Pepperdine University

At the EdgeDiscovering 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

Burdick, Autumn. "Kuiper Belt & Oort Cloud: Read More." Solar System Exploration. NASA, 17 Oct. 2013. Web. 18 July 2014. <http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong>.

Chappell, Bill. "Voyager 1 Speeds Toward The Brink Of Interstellar Space."NPR. NPR, 26 Dec. 2011. Web. 21 July 2014. <http://www.npr.org/blogs/thetwo-way/2011/12/26/143676838/voyager-1-speeds-toward-the-brink-of-interstellar-space>.

Elbaz, J., and R. L. McNutt, Jr. "Legends to This Figure: A Schematic of the Heliosphere and Its Interaction with the Very Local Interstellar Medium." Space Science Reviews 81.1-2 (1997): 3. Springer Link. Web. 20 July 2014. <http://download.springer.com/static/pdf/47/art%253A10.1023%252FA%253A1005035320913.pdf?auth66=1406052968_2059189daa4d83d60fc577d38ae2c130&ext=.pdf>

Fernandez, Julio A. "Long-Period Comets and the Oort Cloud." Earth, Moon, Planets 89.1-4 (2000): 325-43. Springer Link. Web. 20 July 2014. <http://link.springer.com/article/10.1023%2FA%3A1021571108658>.

Fox, Karen C. "Five Years of Great Discoveries for NASA's IBEX." NASA. NASA, 30 Oct. 2013. Web. 21 July 2013. <http://www.nasa.gov/content/goddard/five-years-of-great-discoveries-for-nasas-ibex/#.U81XuPldWSo>.

Frank, Adam. "The Bubble At The Edge Of The Solar System." NPR. NPR, 17 Sept. 2013. Web. 21 July 2014. <http://www.npr.org/blogs/13.7/2013/09/17/223129177/the-bubble-at-the-edge-of-the-solar-system>.

Harris, Richard. "See Ya, Voyager: Probe Has Finally Entered Interstellar Space." NPR. NPR, 12 Sept. 2013. Web. 21 July 2014. <http://www.npr.org/2013/09/12/221732909/see-ya-voyager-probe-has-finally-entered-interstellar-space>.

Kerr, Richard A. "Getting in touch with the edge of the solar system." Science 260.5114 (1993): 1591. Opposing Viewpoints in Context. Web. 19 July 2014.

Lewis, Alexia R., Thomas Quinn, and Nathan A. Kaib. "The Influence Of Outer Solar System Architecture On The Structure And Evolution Of The Oort Cloud." The Astronomical Journal 146.1 (2013): 16. No Records. Web. 20 July 2014. <http://arxiv.org/pdf/1305.5253v1.pdf>.

Mann, William. "Exploring the Edge of Our Solar System." West Chester Technological Blog. N.p., 28 Mar. 2014. Web. 19 July 2014. <http://wctechblog.com/?p=1227>.

O'Neill, Ian. "Voyager 1 Detects Weirdness at Solar System Edge : DNews." DNews. Discovery Communications, 31 Oct. 2012. Web. 21 July 2014. <http://news.discovery.com/space/voyager-1-detects-wierdness-at-solar-system-edge-121030.htm>.

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Redd, Nola T. "Oort Cloud: The Outer Solar System's Icy Shell." Space.com. N.p., 02 July 2012. Web. 20 July 2014. <http://www.space.com/16401-oort-cloud-the-outer-solar-system-s-icy-shell.html>.

Swisdak, M., J. F. Drake, and M. Opher. "A Porous, Layered Heliopause." The Astrophysical Journal 774.1 (2013): L8. IOP Science. Web. 21 July 2014. <http://iopscience.iop.org/2041-8205/774/1/L8/>.

Trujillo, Chadwick A. "Discovering the edge of the solar system; recent discoveries suggest that planets larger than Pluto may exist in the outer reaches of our solar system." American Scientist 91.5 (2003): 424+. Biography in Context. Web. 19 July 2014.

Trujillo, Chadwick A., and Scott S. Sheppard. "A Sedna-like Body with a Perihelion of 80 Astronomical Units." Nature 507.7493 (2014): 471-74. Nature.com. Web. 20 July 2014. <http://www.nature.com/nature/journal/v507/n7493/full/nature13156.html>.

Villard, Ray. "Where's the Edge of the Solar System? It's Complicated... : DNews." DNews. Discovery Communications, 25 Mar. 2013. Web. 21 July 2014. <http://news.discovery.com/space/voyager-marathon-puts-scientists-on-edge-130325.htm>.