Measurements from Ulysses give new clues to dark matter

17 Jun 2002

Measurements from the joint NASA/European Space Agency Ulysses mission found a surprisingly small increase in the amount of helium-3 since the formation of the solar system, allowing a more precise estimate of the amount of dark matter in the universe. The findings from measurements of the Solar Wind Ion Composition Experiment aboard Ulysses were published this week in Nature magazine.

Drs. George Gloeckler, professor of physics at the University of Maryland, and Johannes Geiss, director at the International Space Sciences Institute in Bern, Switzerland, reported the first measurements of helium-3 in the interstellar cloud surrounding our solar system. They said their findings of this lighter isotope of helium give additional clues to the amount of dark, or invisible matter, that was produced at the beginning of the universe -- the Big Bang -- 15 billion years ago.

"Our measurements indicate the amount of dark matter in the early universe was fairly high," Gloeckler said. "Visible matter is a small fraction of the total. By measuring the relative portions of the lightest elements and their isotopes, one can infer the amount of ordinary matter in the universe."The researchers reported that the amount of helium-3 indicates a surprisingly small increase -- about 50 percent -- since the time of the formation of the solar system 4.6 billion years ago. Since the change was smaller than earlier models indicated, Gloeckler and Geiss predict the density of dark, or unseen, matter relative to that matter which we can see must be correspondingly greater.