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What is IBEX?

IBEX is a NASA-funded satellite, a Small Explorer mission to map the boundary of the Solar System. The acronym IBEX stands for “Interstellar Boundary Explorer”.

The spacecraft is the size of a bus tire. It orbits the Earth and collects particles called “energetic neutral atoms” (ENAs), particles with no charge that move very fast. The boundary is created by the interaction between particles from the Sun that are streaming outward, called the “solar wind”, and material between the stars, called the “interstellar medium”.

Outer space is not empty space. The interstellar medium (ISM) is the name for the stuff that is in space between stars in our Milky Way Galaxy. This stuff is mostly made of clouds of hydrogen and helium, though there are heavier elements like carbon, and one percent of the ISM is in the form of dust.

The solar wind streams out into space and carves out a protective bubble, called the “heliosphere”, in the ISM around our Solar System. IBEX maps the solar wind particles that interact with interstellar medium particles. The mass, location, and energy of the ENAs provide information about the Solar System’s boundary, allowing scientists to map it for the first time.

What came prior to IBEX?

In the late 1970s and 1980s, the Voyager spacecraft expanded our knowledge of the outer Solar System. Voyager 1 and 2 both explored the planets Jupiter and Saturn, and Voyager 2 went on to take advantage of a good arrangement of orbits to explore Uranus and Neptune, the only spacecraft to ever have done so. After their planetary observations, both spacecraft continued outward in different directions. The Voyagers were only supposed to last a few years, but they have continued to operate for over 30 years, well past their designed lifetime. Both Voyagers are located around 100 times the distance between the Earth and the Sun, which is the distance of the region which IBEX maps. The Voyagers have been able to directly measure the area where the solar wind meets the interstellar medium. This data will be combined with IBEX’s data, allowing scientists to create a more complete model of the boundary of our solar system.

What will we learn from IBEX?

By analyzing the heliosphere map created from IBEX data, scientists can determine what the interaction of the solar wind and the interstellar medium is like in all areas of the heliosphere bubble around the Solar System. For example, scientists are trying to find out if there are some areas where the interstellar medium stops the solar wind from flowing outward more quickly (like slamming on the brakes) than other places (where a slow gradual stop may occur). Also, scientists are trying to determine the overall shape of the bubble, which may be affected by differences in density and magnetic fields in the interstellar medium.

Why is IBEX’s mission important?

The heliosphere is a layer that protects our solar system from incoming cosmic rays, energetic particles that come from outside the Earth. Cosmic rays are often made when a star explodes; others come from the Sun or from as far away as other galaxies. If cosmic rays impact something, they can do damage to atoms and molecules. The heliosphere protects our Solar System from some of these dangerous particles. If the Solar System did not have this boundary, then there would be around 4 times more high-energy cosmic rays that would enter our solar system.

Life on Earth benefits from two other layers that protect us from cosmic rays – our planet’s magnetic field, or “magnetosphere”, and its atmosphere. If there were a dramatic increase in the number of cosmic rays entering the Solar System, such as from a nearby supernova, more cosmic rays may then reach the Earth’s surface. Damage to the Earth’s ozone layer could occur, and cosmic rays could cause damage and mutation to DNA. Mapping the current state of the heliosphere will help scientists to determine what this important protective boundary is like. Additionally, when mankind travels to the Moon again or to other locations in our Solar System, astronauts would be outside of the Earth’s atmosphere and magnetosphere, so knowing more about the protective abilities of the heliosphere will help us plan for future long-term space travel that is safer for humans.

How does IBEX get into space? Where does IBEX orbit?

IBEX begins its ride to space during a launch from Kwajalein Island, Marshall Islands in the middle of the Pacific Ocean. An L-1011 airplane takes a Pegasus rocket to a high altitude. Then, the Pegasus fires its own rockets to propel it, and the IBEX spacecraft, into space. This is an inexpensive launch option, especially for smaller spacecraft. The satellite has its own small rocket engine that will allow it to climb into an orbit that takes it 5/6 of the distance to the Moon, or around 200,000 miles (325,000 km) away. This orbit is very high, which allows the satellite to spend much of its time outside of the Earth’s magnetosphere, which can interfere with observations. Even though this orbit is high, it is still far from the Solar System boundary that it is measuring. The distance to the edge of the heliosphere is around 9 billion miles (14 billion km) from the Earth, or about 100 times the distance between the Earth and the Sun. How does IBEX collect data?

IBEX uses two sensors to collect Energetic Neutral Atoms, or ENAs. ENAs are particles with no charge that move very quickly. ENAs are made from solar wind particles. Solar wind particles are charged, meaning they have lost electrons. Another name for a particle that has lost one or more electrons is an “ion”. Sometimes these solar wind ions interact with neutral atoms that come from the Interstellar Medium, the material between the stars. The solar wind ions take electrons from these neutral atoms and get knocked away. Since the solar wind particles are no longer charged, meaning they have equal numbers of protons and electrons, they no longer react to magnetic fields in the area, and they travel very fast in a straight line from the spot where the interaction occurred.

Some of the ENAs happen to get knocked in a straight line in just the right way so that they travel toward the IBEX spacecraft. This is how the scientists can map the boundary – they know exactly where a particle came from since it did not change direction in its travels between the heliosphere boundary and the IBEX spacecraft.

To make sure that only ENAs enter IBEX’s collectors, ions are deflected before they even enter the collectors. The sensors sort the particles and keep track of the area the particles come from, the time they entered the sensor, the mass of the particles, and the amount of energy each particle has. From all of this information, a map of the boundary can be created.

How does IBEX communicate with Earth?

IBEX will complete one orbit every five to eight days, depending on conditions at launch. During each orbit, there is a period of time when the spacecraft is within the Earth’s magnetosphere. Since that is not the best time for making observations, the spacecraft uses that time to communicate with Earth. It uses antennae that are attached to the outside of the spacecraft to send radio signals to receivers on Earth. Due to the rotation of the Earth each day, the IBEX team needs a global network of receivers so that no matter how the satellite and Earth are lined up, there is a receiver available to accept the signal. IBEX is never further away from Earth than the Moon, so it takes a second or less for signals to travel between IBEX and Earth. However, IBEX communications are slow. Communication from the satellite to the ground is only 320,000 bits of information per second, and from the ground to the satellite is only 2,000 bits per second. Compare this to a typical home cable modem connection, where the download speed is often 6 million bits per second, and the upload speed is about 500,000 bits per second! IBEX does not need a hig- speed connection, though, because it will not have vast amounts of data to transmit. Once the signal is collected by the receivers on Earth, the signal is carried to the IBEX Mission Control Center in Dulles, Virginia and to the IBEX Science Operations Center in San Antonio, Texas.

What is in store for IBEX’s future?

The primary mission of IBEX will last for two years. It takes this amount of time for IBEX to map the heliosphere once. If the spacecraft is healthy in mid-2010, and if budget permits, then the mission may be extended. From 2008 to 2010, the Sun’s activity level will increase, which may push the heliosphere outward and/or change its shape. Over the next few years, as the Sun’s activity level decreases, the heliosphere may change, as well. Because the amount of solar wind particles streaming from the Sun depends, in part, on how active the Sun is, scientists are eager to make several maps of the heliosphere, not just one.