The Latest on Planet X
A mystery revolves around the sun - Researchers suggest that huge unseen
object orbits on fringe of solar system
SPECULATION ABOUT the existence of unseen celestial companions dates
back far before the discovery of Pluto in 1929 - and even figures in
more recent fringe phenomena such as the 1997 "Heaven's Gate" tragedy
and talk of a new "Planet X." This latest hypothesis, however, is aimed
at answering nagging scientific questions about how particular types
of comets make their way into the inner solar system.
Some comets, like Halley's Comet, follow relatively short-period orbits
- circling the sun in less than two hundred years. These comets are
thought to originate in the Kuiper Belt, a disk of cosmic debris that
lies beyond Neptune's orbit.
The best way to think of the distances involved is in terms of Astronomical
Units. One AU is the distance from Earth to the sun (93 million miles
or 149.6 million kilometers). Pluto, the most distant of the planets,
is at 39 AU. The Kuiper Belt extends from 30 AU to perhaps 1,000 AU.
Even further out is the Oort Cloud, a spherical haze of comets surrounding
the solar system at distances between 10,000 AU and more than 50,000
AU. That's where long-period comets such as Hale-Bopp are thought to
come from. For some time, astronomers have noticed that the directional
patterns of these comets are not completely random. And after years
of study, some researchers are reporting that the patterns hint at something
big out there perturbing the cometary paths.
What could it be?
No telescope has yet detected this object. But on the basis of its
gravitational effect, John B. Murray, a planetary scientist at Britain's
Open University, speculates that the object could be a planet larger
than Jupiter, the biggest of the solar system's known planets. Murray
puts the object's orbit at 32,000 AU, or 2.98 trillion miles from the
sun. His proposal appears in the Oct. 11 issue of the Monthly Notices
of the Royal Astronomical Society.
Meanwhile, researchers at the University of Louisiana at Lafayette say
the object could be a planet or brown dwarf - that is, a dark, failed
star - roughly three times the size of Jupiter and orbiting at 25,000
AU. The researchers, led by physicist John Matese, say their paper is
to be published by the journal Icarus.
Both studies acknowledge that other factors could influence the pattern
seen in long-period comets: for example, the Milky Way's gravitational
tidal effects. But the Louisiana researchers say the cometary patterns
are best explained by the existence of "a perturber, acting in concert
with the galactic tide."
Matese said the proposed object should make one orbit around the sun
every 4 million to 5 million years. Murray said the object he had in
mind would make one orbit every 6 million years, circling the sun in
a direction counter to that followed by the nine traditional planets.
The two researchers said they were familiar with each other's work but
hadn't taken a close look at each other's studies. They acknowledged
that their estimates for the mass and orbit of a mysterious object were
similar, but couldn't say whether they were talking about the same object.
How could such a massive object exist so far from the sun? The researchers
say a planet or dark star could have coalesced during the formation
of the solar system billions of years ago, but more probably would be
a passing celestial body that was captured by the sun's subtle gravitational
Another question: Why hasn't such an object been seen? Murray says that
even a Jupiter-scale planet could not be observed at the immense distances
involved. Matese and his colleagues say that their hypothetical brown
dwarf wouldn't have been detected even by the Infrared Astronomical
Satellite, which surveyed the heavens in 1983 - but that the yet-to-be-launched
Space Infrared Telescope Facility just might be able to pick it up.
All this may sound like science fiction, but an expert in the field
notes that the hypothesis has been a subject of serious speculation
"We've all wondered whether there was something out there," said Brian
Marsden, who heads the International Astronomical Union's Central Bureau
for Astronomical Telegrams as well as the Minor Planet Center at the
Smithsonian Astrophysical Observatory.
However, Marsden also expressed some skepticism about the evidence behind
the latest research.
"I'm not convinced it is not due to chance," he told MSNBC in an e-mail
message. "In any case, the data may not be as good as one would like."
If the research holds up, it could open the door for renewed speculation
on even spookier questions: Some theorists have proposed that the gravitational
effect of a massive unseen object in a distant orbit - nicknamed "Nemesis"
or the "Death Star" - could set off periodic cometary storms, which
would increase the chances of a catastrophic impact with Earth. Indeed,
physicist Daniel Whitmire, a colleague of Matese's who is a co-author
of the new research, laid out just such a scenario in 1985 to explain
mass extinctions on Earth, such as the demise of the dinosaurs.
Matese also speculated back then about such an effect, but he emphasized
that the newly detected object didn't fit the doomsday profile.
"This object is not a Nemesis," he told MSNBC. "It does not create comet
He said his proposed object appeared to have an influence on about 25
percent of the long-period comets coming in from the Oort Cloud.
Matese noted that theories proposing a correlation between extinctions
on Earth and celestial orbits had fallen out of scientific favor in
recent years. But he said there could be a "much more gentle" effect
that links periodic changes in cratering to the solar system's oscillating
motion through the galactic plane.
As the solar system moves around the Milky Way's center, it bobs slowly
up and down through the galactic disk, Matese explained. The gravitational
effects could cause changes in the number of comets sent into the inner
solar system, he said.
"We don't know the precise period of that motion" through the plane
of the galaxy, he said. "If we discover that it's closer to a 35-million-year
period, then a case can be made that it causes periodic changes in cratering."
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