If a Japanese space capsule that recently returned to Earth is found to have collected particles from a billion-year-old space rock, it will join the short history of lucrative sample-return missions. ?
Retrieving samples from space is considered more complicated, potentially more costly, and riskier than conducting remote or robotic expeditions, but successful retrievals can confirm or disprove theories more accurately and can fuel or accelerate decades of scientific research.
As researchers and mission scientists await an analysis of what the plucky Hayabusa asteroid probe has brought back from space, they say previous sample-return missions have proven their usefulness. And, with improvements in technology and in methods of cleaning and sterilizing storage facilities, future missions to retrieve samples from Mars and beyond could provide even more valuable insights into the unknowns of our solar system.
"With a sample-return mission, you have a resource from which you can harvest information for generations," Michael Zolensky from NASA's Johnson Space Center in Houston told Space.com. "It is much easier and more efficient to perform analyses on Earth than anywhere else."
Hayabusa and asteroid Itokawa
Zolensky, an associate curator for the interplanetary dust stored at Johnson Space Center, was a co-investigator for NASA's Stardust mission, the first to return samples from a comet and from interstellar space. He is also a member of the sample-analysis team for the Japanese Hayabusa mission.
The Hayabusa asteroid probe plunged through Earth's atmosphere over part of the Australian outback June 13, returning to our planet after a seven-year journey in which it encountered the asteroid 25143 Itokawa.
A re-entry capsule containing particles was released from the probe about three hours before it plummeted to Earth.
Hayabusa team scientists are now in the process of analyzing the particles to determine if they are from Itokawa. If so, the sample could shed light on two mysterious types of cosmic objects, said Zolensky. ?
"I'm very optimistic, since these samples would forge the first direct link between meteorites and asteroids," he said.
Past sample-return missions
Sample-return missions essentially began with the Apollo moon missions. Between 1969 and 1972, six Apollo expeditions returned with a combined 842 pounds (382 kilograms) of lunar rocks, core samples, pebbles, sand and dust from the lunar surface. These samples were collected from six different exploration sites.
Following the sample returns from Apollo 11 and 12, three Soviet robotic spacecraft ? part of the Soviet Luna program ? retrieved lunar materials totaling about three-quarters of a pound (300 grams) from three separate sites. ?
NASA's Genesis mission collected particles from the solar wind, providing the space agency with its first extraterrestrial sample since the Apollo program, which ended in 1975.
The goal of Genesis, which launched in 2001 and crash-landed on Earth in 2004, was to gather solar-wind atoms in order to analyze and measure the composition of the sun. Determining the sun's elemental and isotopic composition can help astronomers better understand the chemical evolution of the solar nebula, when the planets in our solar system were being formed.
The Stardust mission launched in 1999, prior to Genesis, but had a longer journey to its target, the comet Wild-2. Stardust encountered Wild-2 on Jan. 2, 2004, and collected samples from the comet and interstellar space in a return capsule that parachuted to Earth in 2006.
Multiple chances for research
Samples are cataloged and preserved by curators at the Astromaterials Acquisition and Curation Office at Johnson Space Center. The curators also manage requests for the samples' use.
The Curation Office currently holds five collections: Apollo lunar rocks and soils, meteorites from Antarctica, cosmic dust collected in the stratosphere, solar-wind samples from the Genesis spacecraft, and interstellar and cometary dust samples collected during the Stardust mission.
Judith Allton, curator of the Genesis solar-wind sample, stressed that sample-return missions are invaluable in providing scientists with the tools to yield accurate measurements and analyses.
"We get much more precise data off of returned samples," Allton told SPACE.com. "You can have a sample and test it with different state-of-the-art instruments, and different teams can confirm or dispute the results. People have been looking at the sun with remote sensing, but they're not anywhere near close to the accuracy and precision that you can get with a return sample."
Zolensky, who works with Allton at the Curation Office, added that maintaining a collection of samples gives scientists the flexibility to test various ideas over the course of their research.
"With remote analyses, you only have one chance to get it right," he said. "With analyses in the lab, you can retry and refine analytical procedures."
Sampling the Red Planet
Scientists also say there are certain limitations to the measurements that are made remotely. A sample-return mission to Mars has the potential to produce findings that could not be made even on the surface of the Red Planet.
"There are some things we can't do on Mars ? dating a rock is one of the critical things," Michael Meyer, Mars chief scientist at NASA Headquarters in Washington, D.C., told SPACE.com. "We know that water was a critical part of the planet's history, but we won't know for how long until we can date some of the rocks."
Meyer has been part of a longstanding effort to design a sample-return mission to Mars. Several attempts to jump-start the project were met with lackluster support, but recent developments and an important partnership are cause for renewed optimism, he said.
"We've been working hard over the last year and a half to develop a joint Mars program with the European Space Agency," Meyer said. "We've been wanting to do a sample-return mission for quite some time, and one of the things we've done through the years is gone through a learning process."
Part of that process has involved coping with the enormity of the project.
"It's big ? really big ? and everything is in one basket," Meyer said. "It's very expensive in any one fiscal year, so we've split it up into three different segments. This spreads out the risk itself and spreads out the cost. It's kind of like making a down payment."
Step by step ? managing risk
The proposal calls for a joint mission in 2016 to place an orbiter around Mars, followed by putting two rovers (one belonging to NASA and one belonging to ESA) on the planet's surface in 2018. The rovers will have the ability to collect and cache samples that can be sealed off in preparation for transportation back to Earth.
The next step would involve sending a lander to the surface with an ascent rocket attached. A small rover would retrieve the collected material and bring it back to the rocket, which would then be launched into Mars orbit.
The orbiter would be dispatched to recover the sample and bring it back to Earth.
"By splitting it up like that, we spread out the risk and each element becomes manageable," Meyer said. "There are also other advantages, because if one part of the process breaks, we can repeat it, and whatever step the sample is in, it can stay there until the next step is accomplished."
Why do sample-return missions?
Another hurdle for a sample-return mission to Mars, and sample-return missions in general, is the cost, said Meyer. This has been a subject of debate within the scientific community.
"It's an expensive thing to do," Meyer said. "But there are huge advantages to sample return. You get to interrogate the sample, and when you do experiments here on Earth, you actually pick apart a rock and look at separate minerals. You can't do that on Mars."
Curated samples can benefit future generations of scientific discovery, Meyer added. As techniques for storing and safely preserving samples improve, researchers will be able to refer back to these collected samples time and again.
"You can revisit a sample, or a couple of years later, someone can go back and interrogate the sample with a new approach," he said. "To be able to bring something back that has context ? it's sort of the Holy Grail. It's the gift that keeps on giving."
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