by Shannon Hall
May 28, 2013
of two tidally locked
objects orbiting the Sun from afar.
The system: 2010 WG9
may likely look like this.
What if we could journey to the outer edge of the Solar System -
beyond the familiar rocky planets and the gas giants, past the
orbits of asteroids and comets - one thousand times further still -
to the spherical shell of icy particles that enshrouds the Solar
This shell, more commonly known as
the Oort cloud, is believed to be a
remnant of the early Solar System. Imagine what astronomers could
learn about the early Solar System by sending a probe to the Oort
Unfortunately 1-2 light years is more
than a little beyond our reach. But we’re not entirely out of luck.
2010 WG9 - a trans-Neptunian object - is actually an Oort Cloud
object in disguise. It has been kicked out of its orbit, and is
heading closer towards us so we can get an unprecedented look.
But it gets even better! 2010 WG9 won’t get close to the Sun,
meaning that its icy surface will remain well-preserved.
Dr. David Rabinowitz, lead author
a paper about the ongoing observations of this
object told Universe Today,
“This is one of the Holy Grails of
Planetary Science - to observe an unaltered planetesimal left
over from the time of Solar System formation.”
Now you might be thinking: wait, don’t
comets come from the Oort Cloud?
It’s true; most comets were pulled out
of the Oort cloud by a gravitational disturbance. But observing
comets is extremely difficult, as they are surrounded by bright
clouds of dust and gas. They also come much closer to the Sun,
meaning that their ices evaporate and their original surface is not
So while there is a surprisingly high number of Oort cloud objects
hanging out within the inner solar system, we needed to find one
that is easy to observe and whose surface is well preserved.
2010 WG9 is just the object for the job!
It is not covered by dust or gas, and is believed to have spent most
of its lifetime at distances greater than 1000 AU. In fact, it will
never approach closer than Uranus.
Astronomers at Yale University have observed 2010 WG9 for over two
years, taking images in different filters. Just as coffee filters
allow ground coffee to pass through but will block larger coffee
beans, astronomical filters allow certain wavelengths of light to
pass through, while blocking all others.
Recall that the wavelength of visible light relates to color. The
color red, for example, has a wavelength of approximately 650 nm. An
object that is very red will therefore be brighter in a filter of
this wavelength, as opposed to a filter of, say, 475 nm, or blue.
The use of filters allow astronomers to study specific colors of
Astronomers observed 2010 WG9 with four filters: B, V, R, and I,
also known as blue, visible, red, and infrared wavelengths.
What did they see? Variation - a change
in color over the course of just days.
The likely source is a patchy surface. Imagine looking at the Earth
(pretend there’s no atmosphere) with a blue filter. It would
brighten when an ocean came into view, and dim when that ocean left
the field of view. There would be a variation in color, dependent on
the different elements located on the surface of the planet.
The dwarf planet Pluto has patches of methane ice, which also show
up as color variations on its surface.
Unlike Pluto, 2010 WG9 is small (100 m
in diameter) and cannot hold on to its methane ice. It’s possible
that part of the surface is newly exposed after an impact. According
to Rabinowitz, astronomers are still unsure what the color
Rabinowitz was very keen to explain that 2010 WG9 has an unusually
Most trans-Neptunian objects rotate
every few hours. 2010 WG9 rotates on the order of 11 days! The best
reason for this discrepancy is that it exists in a binary system. If
2010 WG9 is tidally locked to another body - meaning that the spin
of each body is locked to the rate of rotation - then 2010 WG9 will
be slowed down in its rotation.
According to Rabinowitz, the next step will be to observe 2010 WG9
with larger telescopes - perhaps the Hubble Space Telescope - in
order to better measure the color variation. We may even be able to
determine if this object is in a binary system after all, and
observe the secondary object as well.
Any future observations will help us further understand the Oort
“Very little is known about the Oort
cloud - how many objects are in it, what are its dimensions, and
how it formed,” Rabinowitz explained. “By studying the detailed
properties of a newly arrived member of the Oort cloud, we may
learn about its constituents.”
2010 WG9 will likely hint at the origin
of the Solar System in helping us further understand its own origin:
the mysterious Oort cloud.