A scientist using the Solar and Heliospheric
Observatory (SOHO) has found a way to forecast solar radiation
storms. The new method offers as much as one hour advance
warning, giving astronauts time to seek shelter and ground
controllers time to safeguard their satellites when a storm
is approaching.
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Artist's concept of a radiation storm approaching Earth. [More]
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"Solar
radiation storms are notoriously difficult to predict - they
often take us by surprise, " says physicist Arik Posner
who developed the technique. "But now we've found a way
to anticipate these events."
Posner
is a member of the research staff of the Southwest Research
Institute in San Antonio, Texas; he also works at NASA Headquarters
in Washington, DC. His study, Up to one-Hour Forecasting
of Radiation Hazards from Solar Energetic Ion Events,
appears in the journal Space Weather.
Solar
radiation storms are swarms of electrons, protons and heavy
ions accelerated to high speed by explosions on the sun. Here
on Earth we are protected from these particles by our planet's
atmosphere and magnetic field. Astronauts in Earth orbit are
fairly safe, too; Earth's magnetic field extends out far enough
to shield them. The danger begins when astronauts leave this
protective cocoon. The Moon and Mars, for instance, have no
global magnetic fields, and "astronauts working on the
surface of those worlds could be at risk, " says Posner.
"A
one hour warning would reduce the odds of an astronaut being
caught in a solar storm outside of a lunar habitat, where astronauts
are most vulnerable, " notes Francis Cucinotta, chief scientist
for NASA's Space Radiation Program.
Spacecraft
and satellites would also benefit. Subatomic particles striking
CPUs and other electronics can cause onboard computers to
suddenly reboot or issue nonsense commands. If, say, a satellite
operator knows that a storm is coming, he can put his craft
in a protective "safe mode" until the storm passes.
The
type of particle most feared by astronaut safety experts is
the ion, that is, an atom which has lost one or more of its
charge-balancing electrons. "Energetic ions can damage
tissue and break strands of DNA, causing health problems ranging
from nausea to cataracts to cancer, " says Cucinotta.
So
the goal is to predict when the ions will arrive. The key
to that, it turns out, is electrons. "Electrons are always
detected ahead of the more dangerous ions, " says Posner.
This has been known for years, but only recently has Posner's
research turned the "electrons first" aspect of
radiation storms into a tool for forecasting.
Posner's forecasts for the intense "Halloween storms" of 2003. Black denotes the predicted ion flux; red is what was actually observed. [More]
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Above:
Posner's forecasts for the intense "Halloween storms"
of 2003. Black denotes the predicted ion flux; red is what
was actually observed. [More]
Every
radiation storm is a mix of electrons, protons and heavier
ions. The electrons, being lighter and faster than the others,
race out ahead. They are like heralds proclaiming the
ions are coming! Posner realized that by measuring the
"rise time and intensity of the initial electron surge"
he could tell how many ions were following and when they would
arrive.
The
key to the breakthrough was the COSTEP instrument onboard
SOHO. COSTEP is short for "Comprehensive Suprathermal
and Energetic Particle Analyzer." Essentially, the device
counts particles coming from the sun and measures their energies.
Posner
looked at hundreds of radiation storms recorded by COSTEP
between 1996 and 2002, and he was able to construct an empirical,
predictive matrix: "Plug electron data into the matrix,
and an ion forecast pops out."
The
next step was to test his results. He decided to try out the
matrix on COSTEP data gathered in 2003, a year he hadn't yet
analyzed and which formed no part of the matrix itself. "I
applied the matrix to the electron data; it successfully predicted
all four major ion storms of 2003 with advance warnings ranging
from 7 to 74 minutes."
Posner's ion storm forecasting matrix.
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Posner
says the method is not yet perfect. He points out, for instance,
the brief seven minute warning for one storm in 2003. "I'd
like to improve that, " he says. "The matrix also
generated three false alarms for 2003 - that is, storm alerts
followed by weak storms or no storms at all." In those
few cases, astronauts would have dashed to safety unnecessarily.
Improvements
will come as Posner works his way through even more of COSTEP's
rich dataset: "Launched with SOHO in 1995, COSTEP has
been operating through an entire solar cycle including the
solar maximum in 2001 - and it is still going strong, "
says Prof. Bernd Heber, COSTEP's principle investigator at
the University of Kiel in Germany.
The
method is currently being considered by planners at the Johnson
Space Center in their design of future lunar missions. "Posner's
technique reduces the odds of exposure by more than 20 percent
compared to current methods, allowing astronauts to venture
farther from their outpost, " says Cucinotta. "That's
good news for both science and exploration."
SOHO
is a project of international cooperation between the European
Space Agency and NASA. To learn more about SOHO, visit the
mission's home page: http://sohowww.nascom.nasa.gov/
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