Artist’s conception of the cold distant Sedna. The sun is a tiny point of light 8 billion miles away from the red planetoid. A hypothesized tiny moon appears nearby.
Our known Solar System can be divided into three parts: the rocky planets like Earth, which are close to the Sun; the gas giant planets, which are further out; and the frozen objects of the Kuiper belt, which lie just beyond Neptune’s orbit. Beyond this, there appears to be an edge to the Solar System where only one object, Sedna, was previously known to exist for its entire orbit. But the newly found 2012 VP113 has an orbit that stays even beyond Sedna, making it the furthest known in the Solar System.
Sedna was discovered beyond the Kuiper Belt edge in 2003, and it was not known if Sedna was unique, as Pluto once was thought to be before the Kuiper Belt was discovered. With the discovery of 2012 VP113 it is now clear Sedna is not unique and is likely the second known member of the hypothesized inner Oort cloud, the likely origin of some comets.
Some of these inner Oort cloud objects could rival the size of Mars or even Earth. This is because many of the inner Oort cloud objects are so distant that even very large ones would be too faint to detect with current technology.
The Oort Cloud is a hypothesized spherical cloud of predominantly icy planetesimals that may lie roughly 50,000 AU, or nearly a light-year, from the Sun.
Exploring the Oort Cloud
There are three competing theories for how the inner Oort cloud might have formed. As more objects continue to be found, it will be easier to narrow down which of these theories is most likely accurate. Here are the three theories.
A rogue planet could have been tossed out of the giant planet region and could have perturbed objects out of the Kuiper Belt to the inner Oort cloud on its way out. This planet could have been ejected or still be in the distant solar system today.
A close stellar encounter could have put objects into the inner Oort cloud region.
Inner Oort cloud objects are actually captured extra-solar planets from other stars that were near our Sun in its birth cluster.
The outer Oort cloud is distinguished from the inner Oort cloud because in the outer Oort cloud, starting around 1500 AU, the gravity from other nearby stars disturbs the orbits of the objects, causing objects in the outer Oort cloud to have orbits that change drastically over time. Many of the comets we see were objects that were perturbed out of the outer Oort cloud. Inner Oort cloud objects are not highly affected by the gravity of other stars and thus have more stable and more primordial orbits.
Beyond the Oort Cloud
As you can see we are still learning about our solar system and no one is 100% sure of where it really ends and interstellar space begins. What is known however is that the Oort cloud is the boundary between confines of our solar system and deep space. Interstellar space, beyond the Oort cloud is where our sun no longer has any gravitational influence.
Artist concept of Voyager 1 and Voyager 2 leaving our solar system.
There is solid evidence Voyager 1 has left the heliosphere and entered interstellar space.
Scientists say the spacecraft became the first man-made object to enter interstellar space on August 25, 2013. It is believed that Voyager 1 is now beginning is exploration of the deeper Milky Way. Not bad for a spacecraft launched back in 1977!