NASA launches mission to map bubble around solar system

(NEW YORK TIMES)

A SpaceX rocket launched on Wednesday morning carrying two spacecraft for NASA and one for the National Oceanic and Atmospheric Administration.

The missions will all study the solar wind - a stream of charged particles from the sun - and its effects on Earth and interstellar space. The flow of electrical charge creates the heliosphere, a giant magnetic bubble that surrounds the solar system and protects us from powerful and dangerous cosmic rays that crisscross the universe.

The NOAA spacecraft will provide crucial warnings when the sun belches a fusillade of high-energy particles at Earth. Such solar storms can disable satellites in orbit and crash electrical power networks on the ground.

The Falcon 9 rocket launched at 7:30am from NASA’s Kennedy Space Center in Florida, shortly after sunrise. About an hour and a half later, the three spacecraft separated from the rocket’s second stage.

They are all headed to the same part of the solar system - a region between the Earth and the sun known as Lagrange 1 where gravitational forces between the two are in balance. They are to arrive at their destination, close to 1 million miles away, in January.

Ten instruments on IMAP will measure various aspects of the solar wind, the particles streaming from the sun outward through the solar system. They will also study the magnetic bubble of the heliosphere, which is generated by the solar wind.
That protective bubble deflects much of the high-energy radiation from outside the solar system. Without the protection of the heliosphere, life might not have arisen on Earth.

"Understanding that shielding, why it works, how it works, how much it can vary over time is obviously very important for human exploration beyond the near-Earth environment,” said David McComas, a professor of astrophysics at Princeton University who serves as the principal investigator for IMAP, including places like Mars.

One process that IMAP will study is charge exchange, when positively charged protons in the solar wind occasionally pick up an electron as they reach the outer part of the heliosphere. That changes them into electrically neutral hydrogen atoms, which can then fall back toward the inner solar system a few years later, where they can be detected by IMAP.

Such events are highly improbable - McComas calls it a 10 billion-mile hole-in-one - but there are so many solar wind particles that the rate will be high enough for IMAP to measure.

IMAP will also detect neutral particles entering the heliosphere from outside the solar system.

In 1972 an ultraviolet camera deployed on the moon by astronauts during Apollo 16 revealed that the exosphere glows. When sunlight hits hydrogen atoms in the exosphere, it often pushes electrons in the atoms into a higher-energy state. When the electrons fall back into their lowest-energy state, the hydrogen atoms emit a specific wavelength of ultraviolet light known as the Lyman-alpha line.

George Carruthers, the scientist who designed the Apollo ultraviolet camera, called that glow the geocorona - Latin for "Earth’s crown.”

The exosphere is almost empty. The densest part, about 300 miles above the surface, contains 30,000 to 100,000 atoms per cubic centimeter, Waldrop said. That may seem like a lot, but many satellites, including the International Space Station, slip through these wisps of atmosphere at lower altitudes.

At an altitude of 50,000 miles, the density drops to about 25 atoms per cubic centimeter. Even with so few atoms, the exosphere appears to play a key role in how Earth’s atmosphere recovers from a solar storm. Electrons in the exosphere’s hydrogen atoms occasionally jump to high-speed protons in the solar wind, dissipating the powerful electrical currents that can disable satellites in orbit and power grids on the ground.