NASA to Probe Sun "in situ"

Until the SOHO satellite was launched, astronomers had to be content to look through earth bound telescopes at the sun. Now that the sun is key to “the biggest threat facing mankind – climate change” it seems only sensible that NASA send a probe for direct measurment.

Now if we can just get Jim Hansen out of his office to look at some of the weather stations he keeps using in the GISS surface temperature database, we’ll really have something.

No word yet on whether Quizno’s will be putting a “Mmm…Toasty!” bumper sticker on the probe in exchange for scientific funding assistance.

From NASA Science News

For more than 400 years, astronomers have studied the sun from afar. Now NASA has decided to go there.

Right: An artist’s concept of Solar Probe Plus. [

The name of the mission is Solar Probe+ (pronounced “Solar Probe plus”). It’s a heat-resistant spacecraft designed to plunge deep into the sun’s atmosphere where it can sample solar wind and magnetism first hand. Launch could happen as early as 2015. By the time the mission ends 7 years later, planners believe Solar Probe+ will solve two great mysteries of astrophysics and make many new discoveries along the way.

The probe is still in its early design phase, called “pre-phase A” at NASA headquarters, says Guhathakurta. “We have a lot of work to do, but it’s very exciting.”

Johns Hopkins’ Applied Physics Lab (APL) will design and build the spacecraft for NASA. APL already has experience sending probes toward the sun. APL’s MESSENGER spacecraft completed its first flyby of the planet Mercury in January 2008 and many of the same heat-resistant technologies will fortify Solar Probe+. (Note: The mission is called Solar Probe plus because it builds on an earlier 2005 APL design called Solar Probe.)

At closest approach, Solar Probe+ will be 7 million km or 9 solar radii from the sun. There, the spacecraft’s carbon-composite heat shield must withstand temperatures greater than 1400o C and survive blasts of radiation at levels not experienced by any previous spacecraft. Naturally, the probe is solar powered; it will get its electricity from liquid-cooled solar panels that can retract behind the heat-shield when sunlight becomes too intense. From these near distances, the Sun will appear 23 times wider than it does in the skies of Earth.

Above: A simulated view of the Sun illustrating the trajectory of Solar Probe+ during its multiple near-Sun passes.

The two mysteries prompting this mission are the high temperature of the sun’s corona and the puzzling acceleration of the solar wind:

Mystery #1—the corona: If you stuck a thermometer in the surface of the sun, it would read about 6000o C. Intuition says the temperature should drop as you back away; instead, it rises. The sun’s outer atmosphere, the corona, registers more than a million degrees Celsius, hundreds of times hotter than the star below. This high temperature remains a mystery more than 60 years after it was first measured.

Mystery #2—the solar wind: The sun spews a hot, million mph wind of charged particles throughout the solar system. Planets, comets, asteroids—they all feel it. Curiously, there is no organized wind close to the sun’s surface, yet out among the planets there blows a veritable gale. Somewhere in between, some unknown agent gives the solar wind its great velocity. The question is, what?

“To solve these mysteries, Solar Probe+ will actually enter the corona,” says Guhathakurta. “That’s where the action is.”

The payload consists mainly of instruments designed to sense the environment right around the spacecraft—e.g., a magnetometer, a plasma wave sensor, a dust detector, electron and ion analyzers and so on. “In-situ measurements will tell us what we need to know to unravel the physics of coronal heating and solar wind acceleration,” she says.

Right: The re-designed Solar Probe+ spacecraft. [more]

Solar Probe+’s lone remote sensing instrument is the Hemispheric Imager. The “HI” for short is a telescope that will make 3D images of the sun’s corona similar to medical CAT scans. The technique, called coronal tomography, is a fundamentally new approach to solar imaging and is only possible because the photography is performed from a moving platform close to the sun, flying through coronal clouds and streamers and imaging them as it flies by and through them.

With a likely launch in May 2015, Solar Probe+ will begin its prime mission near the end of Solar Cycle 24 and finish near the predicted maximum of Solar Cycle 25 in 2022. This would allow the spacecraft to sample the corona and solar wind at many different phases of the solar cycle. It also guarantees that Solar Probe+ will experience a good number of solar storms near the end of its mission. While perilous, this is according to plan: Researchers suspect that many of the most dangerous particles produced by solar storms are energized in the corona—just where Solar Probe+ will be. Solar Probe+ may be able to observe the process in action and show researchers how to forecast Solar Energetic Particle (SEP) events that threaten the health and safety of astronauts.

Solar Probe+’s repeated plunges into the corona will be accomplished by means of Venus flybys. The spacecraft will swing by Venus seven times in six years to bend the probe’s trajectory deeper and deeper into the sun’s atmosphere. Bonus: Although Venus is not a primary target of the mission, astronomers may learn new things about the planet when the heavily-instrumented probe swings by.

“Solar Probe+ is an extraordinary mission of exploration, discovery and deep understanding,” says Guhathakurta. “We can’t wait to get started.”

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June 12, 2008 4:09 am

I am reminded of the story of the Polish Space Agency announcing that they are going to land on the sun. A reporter asks how they will keep from burning up. The project leader replies that they will land at night.

June 12, 2008 4:19 am

I wonder where the reporter got that 2015 would be near the end of solar cycle 24?
Hathaway, whom I’m beginning to wonder about has weighed in claiming that the sun ‘probably causes 10-30 percent of climate change’. What does he know?

Steve Stip
June 12, 2008 4:29 am

Very fine! I am surprised that they do not use a grazing incidence shield/ solar panels. This might allow even closer approach. What am i missing, thems with brains?

Leon Brozyna
June 12, 2008 6:09 am

With a launch in 2015, it should be interesting to see if the probe is examining the sun as it moves from SC24 to SC25, or if it is peering at a relatively quiescent body, a possibility raised in that Livingston/Penn paper in a previous post:
At least this is one idea that can be measured against reality in fairly short order, unlike climate models whose forecasts are for a time when most everyone will be dead.

June 12, 2008 6:22 am

I am glad that I don’t have to certify the radiation hardness of the electronics that we be on board. Now that I think about it, I might get to do some of that testing. It should be a real challenge.

June 12, 2008 6:35 am

My advice to NASA, go at night.
Seriously, this is a good scientific enterprise. Amazing how little we do know about the closest star. Hope I’m still here post 2015 to see the results.

June 12, 2008 6:49 am

Mystery #1 is claimed to be a pinch by some plasma theorists – not without what looks to me like some pretty good backup.
There is a hell of a lot we don’t know about the sun. If the coronal temps are from a pinch there is not only a lot we don’t know, but a lot of what we think we know is wrong.

Andrew Upson
June 12, 2008 8:29 am

Cool. Wonder who will build the bus? I’ll have to call my buddies at my previous employer to see if they’ll be getting in that action.

June 12, 2008 10:45 am

It sound as if they are saying a trillion dollars for a test., a lot of ifs and don’t knows.

Gary Gulrud
June 12, 2008 1:57 pm

Maybe with some hard corona data we can put the TSI goblins in the closet while the Solar Wind fascinates the heliophysicists. I’d think after their cycle 24 debacle, they’ll be happy to redirect our gaze!

June 13, 2008 5:30 am

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