amount of gravity that some expect might dislodge comets from the Oort Cloud.
There are doubts, however, about the amount of mass in the galactic plane and whether or not the timing coincides with the periodicity of mass extinctions.
Others have suggested a dim failed star known as a brown dwarf might be lurking in the distant fringes of the solar system. Muller called the increasing rate of discovery of brown dwarfs, including one that is just 13 light-years away, "extremely discouraging." For if Nemesis were a brown dwarf, it would be harder to find.
Yet another enduring idea is that another large planet lurks beyond Pluto. This so-called Planet X would be a gas ball up to five times the size of Earth, according to some predictions. Even the possibility of a black hole has been raised. Few researchers support these two ideas.
Evidence from the Moon
The best evidence for periodic impacts on Earth may ultimately come from the Moon. While the Earth's crust has been stretched, squashed and folded violently its whole life, the Moon is relatively static, preserving a far more accessible geologic record.
A year ago Muller, Berkeley geologist Paul Renne and then-graduate student Timothy Culler found the Moon underwent a flurry of impacts between 400 million and 600 million years ago. The active period (which may still be going on) presumably affected Earth as well since both bodies are in roughly the same spot in the solar system.
Muller says the sudden increase offers indirect evidence for a sudden change in the orbit of Nemesis, which might have been caused by a passing star.
But the study did not turn up evidence for the 26 million-year periodicity, as hoped. Muller says there was not enough data. The study involved 155 microscopic glass beads formed in the intense heat of lunar impacts and later brought to Earth, in a single gram of soil, by the Apollo 14 crew.
But given that there are "several hundred pounds (kilograms) of [lunar] dust and rocks that have not been analyzed," Muller plans another more detailed study.
Whether or not he finds evidence for Nemesis in Moon dust, it's clear that Muller won't stop looking. He is a man of enduring confidence. But he is also a remarkably conservative scientist, quick as anyone to point out that there is no proof until there is proof.
"I'm realistic," he said. "I may be wrong."
And he recognizes that if the Death Star is not found, the whole idea could become a real Nemesis for the big thinker who dreamed it up.
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