Local Interstellar Cloud
Encyclopedia
The Local Interstellar Cloud (or Local Fluff) is the interstellar cloud
roughly 30 light years across through which the Earth's solar system
is currently moving. The Solar System is thought to have entered the Local Interstellar Cloud at some time between 44,000 and 150,000 years ago and is expected to remain within it for another 10,000 to 20,000 years. The cloud has a temperature of about 6000 °C, about the same temperature as the surface of the Sun
. It is very tenuous, with 0.1 atoms per cubic centimeter; approximately one-fifth the density of the galactic interstellar medium
(0.5 atoms/cc), but twice that of the gas in the Local Bubble
(0.05 atoms/cc). The Local Bubble is an area of low-density in the interstellar medium, with the Local Cloud a small, more dense area. In comparison, Earth's atmosphere
at STP
has 2.7 × 1019 molecules per cubic centimeter.
The cloud is flowing outwards from the Scorpius-Centaurus Association
, a stellar association that is a star-forming region.
The cloud formed where the Local Bubble and the Loop I Bubble
met. The Sun is embedded in the Local Fluff, as are a few other nearby star
s including Alpha Centauri
, Altair, Vega
, Fomalhaut
, and Arcturus.
The Local Interstellar Cloud's potential effects on Earth are prevented by the solar wind
and the Sun's magnetic field
. This interaction with the heliosphere
is under study by the Interstellar Boundary Explorer
(IBEX), a NASA
satellite mapping the boundary between the Solar System and interstellar space.
Interstellar cloud
Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it...
roughly 30 light years across through which the Earth's solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
is currently moving. The Solar System is thought to have entered the Local Interstellar Cloud at some time between 44,000 and 150,000 years ago and is expected to remain within it for another 10,000 to 20,000 years. The cloud has a temperature of about 6000 °C, about the same temperature as the surface of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. It is very tenuous, with 0.1 atoms per cubic centimeter; approximately one-fifth the density of the galactic interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
(0.5 atoms/cc), but twice that of the gas in the Local Bubble
Local Bubble
The Local Bubble is a cavity in the interstellar medium of the Orion Arm of the Milky Way. It is at least 300 light years across and has a neutral hydrogen density of about 0.05 atoms per cubic centimetre, or approximately one tenth of the average for the ISM in the Milky Way , and half that for...
(0.05 atoms/cc). The Local Bubble is an area of low-density in the interstellar medium, with the Local Cloud a small, more dense area. In comparison, Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
at STP
Standard conditions for temperature and pressure
Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...
has 2.7 × 1019 molecules per cubic centimeter.
The cloud is flowing outwards from the Scorpius-Centaurus Association
Scorpius-Centaurus Association
The Scorpius-Centaurus Association is the nearestOB Association to the Sun. This stellar association is composed of three subgroups The Scorpius-Centaurus Association (sometimes called Sco-Cen or Sco OB2) is the nearestOB Association to the Sun. This stellar association is composed of three...
, a stellar association that is a star-forming region.
The cloud formed where the Local Bubble and the Loop I Bubble
Loop I Bubble
The Loop I Bubble is a cavity in the interstellar medium of the Orion Arm of the Milky Way. From our Sun's point of view, it is situated towards the Galactic Center of the Milky Way galaxy. Two conspicuous tunnels connect the Local Bubble with the Loop I cavity .The Loop I Bubble is located...
met. The Sun is embedded in the Local Fluff, as are a few other nearby star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s including Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
, Altair, Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
, Fomalhaut
Fomalhaut
Fomalhaut is the brightest star in the constellation Piscis Austrinus and one of the brightest stars in the sky. Fomalhaut can be seen low in the southern sky in the northern hemisphere in fall and early winter evenings. Near latitude 50˚N, it sets around the time Sirius rises, and does not...
, and Arcturus.
The Local Interstellar Cloud's potential effects on Earth are prevented by the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
and the Sun's magnetic field
Stellar magnetic field
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively...
. This interaction with the heliosphere
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
is under study by the Interstellar Boundary Explorer
Interstellar Boundary Explorer
Interstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC...
(IBEX), a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
satellite mapping the boundary between the Solar System and interstellar space.