1. Pepperdine University
At the Edge
Discovering the characteristics and objects at the edge of our Solar System
Kailey Schaneberg
NASC 109
Dr. John Armstrong
21 July 2014

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At the Edge
What really is out there? This question has haunted astronomers and civilians alike for
centuries, or perhaps since the beginning of civilization. Through increases in the
technological ability and resources, astronomers have been able to chart stars and planets,
calculate masses and temperatures and even make sketches of the layout of our universe. But
what can we actually see? Most astronomical questions derive from a comparison to our
place in the universe. What planet is most like Earth? What is our solar system made of?
Where does our solar system end? What really is out there? This paper will explore the
strange phenomena and prominent theories that surround the edges of our solar system
including a detailed look at the inner and outer Oort cloud and objects floating out along the
edges.
The majority of astronomical revelations, past the idea that we are revolving around
the sun, occurred in the 20th century. The edges of the solar system were not studied in depth
until the discovery and theory of the Oort cloud as the source of long period comets. In 1950,
a Dutch astronomer named Jan Oort proposed that the frozen and icy objects that travel closer
towards the Sun originate from a large body of objects on the outer edge of our solar system.
This swarm of objects is now called the Oort cloud and occupies a space of 5,000 and
100,000 astronomical units (Burdick). This is where astronomers believe the “edge” of our
solar system may lie, if it is defined as where the gravitational attraction from our solar
system’s Sun is too weak and objects begin to be attracted to nearby stars. There are three
competing theories for how the inner Oort cloud might have formed. The first is that a rogue
planet could have been tossed out of the giant planet region and perturbed objects out of the
Kuiper Belt into the inner Oort cloud on its way out. This planet could still be in the distant
solar system today or could have been ejected years ago. Another theory is that a close stellar
encounter could have put objects into the inner Oort cloud region, much like a “wandering

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Jupiter”. A third theory suggests that inner Oort cloud objects are captured extra-solar planets
from other stars that were near our Sun in its birth cluster (Trujillo 2014). Each theory
suggests that the populations in these clouds were gathered after the formation of the Oort
cloud.
There is supposed to be 0.1 to 2 trillion icy bodies in the solar orbit of the Oort cloud,
some of these being comets or beginnings of comets. The most common item to be found in
the Oort cloud is a long-period comet. These comets differ from short term comets that derive
from the Kuiper Belt. The Kuiper belt is a pancake of icy objects that lay just outside the
orbit of Pluto. The Kuiper belt is much smaller and much closer, which makes objects easier
to discern with telescopes and flybys. Short term comets have about 100 year orbits, while
long-term comets can have orbits thousands of years long (Redd). Famous comets such as the
Halley Comet are believed to have originated from the Oort cloud, even though now it has
now become a Kuiper Belt Object, as most long-term comets have done (Fernandez). The
Oort cloud is far enough away from the heat and gravitational pull of the Sun that large icy
bodies are free to form and roam in this Oort cloud until gravitational perturbations pull them
out.
The difference between the inner and outer Oort cloud explain the difference between
objects only effected by our solar system and ones effected by other stars. Past 1500 AU from
the Sun, objects are drastically affected by other forces and therefore their paths are in
constant change throughout time (Mann). A study done by professors from the University of
Washington and Northwestern University performed four simulations of the creation of the
Oort cloud to discover the architecture and the role that the outer planets play in protecting
our inner planets from an onslaught of comets. They discovered that the existence of gas
giants significantly reduced the amount of objects that came within two AU of the sun
(Lewis). The formation of the Oort cloud occurred at the beginning of our solar system, and

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was highly influenced by external stars and galactic tides which give even more evidence to it
being the edge of our solar system. Resting in the Oort cloud is a dangerous place because of
the constant gravitational effects of other objects flying nearby. Objects are often pulled out
of orbit or pulled into another orbit (Burdick). The history behind the Oort cloud is still a
young science and unfortunately is highly theorized, because our telescopes have not
collected clear photographs, due to its extreme remoteness.
The Oort cloud plays an important role in the protection of our solar system, but what
defines its edge? One predominant theory is the bubble at the edge of our solar system. This
bubble was created through solar winds during the creation of our sun. Because our sun is
fairly weak compared to other Galactic giants, the solar winds were fairly calm. If it were not
for interstellar medium, such as gas and dust, the solar wind would travel on forever. When
our solar system was formed, the left over planetesimals began to form planets and also
began to gather at the edges of our sun’s gravitational reach (Kerr). When the solar winds
reached these objects they were stopped, but also formed a wind-blown bubble. This bubble
now rests on the edge of our solar system dividing us from “them” (Frank), see figure 1.
Figure 1: Artist rendition of the Heliosphere and “bubble” from NASA- Caltech

