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Like Mars, Like Earth
Who are NASA's Earth and Space Science Explorers?

The middle school students who track weather to study its effect on bursting tree buds. And the scientist studying black holes in distant galaxies. But also the teacher whose class shares Earth science data with students around the world. And the engineer who designs robotic instruments to probe hard-to-reach planets. All of these people are Earth Explorers, Space Science Explorers or both. The Earth Explorers and Space Science Explorers series features NASA explorers, young and old, with many backgrounds and interests.

Phil Christensen stands in front of a rocket

Phil Christensen stands in front of a Delta rocket three days before it would carry the Mars Odyssey spacecraft to space. Image Credit: Phil Christensen

Two things have fascinated Phil Christensen since he was young -- Mars and rocks. As a kid, he spent hours looking at Mars, other planets and the moon through a telescope. Then, in high school, a book about the moon's geology triggered his interest in rocks and planetary surfaces.

Now a professor and planetary geologist, Christensen combines his love for space science and geology by studying the surfaces of Mars and Earth. He has helped build several NASA instruments launched into space to map the Martian surface and study the history of water on Mars.

Mars is particularly interesting to scientists not only because it is similar to Earth, Christensen said, but also because it seems possible to go there. He believes a good chance exists that humans will go to Mars within the next 50 years. But until that happens, sending instruments there is crucial to exploring Mars.

"That can tell us a lot about the planet, tell us what the environment is like and what humans have to be prepared for when they get there," he said.

Scientists already know that Mars has an atmosphere. Mars is farther from the sun than Earth, and thus colder. Although temperatures near the planet's poles can drop as low as about minus 125 degrees Celsius (minus 195 degrees Fahrenheit), they can also rise as high as about 20 C (70 F) near the equator, which means that humans may some day go to Mars and experience temperatures similar to those found on Earth.

Like Earth, Mars also has glaciers, dust storms, river channels and volcanoes. In fact, Mars is fundamentally a volcanic planet, said Christensen, which means the planet has many different types of rocks made from cooled-down lava.

To find out whether Martian lava rocks are similar to any of those found on Earth, Christensen started to collect different rocks from around the world to study them. One day he was in Iceland to collect a sample, when he realized that a school was right across the street. That gave him an idea that would involve students in his exploration of Mars, and that would help him create a library of rock samples without leaving his work.

"It dawned on me that I could have written to the school, and the students probably would've loved it if I'd said 'I'm a NASA scientist. Can you go across the street and collect a rock and mail it to me?'" he recalled.

That idea was the start of the Rock Around the World program, which has now collected more than 8,000 rock samples sent in from students around the world. "It's gratifying to see kids get excited about Mars," Christensen said. "For some of these students, this may be the beginning of a career in Earth sciences."

Christensen and other researchers analyze these rocks with instruments called spectrometers. Spectrometers bounce waves of light off objects. Depending on what the object is made of, certain wavelengths are absorbed by the object while others are not. By studying the new makeup of the reflected light, scientists can figure out what minerals are present in the rocks.

A triangular-shaped, bumpy white and brown rock that is almost 2 inches wide

From Australia, this is one of more than 8,000 rocks sent in by students for the Rock Around the World program. Image Credit: Arizona State University

Analyzing Earth rock samples using a spectrometer in the laboratory is one thing, but to compare the rocks with those on Mars, Christensen has to find out which minerals are present in Martian rocks. For that, he has helped to design different spectrometers that have been sent to Mars on NASA spacecraft.

Christensen led the design and development of an analyzing instrument called THEMIS, which stands for Thermal Emission Imaging System. The instrument was attached to the Mars Odyssey spacecraft that launched in 2001. Now it circles Mars every two hours, taking visible and infrared images of the planet. Christensen and his colleagues then decipher the images to understand the composition of Martian rocks.

The researchers are also using the data to understand the history of water on Mars. To do that, they keep an eye open for minerals that could have formed in the presence of water. Also, because THEMIS detects heat, it has the ability to reveal underground "hot spots," which could be indicative of liquid water below the surface.

When Christensen first gazed at Mars through his telescope more than 40 years ago, he never thought he'd be creating instruments to study the planet up close. Being a space scientist seemed out of reach when he was young, he said. But as he found out, if you love to do something and you are ready to work hard, you can be what you want.

"Regular people can become planetary scientists and explore Mars," he said.

Related Resources
Rock Around the World  →
JASON Expedition: Mysteries of Earth and Mars  →
Previous Space Science Explorers Articles
Previous Earth Explorers Articles

Prachi Patel, Institute for Global Environmental Strategies