Astronomy Now Home
Home Magazine Sky Chart Resources Store

On Sale Now!



The September 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








MESSENGER gets closest
look at solar flare

DR EMILY BALDWIN
ASTRONOMY NOW
Posted: October 27, 2009


Bookmark and Share

On 31 December 2007 NASA's MESSENGER spacecraft made the first detection of solar neutrons at less than one astronomical unit from the Sun.

MESSENGER was just 0.5 AU from the Sun when it was bathed in high energy neutrons ejected in a solar flare, giving scientists a first close up look at neutron production from a solar flare. Previously, only the neutron bursts from the most powerful solar flares have been recorded on neutron spectrometers on Earth or in near-Earth orbit, which typically last for up to a minute at the Sun.

Coronal mass ejections blast billions of tons of matter out into space at millions of kilometers per hour. Image: SOHO (ESA & NASA).

“But we recorded neutrons from this flare over a period of six to ten hours, and what that’s telling us is that at least some moderate-sized flares continuously produce high-energy neutrons in the solar corona,” says William Feldman, Co-Investigator for MESSENGER's Neutron Spectrometer, one of two sensors on the Gamma-Ray and Neutron Spectrometer instrument. “From this fact, we inferred the continuous production of protons in the 30-100 million electron volt (MeV) range due to the flare.”

Around 90 percent of all ions produced in a solar flare remain locked to the Sun on closed magnetic field lines, but a second population results from the decay of neutrons near the Sun which can be accelerated through interplanetary space by the shock waves produced by flares.

“So the important results are that perhaps after many flare events two things may occur: continuous production of neutrons over an extended period of time and creation of seed populations of neutrons near the Sun that have decayed into protons,” explains Feldman. “When coronal mass ejections (nuclear explosions in the corona) send shock waves into space, these feedstock protons are accelerated into interplanetary space.”

MESSENGER is on its way to orbiting the innermost planet in March 2011 and is ideally located to soak up solar flare radiation from the Sun. Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

There has always been some debate as to why some coronal mass ejections produce almost no energetic protons that reach the Earth, while others produce huge amounts, and now it seems that the answer lies within the seed populations of energetic protons residing near the Sun. “It’s easier to accelerate a proton that already has an energy of 1 MeV than a proton that is at 1 keV (the solar wind),” adds Feldman.

The seed populations are not evenly distributed, however, and it is pot luck as to whether they are in the right place for shock waves to send them careering towards the Earth or in a different direction entirely.

Studying the effects of solar flare radiation is of high level interest to spaceflight programs since flares can damage satellites and of course endanger astronauts working on the International Space Station, the Moon or Mars. Fortunately MESSENGER is in an ideal location – between 0.3 and 0.6 AU – to build up a picture of this type of activity over the coming years.

“What we saw and published is what we hope will be the first of many flares we’ll be able to follow through 2012,” says Feldman. “The beauty of MESSENGER is that it’s going to be active from the minimum to the maximum solar activity during Solar Cycle 24, allowing us to observe the rise of a solar cycle much closer to the Sun than ever before.”

MESSENGER will reach orbit around Mercury in March 2011 where it will be within 0.45 AU of the Sun for one year. The results from the December 2007 flare are discussed in a forthcoming paper to be published in the Journal of Geophysical Research.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.