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.”

Surprise: Leaves Maintain Temperature,

Surprise: Leaves Maintain Temperature, new findings may put dendroclimatology as metric of past temperature into question


Dendroclimatology: thermometer or hygrometer?

Hot climate or cold, tree leaves stay in comfort zone

From the Google Climate Discussion Group, see an article also in Science News

Paris, June 11; Agence France-Presse

A new study that shows their internal temperature remains constant at 21.4deg could challenge the way trees are used to determine historical climate data

The internal temperature of leaves, whether in the tropics or a cold-clime forest, tends toward a nearly constant 21.4 degrees Celsius, reports a study released today.

It had long been assumed that actively photosynthesising leaves - using energy from sunlight to convert carbon dioxide and water into sugar - are nearly as cold or hot as the air around them.

The new findings not only challenge long-held precepts in plant biology, but could upend climate models that use tree rings to infer or predict past and present temperature changes.

For decades, scientists studying the impact of global warming have measured the oxygen isotope ratio in tree-rings to determine the air temperature and relative humidity of historical climates.

Oxygen atoms within water molecules evaporate more or less quickly depending on the number of neutrons they carry, and the ratio between these differently weighted atoms in tree trunk rings has been used as a measure of year-to-year fluctuations in temperatures and rainfall.

“The assumption in all of these studies was that tree leaf temperatures were equal to ambient temperatures,” lead researcher Brent Helliker told AFP. “It turns out that they are not.”

Helliker and University of Pennsylvania colleague Suzanna Richter turned those assumptions upside down in examining 39 tree species, across 50 degrees of latitude ranging from sub-tropical Columbia to boreal Canada.

They compared current observed records of humidity and temperature against the isotope ratios in the trees, and found that tree leaves were internally cooler than surrounding air temperatures in warm climes, and warmer in cool climes.

Even more startling was that in all cases the average temperature - over the course of a growing season - was about 21degC.

“It is not surprising to think that a polar bear in northern Canada and a black bear in Florida have the same internal body temperature,” because both animals have internal thermostats to prevent overheating or freezing to death, he said.

“But to think that a Canadian black spruce and a Caribbean Pine have the same average leaf temperature is quite astonishing,” he added.

Tree leaves keep cool through constant evaporation and reducing sun exposure through leaf angles or reflective qualities. Warmth is gained by decreasing evaporation and increasing the number of leaves per branch.

All these tricks should be seen as evolutionary adaptations that help the trees attain a maximum of nutrients through optimal photosynthesis, Helliker said.

The fact that part of this adaptation occurs at the level of entire forest canopies, and not just within individual leaves, is one reason direct measurements of tree temperatures have been so hard.

The new findings, published in the British journal Nature, are bolstered by a recent study of a mixed species forest in Switzerland based on infrared thermal imaging.

Measured across an entire growing season, the forest canopy temperatures were found to be 4degC to 5degC higher than the cool, ambient air in the Swiss Alps.