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NASA's newest solar observatory launched into space late Thursday, beginning a two-year quest to probe some of the sun's biggest mysteries.

An Orbital Sciences Corp. Pegasus XL rocket carrying the new solar telescope — called the Interface Region Imaging Spectrograph satellite, or IRIS — left California's Vandenberg Air Force Base underneath a specially modified aircraft at 9:30 p.m. ET Thursday (6:30 p.m. PT).

Nearly one hour later, at 10:27 p.m. ET (7:27 p.m. PT), the plane dropped its payload 39,000 feet (11,900 meters) above the Pacific Ocean, about 100 miles (160 kilometers) northwest of Vandenberg. After a five-second freefall, the Pegasus rocket roared to life and carried the sun-watching IRIS into Earth orbit. [NASA's IRIS Solar Observatory Mission in Pictures]

Scientists hope IRIS' observations help them better understand how energy and material move around the sun. They want to know, for example, why the outer atmosphere of the sun is more than 1,000 times hotter than the star's surface.

Solar mysteries

IRIS is part of NASA's Small Explorer program, which caps the cost of a space mission at $120 million. Like its budget, the spacecraft is small — weighing just 400 pounds (181 kilograms) and measuring 7 by 12 feet (2.1 by 3.7 meters) with its power-generating solar panels deployed.

After a 60-day checkout period on orbit, IRIS will begin its science campaign. The probe will stare at a mysterious sliver of the sun between the solar surface and its outer atmosphere, or corona.

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NBC LA : IRIS on a mission to solve burning questions

Researchers hope a better understanding of this interface region, which is just 3,000 to 6,000 miles (4,800 to 9,600 kilometers) wide, will help explain why temperatures jump from 10,000 degrees Fahrenheit (5,500 degrees Celsius) at the sun's surface to 1.8 million degrees F (1 million degrees C) or so in the corona.

"What causes this rise? How does the energy transfer from the surface, the cool surface, to this hot outer atmosphere?" Jeffrey Newmark, IRIS program scientist at NASA Headquarters in Washington, said Tuesday during a pre-launch briefing. "These are the questions that IRIS, the science of IRIS, is going to address."

A more focused look at the sun

Other NASA solar spacecraft — such as the Solar Dynamics Observatory and the two STEREO (Solar TErrestrial RElations Observatory) probes — record views of the entire sun. In contrast, IRIS' spectrograph will focus on just 1 percent of our star at a time, resolving features as little as 150 miles (240 kilometers) across.

IRIS' relatively narrow view should complement other solar probes' broader look nicely, mission scientists said.

"Relating observations from IRIS to other solar observatories will open the door for crucial research into basic, unanswered questions about the corona," Joe Davila, IRIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., said in a statement.

IRIS was orginally slated to launch Wednesday, but a power outage across California's central coast knocked out key elements of Vandenberg's tracking and telemetry systems, causing a one-day delay.

Powerful sun storms can wreak havoc with electrical grids here on Earth. So the delay was appropriate in a way, highlighting the importance of IRIS' mission, said Pete Worden, director of NASA's Ames Research Center in Moffett Field, Calif., which is responsible for IRIS mission operations and ground data systems.

"The better we can understand the physics going on, the better we can understand the [solar] activity, the better that we can potentially predict and mitigate some of these problems," Worden said Tuesday.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

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