stretch behind it as it moves; it is always pointing away from the Sun). The tail is a region where the Sun's solar wind slows down and ultimately escapes the heliosphere, slowly evaporating because of charge exchange. The shape of the heliotail (newly found by NASA's Interstellar Boundary Explorer – IBEX), is that of a four-leaf clover. The particles in the tail do not shine, therefore it cannot be seen with conventional optical instruments. IBEX made the first observations of the heliotail by measuring the energy of "energetic neutral atoms", neutral particles created by collisions in the Solar System's boundary zone. The tail has been shown to contain fast and slow particles; the slow particles are on the side and the fast particles are encompassed in the center. The shape of the tail can be linked to the Sun sending out fast solar winds near its poles and slow solar winds near its equator more recently. The clover-shaped tail moves further away from the Sun, which makes the charged particles begin to morph into a new orientation. Cassini and IBEX data challenged the "heliotail" theory in 2009. In July 2013, IBEX results revealed a 4-lobed tail on the Solar System's heliosphere. Outside structures The heliopause is the final known boundary between the heliosphere and the interstellar space that is filled with material, especially plasma, not from the Earth's own star, the Sun, but from other stars. Even so, just outside the heliosphere (i.e. the "solar bubble") there is a transitional region, as detected by Voyager 1. Just as some interstellar pressure was detected as early as 2004, some of the Sun's material seeps into the interstellar medium. The heliosphere is thought to reside in the Local Interstellar Cloud inside the Local Bubble, which is a region in the Orion Arm of the Milky Way Galaxy. Outside the heliosphere, there is a forty-fold increase in plasma density. There is also a radical reduction in the detection of certain types of particles from the Sun, and a large increase in galactic cosmic rays. The flow of the interstellar medium (ISM) into the heliosphere has been measured by at least 11 different spacecraft as of 2013. By 2013, it was suspected that the direction of the flow had changed over time. The flow, coming from Earth's perspective from the constellation Scorpius, has probably changed direction by several degrees since the 1970s. Hydrogen wall