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Other prevailing theories give names to this cosmic bubble, such as the Heliosphere
and the edge of this bubble named the Heliopause. There is also a layer called the
Heliosheath, which is defined as where the solar wind slows to zero and the magnetic field
becomes compressed and begins to fluctuate. Because of this fluctuation, the magnetic
particles should scatter and be more difficult to detect (O’Neill). Once an object passes the
through the “termination shock” then it can reach the Heliosphere which contains the
Heliosheath then lastly the Heliopause (Villard). The Heliopause separates the magnetic field
and plasma associated with the Sun from that of the local interstellar medium. These terms
are new to the astronomical field and are roughly based off theories and mathematics,
although recent measurements have added legitimization to these claims.
Despite all of astronomy’s discoveries, theories and remote measurements, the actual
distances into our universe that we have travelled are very minimal. The human extent of
travel is only just past our moon, but we now finally have substantial travel of a man-made
object. The Voyager 1 was first launched in September 1977 with an initial mission to Saturn
and Jupiter (Elbaz). A fun fact about the Voyager is that it carries musical recordings of
sounds and greetings from our planet in case it encountered extraterrestrial life in its travels
through space (Chapell). That is a direct reflection of the lack of understanding of the
universe and even our solar system at the time of its departure. We now know that
extraterrestrial life, at least to the extent of breathing beings, cannot exist within our solar
system. 30 years later Voyager 1 is more than three times as far as Pluto, and it takes 17
hours for the radio signal to get back to Earth. In 1990 the cameras were turned off to save
battery power because there would be no more planetary encounters as the instruments
travelled deeper into empty space. In 2005 the Voyager left the Termination Shock, where the
supersonic solar wind becomes subsonic, and has since been travelling in the Heliosheath.
The exact moment where the Voyager left the solar system is highly contentious and has been

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a point of confusion for astronomers and interested humans alike. Scientists were waiting for
Voyager to cross over this magnetic edge of our solar system and into the magnetic field of
interstellar space. The main reason behind the confusion is explained in a paper in the
September issue of Astrophysical Journal Letters. Swisdak and his colleagues say the
magnetic fields may blend together, in a layering effect of magnetic fields that would send
contradictory messages to Earth regarding the magnetic readings. When the Voyager crosses
each of these layers it sends out drops in electron fluxes. Figure 2 shows a theorized
schematic based on the observations of the Voyager 1.
Figure 2: Swisdak (2013)
Being that there is no sign post to mark “leaving our Solar System” there has been much
contention over the issue. In September 2013, astronomers finally agreed that leaving our

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solar system is when solar wind dies and an object is outside the effects of these plasma
particles. Interestingly enough, this means that Voyager 1 actually left our Solar System on
August 25, 2012 (Harris). This means that Voyager 1 was the first man-made object to leave
our solar system and Voyager 2 is close behind as it begins to enter the Heliosheath.
It is important to note that while it seems as though Voyager 1 was travelling out in
space alone, there are recent discoveries of two other large objects, the dwarf planet Sedna
and the dwarf planet 2012 VP113 (Trujillo 2003 and 2014). Both of these objects reside in
the inner Oort cloud. The presences of these objects are very important to understanding the
formation of our solar system and how the edge of our solar system reacts. During Trujillo
and Sheppard observations of the sky using a DECam (Dark Energy Camera) they
determined that about 900 objects with orbits like Sedna and 2012 VP113 are out there with
sizes larger than 1000 km, which would mean that the total population of the inner Oort cloud
is bigger than the Kuiper Belt and main asteroid belt. "Some of these inner Oort cloud
objects could rival the size of Mars or Earth. This is because most of the inner Oort cloud
objects are so distant that even very large ones would be too faint to detect with current
technology", says Sheppard (Trujillo 2014). These objects are definitely something
astronomers will spend time mapping for years to come.
The most recent discoveries on the characteristics of the edges of our solar system
have come from a space mission launched in 2008 called IBEX or Interstellar Boundary
Explorer. This satellite orbits Earth and receives data on the workings of the edges of the
Heliosphere. It does not collect data from images or light sources, but rather energy particles,
called energetic neutral atoms. During its five years of orbit, IBEX has gathered information
regarding mapping the boundaries of our solar system and discovering that these boundaries
actually change quite rapidly. Figure 3 shows the discovery of a giant ribbon at the edge of
the solar system, an anomaly that has now been determined to be a reflection where solar

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wind particles heading out into interstellar space are reflected back into the solar system by a
galactic magnetic field. The data collected from the IBEX have contradicted previous
theories that at the edge of the Heliosphere there is a “bow shock” or a shock formed by the
entire Heliosphere pushing through the interstellar material around it. IBEX also discovered
more characteristics of the “tail” of our Heliosphere (Heliotail), and its strange four-leaf
clover like shape (Fox). All of these discoveries are just the beginning of unearthing the
mysteries of our solar system for the IBEX and for astronomers who wonder what really is
out there.
Figure 3: NASA/IBEX (Fox)
Discovering what is truly “out there” takes years of theorizing, mathematical testing
and eventually telescopic or space exploration missions to confirm those hypotheses. The
history of the edges of our Solar System began in 1950 with the simple idea of where long-
period comets derived from and has now began touching the layout of our entire galaxy. The
discoveries of particles, solar wind and other dwarf planets have made the understanding of
the edge of our solar system more complex. In a mere 60 years we have challenged
astronomical thought and received great rewards and will only increase as new technologies
are created and new space craft are launched.

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Works Cited
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