by Charles Q. Choi
01 December 2010
Diagram showing the
position of the Oort Cloud.
Southwest Research Institute
Our sun may have a companion that
disturbs comets from the edge of the solar system - a giant planet
with up to four times the mass of Jupiter, researchers
A NASA space telescope launched last year may soon detect such a
stealth companion to our sun, if it
actually exists, in the distant icy realm of the comet-birthing
Oort cloud, which surrounds our
solar system with billions of icy objects.
The potential jumbo Jupiter would likely be a world so frigid it is
difficult to spot, researchers said. It could be found up to 30,000
astronomical units from the sun. One AU is the distance between the
Earth and the sun, about 93 million miles (150 million km).
Most systems with stars like our sun - so-called
class G stars - possess
Only one-third are single-star systems
like our solar system.
Not a nemesis
Scientists have already proposed that a hidden star, which they call
might lurk a light-year or so away from our sun.
They suggest that during its orbit, this
red dwarf or brown dwarf star would regularly enter the Oort cloud,
jostling the orbits of many comets there and causing some to fall
toward Earth. That would provide an explanation for what seems to be
a cycle of mass extinctions here.
Still, other astronomers recently found that if Nemesis did exist,
its orbit could not be nearly as stable as claimed.
Now researchers point to evidence that our sun might have a
different sort of companion.
To avoid confusion with the Nemesis model, astrophysicists John
Matese and Daniel Whitmire at the University of Louisiana
at Lafayette dub their conjectured object "Tyche" - the good sister
of the goddess Nemesis in Greek mythology, and a name proposed by
scientists working on NASA's Wide-Field Infrared Survey Explorer
It is the WISE observatory that, using its all-seeing infrared eye,
stands the best chance of having spotted
Tyche, if this companion to the sun
exists at all, the researchers said.
Matese and Whitmire detailed their research November 17 online
edition of the journal Icarus.
The researchers noted that most comets that fly into the inner solar
system seem to come from the outer region of the Oort cloud. Their
calculations suggest the gravitational influence of a planet one to
four times the mass of Jupiter in this area might be responsible.
Two centuries of observations have indicated an anomaly that
suggests the existence of Tyche, Matese said.
"The probability that it could be
caused by a statistical fluke has remained very small," he
The pull of Tyche might also explain why
dwarf planet Sedna has such an
unusually elongated orbit, the researchers added.
If Tyche existed, it would probably be very cold, roughly minus 100
degrees F (-73 degrees C), they said, which could explain why it has
escaped detection for so long - its coldness means that it would not
radiate any heat scientists could easily spot, and its distance from
any star means it would not reflect much light.
"Most planetary scientists would not
be surprised if the largest undiscovered companion was
Neptune-sized or smaller, but a Jupiter-mass object would be a
surprise," Matese told SPACE.com.
"If the conjecture is indeed true,
the important implications would relate to how it got there -
touching on the early solar environment - and how it might have
affected the subsequent distributions of comets and, to a lesser
extent, the known planets."
really out there?
The fact of Tyche's existence is questionable, since the pattern
seen in the outer Oort cloud is not seen in the inner Oort.
"Conventional wisdom says that the
patterns should tend to correlate, and they don't," Matese said.
If the WISE team was lucky, it caught
evidence for the Tyche solar companion twice before the
space observatory's original mission
ended in October. That could be enough to corroborate the object's
existence within a few months as researchers analyze WISE's data.
But if WISE detected signs of Tyche only once (or not at all),
researchers would have to wait years for other telescopes to confirm
or deny the potential solar companion's existence, Matese said.