The solar system is not in a large, glowing nebula often seen in astronomical images. Instead, we are currently passing through an extremely tenuous region of space known as the Local Interstellar Cloud (LIC). This faint, wispy cloud is a small part of the larger structure of gas and dust that permeates our galaxy.
Identifying Our Local Interstellar Cloud
The Local Interstellar Cloud (LIC) is a small, relatively dense clump of the interstellar medium, often called the “Local Fluff.” It is composed primarily of neutral hydrogen and helium atoms and stretches approximately 30 light-years across.
Its density is low, measuring about 0.3 atoms per cubic centimeter. While significantly denser than the surrounding area, it is far more diffuse than the molecular clouds where stars are born. Scientists detect the LIC indirectly by observing the absorption lines created when starlight passes through its gas.
The solar system is currently moving through this cloud, a journey estimated to have begun within the last 10,000 years. The boundary where the solar wind meets the LIC creates a protective barrier called the heliosphere. Spacecraft data, such as from the Interstellar Boundary Explorer (IBEX), help map this interaction and confirm the cloud’s physical properties.
The Larger Structure Surrounding Our Solar System
The Local Interstellar Cloud resides within a much larger, vast expanse known as the Local Bubble. This immense, super-heated region acts as a massive cavity in the interstellar medium (the sparse material found between star systems). The Local Bubble spans about 1,000 light-years across.
This enormous void was likely created by a series of powerful supernova explosions that occurred over the last 14 million years. These stellar detonations pushed gas and dust outward, carving a low-density cavity. Scientists estimate at least 15 supernovae contributed to the bubble’s formation and expansion.
The shockwaves from these events compressed the surrounding material, which helped trigger the formation of new stars on the bubble’s surface. The material inside the Local Bubble is sparse and hot, with a density of only about 0.05 atoms per cubic centimeter. This hot, tenuous plasma contrasts sharply with the cooler, denser gas of the Local Interstellar Cloud. Our solar system entered this low-density region approximately five million years ago and now travels near its center.
Locating Our Position in the Milky Way Galaxy
The Local Interstellar Cloud and the Local Bubble are situated within the larger structure of the Milky Way Galaxy. Our solar system resides in a minor spiral arm called the Orion Arm, also referred to as the Orion Spur or Local Arm. This spur is a relatively small feature located between the two major spiral arms: the Perseus Arm and the Sagittarius Arm.
The Sun is located roughly 27,000 light-years away from the supermassive black hole at the galaxy’s center. Our position is relatively close to the galactic plane, currently sitting between 16 and 98 light-years above it.
The solar system is in constant motion, orbiting the galactic center at a speed of about 515,000 miles per hour. Due to the sheer scale of the galaxy, one complete orbit takes approximately 230 million years.