The primitive horseshoe crab lived on the Earth 250 million years ago, and is still with us today. Now scientists think they can use its blood to detect life on other planets. When a horseshoe crab is injured, its blood, which is the color blue, clots in order to keep infection out. “One of the reasons the horseshoe crab has survived for so long is its advanced immune system,” says biologist Norman Wainwright. “This system can be used to find microbial life.” Scientists have put the crab’s blood enzymes into a hand-held instrument that can test for signs of life.

“If there are microbial species that evolved outside the Earth, that life may have originated here and spread throughout the solar system,” says Wainwright. “It’s possible the cell walls of microbes on other planets may be similar enough to detect using the test.”

The clotting enzymes are extracted from the blood and freeze dried. When inserted into the instrument, they cause a clear solution to turn bright yellow when it encounters microbes. “The more yellow the sample, the more microbes it’s finding,” Wainwright says.

To get the blood, he inserts a needle into the crab’s heart, then releases it back into the ocean. Horseshoe crabs are so tough, most of them survive. Neurobiologist Robert Barlow says, “There’s about a 10 percent mortality rate.”

The “Crab SETI” (SETI means “Search for Extraterrestrial Intelligence”) has been used to check spacecraft to make sure they’re free from Earth microbes before heading out to space. Craft could also be tested after returning to Earth, to see if they brought any extraterrestrial microbes home with them. These might not be the intelligent extraterrestrials we’re hoping to find?but it would be life from other planets.

What we’d really like to encounter is alien energy. Find out what it is on Dreamland this weekend.

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