Protons from the Sun: What You Can't See Can Hurt You in Space
Written by Bruce McCollum, Spitzer Science Center
July 26, 2006
|A NASA/ESA SOHO image of turbulent activity on the Sun. A large loop of superheated gas is erupting from the upper right.
Credit: SOHO-EIT Consortium, ESA, NASA
Satellites and space observatories beware! Microscopic protons are shooting out of the Sun at speeds thousands of times faster than bullets. Although these protons cannot be spotted with the naked eye, they can cause some serious damage.
For example, if enough protons hit a human body, the person could suffer from enough damaged cells that it would make them sick or even kill them. This type of damage has a name: "radiation sickness." Fortunately for living creatures, Earth's atmosphere stops most of the speeding protons coming in from space. The protons just hit air molecules and not human cells.
However, unlike humans, satellites and space observatories, like NASA's Spitzer Space Telescope, aren't so lucky. There is nothing to shelter them from the solar protons zipping around in space. Thus, astronomers on Earth sometimes take extra precautions to protect their space telescopes during solar storms, when large amounts of protons are shot out of the Sun.
What are Protons?
Every atom in the universe has at least one proton, and atoms are the microscopic building blocks of all of the matter we can see, including stars, planets, rocks, and people. Since the Sun is more than a hundred times bigger than the Earth, we know that there are a LOT of atoms with their protons just in the Sun. Astronomers estimate that there are approximately 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 protons living in the Sun. That's a one with 57 zeros following it!
That's more than the total number of grains of sand in the world. In fact, if you had one grain of sand for each proton in the Sun, you could cover the entire surface of the Earth millions of miles deep with sand. You could even pile sand way out past the Moon, which is a quarter of a million miles away.
The Sun is extremely hot, hotter than anything on Earth except the inside of a nuclear explosion. When atoms are heated up that much they come apart and the protons that are usually trapped inside of them are free to fly around at incredible speeds. Although heat may have released protons from the confines of an atom, most are still trapped by the Sun's gravity. However, some of them are fast enough to escape even the Sun's gravity, and race out to the planets and beyond. The fastest protons that leave the Sun fly through space at hundreds or thousands of miles per second.
In every nook and cranny of space between the planets of our solar system, there are solar protons racing around moment by moment. This is called the "solar wind," because it's like a wind of protons (and electrons) blowing out from the Sun in all directions. Any object in space, be it a spacecraft, an astronaut, or a planet, is getting hit all the time with these. Most of the time there aren't enough of the dangerously fast solar protons leaving the Sun to hurt anything or anybody in space.
But sometimes the Sun has a big explosion on its surface. These eruptions are called "solar storms" when they throw fast protons or electrons out into space. They can produce a lot of dangerous, fast protons that can have speeds as much as 100,000 times faster than bullets. Because of these solar storms, scientists use the term "space weather."
Sometimes during a solar storm, a whole lot of electrons race out from the Sun at high speeds. If lots of solar electrons reach the Earth all at once, it can mess up our electric power lines and even cause power blackouts. In fact, a solar storm event in 1989 almost caused the US one of its worst power blackouts ever, and it did make 6 million people in Quebec lose power for several hours.
Solar storms can sometimes make big parts of interplanetary space fill up with fast protons called a solar "proton event." Solar proton events are the most dangerous space weather event. They are dangerous to both astronauts and spacecraft. Whenever there is a big proton event, the astronauts in the International Space Station hurry to a specially protected part of the station for safety. They wait there until the proton event dies down. A space suit doesn't give enough protection during a big proton event.
Since protons are too small to be seen we can't see them coming, but we can detect them when they get here. There are special proton detectors on several ongoing space missions like SOHO and GOES. These detectors alert us when a big blast of fast protons arrives at Earth, but not before.
Space weather forecasting is a whole field of science different from "classical" astronomy. Scientists are working on ways to tell if dangerous proton events can be forecast like we can forecast storms on Earth. The government has a research center just for understanding and forecasting all types of solar storms. It's called the Space Environment Center. They send out immediate warnings to the world whenever dangerous solar events are detected or predicted, and even have a web site at www.sec.noaa.gov. Another informative site is: www.spaceweather.com.
Fortunately, big solar proton events don't happen very often. They usually happen when the Sun is having an "active year". The Sun goes through cycles where it's active with storms and eruptions for several years, then quiet for several years, then back to stormy. In active years there are several big solar storms every year. The Sun is currently in a quiet period, and is expected to be quiet at least until about 2008.
Protecting Spitzer from Space Weather
Unlike the astronauts, spacecraft like Spitzer have no place to hide when there's a solar proton event. Metal isn't as sensitive to fast protons hits as people but spacecraft
still can be damaged in some ways.
The most vulnerable part of any spacecraft to space weather damage is usually its electronics. All satellites and space telescopes have a central computer. Because microchips have delicate engineering on a microscopic scale, even microscopic hits from fast protons can do serious damage. It's a matter of chance. Most of the protons that hit won't hit anything vital. But, if enough fast protons hit the spacecraft, then by chance a vital point in a microcircuit may be damaged. A number of expensive satellites have been lost because of solar storms. Sometimes when a proton event happens, Spitzer's operators on Earth may temporarily shut down its on-board computer for safety reasons. Microcircuits are less easily damaged by proton hits if they aren't operating when the hit occurs.
Solar protons can also damage a space observatory's detector. Spitzer's detectors are small devices that sense infrared starlight and record an image that scientists use. It functions kind of like the film in a camera, or the light-sensing CCD chip in a home digital camera. A fast proton hitting the detector can make that one spot in the detector permanently stop detecting properly. In any detector, just a few damaged points out of many thousands of points (the points are technically called "pixels") won't matter much in the overall image, but you don't want a lot of permanently damaged spots in the detector.
Scientists want to keep that kind of damage to a minimum, so there is a special layer of metal around Spitzer's detectors that stop most, but not quite all, of the fast protons. It doesn't take a huge amount of shielding to do the job. Spitzer's detectors only need a layer of about an inch of aluminum alloy to keep out most of the dangerous protons. (A modern tank's armor, for comparison, is typically several inches thick and made of tougher material than aluminum.)
How the Spitzer Space Telescope Weathers a Proton Storm
Spitzer has gone through several solar proton events and the telescope's detectors have weathered fast solar protons well. The detectors have received only a very few permanently damaged spots as a result and the telescope's images are still of very high quality. Also, thanks to Spitzer's mission operations team, none of the electronics aboard Spitzer have been damaged.
When the Sun produces a big proton blast, here's what happens at the Spitzer mission:
- GOES satellites detect a sudden big increase in the number of fast protons (it can increase ten thousand times over normal in just a few hours).
- Solar storm specialists, who receive data from GOES round the clock at the NOAA Space Environment Center in Boulder, Colorado, immediately send a proton storm warning to the Spitzer Flight Control Engineer on duty at the Jet Propulsion Laboratory (JPL), in Pasadena, California.
- The Spitzer Flight Control Team begins continuous monitoring of the GOES proton counts.
- If the number of protons arriving each second increases up to a certain danger threshold, the Flight Control Team initiates a procedure to put the spacecraft in what is called Standby Mode, where most of the electronics are turned off.
- The spacecraft waits out the proton storm in Standby, with the Flight Control Team keeping a continuous eye on the GOES proton counts.
- When the proton counts have gone back down to a safe level for Spitzer, the spacecraft is commanded to resume normal operations.